12 - The regulation of migration in Helicoverpa armigera

Summary

Introduction

The Cotton Bollworm Helicoverpa armigera(Hübner) is an agricultural pest occurring throughout Africa, southern Europe, the Middle East, Asia and Australasia (Commonwealth Institute of Entomology, 1968). An important factor contributing to its pest status is its ability to undertake long-distance migratory flights (review by Farrow & Daly, 1987; see also Chapter 8, this volume), that may occasionally exceed 2000 km (Bowden & Johnson, 1976).

Radar studies and field observations have shown that noctuid migration typically involves a characteristic sequence of behaviours (see e.g. Rose et al., 1985). Takeoff occurs shortly after sunset, with moths climbing at a rate of ~0.5–2.0 m s⁻¹ until they reach the top of the temperature inversion where windspeeds are usually at a maximum, often 20–50 km h⁻¹ (Drake & Farrow, 1988). The insects then maintain their altitude, continuing their wind-assisted progress until they descend at some time during the night or around dawn (Drake, 1985).

Because of the long distances migratory insects travel and their relatively small size, the study of migration at the ecological level presents major logistic and technological challenges. No less problematic, however, is the laboratory-based approach, in which the behavioural, physiological and genetic mechanisms that regulate migratory behaviour are investigated.

This chapter describes the contribution of laboratory studies to our understanding of the migratory behaviour of H. armigera.

Flight activity and the pre-reproductive period

Two components of migratory potential that are amenable to examination in the laboratory are flight activity and the pre-reproductive period (PRP).