Effects of intraspecific larval competition on the development of the African buffalo fly Haematobia thirouxi potans

Abstract

The effects of larval crowding on development, survival and size of the African buffalo fly, Haematobia thirouxi potans (Bezzi), were examined in small (10 or 20 g) and 1000 g masses of cattle dung in the laboratory at 25°C. Dung was infested with fly eggs at densities which ranged from 0.05 to 32.0 eggs per g dung; in most cases 90–100% of eggs hatched. The duration of larval development in 10 g dung masses was extended by larval crowding at densities above 0.8 eggs per g dung and the development period with 32 eggs per g dung (11 days) was double that observed in uncrowded dung masses. Both size and survival decreased with increasing larval density, but stunting was observed at lower densities than those which reduced survival and so size was the more sensitive index of the adequacy of the larval environment. The effects of larval crowding became evident at lower larval densities in the 1000 g dung masses than in the 10 g dung masses. There was a minimum size below which third instar larvae failed to pupariate. The probability of survival was related to pupal size and a high proportion of the smaller individuals failed to eclose. Résumé Effets de la competition intraspécifique sur le développement des larves, la taille des pupes et la survie d'Haematobia thirouxi potans Les effets du surpeuplement larvaire sur le développement, la survie et la taille d'Haematobia thirouxi potans, ont été examinés sur de petites quantités de bouse (10 et 20 g) et de plus importantes (1000 g), au laboratoire à 25°C. Les bouses étaient contaminées avec des oeufs de la mouche à des densités de 0,05 à 32 oeufs par gramme de bouse. Dans la plupart des cas le taux d'éclosion était de 90–100%. La durée du développement larvaire dans 10 g de bouse a été prolongée pour les densités supérieures a 0,8 oeuf per g, et la durée développement pour 32 oeufs per g (11 jours) était le double de celle obtenue grand il n'y avait pas surpeuplement. La taille et la survie diminuent toutes les deux avec la densité larvaire, mais la miniaturisation était observée à des densités où la survie n'était pas modifiée; ainsi la taille est un indice plus sensible de l'adéquation de l'habitat larvaire. Les effets du surpeuplement larvaires deviennent clairs à des densités plus faibles avec 1000 g de la bouse qu'avec 10 g. Il y a eu une taille minimale endessous de laquelle les larves étaient incapables de former une pupe. La probabilité d'éclosion était liée à la taille de la pupe, et une plus forte proportion de petits individus ne sont pas parvenu à éclore.

Re‐examination of Competition Between Musca Vetustissima Walker (Diptera:muscidae) Larvae and Seasonal Changes in Favourability of Cattle Dung

“…There was a significant positive correlation between survival and HW for flies of less than 2 mm HW (Y = 85X -97,29df, P < 0.001) and explained 46% of the variation, while the correlation for flies of 2 mm or more was not significant and explained less than 1% of the variation. This relationship confirms the findings for several dung-feeding Diptera (Hughes and Sands 1979;Moon 1980;Palmer and Bay 1983;Ridsdill-Smith et al 1986;Doube and Moola 1987).…”

“…Matthiessen et al (1984) conclude that headwidth best reflects seasonal changes in dung quality, while survival was probably more affected by the physical characteristics of the dung, or by dung so unfavourable that starvation occurred. When physical conditions are favourable, the time taken by larvae of a Haematobia species to mature in dung was increased by competition (Doube and Moola 1987), but when dung becomes unsuitable while larvae are still feeding, the larvae will leave the dung prematurely, and adults will be stunted (Hughes et al 1972). Presumably, the ability of larvae at different densities to complete their development before being forced to leave the pad determined the interactions affecting size seen here in dung of different qualities.…”

Impact of fauna on mortality and size of Haematobia spp. (Diptera: Muscidae) in natural dung pads in Australia and South Africa

“…Drought conditions were experienced in Hluhluwe in 1982-83 ( fig. 4b) and on nine out of 17 occasions the head widths of flies from platform pads averaged less than 0.9 mm, a level below which large reductions can occur with relatively small increases in larval density or decreases in nutrient availability (Doube & Moola, 1987). Low soil moisture and hot weather would rapidly reduce dung pad moisture levels, and disturbance of pads by other fauna would accelerate moisture loss and have a compounding influence on the size of surviving flies (Cook et al, 1980).…”

“…At Rockhampton, exposure of dung pads beyond one day did not significantly increase the level of faunainduced mortality of the immature stages of Hacmatobia suggesting that the bulk of the effective fauna arrived within 24 h of pad drop and that subsequent colonization failed to increase fly mortality. The headcapsule width of flies provides an indication of the nutrition of developing larvae and has implications for adult survival and fecundity (Doube & Moola, 1987;Fay & Doube, 1987). In morning pads at Rockhampton, fly size decreased significantly as the duration of exposure to dung fauna increased from zero to four days, but this did not occur in pads produced in the afternoon.…”

“…Haematobia mortality arising from the activities of other fauna could substitute rather than add to that resulting from intraspecific competition, which would affect comparisons if it occurred or was more frequent at one locality. As intraspecific competition for dung nutrients in Haematobia generally manifests itself as a reduction in fly size at a lower density than that required to increase mortality (Doube & Moola, 1987), evidence for its occurrence can be gauged from the relationship between the number of flies produced by protected pads and mean head width. Normally, production of Haematobia from natural pads is independent of pad size (unpublished data).…”