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Maternal Induction of Diapause in the Larva of Lucilia Caesar L. (Diptera: Calliphoridae)
1 Entomology Research Institute, Central Experimental Farm, Ottawa, Ontario; Department of Biology, University of Victoria, Victoria B.C.
1. The seasonal pattern of diapause incidence in Lucilia caesar L. shows that diapause in the 3rd-instar larvae of field-captured females increases rapidly during the month of July. By rearing and testing all larvae under standard laboratory conditions confirmation has been given to the hypothesis that this sudden increase, which occurs soon after the summer solstice, is due to a maternal influence.
2. It has been shown that photoperiod is the most important factor controlling this maternal influence, with temperature playing a modifying role in the photoperiodic response. Females do not respond to the intrinsic rate of change in the photoperiod, but to the absolute levels of the light/dark phases. Long photoperiods (20 hr.) tend to avert, and short ones (12 hr.) tend to induce, larval diapause. Thus L. caesar is another example of a ‘long-day’ species as described by Lees (1955).
3. Under laboratory conditions there is a time lag of 8-10 days before a change in the absolute length of the photoperiod acting on the mother reflects its diapause influencing effect on the larvae.
4. Maternal ageing produces an increase in larval diapause incidence after 6-10 weeks.
5. It is not yet known whether or not the maternal influence is hormonal in character.
Submitted on September 9, 1966
