Pennsylvania Game News - September 2010 - 54

wing beats of parasitoid wasps so they can hide. Fall webworms, for instance, are parasitized by more than 50 species of parasitic wasps and flies, creating what David L. Wagner in his Caterpillars of Eastern North America calls a “parasitoid hotel” in their nests. When arctiids metamorphose into moths, they have ears on the third and last segment of the thorax or body. Instead of flying in loops to avoid bats, they answer the bats ultrasonically. Even headless dogbane tiger moths will continue to click in response to bats as long as three hours after their decapitation. When moths ultrasound, bats break off their pursuit for one of three reasons, according to researchers. In the case of the southwestern tiger moth species Grote’s Bertholdia (Bertholdia trigona), and probably other species as well, they jam the sonar of their main predators — big brown bats. For other tiger moths, the sounds startle the bat, giving the moths time to escape. Still other moths use their ultrasound to warn bats they are toxic, so the bats will leave them alone. Many species of arctiid moths, though, including the Isabella tiger moth, also use their ultrasonic buzzes for courtship. The males of most species emit these sounds before releasing pheromones (odors that attract another member of the same species) to attract females, but Isabella tiger moths, along with ruby tiger moths (Phragmatobia fuliginosa), are unique, because only the females produce their ultrasonic buzzes. Sound is particularly important to milkweed tussock moths and other species that courtship feed on cardenolide plants, because they don’t produce pheromones and need sound to attract mates. But in most arctiid species, a female begins the courtship process by releasing a volatile pheromone from a gland near the tip of her abdomen. This forms an odor plume that a male follows upwind to a female. Such a pheromone release is known as “calling” and occurs at a certain time of
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day or night depending on the species. To emit these pheromones, a female takes an elevated post with her wings in a V shape, turns her pheromone gland inside out and then rhythmically pumps out many droplets of pheromone once every few seconds and for several minutes at a time. Some of this scent enters the wind stream. The Isabella tiger moth is particularly adept at this, emitting copious amounts of her pheromone that wafts her odor plume farther downwind than most moths. A male tiger moth finds a calling female by flying upwind. If he loses contact with her odor plume he practices “casting behavior,” by zigzagging laterally across the wind until he makes upwind progress toward the female. Once he gets close, he emits ultrasonic clicks that she answers with her own clicks. Some arctiid males also have scent organs they use during courtship to release pheromones. Apparently, they are advertising that they have fed on PAs and can offer females a nuptial gift containing a defensive alkaloid that will protect them and, when transferred to their eggs, their offspring. As researchers work with more of these interesting species they discover fascinating variations in their behavior patterns. The dogbane tiger moth male emits a 6-second sound at the same time he releases a cloud of pheromone. If he can’t produce one of these cues, a female flees. A denizen of fields, powerline right-of-ways and other open habitats, one of these caterpillars that feed on dogbane will deposit 50 to 60 eggs on the underside of a dogbane leaf. The virgin tiger moth plays possum when it is handled roughly. It flips its wings over its thorax and curls its abdomen downward, conspicuously displaying its bright yellow-and-black coloration until danger has passed. The great leopard moth engages in chemical warfare by exposing its orangemarked, metallic blue abdomen and secretGAME NEWS

Pennsylvania Game News - September 2010

Table of Contents for the Digital Edition of Pennsylvania Game News - September 2010