Helicoverpa armigera preference and performance on three cultivars of short‐duration pigeonpea (Cajanus cajan): the importance of whole plant assays

Abstract

BACKGROUND: Helicoverpa armigera is a major pest of pigeonpea (Cajanus cajan). Efforts to develop pigeonpea varieties resistant to H. armigera attack have been met with limited success, despite reports of high levels of resistance to H. armigera in wild relatives of pigeonpea and reports of low to moderate levels of resistance in cultivated varieties. Here we examined H. armigera oviposition preference and larval performance on whole plants of three cultivars of short-duration pigeonpea: a susceptible control (ICPL 87) and two cultivars with purported host-plant resistance (ICPL 86012 and ICPL 88039).RESULTS: In our no-choice oviposition experiment, H. armigera laid similar numbers of eggs on all three cultivars tested, but under choice conditions moths laid slightly more eggs on ICPL 88039. Larval growth and development were affected by cultivar, and larvae grew to the largest size (weight) and developed fastest on ICPL 86012. Moths laid most of their eggs on floral structures, sites where subsequent early instar larvae overwhelmingly fed. Experimentally placing neonate larvae at different locations on plants demonstrated that larvae placed on flowers experienced greater survival, faster development, and greater weight gain than those placed on leaves. The type and density of trichomes (a potential resistance trait) differed among cultivars and plant structures, but larvae selected to feed at sites where trichomes were absent. CONCLUSION: Future work examining host-plant resistance against H. armigera should incorporate the behavioural preference of moths and larvae in experiments using whole plants as opposed to bioassays of excised plant parts in Petri dishes.

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

“…On whole pigeonpea plants, the foraging environment is more heterogenous ( Figure 1 ) and it is important we place our results into the context of our knowledge of the H. armigera –pigeonpea system. As we have shown elsewhere [ 19 , 21 ], H. armigera moths are highly attracted to flowering pigeonpea plants and lay most of their eggs on flowers. Although eggs may be laid at other crop stages, floral structures are important for the establishment and development of early instar larvae, which preferentially feed at these sites.…”

“…The filter paper was allowed to air dry, then placed in 90 mm Petri dishes with the edges sealed with parafilm until the neonates hatched. Upon hatching, neonate larvae were placed in groups onto a soybean-flour-based artificial diet (recipe modified from [25], ingredients provided in [21]) in 500 mL rectangular plastic containers. When larvae developed to the third instar, they were transferred to fresh diet in 32-well plastic trays, where they remained until pupation.…”

“…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 ].…”

Registration of indeterminate and photoperiod‐insensitive IIPG‐7 and IIPG‐11 pigeonpea germplasm

“…Also, the control of important pests like tobacco budworm [ Heliothis virescens (F.) Lepidoptera: Noctuidae] (Viteri et al., 2019) or pod borers ( Helicoverpa spp. Lepidoptera: Noctuidae) (Volp et al., 2023) may be easier in indeterminate genotypes that have long fruiting branches and loose inflorescences than in determinate genotypes that possess clustered racemes. However, indeterminate genotypes are usually harvested later than determinate genotypes (Sarmiento et al., 2021; Saxena et al., 2019).…”

“…Thus, the plants and seeds may be exposed to attack by bruchids ( Callosobruchus spp. Coleoptera: Bruchidae) (Nadhy et al., 1998), larvae of Lepidopteran species (Viteri et al., 2019; Volp et al., 2023), infection of fungal species ( Aspergillus spp., Botryodiplodia theobromae Pat., Fusarium spp., and Phomopsis spp. ([Ellis et al., 1978; Hepperly & Rodríguez, 1984]), and/or adverse environmental effects (e.g., waterlogging [Hepperly & Rodríguez, 1986]) that can significantly reduce seed yield and quality.…”