Submitted to: Annals of the Entomological Society of America
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/29/1998
Publication Date: N/A
Interpretive Summary: Cattle grubs are an important pest of cattle, responsible for economic losses to the cattle industry through damage to meat and hides. These flies have an intricate life cycle, and are highly specialized in their behavior, morphology and physiology. Adult flies attach their eggs proximally to hairs of their hosts. This study was conducted to investigate one of the specializations of the oviposition process, specifically hair diameter selection. Comparisons were made between randomly sampled bovine hairs and those selected for oviposition by cttle grubs. It was evident that ovipositing females rejected the more abundant narrow hairs (mean diameter = 0.04 mm) in favor of the relatively scarce larger diameter hairs (mean diameter = 0.07 mm). This difference was statistically significant. The number of eggs attached to a hair increased as a positive linear function of increasing hair diameter. Ovipositor tip morphology was shown to be specialized for grasping large diameter hairs. Hair selection during oviposition appears to be an integral part of the oviposition process, and has likely contributed to the evolution of oviposition site selection, promoting egg hatch and short incubation period.
Technical Abstract: Tethered females of the common cattle grub, Hypoderma lineatum (de Villers), were allowed to oviposit on Hereford calves. The diameters of hairs selected for oviposition were compared with the diameters of randomly sampled hairs from the backs of each animal. Also, the number of eggs attached to a hair was compared with the diameter of the hair to which they ywere attached. The mean diameter of hairs selected for oviposition was 0.07+/-0.002 mm, whereas the mean diameter of randomly sampled hairs was 0.04+/-0.001 mm. These means were significantly different, demonstrating that H lineatum females rejected the more abundant narrow diameter hairs in favor of the relatively scarce larger diameter hairs during oviposition. The number of eggs deposited per hair increased linearly with increasing hair diameter, again demonstrating a propensity for selection of large diameter hairs during oviposition. Measurements of the circular area formed dby the opposing, concave, hair grasping surfaces of the 9th sternites and 10th tergites resulted in a mean diameter of 0.10+/-0.01 mm, conforming to the diameter of the largest hairs selected during oviposition. The possible selective advantages driving hair selection by H. lineatum are discussed, as well as characteristics related to hair suitability and ovipositor tip morphology.