monarch-esa-petition-final_61585

pesticides commonly used for Mormon cricket and grasshopper control: diflubenzuron (Dimilin),
carbaryl (spray and granular formulations), and malathion (USDA APHIS 2002).
All pesticides that can be used to control native grasshoppers are thought to be highly toxic to all
life stages of the monarch butterfly, since they are broad-spectrum insecticides, with the
exception of diflubenzuron which is primarily toxic to the larval stage. Carbaryl is a carbamate
insecticide that inhibits the action of the enzyme acetyl cholinesterase (AChE) that is an essential
component of insect, bird, fish, and mammal nervous systems. Carbaryl has “very high” toxicity
levels for terrestrial invertebrates (Cox 1993), including butterflies. Malathion is an
organophosphate insecticide and is highly toxic to a broad range of insects including butterflies.
Dimilin is the trade name for the pesticide diflubenzuron. Dimilin acts as an insect growth
inhibitor by arresting chitin synthesis, i.e., the formation of an insect’s exoskeleton. Dimilin is
lethal to lepidoptera caterpillars at extremely small quantities (Martinat et al. 1987). Dimilin
caused 100 percent mortality of Douglas-fir tussock moth larvae up to seven weeks following
application (Robertson and Boelter 1979). Another study found residue on foliage 21 days after
application (Martinat et al. 1987). Sample et al. (1993) found that after Dimilin spraying, the
number of lepidoptera larvae was reduced at treated sites.
Herbicides
In addition to indirect effects of herbicides on the monarch population via loss of milkweeds, as
described in the Modification and Curtailment of Habitat section of this petition, some herbicides
also exert toxic lethal and sub-lethal effects against butterflies (Russell and Shultz 2009).
Herbicides may directly harm exposed insects, such as monarchs. Some herbicides have been
shown to leave residues that cause lepidopteran larvae to stop feeding on herbicide- exposed
plants, and also some herbicides directly inhibit enzymes within the exposed insects (Russell and
Shultz 2009, Bohnenblust et al. 2013). For example, glufosinate may have direct effects on
lepidopteran pollinators when larvae eat glufosinate-containing pollen, nectar or leaves, either
after direct over-spray or from drift. Glufosinate is one of the herbicides utilized on several
currently grown genetically engineered, herbicide-resistant crops, and several new genetically
engineered crops resistant to glufosinate and oher herbicides are slated for introduction in the
coming years (Table 1); should these crops be approved for planting, glufosinate use could rise
significantly.
Laboratory experiments with the skipper butterfly (Calpodes ethlias) showed that larvae fed
glufosinate-coated leaves were injured or killed by inhibition of glutamine synthase, at doses
comparable to the amount that might realistically be acquired by feeding on GLA [glufosinate]-
treated crops. These studies were done with the active ingredient, not a full formulation, and so
may have underestimated field toxicity (Kutlesa and Caveney 2001). Although monarchs will
not use these crops as host plants for larvae, glufosinate may accumulate in nectar, pollen and
guttation liquid of treated crops and be consumed by monarch butterflies. Also, glufosinate may
drift onto milkweeds, exposing immature stages of monarchs to residues.
In sum, a plethora of pesticides used in a variety of applications threaten monarch adults and
larvae across their range.
Monarch ESA Petition 100