Predatory Arthropods in Australian Cotton Fields

ABSTRACT
Over 50 species of predatory arthropods have been recorded in Australian cotton fields. The complex of generalist predators in Australian cotton has similarities and differences to those in other countries. It is dominated by coccinelids and other beetle species, bugs, ants and spiders. These predators attack Helicoverpa armigera and H. punctigera, the key pests of Australian cotton but also affect other pests such as mites and aphids and prey species with little economic impact suck as leafhoppers. Helicoverpa spp. are primary pests in Australian cotton. Under most pest management regimes predators do not maintain Helicoverpa numbers below current economic thresholds and predator population densities do not appear to be related to Helicoverpa abundance. In contrast, mites and aphids are usually secondary pests whose abundance is determines in part by the impact of pesticides on their natural enemies. This paper will review the predatory species involved, their abundance and seasonal phenology in cotton other crops and non-crop vegetation and the relatively limited data on their impact on Helicoverpa spp. The prospects for enhancing the role of predators of IPM will be discussed in relation to current trends in Australian cotton pest management.

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COMPARATIVE INFORMATION ON THE LOCAL ABUNDANCE OF TWO PESTS, HELICOVERPA ARMIGERA (HÜBNER) (LEPIDOPTERA: NOCTUIDAE) AND APHIS GOSSYPII (GLOVER) (HOMOPTERA: APHIDIDAE) AND SELECTED PREDATORS ON COTTON IN EASTERN TANZANIA

Abstract                                                                         Back to Table of contents

Seasonal occurrence of predators of Helicoverpa armigera (Hübner) and Aphis gossypii (Glover) on cotton was studied between 1989 and 1991 in eastern Tanzania. Major predators were chrysopids, coccinellids, syrphids and ants. These predators moved onto the cotton crop at flowering time, coinciding with the initial colonisation of the crop by H. armigera and A. gossypii. Coccinellids and syrphids tended to be most abundant on cotton during the first four weeks of flowering. Ants were most active between the fourth and seventh weeks following the onset of flowering. Chrysopids were most abundant midway through the flowering period.

The effect of currently used pesticides on predators was assessed in 1989 and 1991.  Endosulfan significantly reduced populations of ants and chrysopids. Similarly, use of deltamethrin significantly reduced populations of syrphids, but not of chrysopids and coccinellids. The relevance of these findings for integrated management of H. armigera and A. gossypii is discussed.

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