Effects of the agricultural adjuvant Sylgard 309 and the insecticide pymetrozine on demographic parameters of the aphid parasitoid, Diaeretiella rapae

Abstract

In this study we evaluated the effects of a purportedly selective aphicide, pymetrozine (Fulfill), and a commonly used agricultural adjuvant, Sylgard 309, which is often applied with pymetrozine, on the life table parameters of the aphid parasitoid Diaeretiella rapae (McIntosh). We found that pymetrozine was not toxic to D. rapae at the concentration we evaluated (0.212 g ai/ha). Instead of reducing the intrinsic rate of increase (rm) of D. rapae after adult exposure to the recommended field rate for aphid control in broccoli, rm actually increased 11%. However, Sylgard 309 alone was toxic and reduced rm by 18% compared to the control. The combination of Sylgard 309 and pymetrozine acted synergistically, reducing D. rapae rm 39% compared to the control. When the mummy stage of D. rapae developing in the cabbage aphid, Brevicoryne brassicae (L.), was exposed to a mixture of pymetrozine and Sylgard 309, rm was reduced 13%. Thus, the mummy stage was less susceptible than the adult stage. The stable age distribution of D. rapae was altered after exposure to pymetrozine and Sylgard 309; the proportion of adults in the population increased from 4.67% (control) to 10.96%. The highest proportion of eggs (53%) in the population was achieved when adults were exposed to pymetrozine alone. The stable age distribution for the larval stages did not differ among the various treatments. Results of this study indicate that pymetrozine is not toxic to D. rapae at the rate we tested. However, the agricultural adjuvant, Sylgard 309 is toxic and Sylgard 309 and pymetrozine act synergistically. Because agricultural adjuvants are regularly used on various crops, additional research on their potential impact on biological controls is warranted. It may be found that agricultural adjuvants are not a good fit for IPM.