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Evaluation of pyrethroids and organophosphates in insecticide mixtures for management of western corn rootworm larvae
Author(s) -
St. Clair Coy R,
Norris Edmund J,
Masloski Kenneth E,
Coats Joel R,
Gassmann Aaron J
Publication year - 2020
Publication title -
pest management science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.296
H-Index - 125
eISSN - 1526-4998
pISSN - 1526-498X
DOI - 10.1002/ps.5938
Subject(s) - pyrethroid , cyfluthrin , organophosphate , bifenthrin , western corn rootworm , chlorpyrifos , biology , toxicology , bioassay , pesticide , integrated pest management , pest analysis , agronomy , botany , ecology
BACKGROUND The western corn rootworm is an economically important pest of corn. Management tactics include pyrethroid and organophosphate insecticides, which may be applied as a mixture to protect corn roots. The goal of our study was to characterize the effects of pyrethroids and organophosphates alone and in combination on larval corn rootworm mortality and injury to corn roots. We evaluated two insecticide combinations: tebupirimphos with β‐cyfluthrin and chlorethoxyfos with bifenthrin. Using a soil‐based, laboratory bioassay, we exposed larvae to five concentrations of the pyrethroid alone, the organophosphate alone, the combined formulation, and a water control. We calculated LC 50 values and co‐toxicity factors to determine synergism or antagonism between organophosphates and pyrethroids. We also measured adult emergence and root injury in a field experiment that tested tebupirimphos alone, β‐cyfluthrin alone, the combined formulation, and an untreated control. RESULTS Bioassay results indicated antagonism between the pyrethroid and organophosphate at most concentrations for both insecticide combinations. In the field experiment, tebupirimphos alone or in combination with β‐cyfluthrin significantly reduced adult emergence and root injury compared to the untreated controls, but β‐cyfluthrin alone did not differ from the untreated control for either metric. CONCLUSIONS These results suggest that, at the concentrations tested, the pyrethroid component of pyrethroid–organophosphate mixtures may not contribute to a reduction of rootworm emergence or root injury. While these pyrethroids may confer a management benefit for other pests, such as seedcorn maggot, the concentrations of pyrethroids present in current formulations of these mixtures are likely too low for effective rootworm management. © 2020 Society of Chemical Industry