Predicting population dynamics of the parasitoid Cotesia marginiventris (Hymenoptera: Braconidae) resulting from novel interactions of temperature and selenium

Abstract

Changes in trophic level interactions due to global climate change and the increasing occurrence of pollution are likely to have consequences for natural enemies. Specifically, information regarding the effects of these factors on insect parasitoids is relatively sparse. We examined the individual and joint effects of temperature and the pollutant selenium on the fitness correlates of the parasitoid wasp Cotesia marginiventris (Cresson) (Hymenoptera: Braconidae), parasitizing Spodoptera exigua (Hubner) (Lepidoptera: Noctuidae). Our specific objective was to determine in a factorial experiment how three temperatures (constant 28.6°C, constant 33°C and a fluctuating temperature between 28.6 and 33°C) and three concentrations of seleno-dl-methionine (0.00, 21.21, and 42.42 µg/g) affected the parasitoid's fitness and life history. Parasitoids failed to complete development at the constant 33°C, but developed significantly faster at the fluctuating temperature compared to the constant 28.6°C. There were significant declines due to increased temperature, but not selenium, on C. marginiventris survival time, adult body weight, body size, hind tibia length, female life span and number of progeny that survived to adulthood. Mean generation times and the intrinsic rate of increase (r) further show that both of these life table statistics declined under conditions of increased temperatures. We discuss the implications of these results in helping to understand and predict the effectiveness of biological control programs and pest management strategies as climate changes in the presence of metal and metalloid pollution.

Keywords:

• climate change
• pollution
• selenium
• parasitoids
• fitness correlates

Acknowledgements

We thank M. Chase-Dunn, G. Kund, B. Carson, L. Johnson, R. Valdez, B. Gonzales, and K. Gilbert for assistance with colony maintenance and assistance with experiments. We also thank James Whitfield (University of Illinois) for identification of C. marginiventris, and John Ruberson (University of Georgia) who supplied the initial colony of C. marginiventris. Benzon Research Inc. supplied the S. exigua. We thank Scott Lesch for statistical advice. We thank K. Thrippleton-Hunter and David Parker (University of California, Riverside) for use of laboratory space and equipment as well as advice on the analysis of selenium in samples. We thank TestAmerica Inc. and E. S. Babcock and Sons, Inc. for analysis of Se in samples. We thank R. Stouthamer, M. Hoddle, K. Hladun, G. Kund, B. Carson and C. Mogren whose comments and suggestions greatly improved an earlier version of this manuscript.