Nocturnal observations on the emergence and flight behaviour of Helicoverpa armigera (Lepidoptera: Noctuidae) in the post-rainy season in central India.
A range of techniques was used to quantify the nocturnal flight behaviour of Helicoverpa armigera in pigeon pea (Cajanus cajan) crops near Hyderabad, Andhra Pradesh, in central India. These included visual observations in the field, the use of field cages and a vehicle-mounted net, optical and video imaging in the infra-red, and radar. Moth emergence from the soil was observed to start at dusk and recruitment continued steadily throughout the first half of the night. Moths exhibited little activity on the night of emergence, except for weak flying or crawling to daytime refuges. Flight activity of 1-day-old moths started about 20 min after sunset, peaked 15 min later and within about an hour of sunset had declined to a low level which persisted for the rest of the night. The flight of reproductively mature moths was most frequent about 1 h after sunset and at this time mainly comprised females searching for oviposition sites and nectar sources. By about 2 h after sunset, flight had decreased markedly, but there was a slight increase in activity in the 2nd half of the night caused by males undertaking mate-finding flights. Under the conditions studied, the majority of H. armigera adults dispersed below 10 m, and there were no mass ascents to higher altitudes like those observed at outbreak sites of another noctuid, Spodoptera exempta. The contrasting migratory strategies of H. armigera and S. exempta are briefly discussed.