Image of gypsy moth larvae from: USDA Forest Service Archive, Bugwood.org
According to the Smithsonian Encyclopedia, the gypsy moth (Lymantria dispar) was brought to the United States in the mid-19th century in an attempt to find a silk-producing moth that would not be susceptible to diseases that afflicted Silkworm Moths. Deserving of their name, these moths could not be contained and in 1868 or 1869 some escaped from the breeder’s house. In only 10 years time, the neighborhood trees were badly damaged by this foliage-eating moth. Since then these larvae are infamous for their destruction of forests. In fact, according to the University of Illinois, the larvae can consume up to one square foot of foliage per day!
Image of damage caused by gyspy moth larvae from: The University of Wisconsin, Madison.
What is alarming is their wide range across the Northeastern United States as shown in this image from the US Forest Service:
How do such small larvae spread so fast? Take a look at the picture of the larva shown above. Those cute little hairs have air pockets that make the insects bouyant and are especially good at encouraging long distance travel in strong winds. Female moths also lay their eggs on cars near the trees they inhabit further ensuring their distribution far and wide.
Understanding the physiology of these pests may help us to control their numbers and limit their destruction.
Studies presented at the recent Experimental Biology Conference in Washington DC have shown that in addition to being attracted towards certain smells and tastes, these larvae may also be attracted to certain colors. In fact, the larvae migrated towards green (not suprising), blue, white, orange, red and yellow wavelengths of light compared to simple darkness. Researchers are currently comparing which colors the larvae prefer when given the choice. (KF Beattie, JL Sanford, W Carter III, VDC Shields, F Otolora-Luna, JC Dickens. “Visual Orientation behavior of gypsy moth larvae to emissive colors”)
Gypsy moth larvae have organs designed to sense specific tastes, the medial and lateral styloconic sensilla. Researchers have shown these organs to be comprised of different cells capable of detecting alkaloid substances that may be used as deterrents including strychnine, aristolochic acid, nicotine and caffeine as well as cells that can sense sugars (sucrose and inositol) or salt (potassium chloride). (T Martin, VDC Shields. “Taste receptor cells of gypsy moth larvae exhibit varying sensitivities to various phytochemicals”)
Researchers then pre-exposed the larvae to food containing alkaloid deterrents for 24 or 48 hours. They found the larvae ate less food when it contained aristocholic acid or nicotine. Tests also showed that the cells sensitive to alkaloid deterrents developed tolerance to the substances…definitely not good news for those interested in eradicating this species. (JL Sanford, N Aginam, M Khalid, VDC Shields. “Gustatory habituation to selected alkaloids by gypsy moth larvae”)