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Volume XXXVII, Number 5/6 (Published April 2021)
Saving the Monarchs
By William Quarles
Courtesy Jim Lovett, www.MonarchWatch.org
T
he pandemic year of 2020
was bad for almost every-
body, but it was an especial-
ly bad year for U.S. populations
of the western migratory monarch
butterfly, Danaus plexippus. Over-
wintering numbers have plunged
from about 167,000 in 2016 to
about 1,600 in 2020 (Schultz et
al. 2017; McKnight 2021a). The
current population has dropped
99.9% from the four million seen
in the 1980s, and is only about 1%
of that seen in 2016. Western mi-
gratory monarchs are on the brink
of extinction (Pelton et al. 2019;
Schultz et al. 2017).
There are two populations of
migrating monarchs in the U.S.—
the eastern population that breeds
Monarchs form overwintering clusters that protect against cold and predators.
east of the Rockies, then travels
Winter populations of western migrating monarchs have dropped from millions
to overwinter in Mexico, and the
to about 2,000. Western monarchs are on the brink of extinction.
western population that breeds in
California, Oregon, Utah, and Ida-
ho, then overwinters on the Califor- fortunate enough to witness this themselves lead to further popu-
nia coast, especially in areas such amazing spectacle. Wiggling clus- lation losses. Monarchs cluster to
as Monterey and Pacific Grove near ters of brightly colored monarchs protect against predators and get
the San Francisco Bay Area (Urqu- completely covered tree canopies. warmth from the aggregate as-
hart 1976; Brower 1977; Tuskes Populations have seen a sharp sembly. But fewer monarchs mean
and Brower 1978; Urquhart 1987; drop, and at many sites there are more exposure to cold weather
Oberhauser and Solensky 2004; now no monarchs at all (McKnight and predators. In fact, overwin-
Oberhauser et al. 2015). 2021a; Malcolm 2018). tering monarchs may shift sites
The Xerces Society for Inverte- to compensate for the low num-
brate Conservation has been mon- Tipping Point bers. Xerces monitored 149 sites
itoring western migratory popula- Fewer monarchs have been at Thanksgiving in 2020 and New
tions at overwintering sites along showing up at overwintering sites, Years in 2021. At 77 sites (52%), no
the California coast at Thanksgiv- and the destruction continues even monarchs were found. At 15 sites
ing and New Years for the last five there. Over the last five years there (10%) numbers increased between
years. Despite an increase in the have been 36-49% monarch losses Thanksgiving and New Years,
number of sites monitored, the each year at western overwintering
monarch numbers have been drop- sites. And about 21 overwintering
ping dramatically (McKnight 2021a; sites have been damaged or de- In This Issue
Pelton et al. 2019). (See Table 1). stroyed (McKnight 2021a; Malcolm
In the 1980s millions of mon- 2018; Pelton et al 2019). Saving Monarchs 1
archs were seen at the West Coast We may have reached a tip- Conference Notes 10
overwintering sites. The author was ping point where population losses
Update
Courtesy of the University of Minnesota Monarch Lab
Western monarchs leave overwintering sites on the California coast in the spring
and fly inland. On return flights in the fall, they may have to fly through forest
fires. Eastern monarchs leave Mexico in the spring, establishing new generations
in Texas, the Midwest, and the Northeast.
and at 54 sites (36%) populations tures (10°C; 50°F), but some of
decreased (McKnight 2021a). In them died as they were subjected
1978, when populations were large, to increased temperatures in the
monarchs rarely moved from an laboratory (19°C; 66.2°F) (Leong et
overwintering site until the spring al. 1997ab; Leong et al 2004).
(Tuskes and Brower 1978).
Hazardous Migrations
Importance of Parasites In contrast, Satterfield et al.
Much has been written about (2016) measured infection frequen-
the importance of monarch para- cy at several western overwintering
sites. Monarchs are weakened by sites between 2013 and 2016, and
the protozoan parasite, Ophryocys- found a low 8% (N=2135) infection
tis elektroscirrha. Spores deposited rate. The discrepancy between the
by infected females on milkweed 53-68% infection rate in 1990 and
plants during egglaying are the the low 8% infection rates seen
major source of infection. New recently may be important.
infections start when larvae eat the In the early 1990s there were
spores (Altizer 2001; Altizer and fewer hazards during the western
deRoode 2015). migration, and millions of infected
But by themselves, parasites monarchs were able to make the
are not a likely cause of the cata- journey successfully. There were
strophic decline. Leong et al. (1992) no systemic pesticides, no genet-
found that monarchs collected in ically engineered crops using gly-
1990 at two western overwintering phosate, and catastrophic wildfires
2021 sites had infection rates of 53-68% were fewer. Hazards increased in
(N= 540). About 17% were heavily 2013-2016, and more of the weak-
infected (>50,000 spores). Migrating er infected monarchs were killed.
populations were still robust at that Systemic pesticides were used
time, numbering about a million. during this time, and the effects of
Infection caused no adult mortality climate change, such as drought
at the cool overwintering tempera- and wildfires had increased. Fewer
IPM Practitioner, XXXVII (5/6) Published April 2021 2 Box 7414, Berkeley, CA 94707
Update
monarchs arrive at overwintering are exposed to the extreme weather
Courtesy Glenda Dennison, UW Madison LNP
sites now, but those that do have events caused by climate change.
less disease (Quarles 2012; 2018). The eastern population is exposed
to many of the same negative
Pesticides and Land Use factors as the western population,
Monarch decline is part of the except there is one big difference—
worldwide disappearance of insects the widespread western forest fires
and wildlife. Human populations (WWF 2021).
have nearly doubled in the last 40 Table 1 shows western over-
years, and wildlife populations have wintering populations and the
decreased by 50% or more. Special- number of acres burned in Cali-
ist insects such as the monarchs fornia each year. There is a rough
are affected more than generalists Western migrations are hazardous. correlation between acres burned
(Quarles 2019; Sanchez-Bayo and Pesticides, loss of milkweed and and overwintering numbers. As
Wyckhuys 2019). nectar plants, drought and forest acres burned go up, overwintering
fires are killing the monarchs. populations go down. The most
Pesticides, loss of milkweed
and nectar plants, climate change, catastrophic reductions occur
But drought and wildfires
development, and forest fires have during, or one year after, the most
associated with climate change
likely led to the vanishing monarch devastating forest fires. Populations
may be becoming more important.
population. Crone et al. (2019) found dropped 6-fold from about 150,000
Flying through burning vegetation
that land use factors such as de- in 2017 to about 25,000 in 2018
could not be pleasant. Monarchs fly
velopment at overwintering sites, when fire acreage approximately
across California toward the coast in
destruction of breeding habitat, and doubled from less than a million in
September, October and November
pesticide applications in breeding 2016 to more than 1.5 million acres
when the fires are most frequent.
areas were more important for west- in 2017 and 2018. The 10-fold cat-
And due to drought, levels of early
ern migratory monarch decline than astrophic drop from about 20,000
season milkweed in coastal hills and
climate change and global warming. to about 2,000 in 2020 occurred
the Central Valley of California in the
Neonicotinoids accumulate in milk- when fires increased about 16-fold
spring are often not sufficient to sup-
weed and nectar plants, and nectar to more than 4 million acres (McK-
port monarch caterpillars (Frey and
plants and milkweed can be killed by night 2021a; Cal Fire 2020).
Schaffner 2004; McKnight 2021a;
herbicide drift from glyphosate crop Milkweed, nectar plants, and
Malcolm 2018).
applications (Pecenka and Lundgren monarchs are likely burned during
2015; Krischik et al. 2015; Goulson Monarchs and Fire these periods. Dense smoke may in-
2013; Malcolm 2018). Permethrin The eastern migratory popu- terfere with the migratory pattern.
and other mosquito sprays contami- lation has also seen steep declines Fires are also markers for drought
nate milkweed, killing larvae that eat (see below), but declines have so far conditions that impact survival of
it and adults that contact it (Ober- been limited to about 80-84%. Both milkweed and nectar plants (McK-
hauser et al. 2006). eastern and western populations night 2021a; Malcolm 2018).
Table 1. California Fires and Overwintering Monarch Populations*
Number Number
Sites Number Average
Year Monarchs Monarchs Fire Acres
Monitored Fires Fire Acres
Thanksgiving New Years
2016 167,582 94,908 (2017) 44 669,534 6,954 96
2017 147,343 74,728 (2018) 115 1,548,429 9,270 167
2018 25,253 16,063 (2019) 130 1,975,086 7,948 248
2019 21,944 11,970 (2020) 117 259,823 7,860 33
2020 1642 1039 (2021) 149 4,257,863 9,917 429
*From McKnight 2021a and Cal Fire 2020, 2019, 2018, 2017, 2016
Box 7414, Berkeley, CA 94707 3 IPM Practitioner, XXXVII (5/6) Published April 2021
Update
Chance for Recovery
Photo courtesy Jim Lovett, www.MonarchWatch.org
There is a hard road ahead for
the western migratory monarch. At
New Years 2021, there were only
about 1,000. Since adult monarch
populations are about 50% female,
approximately 500 of the survivors
were probably females (McKnight
2021a). Each female lays 300-400
eggs, but there is a high attrition
rate from natural enemies, weather
and humans. More than 90% are
killed in the egg, larval, and pupal
stage. Natural enemies include
spiders, ants, ladybugs, lacewing
larvae, paper wasps, parasitoid
wasps, and tachinid flies. In many
cases, 98% are dead before they
become 3rd larval instars. In realis-
tic conditions, about 3-8 survive to
become reproductive adults (Prysby
et al. 2004; Oberhauser 2004). Mating monarchs are capable of producing large numbers of replacements.
From these figures, the best Monarchs are resilient and survived the asteroid that killed all the
case for the 2021 western monarch dinosaurs 65 million years ago. But they will need help to survive the
is about 4,000 adults in the first environmental insults created by humans.
generation, but 2021 is expected
decide to become local residents. tion of about 2,000, but does not
to be a drought year in Califor-
Because of global warming with its explain the drop from millions in
nia. If the trend follows that of the
milder winters and early springs, the 1980s or even the drop from
last three years, the overwintering
resident populations have been about 167,000 seen at overwinter-
population will likely be the same
increasing slightly. There have been ing sites in 2016.
or smaller than in 2020 (see Table
resident populations in Los Ange-
1). In the worst case, if there are
catastrophic fires similar to 2020,
les since 1970. Recently, resident Eastern Populations Also
the population might vanish.
populations have been found in the Decline
San Francisco Bay Area. Residents The eastern monarch popu-
may have been encouraged by lations are also declining. Possible
Resident Populations conservation efforts in urban areas factors are phenological disruption
Some monarchs do not take with the planting of milkweed and due to global warming, loss of milk-
part in the annual migration, but nectar resources (McKnight 2021b; weed breeding sites, nectar food
Satterfield et al. 2016). supply disrupted by pesticides and
Planting of milkweed and habitat destruction, bad weather,
Photo courtesy Michelle Solensky
nectar sources in urban gardens and logging at the overwintering
should continue, even if this sites in Mexico (Thogmartin et al.
encourages residents in warmer 2017).
areas. If the migrating monarchs The World Wildlife Fund has
go extinct, at least we will have been monitoring overwintering
the residents. The slight increase populations in Mexico for the last
in resident populations has not 28 years. There is considerable year
caused the dramatic decrease at to year fluctuation, but the trend
overwintering sites. One estimate is generally downward from a high
of the resident population in the SF of 44.95 acres (18.2 ha) in 1996
Bay Area in 2020 is about 12,000 to a low of 1.66 acres (0.67 ha) in
(Crone et al 2021). This number is 2013—a drop of 96.3%. Using ex-
about 7% of the western migratory treme endpoints for measurement
population seen in 2016 and 0.3% may overestimate the losses, and
Each female can lay 300-400 eggs, of the population seen in 1980. The use of trend lines gives estimates of
but 98% of developing monarchs resident population may outnum- 80-84% loss since 1996 (Saunders
are killed before the pupal stage. ber the current migratory popula- et al. 2019; Pleasants 2017).
IPM Practitioner, XXXVII (5/6) Published April 2021 4 Box 7414, Berkeley, CA 94707Update
Overwintering populations
Photo courtesy Joop de Roode
are measured by the area of the
site. Brower (1977) calculated that
each acre contained about 4 mil-
lion monarchs (9.9 million/ha).
The U.S. Fish and Wildlife Service
has estimated 8.5 million/acre (21
million/ha) (USFWS 2020).
The World Wildlife Fund Mex-
ico announced February 25, 2021
that the overwintering population
occupied 2.1 ha (5.10 acres) during
the winter of 2020-2021. This acre-
age represents a drop of about 26%
compared to the previous winter
(2.83 ha; 6.99 acres) (McKnight
2021c). The population size consid-
ered to be a buffer against extinc-
tion is 6 ha (15 acres)(Pleasants
2017).
Milkweed Loss Monarch caterpillars such as this one feed only on milkweed. Milkweed
Milkweed destruction in breed- contains cardenolide steroids that protect them against their protozoan
ing sites is a major factor in the East parasite, O. elektroscirrha. The steroids also give them a bad taste that
(Pleasants and Oberhauser 2013). deters vertebrate predators.
The milkweed population dropped
from 2.2 billion in the Midwest in Failing Fall Migration State of Indiana was contaminated
Some researchers cite citi- by neonicotinoids. Neonicotinoid
1999 to 1.34 billion in 2014, a de-
zen surveys of summer monarch contamination goes out at least 100
cline of 40%. Much of the loss was
populations to claim that there has m (328 ft) beyond fields, and may
in agricultural fields treated with
not been a loss in summer mon- be poisoning monarch food plants
glyphosate (Roundup®). Because
arch populations despite the loss of and milkweed through drift and
3.4 times as many eggs are laid on
milkweed. Their conclusion is based water runoff (Hladik et al. 2018;
milkweed inside agricultural fields,
on surveys of egg and adult mon- Mogren and Lundgren 2016).
the decline in reproductive capacity
arch populations in the Midwest Saunders et al. (2019) propose
was 71% (Pleasants 2017).
and other areas (Davis and Dyer that drought encountered by the
The milkweed decline from
2015; Ries et al. 2015; Inamine et fall migration in Texas has con-
2000 to 2008 was exponential, and
al. 2016). tributed to smaller overwintering
the most favorable milkweed has
These surveys have led to the populations. When satellite imagery
been lost. If half of the milkweed is
conclusion that monarchs are not shows the migratory route is less
destroyed, egglaying on that remain-
making it back to Mexico during the green, overwintering populations
ing must double up to maintain the
fall migration. Populations may be are smaller. Drought and less green
population. The more crowded the
weaker due to crowding on remain- landscapes mean fewer nectar
plant, the less available nutrition
ing milkweed plants. Or because of plants to feed the migrating butter-
(Pleasants 2017). Pleasants et al.
global warming they may start the flies.
(2017) believe that less milkweed
has simply made it more difficult for migration late and do not find the
females to find it, and that has led to same food supply as before (Agar- Systematic Flaws and
the monarch population decline. wal and Inamine 2018; Agarwal Climate
The milkweed hypothesis 2019). Pleasants et al. (2017) believe
fits with data obtained from oth- Migrating monarchs may that the summer counts have a
er butterfly species. Conservation also encounter poisoned nectar systematic error. Citizen scientists
biologists believe that crashing plants. Nectar plants and milkweed have not included agricultural
populations of butterflies can best throughout the breeding grounds areas in their counts. Milkweed
be restored by establishing optimum have been poisoned by pesticides. and monarchs have vanished from
stands of larval habitat (Thomas et Neonicotinoid insecticides are used agricultural fields, and populations
al. 2011). in corn and soybean fields through- have shifted into areas where citizen
out the Midwest. Krupke et al. scientists have made their counts.
(2017) estimated that 42% of the This systematic error leads to an
Box 7414, Berkeley, CA 94707 5 IPM Practitioner, XXXVII (5/6) Published April 2021Update
overestimate of summer populations. coneflower, Echinacea purpurea;
Photo courtesy of the University of Minnesota Monarch Lab
Monarch overwintering losses, then, and blazing stars, Liatris spp. can
are mostly due to milkweed and hab- provide nourishment. And in the
itat losses in the breeding grounds, fall, asters, Symphyotricum spp.
but there are undoubtedly losses and witch hazels, Hamamelis spp.
during the fall migration (Flockhart can provide nectar (Popkin 2014).
et al. 2015; Saunders et al. 2019). Organizations such as Monarch
Climate may also be a factor. Watch, Wild Ones, and Monarch
Flockhart et al. (2017) found mon- Joint Venture have online lists of
arch origins at overwintering sites monarch friendly plants (see Re-
varied from year to year according sources).
to regional climate in the breeding If natives are not available,
grounds, but numbers from all areas plants attractive to butterflies
have recently shrunk. About 40% of include butterfly bush, Buddleia
the overwintering population came davidii; yarrow, Achillea millefolium;
from the Midwest. aster, Callistephus sp.; lavender,
Lavendula sp.; lilac, Syringa sp.;
Conservation Efforts Mexican sunflower, Tithonia diversi-
Should Continue folia; burning bush, Dictamnus sp.
The Xerces Society recom- and others. Much information on
mends planting native milkweed butterfly gardens is available on the
and nectar sources more than five internet and in classic books on the
miles from the California Coast About 92% of eastern monarchs
subject (Xerces 1990; 2016).
in the Sierra Foothills, Central develop on common milkweed,
Valley, and in the Northern part Asclepias syriaca.
Tropical Milkweed
of the state toward Oregon. They One argument against encour-
recommend California milkweed, aging residents where migrations
Asclepias californica; heartleaf milk- gardeners do not like to plant it
because it is aggressive in gardens, are vanishing is that this may lead
weed, A. cordifolia; and woollypod to increased monarch infections.
milkweed, A. eriocarpa in Northern spreading from root buds. Growing
in raised beds will minimize this, Some resident populations have
California and desert milkweed, A. shown increased parasites com-
erosa in Southern California. The but there are other native milk-
weeds such as butterfly weed, A. pared to migrating monarchs in
Xerces Society should be contacted the same area. Satterfield et al.
for seed sources (McKnight 2021a). tuberosa, or purple milkweed, A.
purpurascens that may be more ap- (2016) monitored monarch disease
Milkweed and nectar plants frequency in Southern California
should also be established for the propriate in some gardens (Popkin
2014). from 2013 to 2016. They found the
eastern migration. Monarch Watch, infection rate was nine times higher
Monarch Joint Venture, and oth- (N=1290, 74% infected) for mon-
er organizations (see Resources) Nectar Plants archs breeding on tropical milk-
should be contacted for the types Monarch adults need nectar to
weed, Asclepias curassavica, in ur-
of milkweed and nectar plants. survive, and the migrating gener-
ban gardens compared to monarchs
Milkweed species most frequently ation consumes nectar to build fat
at overwintering sites (N=2135, 8%
utilized by the eastern monarchs reserves for overwintering. Some
infected).
are A. viridis and A. humistrata that of the nectar can come from milk-
As mentioned above, infec-
support spring monarchs in the weed, but other sources are neces-
tions are low in overwintering sites
south, and A. syriaca that supports sary. When planting, choose natives
because current migrations are
summer and fall monarchs in the when possible. Fall nectar sources
hazardous, and the weakest indi-
north (Malcolm and Brower 1989). are important, and these include
viduals are killed. Attrition occurs
If you cannot obtain locally Ageratina hvanensis, Bacharis
both in the west and in the east.
sourced seeds, and you are in the neglecta, Helianthus maximiliani,
The eastern migration is a difficult
Eastern U.S., it is better to buy Liatris mucronata, Solidago nemora-
journey over 2500 miles, and in-
commercially available A. syriaca lis, and especially Vebesina virgini-
fection rates at overwintering sites
seeds than to not plant milkweed ca (Brower et al. 2012). Other good
in Mexico are about 9.3%, which
at all (see Resources). About 92% nectar plants are Lupinus, Senecio,
is similar to the 8% now found on
of the overwintering Eastern popu- Stevia, and Bidens (Brower 1977).
the West Coast. Eastern infection
lation feeds on A. syriaca (Malcolm Native nectar sources in the spring
rates at summer breeding grounds
and Brower 1989). include violets, Viola spp. and
are 14.1% (Satterfield et al. 2015;
Although A. syriaca is the serviceberries, Amelanchier spp. In
Altizer and deRoode 2015; Bartel et
best adapted to monarchs, many the summer, sumacs, Rhus spp.;
al. 2011).
IPM Practitioner, XXXVII (5/6) Published April 2021 6 Box 7414, Berkeley, CA 94707Update
ta (de Roode et al. 2008). Though tions have been registered. Other
Photo courtesy Jim Lovett, www.MonarchWatch.org
spores can accumulate when milk- organizations with pollinator and
weed is limited, spores on milkweed butterfly garden certification pro-
lose 80% of their viability over the grams include the Xerces Society,
course of a year (Leong et al. 1997a; Monarch Joint Venture, the North
de Roode et al. 2008). Planting new American Butterfly Association, and
milkweed each year should reduce Wild Ones (see Resources) (Popkin
the accumulation of spores in the 2014).
resident populations.
If resident populations grow Network of Garden Clubs
large, some of the resident mon- There are millions of back-
archs may resume the migrations. yard gardeners in the U.S. and 40
Both monarchs and tropical milk- million acres (16.2 ha) of lawns.
weed are natives of Mexico, and Local action such as planting bee
monarchs evolved with the ances- and butterfly gardens can have
tral tropical milkweed plant. Over- a national impact. A network of
population likely led to the start of Garden Clubs with similar plans
migrations two million years ago. and policies could convert local
Monarchs were so successful popu- conservation efforts into a national
lations outgrew the local milkweed program (Quarles 2019).
supply, and the monarchs went
north looking for additional sourc-
Resident populations often develop Monarchs Along the
es (Rapini et al. 2007; Zahn et al.
on tropical milkweed, Asclepias Roadside
2014).
curassavica. There are 10 million acres (4
million ha) of roadsides in the U.S.
Medical Milkweed Reduce Pesticides Conversion of these from herbicide
One explanation for increased We can help the monarchs by management to integrated vegeta-
infections in residents is that trop- reducing pesticide applications in tion management (IVM) and native
ical milkweed is a sink for infected gardens and in agricultural sit- plants could bring back needed
individuals. Infected monarchs uations. We should be sure that habitat for bees, birds, and mon-
may be drawn out of the migrations nursery plants have not been archs (Quarles 2003). For instance,
toward tropical milkweed in urban treated with systemic pesticides. conversion from herbicide man-
gardens. It has one of the highest IPM methods can be used to control agement to IVM and native plants
steroid contents of any milkweed pests. For example, crop rotation, increased the number of roadside
available (10.6 mg per gram of milk- soil treatment with nematodes, and milkweed sites in Iowa by about
weed dry weight). Tropical milkweed adult beetle baits can be used to 64% (Hartzler 2010).
has 20 times the steroid content control the western corn rootworm,
of A. syriaca (0.5 mg/gram) and Diabrotica virgifera virgifera (Quarles
Photo courtesy Tony Morosco
many other native U.S. milkweeds 2017).
(Malcolm 1991; Quarles 2016).
Cardenolide steroids ingested from Concerted Social Effort
milkweed are known to decrease Monarch restoration is the goal
virulence and lessen the biological of several environmental groups.
impact of the monarch parasite (de Bringing Back the Monarchs is a
Roode et al. 2008; Sternberg et al. project of Monarch Watch. Monarch
2012). Watch encourages home garden-
There are resident populations ers to plant milkweed and nectar
of monarchs in warm areas such as plants, and in return will register
Florida, Texas, Arizona and Cali- the garden as a Monarch Way Sta-
fornia. Some of these are heavily tion (see Resources). Recommen-
infected, but there is no evidence dations include an area of at least
that these populations are declining 100 ft2, six hours of sun a day, low
(Satterfield et al. 2015; Glassberg clay soils with good drainage, at
2014; Majewska et al. 2019). In- least ten milkweed plants, prefer-
fected monarchs feeding on tropical ably from different species, and at Monarchs are fond of sunflowers,
milkweed live longer than those least four species of nectar plants. Helianthus spp.
feeding on the native A. incarna- Nearly 13,000 Monarch Way Sta-
Box 7414, Berkeley, CA 94707 7 IPM Practitioner, XXXVII (5/6) Published April 2021Update
Endangered Species Glassberg, J. 2014. Tropical milkweed and the in-
jurious effects of well meaning people. American
Protection William Quarles, Ph.D., is an IPM Butterflies Winter: 4-10.
The U.S. FWS (US Fish and Specialist, Executive Director of Goulson, D. 2013. An overview of the environmen-
Wildlife Service) received a petition the Bio-Integral Resource Center tal risks posed by neonicotinoid pesticides. J.
Appl. Ecol. 50:977-987.
in 2014 to list Danaus plexippus (BIRC), and Managing Editor of
as an endangered species. On the IPM Practitioner. He can be Hartzler, R.G. 2010. Reduction in common milk-
weed (Asclepias syriaca) occurrence in Iowa
December 15, 2020 the Trump reached by email, birc@igc.org cropland from 1999 to 2009. Crop Protection
administration denied a listing 29:1542-1544.
as endangered, despite finding Hladik, M.L., A.R. Main and D. Goulson. 2018.
that monarchs meet the criteria. References Environmental risks and challenges associated
Agarwal, A.A. and H. Inamine. 2018. Mechanisms with neonicotinoid insecticides. Environ. Sci.
The listing assigned is “warranted behind the monarch’s decline. Science 360 Technol. 52:3329-3335.
but not precluded.” This catego- (6395):1294-1296. June 22, 2018.
Inamine, H., S.P. Ellner, J.P. Springer et al. 2016.
ry means that monarchs will be Agarwal, A.A. 2019. Advances in understanding Linking the continental migratory cycle of the
the long-term population decline of monarch monarch butterfly to understand its population
evaluated each year for endangered butterflies. PNAS 116(17):8093-8095. April 23, decline. Oikos 125:1081-1091.
species protection. U.S. FWS said 2019.
Krischik, V., M. Rogers, G. Gupta et al. 2015. Soil
that the monarchs were not listed Altizer, S. 2001. Migratory behavior and host-par- applied imidacloprid translocates to ornamental
because 161 other species have a asite coevolution in natural populations of flowers and reduces survival of adult Colemegil-
monarch butterflies infected with a protozoan la maculata, Harmonia axyridis, and Hippoda-
higher priority. Perhaps the Biden parasite. Evol. Ecol. Res. 3:611-632. mia convergens lady beetles, and larval Danaus
administration will list monarchs as Altizer, S. and J.C. deRoode. 2015. Monarchs and plexippus and Vanessa cardui butterflies. PLoS
endangered (USFWS 2020). their debilitating parasites. In: Oberhauser et al. ONE 19(3):e0119133
2015, pp. 83-93 of 321 pp. Krupke, C.H., J.D. Holland, E.Y. Long et al. 2017.
Planting of neonicotinoid treated maize poses
Mitigation of Climate Bartel, R.A., K.S. Oberhauser, J.C. de Roode et
al. 2011. Monarch migration and parasite risks to honey bees and other non-target organ-
Change transmission in eastern North America. Ecology isms over a wide area without consistent crop
yield benefit. J. Appl. Ecol. 54:1449-1456.
Efforts should not be limited 92(2):342-351.
Leong, K.L.H., H.K. Kaya, M.A. Yoshimura et al.
to planting milkweed and nectar Brower, L.P. 1977. Monarch migration. Nat. Histo-
1992. The occurrence and effect of a protozoan
ry 86(6):41-52.
resources and reducing pesticide parasite, Ophryocystis elektroscirrha on overwin-
Brower, L.P., O.R. Taylor, E.H. Williams et al. tering monarch butterflies, Danaus plexippus
applications. Drought and forest 2012. Decline of monarch butterflies overwin- from two California overwintering sites. Ecol.
fires linked to climate change may tering in Mexico: is the migratory phenomenon Entomol. 17(4):338-342.
be factors in the western migratory at risk? Insect Conserv. Divers. 5(2):95-100.
Leong, K.L.H., M.A. Yoshimura, H.K. Kaya et al.
collapse. We should encourage in- Cal Fire. 2020. 2020 Incident archives. A summa- 1997a. Instar susceptibility of the monarch
ry of all 2020 wildfires, including those man- butterfly (Danaus plexippus) to the neogregarine
creased use of regenerative agri- aged by Cal Fire and other partner agencies. parasite, Ophyrocystis elektroscirrha. J. Invert.
culture, changes of diet to include Fire.ca.gov/incidents/2020 Pathol. 69:79-83.
more vegetables, increased renew- Cal Fire. 2019, 2018, 2017, 2016. Ibid. Leong, K.L.H., M.A. Yoshimura, H.K. Kaya et al.
able energy, and decreased reliance Crone, E.E., E.M. Pelton, L.M. Brown et al. 2019. 1997b. Occurrence of a neogregarine protozo-
an, Ophryocystis elektroscirrha in populations
on fossil fuels to mitigate effects Why are monarch butterflies declining in the
of monarch and queen butterflies. Pan Pacific
West? Understanding the importance of mul-
of climate change (Quarles 2007; tiple correlated drivers. Ecol. Applications 29: Entomol. 73(1):49-51.
Quarles 2018). e01975. Leong, K.L.H., W.H. Sakai, W. Bremer et al. 2004.
Crone, E. and C. Schultz. 2021. Resilience or ca- Analysis of the pattern of distribution and
abundance of monarch overwintering sites
Conclusion tastrophe? A possible state change for monarch
butterflies in the West. Authorea.com. February along the California coastline. In: Oberhauser
Monarchs have been migrat- 23, 2021. and Solensky 2004, pp. 177-185 of 248 pp.
ing for two million years, and they Davis, A.K. and L.A. Dyer. 2015. Long-term trends Majewska, A.A., D.A. Satterfield, R.B. Harrison
et al. 2019. Urbanization predicts infection
survived the worldwide destruction in eastern North American monarch butter-
risk by a protozoan parasite in non-migratory
flies. A collection of studies focusing on spring,
that killed the dinosaurs 65 mil- summer, and fall dynamics. Ann. Entomol. Soc. population of monarch butterflies from the
lion years ago. We should not let Am. 108:661-663. southern coastal U.S. and Hawaii. Landscape
Ecol. 34:649-661.
such a beautiful work of nature go de Roode, J.C., A.B. Pedersen, M.S. Hunter et al.
Malcolm, S.B. and L.P. Brower. 1989. Evolutionary
extinct. In the short term we can et al. 2008. Host plant species affects virulence
and ecological implications of cardenolide se-
in monarch butterfly parasites. J. Animal Ecol.
help them by providing milkweed, 77:120-126. questration in the monarch butterfly. Experien-
nectar plants and other resources tia 45(3):284-295.
Flockhart, D.T., J.B. Pichancourt, D.R. Norris
they need. In the long run, we must et al. 2015. Unraveling the annual cycle in a Malcolm, S.B. 1991. Cardenolide mediated interac-
tions between plants and butterflies. In: Rosen-
reduce emissions of greenhouse migratory animal: breeding season habitat loss
thal and Berenbaum, pp. 251-296 of 468 pp.
drives population declines of monarch butter-
gases. Monarchs will be encouraged flies. J. Animal Ecol. 84:155-165. Malcolm, S.B. 2018. Anthropogenic impacts on
by mitigation of drought, forest Flockhart, D.T., L.P. Brower, M.I. Ramirez et al. mortality and population viability of the mon-
fires, and the extreme weather 2017. Regional climate on the breeding grounds arch butterfly. Annu. Rev. Entomol. 63:277-302.
effects caused by global warming. predicts variation in the natal origin of monarch McKnight, S. 2021a. Fifth Annual Western Mon-
butterflies overwintering in Mexico over 38 arch New Year’s Count confirms continued
By making things better for the years. Global Change Biol. 23:2565-2576. decline in western monarch population. Xerces
monarchs, we can also make things Frey, D. and A. Schaffner. 2004. Spatial and Society for Invertebrate Conservation. Portland,
better for ourselves. temporal pattern of monarch overwintering OR. Xerces.org.
abundance in western North America. In: McKnight, S. 2021b. Resident monarch population
Oberhauser and Solensky 2004, pp. 167-176 on the rise in California: what does this mean
of 248 pp. for the western migratory population. Ibid.
IPM Practitioner, XXXVII (5/6) Published April 2021 8 Box 7414, Berkeley, CA 94707Update
McKnight, S. 2021c. Monarch numbers from Mex- Ries, L., D.J. Taron, E. Rendon-Salinas et al.
ico point to declining population. Ibid.
Mogren, C.L. and J.G. Lundgren. 2016. Neonico-
2015. The disconnect between summer and
winter monarch trends for the eastern migra- Resources
tory populations. Possible links to differing
tinoid contaminated pollinator strips adjacent
drivers. Ann. Entomol. Soc. Am. 108:691-699.
to cropland reduces honeybee nutrition status. Organizations
Sci. Rpts. 6:29608. Rosenthal, G.A. and M.R. Berenbaum, eds. 1991.
Herbivores: the Interactions with Secondary Bio-Integral Resource Center (BIRC), PO
Oberhauser, K.S. 2004. Overview of monarch
Plant Metabolites, 2nd edition. Vol. 1. The Box 7414, Berkeley, CA 94707; 510-
biology. In: Oberhauser and Solensky 2004, pp.
Chemical Participants. Academic Press, San 524-2567; www.birc.org
3-7 of 248 pp.
Diego. 468 pp.
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Sanchez-Bayo and K.A.G. Wyckhuys. 2019. World-
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Satterfield, D.A., J.C. Maerz and S. Altizer. 2015.
2006. Growth and survival of monarch butter-
flies after exposure to permethrin barrier treat-
Loss of migratory behavior increases infection San Pablo Ave., Suite G, Berkeley, CA
risk for a butterfly host. Proc. Royal Soc. B. 282: 94702; 510-843-2222; www.goldenga-
ments. Environ. Entomol. 35(6):1626-1634.
20141734
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teaudubon.org
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2015. Monarchs in a Changing World: Biology
2016. Migrating monarchs in California experi-
Monarch Joint Venture, 135 Skok Hall,
and Conservation of an Iconic Butterfly. Cornell 2003 Upper Buford Cir., St. Paul, MN
ence low infection risk compared to monarchs
University Press, Ithaca. 321 pp.
breeding year round on non-native milkweed. 55108; 612-624-8706; www.monarch-
Pecenka, J.R. and J.G. Lundgren. 2015. Non-tar- Integrative Comparative Biol. 56:343-352. jointventure.org
get effects of clothianidin on monarch butter-
Saunders, S.P., L. Ries, N. Neupane et al. 2019. Monarch Watch, University of Kansas,
flies. Sci. Nat. 102:19.
Multiscale seasonal factors drive the size of 1200 Sunnyside Ave., Lawrence, KS
Pelton, E.M., C.B. Schultz, S.J. Jepson et al. 2019. winter monarch colonies. PNAS 116(17):8609-
Western population plummets: status, probable 8614. Apr 23, 2019. 66045; 785-864-4441; www.monarch-
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weed loss in agricultural fields due to herbicide North America. Biol. Conserv. 214:343-346. www.naba.org
use: effect on the monarch butterfly population.
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Insect Conserv. Diversity 6(2):135-144. March
plant derived disease tolerance and resistance
2013.
in a natural butterfly-plant-parasite interac-
Francisco, CA 94105; 415-977-5500;
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Midwest for monarch butterfly recovery: esti- Wild Ones, PO Box 1274, Appleton, WI
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mates of milkweeds lost, milkweeds remaining
and milkweeds that must be added to increase
al. 2017. Monarch butterfly population decline 54912; 920-730-3986; www.wildones.
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Box 7414, Berkeley, CA 94707 9 IPM Practitioner, XXXVII (5/6) Published April 2021Conference Notes
ESA 2019 Meeting Highlights
By Joel Grossman mate’, that have been selected for Over a 5-8 year period, four
bloom display, attracted a larger habitat-enhanced vineyards (30-60
The 2020 ESA Conference was number of pollinators compared native plant spp. under 50 m (164
cancelled because of the coronavirus to the straight species,” said Cy- ft) from vineyards) were compared
pandemic. These Conference High- briwsky. In cage studies, monarch to four conventional vineyards
lights were selected from among caterpillars developed well on varied (herbicides sprayed between rows;
2,885 presentations at the Nov. milkweed cultivars; defensive char-Conference Notes
are interested in replicating this but the results convinced golf Caffeine Cures Infected
low-input sustainable program for course superintendents to increase Honey Bees
its multiple benefits, even as far beneficial insect habitat to reduce Honey bees foraging on Cit-
away as Ashland, Oregon, where turfgrass pests. rus spp and Caffea spp regularly
monarch butterfly interest is high. consume 0.5-98 ppm of caffeine,
Similar programs are happening in Quercetin Rescues “which improves longevity of honey
New Zealand and Europe. California Almond Bees bees infected with Nosema cer-
Almost 100% of California al- anae,” said Edward Hsieh (Univ
mond growers spray tank mixtures Illinois-Champaign, 320 Morrill
Golf Biocontrol of insecticides such as chlorant- Hall, Urbana, IL 61801; emhsieh2@
Wildflowers raniliprole (Altacor®) and fungi- illinois.edu). “Caffeine consumption
The USA has 16,000 golf cides such as propiconazole (Tilt®) at naturally encountered concentra-
courses, each about 100 acres (40.5 during bloom, and “beekeepers tions increases survival of infected
ha), with 40-70% of that acreage providing pollination services have bees.” However, in the absence of
out-of-play spaces such as roughs, sporadically reported high mortality infection, higher late season caf-
which when sown with wildflowers of workers and problems in queens feine concentrations can be detri-
can be transformed into beneficial in weeks after almond pollination,” mental to honey bees. Thus, forag-
insect habitats for biological control said Ling-Hsiu Liao (Univ Illi- ing bees may be “self-medicating”
of turfgrass pests otherwise sprayed nois-Champaign, 320 Morrill Hall, by seeking out sources with higher
with pesticides, said Adam Dale Urbana, IL 61801; liao19@illinois. caffeine levels when infected.
(Univ Florida, 1881 Natural Area edu). After spraying, almond pollen This suggests that “caffeine
Dr, Gainesville, FL 32611; agdale@ has 400 ppb of chlorantranilipro- supplementation can be a practical
ufl.edu). “Golf courses around the le and 900 ppb of propiconazole. method of treating viral infection” in
world are converting out-of-play ar- Worker bees feed honey and pollen honey bees, said Hsieh. In caffeine
eas to naturalized or flowering hab- plus pesticide residues to devel- dose experiments on honey bees
itats, but few do so using evidence oping larvae, along with natural infected with Israeli Acute Paraly-
that maximizes their conservation plant chemicals (botanicals; phyto- sis Virus (IAPV): 25 ppm of caffeine
benefit.” Benefits in the urban USA chemicals) in whatever pollens and made no difference; but 100 ppm
could be immense, as golf courses nectars are part of the diet. caffeine helped bees cope with and
are “among the largest, most ubiq- Almond pollen laden with reduce IAPV. Research is underway
uitous highly maintained urban realistic field-levels of insecticide to determine the mechanism by
green spaces in the USA.” and fungicide residues altered which caffeine helps bees fight viral
To provide “evidence” and “de- honey bee nursing behavior, with and other infections.
velop guidelines for tailoring insect fewer visits to tend larvae; normally
conservation practices” for urban larvae are fed royal jelly, which is Citrus Psyllid Exclusion
green spaces, Dale setup three highly antimicrobial. “Consuming Mesh
5,000 ft2 (465 m2) plots, some rich pollen contaminated with both A non-chemical solution to
in wildflowers (9 spp) and others propiconazole and chlorantranilip- Asian citrus psyllid, Diaphorina
with low wildflower diversity (5 role reduced the duration of queen citri, vectoring Candidatus Liberib-
spp), at multiple Florida golf course cell visits and delivery of royal jelly acter asiaticus (CLas), the putative
locations. by nurse bees,” said Liao. causal agent of huanglongbing
“Our results indicate that “Developmental impairments (HLB), is: “Grow citrus under a
golf courses can provide valuable in larvae reared by nurses consum- protective screen (CUPS),” said
resources for beneficial insects, ing pesticide-contaminated pollen Timothy Ebert (Univ Florida, 700
both flying and ground-dwelling, in suggest that pesticide consumption Experiment Station Rd, Lake Alfred,
urban areas,” said Dale. Monitoring by nurse bees alters their behavior FL 33850; tebert@ufl.edu). The key
revealed 13 genera of native bees, or physiology to the detriment of questions are: “What is the size of
with more pollinator diversity with queen quality,” said Liao. However, the psyllid and the size of holes in
more wildflower species. Natural certain phytochemicals, such as the screen? What is the penetration
enemy abundance also increased. quercetin, a common honey bee risk of specific mesh sizes?”
For example, red and black mason dietary component from pollen and Mesh screens should exclude
wasps were observed flying in and nectar foraging, act as pesticide the smallest psyllids, allow suffi-
out of wildflower areas with cater- antidotes. Adding quercetin to lab cient air flow and be reasonably
pillar prey to provision their nests. diets acted as an antidote or “res- priced. Holes that are too small
Biocontrol was measured as a cue,” ameliorating pesticide-related may provide excellent exclusion,
50% reduction in caterpillars from behavioral impairments. but will be more costly and impede
sentinel prey stations. Golf course
chemical use was not measured,
Box 7414, Berkeley, CA 94707 11 IPM Practitioner, XXXVII (5/6) Published April 2021Conference Notes
air flow. “The width of the insect Pepper Weevil Kaolin clay 95%, which provid-
may be more important than height Alternatives ed only 40% control in lab bioas-
in determining whether the psyl- A pest of Central America says, was the best tested compound
lid can pass through the screen,” origin, pepper weevil, Anthonomus in 3-week (3 treatments/week)
said Ebert. “Mesh sizes of 40 or eugenii, is “one of the most econom- greenhouse cage trials; and was
higher are safe for construction of ically damaging arthropod pests of as effective as the neonic thiame-
CUPS. Lower mesh sizes will allow pepper crops” in North America, thoxam (positive control). Mineral
some psyllids to pass through the significantly impacting Ontario, oil and Beauveria bassiana strain
screen.” Canada’s $419 million greenhouse ANT-03 also effectively suppressed
pepper crop, said Roselyne Lab- pepper weevil populations in green-
Plant Oils Tame Resistant be (Agric Agri-Food Canada, 2585 house trials.
Bed Bugs County Rd 20, Harrow, ON N0R “Plants onto which kaolin clay,
During decades of pesticide 1G0, Canada; roselyne.labbe@cana- mineral oil or Bacillus thuringiensis
exposure, bed bugs, Cimex lect- da.ca). Lab bioassays of 15 conven- strain SDS-502 were applied also
ularius, developed resistance to tional, reduced-risk and microbial had significantly lower percentage
synthetic insecticides via over-ex- insecticides found 8 providing over fruit abortion,” said Labbe. “Future
pression of detoxification enzymes, 60% adult pepper weevil mortality: research will investigate the com-
making an IPM approach with 1) spinetoram 25%; 2) Beauveria patibility of these products with
mattress encasements and botan- bassiana strain GHA; 3) Beauve- arthropod biological control agents
icals necessary, said Sudip Gaire ria bassiana strain PPR15339; 4) used to target either the pepper
(Purdue Univ, 901 W State St, cyantraniliprole 10.2%; 5) thiame- weevil or other pests commonly
West Lafayette, IN 47907; sgaire@ thoxam 25%; 6) Beauveria bassiana associated with pepper crops.”
purdue.edu). An advantage of plant strain ANT-03; 7) mineral oil 98%;
oils is that they are EPA-exempt 8) Metarhizium anisopliae strain
and relatively safe for humans and F52.
the environment. Thyme, orega-
no, clove, geranium and coriander
oils were compared with deltame-
thrin, a pyrethroid insecticide, and
EcoRaider®, an essential oil-based
insecticide. Two bed bug strains
were tested: 1) Harlan, a suscepti-
ble strain raised in the laboratory
for over 40 years without pesticide
exposure; 2) Knoxville, a field-col-
lected strain highly resistant to
deltamethrin.
Thyme, oregano, clove, gerani-
um and coriander oils all killed del-
tamethrin-resistant Knoxville bed
bugs; i.e. no cross-resistance. All
five plant-based essential oils also
synergized deltamethrin, increasing
its toxicity against Knoxville bed
bugs. Combining deltamethrin with
thyme and oregano oils gave over
90% control of deltamethrin-resis-
tant bed bugs in 24 hours. Plant
essential oils inhibit bed bug detox-
ification enzymes that would oth-
erwise neutralize insecticides such
as deltamethrin. EcoRaider, with its
essential oil blend, may work in the
same manner.
IPM Practitioner, XXXVII (5/6) Published April 2021 12 Box 7414, Berkeley, CA 94707Box 7414, Berkeley, CA 94707 13 IPM Practitioner, XXXVII (5/6) Published April 2021
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