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

Abstract

Male sexual aggregations are a common territorial, mating-related or resource-based, behaviour observed in diverse organisms, including insects such as thrips. The influence of factors such as plant substrate, time of day, and geographic location on aggregation of thrips is uncertain, therefore we monitored the dispersion of male and female bean flower thrips (BFT), Megalurothrips sjostedti (Trybom) (Thysanoptera: Thripidae), on cowpea, Vigna unguiculata (L.) Walp. (Fabaceae), over three cowpea growth stages and across three cowpea-growing areas of Kenya. Our results indicated that for all the crop growth stages, the density of BFTs varied over the time of day, with higher densities at 10:00, 13:00, and 16:00 hours than at 07:00 hours. Thrips densities did not differ among blocks at the budding stage, but they did at peak flowering and podding stages. Dispersion indices suggested that both male and female BFTs were aggregated. Active male aggregation occurred only on green plant parts and it varied across blocks, crop stages, and locations. Similarly, active female aggregation was observed in peak flowering and podding stages. Such active aggregation indicates a semiochemical or behaviour-mediated aggregation. Identification of such a semiochemical may offer new opportunities for refining monitoring and management strategies for BFT on cowpea, the most important grain legume in sub-Saharan Africa.

Characterization of Male-Produced Aggregation Pheromone of the Bean Flower Thrips Megalurothrips sjostedti (Thysanoptera: Thripidae)

“…The dispersion patterns of M. sjostedti adults in the field indicate that there is active aggregation, which implies a role for intrinsic factors such as pheromones (Niassy et al 2016 ; Salifu and Hodgson 1987 ). Our study of the behavioral responses of M. sjostedti from Mbita, Kenya to conspecific odors revealed that both male and female M. sjostedti were attracted to headspace volatiles from males, demonstrating the presence of a male-produced aggregation pheromone.…”

“…Recently, we observed aggregation of male bean flower thrips on leaves of cowpea, which suggested they used an aggregation pheromone (Niassy et al 2016 ). This is further supported by the presence of sternal glands, implicated in production of aggregation pheromone in other thrips species, in male bean flower thrips (Krueger et al 2015 ).…”

The aggregation pheromones of thrips (Thysanoptera) and their potential for pest management

“…1), F. occidentalis males form aggregations on white surfaces (Terry and Gardner, 1990), Frankliniella schultzei (Trybom) males form aggregations on the upper surfaces of flowers (Milne et al, 2002), Pezothrips kellyanus (Bagnall) males form aggregations on leaves and fruit (Webster et al, 2006), males of Parabaliothrips newmani Gillespie, Mound and Wang form aggregations on leaf buds (Gillespie et al, 2002) and Megalurothrips sjostedti (Trybom) males form aggregations on leaves (Niassy et al, 2016) (Fig. 2).…”

“…In F. occidentalis and M. sjostedti, the extent of aggregation appears to vary considerably with the season, time of day and weather -4-conditions (Terry and Gardner, 1990;Terry and Dyreson, 1996;Niassy et al, 2016), so aggregations are not obvious and can be easily overlooked.…”

“…The finding that male M. sjostedti aggregate on leaves suggested the presence of an aggregation pheromone (Niassy et al, 2016), but the species was thought to have no pore plates (Mound, 2009). Subsequent investigation showed that small pore areas and sternal glands were indeed present (Krueger et al, -5-2015).…”