Box 5.4. Control of mating and oviposition in a blow fly
The sheep blow fly, Lucilia cuprina (Diptera: Calliphoridae), costs the Australian sheep industry many millions of dollars annually through losses caused by myiases or “strikes”. This pestiferous fly may have been introduced to Australia from Africa in the late 19th century. The reproductive behavior of L. cuprina has been studied in some detail because of its relevance to a control program for this pest. Ovarian development and reproductive behavior of the adult female are highly stereotyped and readily manipulated via precise feeding of protein. Most females are anautogenous, i.e. they require a protein meal in order to develop their eggs, and usually mate after feeding and before their oocytes have reached early vitellogenesis. After their first mating, females reject further mating attempts for several days. The “switch-off ” is activated by a peptide produced in the accessory glands of the male and transferred to the female during mating. Mating also stimulates oviposition; virgin females rarely lay eggs, whereas mated females readily do so. The eggs of each fly are laid in a single mass of a few hundred (illustration at top right) and then a new ovarian cycle commences with another batch of synchronously developing oocytes. Females may lay one to four egg masses before remating.
Unreceptive females respond to male mating attempts by curling their abdomen under their body (illustration at top left), by kicking at the males (illustration at top centre), or by actively avoiding them. Receptivity gradually returns to previously mated females, in contrast to their gradually diminishing tendency to lay. If remated, such non-laying females resume laying. Neither the size of the female’s sperm store nor the mechanical stimulation of copulation can explain these changes in female behavior. Experimentally, it has been demonstrated that the female mating refractory period and readiness to lay are related to the amount of male accessory gland substance deposited in the female’s bursa copulatrix during copulation. If a male repeatedly mates during one day (a multiply-mated male), less gland material is transferred at each successive copulation.
Thus, if one male is mated, during one day, to a succession of females, which are later tested at intervals for their receptivity and readiness to lay, then the proportion of females either unreceptive or laying is inversely related to the number of females with which the male had previously mated. The graph on the left shows the percent- age of females unreceptive to further mating when tested 1 day or 8 days after having mated with multiply-mated males. The percentage unreceptive values are based on 1–29 tests of different females. The graph on the right shows the percentage of females that laid eggs during 6 h of access to oviposition substrate presented 1 day or 8 days after mating with multi- ply-mated males. The percentage laid values are based on tests of 1–15 females. These two plots represent data from different groups of 30 males; samples of female flies numbering less than five are represented by smaller symbols. (After Bartell et al. 1969; Barton Browne et al. 1990; Smith et al. 1990.)