Effects of three insecticides on soybean aphid parasitoids

The soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), is a recently introduced pest of soybean in North America. A major effort toward importation biological control utilizing parasitoids has been launched against this pest, with Binodoxys communis Gahan (Hymenoptera: Braconidae) currently being released. We have also observed the native parasitoid Lysiphlebus testaceipes (Cresson) (Hymenoptera: Braconidae) parasitizing soybean aphids. The objective of this study was to assess the susceptibility of the pupae of these two parasitoids (i.e. within their aphid mummies) to selected insecticides applied for soybean aphid control. We used a Potter Tower to spray the recommended low and high field rates of formulated product of three insecticides: Warrior II® (lambda-cyhalothrin), Lorsban® (clorpyrifos), and Pyganic® (pyrethrins), with distilled water as a control. Adult emergence was recorded. The experiment was designed as a two way ANOVA (insecticide x rate) with replication through time, but each parasitoid species was tested independently. For both parasitoids, insecticide was significant but rate was not, and the insecticide x rate interaction was not significant. A multiple range (HSD) test indicated that Lorsban produced significantly higher mortality (essentially 100% at both rates) than either Warrior or Pyganic. Warrior, Pyganic, and water were not significantly different from one another. Although not statistically significant, the high rates of Warrior and Pyganic did result in higher mortality of B. communis than did water, an effect not seen for L. testaceipes. The implications of these results for soybean aphid management will be discussed.