Can larvae of the pod-borer, Helicoverpa armigera (Lepidoptera: Noctuidae), select between wild and cultivated pigeonpea Cajanus sp. (Fabaceae)?

Abstract

Experiments were conducted to observe the feeding and food selection-behaviour of different instars of the pod-borer Helicoverpa armigera (Hübner) in response to choices between the cultivated and a wild species of Cajanus. First and second instars fed upon a cultivated variety of Cajanus cajan in preference to a wild species, C. scarabaeoides and on flowers of C. cajan, rather than pods or leaves of C. cajan. First and second instars preferred pods of C. scarabaeoides with trichomes removed to pods with trichomes present. All instars fed upon pods of C. cajan rather than those of C. scarabaeoides. Solvent extraction of the pod surfaces affected the feeding of larvae, in some instances. They preferred the unextracted pods of C. cajan; the extracted pod of C. scarabaeoides (first and second instars) or the unextracted pod of C. scarabaeoides (fourth and fifth instars). Glass-fibre disc bioassays showed that the methanol, hexane and water extracts from the pod-surface of C. cajan stimulated the feeding of fifth instars. The experiments have shown that characteristics of C. cajan, such as either the compounds present or the type and distribution of trichomes on the plant surfaces, can determine the susceptibility of C. cajan to pod-borer larvae.

Ontogenetic Changes in the Feeding Behaviour of Helicoverpa armigera Larvae on Pigeonpea (Cajanus cajan) Flowers and Pods

“…As larvae develop, flowering pigeonpea plants develop contemporaneously. Other studies have indicated that larvae ‘switch’ feeding from flowers to pods [ 20 , 22 ]. However, rather than a ‘switch’, this phenomenon might be better thought of as an increased capacity of H. armigera larvae to feed on a range of structures as they develop.…”

“…Moths are highly attracted to flowering pigeonpea [ 18 , 19 ]. Larvae may feed on pigeonpea plants throughout vegetative and reproductive plant phenological stages [ 13 ], but when provided with a choice, early instars avoid leaves and prefer to feed on flowers [ 18 , 19 , 20 , 21 ]. As larvae develop into larger instars ( Figure 2 ), they ‘switch’ to feeding on pods [ 20 , 22 ].…”

Pigeon pea crop stage strongly influences plant susceptibility to Helicoverpa armigera (Lepidoptera: Noctuidae)

“…Moths are attracted to pigeon pea volatiles ( Rajapakse et al 2006 ), and eggs are then mostly oviposited on floral structures, sites wherein larvae establish ( Rajapakse and Walter 2007 , Volp et al 2023 ). As larvae develop, they are purported to “switch” to feeding on pods, where they can cause substantial yield loss ( Green et al 2002 , Rajapakse 2007 ). Flowers likely play an important role in pigeon pea susceptibility to H. armigera , but the influence of the pigeon pea plant stage on oviposition and establishment of this species is not fully understood.…”