Dispersion patterns and sequential sampling plans for Megalurothrips sjostedti (Trybom) (Thysanoptera: Thripidae) in cowpeas

Abstract

The within-plant dispersion characteristics of Megalurothrips sjostedti (Trybom) on cowpeas were determined in studies in Nigeria. Iwao's regression procedure and Taylor's power law analysis were used to determine the relationship between the mean and variance of thrips counts. Both methods showed that adult thrips were randomly distributed within cowpea plants at initial low populations. At later high densities, Iwao's method provided a better fit of the population dispersion of larvae and adults and showed that both were aggregated. The negative binomial best described this aggregation at high population densities. Sequential count plans suitable for pest management surveys were developed using critical stop lines derived from Iwao's regression procedure and Taylor's power law, but the latter was found to require less effort to achieve the same level of precision. There was a functional relationship between the variance and mean of untransformed population counts, and the suitability of transformation functions is discussed.

Seasonal abundance and spatial distribution of larval and adult thrips (Thysanoptera) on weed host plants in mango orchards in Penang, Malaysia

“…Steiner (1990) also found that F. occidentalis adults and larvae were aggregated on leaves of greenhouse cucumber, Cucumis sativus L., with a higher level of aggregation of larvae than adults. Availability of space on host plants influences thrips distribution as M. sjostedti (Trybom) adults were distributed randomly in cowpeas, Vigna unguiculata (L.), at low densities, whereas both larvae and adults showed aggregated distribution at higher densities (Salifu and Hodgson 1987). Contagious distribution was reported as typical for T. palmi (Gu et al 2000), and its larvae were more aggregated that the adults, as observed in all thrips species in our study.…”

Active aggregation among sexes in bean flower thrips (Megalurothrips sjostedti) on cowpea (Vigna unguiculata)

“…Previous studies of M. sjostedti have revealed that at higher densities the adults are highly aggregated (Salifu & Hodgson, 1987), which is suggestive of aggregation behaviour. However, beyond this indication and to the best of our knowledge, no detailed studies on aggregation in sexes of BFT or on factors associated with such aggregated dispersion are available in the literature.…”

“…Female BFT occur in cowpea flowers in low numbers during the budding stage, but increased with the crop growth stage. Several authors have observed such increase in BFT population from the initial infestation at the budding stage (macroscopic flower buds to anthesis) to full infestation at later flowering and podding phases (Ezueh, 1981; Salifu & Hodgson, 1987; Salifu & Singh, 1987). Recently, Nyasani et al.…”

“…In this regard, the criteria outlined by Arbous & Kerrick (1951) were used to estimate the mean ‘aggregation’ size λ (Southwood & Henderson, 2000): where λ is the mean number of individuals in the aggregation for the probability level allocated to υ, is the sample mean, k is the dispersion parameter obtained from the negative binomial model, and υ is a function with χ 2 distribution with 2k degrees of freedom. In interpreting λ, we note that λ<2 indicates that aggregation is more due to an environmental effect and not to active behaviour of the insect, whereas λ>2 is an indication that the cause of aggregation is due to either factor, but especially active processes by the thrips (Salifu & Hodgson, 1987; Verghese et al., 1988). Field data collected in Matuu and Mbita were subjected to similar analyses.…”

“…Ecological studies on population dynamics over seasons have revealed that the BFT numbers greatly increase during specific crop growth stages, especially at flowering and podding (Ezueh, 1981; Salifu & Hodgson, 1987; Nyasani et al., 2013). However, prior to this study, in field surveys for thrips on grain legume crops such as dolichos, we noted that BFT males were highly aggregated.…”