Trichogramma egg parasitism ofHelicoverpa armigera on short-duration pigeonpea intercultured with sorghum |
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Authors: | S J Duffield |
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Institution: | (1) International Crops Research Institute for the Semi-Arid Tropics (ICRISAT), 502 324 Patancheru, Andhra Pradesh, India;(2) Present address: School of Biological Sciences, Department of Biology, University of Southampton, Bassett Crescent East, S09 3TU Southampton, Hampshire, UK |
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Abstract: | The levels of egg parasitism byTrichogramma spp. (Hymenoptera: Trichogrammatidae) on populations ofHelicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) were recorded on sorghum (Sorghum bicolor L.) and on two flushes of flowers on short-duration pigeonpea (Cajanus cajan L.).H. armigera oviposition was concentrated on the early flowering stage of sorghum and the flowering and early podding stages of both flushes
of pigeonpea. Parasitism on sorghum increased rapidly as egg density increased and reached a peak of 74.6%. Parasitism on
pigeonpea was concentrated onH. armigera eggs laid on the first flush of pigeonpea flowers with a maximum of 69.2%. These high levels of parasitism on pigeonpea coincided
with the period of parasite activity on sorghum. The levels of parasitism then declined rapidly and only very low levels were
detected on a second flush of flowers. This rapid decline resulted in the overall egg mortality caused byTrichogramma on pigeonpea to be low, with a maximum of 7.8% caused by parasitism, compared to 34.4% on sorghum. The pattern of parasitism
suggests that a transfer of parasites occurred from sorghum to pigeonpea. The rapid decline of parasitism on the pigeonpea
indicates that parasite populations cannot be sustained on pigeonpea once the influx from sorghum stops. The results are discussed
in terms of a possible method of encouraging the transfer of parasites from sorghum to short-duration pigeonpea by producing
a more continuous cropping environment. |
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Keywords: | sorghum pigeonpea Helicoverpa armigera Trichogramma |
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