The Beet Armyworm, Spodoptera exigua; an Economic Pest of Citrus in California1

Abstract

Larvae of the beet armyworm, Spodoptera exigua (Hbn.), caused substantial economic losses in approximately 500 acres of young, recently planted citrus trees and nursery stock during the summer and fall of 1957, 1958, and 1959 in most California citrus areas. The larvae may destroy each succeeding flush of growth and the terminal shoots. The attacks of the larvae have a pruning effect on the young trees, and subsequent retarded tree growth causes infested trees to develop only half as fast as noninfested trees. The new rootstock-scion combinations currently being planted grow two or more times as rapidly as former combinations; consequently, the continuous supply of young and succulent foliage provides food for optimum development of beet armyworm larvae. The facts seem to explain the recent “adaptation” of the beet armyworm, enabling it to infest citrus and cause serious economic losses. The life cycle of this insect lasts 30 to 60 days during the summer and fall, and there are four or more generations a year on citrus in California. No parasites have been taken on citrus thus far. Chemical control measures utilizing DDT and parathion provided excellent but short-term control, since reinfestation was continuous.