Non-target effects of transgenic sugarcane on Parallorhogas pyralophagus (Marsh)

Abstract

Parallorhogas pyralophagus (Marsh) is an important biological control agent of Eoreuma loftini Dyar, the key pest of Texas sugarcane. Transgenic sugarcane containing Galanthus nivalis agglutinin (GNA) was developed to deter E. loftini, and the goal of the studies contained in this thesis was to assess the impact of transgenic sugarcane on the natural enemy of the target pest. In the first study, I measured the effect of transgenic sugarcane on parasitoid life history parameters including size, longevity, egg load, developmental time, and immature stage mortality. The results of this study found no acute toxicity to P. pyralophagus. However, reductions in parasitoid size, longevity, rate of gain of longevity with size, and egg load were evident. Total developmental time was longer for parasitoids that developed on hosts fed transgenic diet. No effect was found on rate of gain of egg load with size, immature stage mortality, and overall survivorship. In the second study, selection and acceptance of E. loftini hosts by P. pyralophagus were compared between hosts fed diet based on conventional or transgenic sugarcane. Females of P. pyralophagus preferentially probed, drilled and oviposited on hosts fed conventional diet. Other experiments assessed the effect of transgenic sugarcane diet on E. loftini activity level and frass volatile profile. A reduction in activity level was detected in E. loftini fed transgenic versus conventional diet, while differences were not evident in frass volatile profiles. The results suggested a positive correlation between host activity level and probability of parasitism, which may render hosts fed transgenic diet less attractive to P. pyralophagus. However, it is concluded that this may not significantly affect biological control of E. loftini by P. pyralophagus because: (1) although those hosts most susceptible to transgenic sugarcane may be less likely to be parasitized, they are also less likely to cause severe crop damage and reproduce successfully; and (2) those hosts least susceptible to transgenic sugarcane and therefore more active are more likely to be parasitized. I conclude that the results of the two studies suggest that GNA transgenic sugarcane may be compatible with an integrated pest management program against E. loftini as there are only slight negative effects on the parasitoid, and tolerant pests will likely be more attractive to the parasitoid. Further studies are needed to assess the impact of transgenic sugarcane on parasitoid field performance.