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November 2007 Faculty Focus: John Lill
By Julia Parmley In the recesses of Bell Hall sit row upon row of plastic containers filled with caterpillars of all shapes, sizes, and colors. Some are as small as a fingertip, while others are as poisonous as a jellyfish. Some are as green as the leaves they feed on; others as brightly colored as a rainbow. The lab is the domain of Assistant Professor of Biological Sciences John Lill, who with the help of a four-year $416,534 grant from the National Science Foundation (NSF), is studying the diet and habitats of the Washington, D.C., area’s native caterpillars, focusing on a little known group called “slug caterpillars.” Lill, who joined GW’s Department of Biology from Washington University in 2002, says he has always been captivated by the complexities of the caterpillar diet. “The larvae of butterflies and moths, or caterpillars, are among the most diverse and the most abundant insect herbivores on the planet,” says Lill. “Their amazing diversity and intimate interactions with their host plants fascinates me. Caterpillars are also abundant in the temperate zone, common in forests, which are nice places to work, and fun to observe and rear in the laboratory—a combination that makes them very attractive!” Lill’s interest in bugs isn’t limited to caterpillars. He is fascinated by what he calls “social insects,” such as bees, wasps, and ants, and has a “soft spot” for stick insects and weevils. “Damselflies are also a favorite,” he says. “They are so delicate and colorful; it’s hard not to like them.” While summertime into early fall is peak season for the caterpillars, finding them is not so easy. Lill and his team of GW student research assistants spend 12 to 14 hours each week combing the Patuxent Research Refuge in Laurel, Md., and the Little Bennett Regional Park in Clarksburg, Md., for four species of slug caterpillar: saddleback, spiny oak, yellow shouldered, and skiff moth. The caterpillars vary tremendously in size and color. Some even have spines that sting potential predators, leaving a burning sensation similar to that of a jellyfish sting, says Lill. He explains that slug caterpillars are “generalists,” meaning they feed on a wide variety of plant species with varying nutritional qualities. “The main thrust of the National Science Foundation grant is to understand the dietary breadth of caterpillars and why they feed on so many species of plant,” says Lill. “We are trying to improve our understanding of which plants they feed on and which predators eat the caterpillars.” Lill says one hypothesis explaining caterpillars’ diverse appetite is that the plants with high nutritional value are often riddled with predators, such as wasps and parasites. To determine the “fitness” of the insects in the wild, Lill and his team place some caterpillars in small plastic “sleeve cages” that protect them from would-be predators, while leaving others unprotected on six different tree species. “Every week we open up the bags to see if the caterpillars have survived or not, and we measure them for growth,” says Lill. “We are looking to see if the best foods might also be the most dangerous for the caterpillars.” Another hypothesis is that a plant’s nutritional value and attraction to predators varies each year, causing caterpillars to adjust their diet accordingly. Lill believes a plant’s scent may vary over time, which could lead a moth to lay its eggs on a different species of plant than the year before. “There’s a whole world of smell that we don’t understand very well,” says Lill. “But there’s a wealth of studies that show that the smell elicited by plants attract enemies, and we think predators played a huge role in the evolution of these caterpillars.” To conduct their study, Lill and his team, including postdoctoral associate Shannon Murphy, must collect and rear thousands of caterpillars every summer. The work is very labor intensive, requiring Lill and his team to search under leaves and trees for specimens as small as two millimeters. Once found, the caterpillars are stored in plastic containers in what Lill calls “a wall of caterpillar fates” in Bell Hall. Lill and his research assistants constantly check on the insects, replacing their food once a week, noting their growth, and recording the species of plant the caterpillar is eating. Small paintbrushes are used to transport the stinging caterpillars from leaf to leaf. In addition, the group spends two nights a week at the Maryland parks collecting female moths. Using a method called backlighting, the team shines a light and collects the moths that land nearby. Lill says the team often stays outside until 1 a.m. collecting the moths. “We have mating chambers in the lab so the moths can lay eggs,” says Lill. “Our moths only have one generation per season so we only get one shot every year.” As required by the NSF grant, Lill and his team also are reaching out to local schools. In September, they brought their “caterpillar zoo” to second grade classrooms in two Montgomery County schools to teach students about insect evolution and have plans to take them backlighting in area parks. Lill also teaches three classes in the Department of Biology and says he feels strongly about bringing his classroom outside. “I really enjoy working with students in the field, because I think that’s where learning really happens,” he says. Given the NSF’s funding rate of only 8 percent, Lill says the grant is “huge.” “I had really good support from GW to get the pilot data necessary for the NSF proposal,” he says. “This grant has really increased my resources; it means a lot to me.”
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