Variegated Cutworm
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Reduction in
Variegated Cutworm (Lepidoptera: Noctuidae)
Injury to Peppermint by Larval Parasitoids
LEONARD B. COOP AND RALPH E. BERRY
Department of Entomology, Oregon State University,
Corvallis, Oregon 97331
© 1986 Entomological Society of America
J. Econ. Entomol. 79: 1244-1248 (1986)
ABSTRACT
Variegated cutworm (VC), Peridroma saucia (Hübner), parasitism rates in
western Oregon and peppermint leaf consumption rates of parasitized and unparasitized
larvae were measured for use in a VC economic threshold model. Instars 46 consumed an
average of 184 cm2, equivalent to 888 mg (dry weight) of peppermint foliage. Total
consumption by larvae parasitized by Meteorus communis (Cresson) was reduced by 93%. Total
parasitism rates averaged 35.1% for instars 24 and 5.4% for instar 5. Parasitism rates
were related to time of season and inversely related to the log of larval instar 24 host
density. M. communis contributed 11% to total parasitism, while Meloboris sp. and
Campoletis sp. composed 84% of larval parasitoids reared from fieldcollected larvae. Based
on final VC head capsule measurements, only 2% of all larval parasitoids reared allowed
hosts to reach a size sufflcient to cause significant damage that occurs during the final
two instars. Accounting for natural biological control by these early instar larval
parasitoids will permit a 34% increase in economic thresholds for VC in peppermint.