D3033: The two-spotted lady beetle, Adalia bipunctata L. (Coleoptera: Coccinellidae) and increased rearing temperatures: Effects on larval development, alkaloid production and microsporidiosis

Most lady beetles display aposematic colouration reinforced by the sequestration of species-specific alkaloids. These alkaloids act as multifunctional defense chemicals and are suspected to play a role in the coccinellid immune system. In this study, the effects of elevated rearing temperatures and microsporidiosis (Nosema adaliae) were observed on larval development and mortality, alkaloid content (adaline), and adult morphometrics of Adalia bipunctata. Uninfected larvae (24 h-old) were provided either an uninfected or N. adaliae-infected conspecific egg and subsequently reared at three temperatures (25°C, 27.5°C or 30°C). Following eclosion, a subsample of adults was photographed for microscopic measurements, had reflex-fluid collected for alkaloid analysis (gas chromatography-mass spectrometry) and were examined to determine spore loads. Development time was delayed significantly for larvae that consumed a N. adaliae-infected egg, and infected larvae took significantly longer to develop at 25°C than at 27.5°C or 30°C. The relative proportion of adaline increased when larvae were reared at 30°C, but adaline concentrations were not significantly affected by infection. Adults reared at 25°C had larger body measurements compared to those reared at 27.5°C and 30°C. Overall, adults that had eaten an infected egg as larvae had similar body measurements to those that ate an uninfected egg. A significant interaction between infection status, temperature, and sex was observed for elytra and head capsule measurements. Both percent infected and average spore count decreased at 27.5°C and 30°C. These results suggest that temperatures above 25°C have a mitigating effect against N. adaliae in A. bipunctata.