Distribution pattern and sequential sampling plan for chilli thrips, Scirtothrips dorsalis Hood (Thripidae: Thysanoptera)

Abstract

Spatial distribution and sequential sampling plan for chilli thrips, Scirtothrips dorsalis Hood were analyzed through Taylor’s power law (TPL) and Iwao’s mean crowding regression (IMC) for rainy and summer seasons during 2016–17 on chilli crop. The results revealed that the mean number of thrips in the field was low (1.07 thrips/plant) at early crop growth stages (32 days after transplanting (DAT)) and increased gradually with a peak (21.53 thrips/plant) at 56 DAT. Inconsistency in the mean number of thrips with shifting variance was noticed. The variance of thrips population increased with increase in its density with the best variance (122.41) observed at 56 DAT. Samples of thrips showed variance to mean ratio (S2/X), Lloyd’s patchiness index (X*/X), as well as Morisita Index more than one, revealing clumped distribution. The data on thrips population was best fit to TPL (a = 0.184, b = 1.27, R2 = 0.66) and the IMC (α = 0.93, β = 1.14, R2 = 0.94). Larger variability in sample size vis-a-vis mean population density was also achieved at 10 and 20% precision levels. Considering TPL parameters, the decisive lines of sequential sampling for S. dorsalis was chosen at d = 13n ± 8.07√n. The sequential sampling plan will thus help in reducing the costs for an effective and efficient management of S. dorsalis on chilli.