Flight initiation in Prostephanus truncatus: influence of population density and aggregation pheromone

Abstract

The influence of population density and aggregation pheromone were investigated as possible flight initiating factors for Prostephanus truncatus (Horn) (Col.: Bostrichidae). Maize grains (175 g in glass jars) were infested with 20, 50, 150 or 300 beetles, all of which were removed after 2 weeks. Flight initiation of the progeny was observed over a period of 4 weeks, with and without the synthetic aggregation pheromone of P. truncatus. Addition of the synthetic pheromone had no influence on the number of beetles taking off. The number of beetles dispersing increased with growing initial and progeny densities. Dispersal rates (% of total progeny dispersing) rose with declining rate till they reached a maximum at ca. 33%. Of the beetles dispersing, 74% left the cultures between 18.00 and 20.00 hours. Surviving progeny per female decreased with increasing initial density. Sex ratios in the initial cultures and in the F1 were ca. 1:1, whereas a higher proportion of females (67%) was found among the dispersing beetles.

Effects of Rearing Density, Age, Sex, and Food Deprivation on Flight Initiation of the Red Flour Beetle (Coleoptera: Tenebrionidae)

“…It could be that our rearing densities were not high enough to stimulate an increase in ßight initiation, although extremely high rearing densities generated experimentally may not accurately reßect conditions found in the Þeld in which females have the freedom to vary the number of eggs laid depending on the quality and quantity of the food resource. The tendency for crowding during development to increase ßight initiation has been reported for other stored-product insects that exploit similar habitats, e.g., R. dominica (Barrer et al 1993;Perez-Mendoza et al 1999a,b) and P. truncatus (Fadamiro et al 1996, Scholz et al 1997. However, those studies tested the ßight initiation ability of adult beetles produced at much higher rearing densities (1Ð20 or 100 Ð500 founding adults laying eggs for 1Ð 4 wk) than in our study.…”

Seasonal and weather factors influencing the annual flight cycle of Prostephanus truncatus (Coleoptera: Bostrichidae) and its predator Teretriosoma nigrescens (Coleoptera: Histeridae) in Benin

“…The flight cycle of the predator showed only one peak, approximately six weeks after the major peak of P. tnincatus. Assuming that the increased flight activity of P. truncatus is at least partially related to adult beetles leaving habitats due to a decreasing nutritive value of the substrate and/or crowding, as shown in recent experiments (Scholz et al, 1997), the predators might react with time delayed emigration. However, experiments on the functional and numerical response of T. nigrescens to test this hypothesis are currently under way.…”

“…However, the December-January peak in flight activity occurred at a time when P. tnincatus densities were high in major season maize stores (Borgemeister et al, 1994). Studies on the dispersal behaviour of P. tnincatus from maize cultures showed that at high densities approximately 30% of the P. truncatus population emigrates (Scholz et al, 1997). Furthermore, many farmers in the region start to remove maize from their long season stores from November onwards, and the majority of these stores are emptied between December and February (Agbaka, 1996).…”

Can observation of climatic variables be used to predict the flight dispersal rates of Prostephanus truncatus?

“…Dispersal of P. truncatus is believed to result from crowding and degradation of food resources (Fadamiro & Wyatt, 1995;Scholz et al, 1997). The rate of insect development and consequently the rate of population growth is affected by long-term climatic conditions.…”