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ARS Home » Southeast Area » Byron, Georgia » Fruit and Tree Nut Research » Research » Publications at this Location » Publication #212083
Title: Soil moisture and strain effects on entomopathogenic nematode suppression of the pecan weevil

Author
item Shapiro Ilan, David
item Cottrell, Ted
item BROWN, IAN - GA SW STATE UNIV
item GARDNER, WAYNE - UGA, GRIFFIN, GA
item Hubbard, Robert
item Wood, Bruce

Submitted to: Pecan Grower
Publication Type: Trade Journal
Publication Acceptance Date: 5/31/2007
Publication Date: 7/5/2007
Citation: Shapiro Ilan, D.I., Cottrell, T.E., Brown, I., Gardner, W.A., Hubbard, R.K., Wood, B.W. 2007. Soil moisture and strain effects on entomopathogenic nematode suppression of the pecan weevil. Pecan Grower 19(1):32-38.

Interpretive Summary: The Pecan weevil is a key pest of pecan. We report here an update of research activities focused on the suppression and eventual control of pecan weevils with beneficial organisms, specifically entomopathogenic (insect-killing) nematodes. These nematodes only attack insects and are safe to humans and the environment. We report here progress regarding intermediate steps key to the achievement of biological control of weevils. Our objectives were to: 1) determine the effects of different moisture levels and different nematode strains on suppression of the weevil’s larval stage, and 2) assess suppression of adult weevils under field conditions using two different nematode strains. In the laboratory, virulence (killing power) of nematodes was tested in soil at varying moisture levels. Pecan weevil larval survival decreased as moisture levels increased. The nematode effect was most pronounced at an intermediate soil moisture level, i.e., 18.5%. At 23.6% moisture, larval survival was ' 5% regardless of nematode presence. In a greenhouse test, pecan weevil larval survival was lower in all nematode treatments compared with the control, and two of the nematodes (S. carpocapsae [Italian strain] and S. riobrave [7-12 strain]) appeared to be especially virulent. In field experiments targeting adult weevils as they emerged, the nematode S. riobrave (7-12) did not cause any observable control, and although S. carpocapsae (Italian) provided some suppression, treatment effects were generally marginal and did not last long. To improve control of weevil adults, new application methods and superior nematode strains will be pursued.

Technical Abstract: The Pecan weevil, Curculio caryae, is a key pest of pecan. We report here an update of research activities focused on the suppression and eventual control of pecan weevils with beneficial organisms, specifically entomopathogenic (insect-killing) nematodes. These nematodes only attack insects and are safe to humans and the environment. We report here progress regarding intermediate steps key to the achievement of biological control of weevils. Our objectives were to: 1) determine the effects of different moisture levels and different nematode strains on suppression of the weevil’s larval stage, and 2) assess suppression of adult weevils under field conditions using two different nematode strains. In the laboratory, virulence (killing power) of nematodes was tested in soil at varying moisture levels. Pecan weevil larval survival decreased as moisture levels increased. The nematode effect was most pronounced at an intermediate soil moisture level, i.e., 18.5%. At 23.6% moisture, larval survival was ' 5% regardless of nematode presence. In a greenhouse test, pecan weevil larval survival was lower in all nematode treatments compared with the control, and two of the nematodes (S. carpocapsae [Italian strain] and S. riobrave [7-12 strain]) appeared to be especially virulent. In field experiments targeting adult weevils as they emerged, the nematode S. riobrave (7-12) did not cause any observable control, and although S. carpocapsae (Italian) provided some suppression, treatment effects were generally marginal and did not last long. To improve control of weevil adults, new application methods and superior nematode strains will be pursued. Key words: biological control, Curculio caryae, entomopathogenic nematode, pecan.