Temperature Effects on Efficacy of Choetospila elegans (Hymenoptera: Pteromalidae) to Suppress Rhyzopertha dominica (Coleoptera: Bostrichidae) in Stored Wheat
Laboratory studies were conducted to assess the effectiveness of the parasitoid wasp Choetospila elegans (Westwood) for controlling Rhyzopertha dominica (F.), lesser grain borer, in wheat at 32 and 25°C. The 2 temperature regimes were used to simulate an unaerated bin of wheat and a bin aerated at harvest time. Two adult male and 2 adult female R. dominica were each released into containers with 19 kg of hard red winter wheat. An equal number of adult C. elegans were released into half of the containers. Half the containers were kept at 2.5°C and half at 32°C. Suppression of R. dominica population growth by C. elegans was much greater at 25 than at 32°C. After 161 d, R. dominica density in the containers with C. elegans was 9,l85/kg at 32°C, and 10/kg at 25°C. At 25°C, C. elegans was able to locate and parasitize most of the larvae that were produced by the adult beetles. This resulted in a very high level of population suppression (99% in comparison to the control at 25°C). In contrast, at 32°C, beetle suppression was only 50% in comparison to containers without C. elegans at this temperature. This study suggests that when augmentative parasite releases are made with C. elegans, better host suppression would be achieved by cooling the grain to 25°C shortly after harvest, rather than leaving it unaerated for the summer.