Effects of Aphicides on Pecan Aphids and Their Parasitoids in Pecan Orchards

SIMPLE SUMMARY: Insecticide application is the primary method for aphid management in commercial pecan orchards in the U.S. However, over-reliance and non-judicious insecticide use has led to numerous downsides, including insecticide resistance and impairment of beneficial insects. It is important to assess the efficacy and potential non-target impact of insecticides in order to create sustainable management programs. The objective of this study was to assess three insecticides (flonicamid, sulfoxaflor, and afidopyropen) on pecan aphids and their parasitoid 7, 14, and 21 days post-application in 2019 and 2020. In 2019, non-treated trees had up to 9-fold more aphids than treated trees 7 days post-application, but these differences diminished by 14 and 21 days after treatment application. Although aphid numbers were low during 2020, non-treated trees had more aphids in the lower canopy than most treated trees 7 days post-application. These differences diminished for the later assessments. Surprisingly, there was no significant difference in abundance of parasitoid adults or mummies between non-treated trees and treated trees. The results of this study indicate that growers have multiple products for aphid management, thus allowing product rotation to slow development of aphid resistance. ABSTRACT: Aphids are important pests of pecans. Traditionally, insecticides have been the primary method of management. However, over-reliance and non-judicious use has led to resistance and damage to natural enemy populations. Therefore, frequent assessment of insecticides is necessary in order to monitor resistance development and non-target impacts. Aphicides, flonicamid, sulfoxaflor, and afidopyropen were assessed for their effects on pecan aphids and parasitoid, Aphelinus perpallidus, in a mature pecan orchard in 2019 and 2020. Post-application assessments were performed 7, 14, and 21 days post-application. Leaf samples from non-treated trees had greater aphid numbers than treated trees 7 days post-application with differences diminishing throughout the other two treatment periods in 2019. In 2020, aphid numbers were lower but leaf samples from non-treated trees had more aphids than treated trees 7 days post-application in the lower canopy. These differences again diminished 14 and 21 days post-application. There was no difference among treatments in number of parasitoid adults or mummies. These findings indicate that pecan growers have multiple potential options available for aphid management that do not negatively impact the primary pecan aphid parasitoid. Implications of the results on pecan aphid management are discussed.