Distribution on cotton of Amrasca devastans and Ayyaria chaetophora in relation to pest scouting techniques for Thailand

Abstract

The distributions of thrips Ayyaria chaetophora Karny and jassids Amrasca devastans (Dist.) on cotton in Thailand show aggregation and can be adequately described by the negative binomial distribution. The majority of thrips are found on the top four or five expanded leaves, while the bulk of the population of jassid nymphs can be located on four adjacent expanded leaves towards the top of the stem which correspond to the zone of ‘working’ leaves. This zone is displaced down the stem as the plant grows and develops. Jassid nymph mortality appears to be highest amongst newly hatched individuals since numbers decrease rapidly and become more evenly distributed down the plant as the nymphs age. There appears to be some movement between leaves by jassid nymphs, particularly the older ones, and the mud‐splash effect during heavy rain provides appreciable natural control. Both pests could be managed in Thailand using a sequential sampling procedure based on binomial sampling theory. Sample units would be restricted to infestation sites and treatment decisions would be made on the proportion of sample units rather than on actual pest counts.

Notes

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