Studies on the biology of immature stages of the buffalo fly, Haematobia irritans exigua de Meijere (Diptera: Muscidae)

Cook, Ian Murray (1980) Studies on the biology of immature stages of the buffalo fly, Haematobia irritans exigua de Meijere (Diptera: Muscidae). PhD thesis, James Cook University of North Queensland.

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This thesis reports the results of experiments designed to provide information on the developmental biology of the immature stages of the buffalo fly. It is divided into six chapters dealing respectively with rates of growth in relation to substrate temperature and moisture, the effects of variation of these two factors on mortality, the effects of sub-lethal temperature and dung moisture conditions on pupal size and shape, the potential significance of the pH and osmotic concentration of dung fluid, the physical nature of cattle dung and its behaviour in the field, and seasonal variation in adult fly numbers.

The durations of individual pre-imaginal stadia were measured at a number of constant temperatures. The rate of development of eggs was not linearly related to temperature, and asymptotic equations were calculated to relate temperature to elapsed time for all instars. Durations of combined pre-imaginal stadia for male and female flies were 777.7 and 745.2 hours respectively at a constant temperature of 17.5°C, and 192.7 and 184.4 hours at 35.0°C. The combined pre-pupal stadia were 584.9 hours at 15.0°C, but pupae did not survive to adulthood at this temperature. Rates of growth were reduced if dung moisture fell below 85 per cent of wet weight.

Several aspects of the physical and physico-chemical nature of dung were examined as possible sources of mortality. These were temperature, moisture content, pH and osmolality. Eggs survived temperatures between 11.0.and 37.0°C, while larval and pupal development was restricted to temperatures between 15.0 and 35.0°C. Larval growth ceased if dung moisture fell to 64 per cent, of wet weight. At near-lethal levels of temperature or dung moisture, the size and shape of pupae were also affected.

Eggs hatched normally within the pH range 4.5 to 9.0, and larvae survived between 5.8 and 9.0. There was no effect of osmolality on hatch within the range 62.5 - 980.0m0sm, and larvae pupated successfully between levels of 62.5 and 510.0mOsm. Mortality among eggs and pupae increased if humidity levels fell below levels close to saturation. Eggs were also killed by even short periods of immersion in water, and very few survived if the immersion period approached the duration of the total pre-hatch period.

The nature of these potential mortality factors in dung was evaluated. Naturally occurring levels of pH and osmolality did not approach lethal levels, either in fresh dung or after periods of exposure. Temperatures within dung pads frequently exceeded upper lethal limits for all instars, and must be considered a probable cause of mortality. Dung moisture was found to fall quickly below the lower limit for larval growth. Estimations on rate of moisture loss from dung and growth rate of flies were made using results of these experiments, and data on fly populations and weather records from Rockhampton. Pre-imaginal stadia appeared to increase about eight-fold in exposed pads and ten-fold in shaded pads during winter, compared to those of summer. However, the rate at which pads lost moisture did not vary much in monthly estimates made for the period from April to November. It is therefore likely that larvae die in winter because dung dries to lethal levels before they have developed to pupation.

Item ID: 33765
Item Type: Thesis (PhD)
Keywords: buffalo flies; buffalo fly; cattle; fly larvae; Haematobia irritans exigua; larval growth; life cycle; pests
Date Deposited: 29 May 2015 04:59
FoR Codes: 06 BIOLOGICAL SCIENCES > 0608 Zoology > 060808 Invertebrate Biology @ 100%
SEO Codes: 96 ENVIRONMENT > 9604 Control of Pests, Diseases and Exotic Species > 960403 Control of Animal Pests, Diseases and Exotic Species in Farmland, Arable Cropland and Permanent Cropland @ 100%
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