Chemicals, including those ingested on food, have adverse effects on organisms. Pesticides are chemicals widely applied in agroecosystems, making them useful in examining the impacts of chemicals and diet on life history. Trichoplusia ni larvae feed on crucifers and are often found in agroecosystems where they are also exposed to chemicals like spinosyn A and B, the main active ingredients in spinosad-based pesticides. Because of their regular exposure to different pesticides and food sources in their natural environment, this study aims to explore how T.ni larvae are affected by spinosyn and diet. In this study, T.ni larvae were divided into four treatments: artificial diet control, artificial diet + spinosyn, organic crucifer control, and organic crucifer + spinosyn. Each treatment consisted of twenty larvae. Three different rounds of the experiment were performed. In round one, organic crucifer treatments were fed commercially available organic cabbage (CAOC) for the entire round starting in the first instar. In round two, organic crucifer treatments were fed young, greenhouse-grown cabbage and transferred to CAOC in the fourth instar. In round three, crucifer treatments were fed young greenhouse-grown cabbage and transferred to commercially available organic kale in the fourth instar. All treatments were fed ad lib, and spinosyn groups were treated with 250 µL of 78 ppm spinosyn in the third instar using an overlay assay. Larval mortality and stadia were recorded until death or pupation. Preliminary results suggest that spinosyn has a greater effect than food type on mortality. There was 100% larval mortality in spinosyn treatments, regardless of food type, but much lower mortality in artificial diet control and organic crucifer control groups (0%-25%). Spinosyn had no noticeable effect on larval stadia. In contrast, transfer to CAOC noticeably extended larval stadia but did not have major impacts on mortality. Spinosyn results suggest that spinosyn is a toxic chemical in the environment, which is consistent with other studies. However, the effect of crucifer type on larval stadia was surprising, as crucifers are a natural food source. Replication is underway for statistical analysis and to verify these results.


We would like to acknowledge a USG STEM IV grant and a John and Mary Franklin Foundation grant, both to J. Layba, for funding.

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