DISSERTATION RESEARCH: Costs and Benefits of Shelter-Building by Lepidopteran Caterpillars in a Tropical Dry Forest

University Of Missouri-Saint Louis, Saint Louis MO

Investigators

Abstract

Tens of thousands of caterpillar species build shelters out of silk and leaves. Many are sufficiently abundant that they are important forest pests. However, little is known about how shelters affect the survival of the caterpillars and ultimately their egg production as adults. This project will provide information on the impact that shelters have on caterpillar survival and adult success. First, the project tests how much protection shelters provide from high temperatures and low humidity. This information will help determine how sensitive the caterpillars are to their environment, clarifying how changes in local and global climate might influence the success of shelter-building species. Second, the project will test the protective effects of shelters against predatory insects and spiders, and against parasitic wasps and flies. Specifically, the experiments will determine whether caterpillars whose shelters provide better protection against predators are more vulnerable to parasitic insects. Both predators and parasitic insects are used to control pest insects, so testing this hypothesis could be applied to pest management. Because the research site is in Costa Rica, the researchers will also increase awareness of an under-studied tropical habitat (tropical dry forests) and foster international connections and training. The researchers will perform two sets of experiments using caterpillar species that cooperatively build group shelters, in which two to ten caterpillars can be found living together. Both sets of experiments will be conducted in the natural forest habitat of the caterpillars. The first experiment will measure the effects of shelters and the environment on caterpillar survival for four species. Caterpillars, along with temperature and humidity sensors, will be placed both inside and outside caterpillar shelters. Caterpillar survival will be monitored to determine whether the caterpillars are protected from the outside environment by their shelters. The second experiment will measure the costs and benefits of building and sharing group shelters for two caterpillar species. Caterpillars will be allowed to build shelters either alone or in groups, and the mortality caused by predators and parasitic insects will be measured. If some treatments are less likely to be killed by predators, the researchers will test whether the caterpillars are also more likely to be attacked by parasitic insects. The positive and negative effects of sharing a shelter with other caterpillars will also be measured by weighing the pupae of surviving caterpillars. Heavier pupae become adults who generally produce more offspring, so this measure will allow the researchers to determine whether sharing a shelter has a negative effect (due to competition with other caterpillars) or a positive one (due to sharing the costs of building and maintaining the shelter).