Impacts of Captive Rearing and Gut Microbe Elimination on the Neotropical Pentatomid, Sibaria englemani
Mentor:Shana Goffredi, Assistant Professor, Department of Biology, Occidental College
Insect-microbe symbioses are an integral component of tropical food web architecture. The neotropical pentatomid stinkbug, Sibaria englemani cultivates endosymbiotic gammaproteobacteria in crypts within specialized midgut structures. These symbionts may augment host fitness by altering the nutritional quality or toxicity of the Piperaceae diet. This study describes the life history of S. englemani reared in captivity and the possible role of resident gut symbionts. Adults (n=86), collected at La Selva Biological Station, Costa Rica, produced 58 clutches in 54 days, with 8 eggs per cohort. The average incubation time was 7.3±0.2d and nymphal development time (from 1st to 5th stadium) was 26.5±0.5 days, when provided with their native diet, Piper sancti-felicis. Nymphs were rendered aposymbiotic by surface sterilization of egg masses prior to hatching, followed by antibiotic treatments while in captivity. Instar mortality among symbiotic and aposymbiotic individuals reared on Piper were similar, counter indicating a role by the symbiont in diet detoxification. To further determine the effects of symbiont elimination on nutrient provisioning, symbiotic and aposymbiotic nymphs were assigned to one of three dietary conditions (natural Piper, artificial soybean-based, and artificial vitamin-deficient substrates). Unfortunately, complete mortality in the second instar suggested that a soybean-based diet is unsuitable for normal development in S. englemani. Therefore, a role of the symbiont in nutritional status is presently unclear. There was no significant difference in size between aposymbiotic and symbiotic siblings raised on a natural diet (p>0.1, Student’s t-test), however, second instar aposymbiotic insects developed more slowly than symbiotic insects (p=0.001, Students t-test). Thus, microbial presence may assist in host development, particularly at early lifestages. We are currently comparing, via microscopy, the morphology and ultrastructural arrangement of the midgut in aposymbiotic versus symbiotic nymphs to determine the role, if any, of microbial symbionts in orchestrating morphogenesis of the symbiont-specific organs in the host insect.