Control of pecan weevil with microbial biopesticides

Authors: Shapiro Ilan, David; Cottrell, Ted; Bock, Clive; Mai, Kim; Boykin, Deborah; WELLS, LENNY - University Of Georgia; HUDSON, WILLIAM - University Of Georgia; MIZELL III, RUSSELL - University Of Georgia

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/30/2017
Publication Date: 12/8/2017
Citation: Shapiro Ilan, D.I., Cottrell, T.E., Bock, C.H., Mai, K.T., Boykin, D.L., Wells, L., Hudson, W.G., Mizell III, R.F. 2017. Control of pecan weevil with microbial biopesticides. Environmental Entomology. 46(6):1299-1304. https://doi:10.1093/ee/nvx144.
DOI: https://doi.org/10.1093/ee/nvx144

Interpretive Summary: Pecans are economically the most important native nut crop in the USA. One of the key pests that reduce pecan yield is the pecan weevil. Pecan weevil is generally controlled with broad spectrum chemicals. These chemical pesticides can be harmful to the environment and garner secondary pest outbreaks and resistance. Our overall goal for this project is to develop alternative production practices for pecans that are sustainable and effective. The focus of the research has been on the use of novel environmentally friendly insecticides based on microbial products. We discovered that a bacteria-based product (Grandevo®, based on a bacteria called Chromobacterium subtsugae), along with beneficial entomopathogenic nematodes (round worms that only attack insects) and an insect-killing fungus (called Beauveria bassiana) significantly reduced pecan weevil damage in USDA and commercial pecan orchards. All the products used are deemed safe to humans and the environment and can be used in organic farming settings. Also, we found that the bacteria-based product (Grandevo®) controlled pecan weevil at the same level as conventionally used chemical insecticides. The findings show great promise for developing environmentally sound pest management tactics in pecan and other crops.

Technical Abstract: The pecan weevil, Curculio caryae (Horn), is a key pest of pecans. Due to regulatory and environmental concerns, effective alternatives to broad spectrum chemical insecticides for C. caryae control must be sought for pecan production in conventional and organic systems. We explored the use of microbial biopesticides for control of C. caryae in Georgia pecan orchards. Three experiments were conducted. The first investigated an integrated microbial control approach. Three microbial agents, Grandevo® (based on byproducts of the bacterium Chromobacterium subtsugae, the entomopathogenic nematode Steinernema carpocapsae, and entomopathogenic fungus, Beauveria bassiana, were applied to each treatment plot (0.6 ha) at different times during the season. A second experiment compared the effects of S. carpocapsae and B. bassiana applied as single treatments relative to application of both agents (at different times); survival of C. caryae was assessed one year after larvae were added to pots sunk in an organic pecan orchard. In a conventional orchard (with 1.0 ha plots), the third experiment compared Grandevo applications to a commonly used regime of chemical insecticides (carbaryl alternated with a pyrethroid). All experiments were repeated in consecutive years. The combined pest management tactic (Experiment 1) reduced C. caryae infestation relative to non-treated control plots in both locations in 2014 and one of the two locations in 2015 (the other location had less than 1% infestation). In experiment 2, no differences among combined microbial treatments, single-applied microbial treatments or different numbers of application were observed, yet all microbial treatments reduced C. caryae survival relative to the control. In the third experiment, both Grandevo and standard chemical insecticide applications resulted in lower weevil infestation than the control (both years) and there was no difference between the insecticide treatments in 2014 although the chemical insecticide regime had slightly lower infestation in 2015. These results provide evidence that microbial biopesticides can substantially reduce pecan weevil infestations in organic and non-organic systems.