Impact of a biorational pesticide on the pecan aphid complex and its natural enemies

Abstract

The pecan weevil, Curculio caryae (Horn) (Coleoptera: Curculionidae), and the pecan aphid (Hemiptera: Aphididae) complex: black pecan aphid, Melanocallis caryaefoliae (Davis), blackmargined aphid, Monellia caryella (Fitch), and yellow pecan aphid, Monelliopsis pecanis Bissell are major pests of pecan production. Management is primarily based on chemical insecticides, and alternative control methods need to be explored. Prior field tests showed that the microbial insecticide Grandevo® (based on Chromobacterium subtsugae) can suppress C. caryae at similar rates to insecticides, and a laboratory test showed that Grandevo is toxic to M. caryaefoliae. However, it was unknown if Grandevo applications targeted towards C. caryae also impact the pecan aphid complex and aphid natural enemies. Hence, we initiated a field study to determine the impact of two rates of Grandevo (2.24 and 3.36 kg/ha) on aphid, Coccinellidae (Coleoptera) and Chrysopidae (Neuroptera) populations. Both Grandevo rates, in both years of the study, suppressed M. caryaefoliae in comparison to the negative control. Only the standard chemical insecticide regimen suppressed M. caryella and M. pecanis combined populations during both years of the experiment. In 2016, both Grandevo rates had more abundant natural enemy populations compared with the chemical insecticide regimen, and the higher Grandevo rate (3.36 kg/ha) had more natural enemies than the non-treated control. In 2017, all treatments had comparable populations of natural enemies. These findings suggest that a microbial insecticide can manage multiple insect pests while preserving the natural enemy community.