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ARS Home » Southeast Area » Byron, Georgia » Fruit and Tree Nut Research » Research » Publications at this Location » Publication #265581
Title: Effects of combining microbial and chemical insecticides on mortality of the pecan weevil (Coleoptera: Curculionidae)

Author
item Shapiro Ilan, David
item Cottrell, Ted
item Wood, Bruce

Submitted to: Pecan Grower
Publication Type: Trade Journal
Publication Acceptance Date: 3/12/2011
Publication Date: 3/15/2011
Citation: Shapiro Ilan, D.I., Cottrell, T.E., Wood, B.W. 2011. Effects of combining microbial and chemical insecticides on mortality of the pecan weevil (Coleoptera: Curculionidae). Pecan Grower. 22(4):14-22.

Interpretive Summary: The pecan weevil is a key pest of pecans. Current control recommendations are based on chemical insecticide applications. Microbial control agents such as the insect-killing nematode, Steinernema carpocapsae and the fungus, Beauveria bassiana, occur naturally in southeastern US pecan orchards and have shown promise as alternative control agents for pecan weevil. Conceivably, the chemical and microbial agents occur simultaneously within pecan orchards or might be applied concurrently. In other systems, synergistic levels of mortality have been observed when certain chemical and microbial agents were combined. The objective of this study was to determine the interactions between two chemicals that are used in commercial pecan weevil control (i.e., carbaryl and cypermethrin applied below field rates) and the fungus and nematode biological agents B. bassiana and S. carpocapsae. In laboratory experiments, pecan weevil larval or adult mortality was assessed following application of microbial or chemical treatments applied singly or in combination with each other (microbial + chemical agent). The nature of interactions (antagonism, additivity, or synergy) in terms of weevil mortality was evaluated. Results for the fungus, B. bassiana, indicated synergistic activity with carbaryl and antagonism with cypermethrin in pecan weevil larvae and adults. For the nematode, S. carpocapsae, synergy was detected with both chemicals in pecan weevil larvae, and additive effects were detected in adult weevils. Our results indicate that the chemical-microbial combinations tested are compatible with the exception of the fungus (B. bassiana) and cypermethrin. Additionally, combinations that caused synergistic mortality may provide enhanced pecan weevil control in commercial field applications; thus, their potential merits further exploration.

Technical Abstract: The pecan weevil, Curculio caryae, is a key pest of pecans. Current control recommendations are based on chemical insecticide applications. Microbial control agents such as the entomopathogenic (insect-killing) nematode, Steinernema carpocapsae and the fungus, Beauveria bassiana, occur naturally in southeastern US pecan orchards and have shown promise as alternative control agents for pecan weevil. Conceivably, the chemical and microbial agents occur simultaneously within pecan orchards or might be applied concurrently. The objective of this study was to determine the interactions between two chemicals that are used in commercial pecan weevil control (i.e., carbaryl and cypermethrin applied below field rates) and the microbial agents B. bassiana and S. carpocapsae. In laboratory experiments, pecan weevil larval or adult mortality was assessed following application of microbial or chemical treatments applied singly or in combination with each other (microbial + chemical agent). The nature of interactions (antagonism, additivity, or synergy) in terms of weevil mortality was evaluated over 9 days (for larvae) or 5 days (for adult weevils). Results for the fungus, B. bassiana, indicated synergistic activity with carbaryl and antagonism with cypermethrin in pecan weevil larvae and adults (Shapiro-Ilan et al. 2011). For the nematode, S. carpocapsae, synergy was detected with both chemicals in pecan weevil larvae, and additive effects were detected in adult weevils (Shapiro-Ilan et al. 2011). Our results indicate that the chemical-microbial combinations tested are compatible with the exception of B. bassiana and cypermethrin. Additionally, combinations that caused synergistic mortality may provide enhanced pecan weevil control in commercial field applications; thus, their potential merits further exploration.