Abstract

The incidence of winter and summer diapause was studied by large-scale field samplings of larvae and pupae of the cotton bollworm, Helicoverpa armigera (Hüb) conducted over a period of 13-years during winter and summer seasons in Andhra Pradesh, India. Induction of winter diapause was associated with cooler prevailing temperatures and shorter day lengths of <12 h in November-January. On the other hand, summer diapause was observed at temperatures >32°C during March-April resulting in greater adult emergence with the onset of the monsoon season during mid-June to early July. In summer, few alternate hosts are available for larvae to sustain by allowing local populations colonizing newly germinated host crops with the onset of the rainy season. In addition, the incidence of winter and summer diapause was higher in male pupae than females in the ratio of 4:1 and 3:1 (♂:♀), respectively. Diapause populations of H. armigera were most common in the cyclonic weather prevailed for several weeks during 1977-78 (15.11%) and 1995-96 (17.64%). Under these conditions, an average of <4% and <6% of pupae entered winter and summer diapause, respectively and was associated with severe outbreaks of H. armigera in subsequent seasons. Higher populations of H. armigera on pigeonpea and chickpea entered winter diapause on pigeonpea and chickpea and summer diapause on irrigated maize, pigeonpea, chickpea and a common weed host, Datura metel.

Keywords:

Heliothis armigera, monsoon, population dynamics, summer diapause, temperature, winter diapause,

References

Competing interests

The authors have no competing interests.

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The authors have no competing interests.