Beet Armyworm (Lepidoptera: Noctuidae) Host Plant Preferences for Oviposition

Abstract

Beet armyworm, Spodoptera exigua (Hubner), oviposition preferences were deter- mined on Þve host plants: cabbage (Brassica oleracea capitata L.), cotton (Gossypium hirsutum L.), bell pepper (Capsicum annuum L.), pigweed (Amaranthus retroflexus L.), and sunsower (Helianthus annuus L.) in no-choice, two-choice, and Þve-choice tests. Tests were conducted in the laboratory, greenhouse, and Þeld cages. Oviposition preferences were compared on the basis of two measure- ments, the proportion of eggs laid on the plants to total that were deposited, and the oviposition preference index deÞned as ((number of eggs laid on the plant) - (number of eggs laid on the cage)) 100/total number of eggs laid. The proportion of eggs laid on the plants to total that were deposited was highest for pigweed and lowest for cabbage in all tests. Beet armyworm females were signiÞcantly deterred from laying eggs on cabbage and sunsower, while pigweed and cotton elicited a positive oviposition preference. Pepper tended to be neutral or slightly unattractive. Apparent interactions among plant species in choice tests produced measurable shifts in oviposition preference. Most notably, female response to pepper was enhanced in the presence of cotton or pigweed. Egg masses laid on the plants contained signiÞcantly higher numbers of eggs than those laid on the surface of the cage, except in the case of cabbage leaves. Knowledge of hierarchies of host plant oviposition preference by beet armyworm females will be useful in understanding the population dynamics of this important agricultural pest, and for developing effective monitoring and management strategies.