Effect of Cotesia rubecula (Hymenoptera: Braconidae) on Survival of Larval Cohorts of Pieris rapae (Lepidoptera: Pieridae) on Collards: Evaluation of an Introduced Biological Control Agent
Abstract
Survival of artificial cohorts of larvae of the imported cabbageworm, Pieris rapae (L.), was assessed in a collard (Brassica oleracea L., var. acephala) patch on an organic vegetable farm in western Massachusetts. We recorded a significant drop in survival of larvae between the 4th and 5th instar due to parasitism by the parasitoid Cotesia rubecula (Marshall), which was introduced to New England from China in 1988. This was a large change from the survivorship pattern of P. rapae observed in the same area in 1985-1986, in which there was a significant drop in survival between 5th instars and pupae due to Cotesia glomerata (L.), the dominant parasitoid of P. rapae in New England at the time. In our study, parasitism by C. rubecula averaged 62.4 ± 8.6%, while no parasitism by C. glomerata was observed. The introduction of C. rubecula is now very likely to be benefitting organic vegetable producers in western Massachusetts, killing more larvae and at an earlier life stage than the previous parasitoid, reducing the potential for damage to cole crops.
La supervivencia de cohortes de larvas del gusano del repollo, Pieris rapae (L.), establecidas artificialmente en plantas de col (Brassica oleracea L., var. acephala), fue evaluada en una finca productora de vegetales orgánicos en el oeste de Massachusetts. Registramos una reducción en la supervivencia de larvas entre el 4to y 5to instar, causado por el parasitismo del agente de control biológico Cotesia rubecula (Marshall), el cual fue introducido al estado de Nueva Inglaterra proveniente de China en 1988. Se observó un cambio considerable en el patrón de supervivencia de P. rapae con respecto a lo registrado en un estudio previo entre 1985-1986 en la misma area, en el cual se encontró una reducción de la supervivencia en el 5to instar y el estado pupal causado por Cotesia glomerata (L.), el parasitoide dominante de P. rapae en Nueva Inglaterra en ese momento. En nuestro estudio el parasitismo por C. rubecula promedio 62.4 ± 8.6%, mientras que no se observó parasitismo por C. glomerata. Estos resultados muestran que la introducción C. rubecula probablemete está beneficiando a los agricultores orgánicos de vegetales en el oeste de Massachusetts, eliminando más larvas y cuando estas son más pequeñas con respecto al parasitoide establecido anteriormente, reduciendo así el potencial de daños significativos a cultivos de coles.
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