The effects of age and weather on egg-laying in Pieris rapae L.
The adult life-span and the factors affecting egg production in Pieris rapae (L.) (especially age, temperature and solar radiation) were investigated in laboratory and large field cages in Vancouver, British Columbia. Adult age was measured in cumulative day-degrees above the larval development threshold of 10 deg C. Egg production reached a peak at about 60 day-degrees C and slowly declined thereafter; it also increased linearly with daily temperature. Solar radiation had both immediate and delayed effects; few eggs were laid on overcast days, and more eggs than were expected were laid on sunny days following overcast ones. Larval rearing conditions affected fecundity but not the timing of egg production of the resulting adults; larvae reared on an artificial medium containing chopped cabbage gave rise to females laying more eggs than did those from larvae reared on chinese cabbage plants growing in pots. An algorithm including all these factors accounted for 67% of the observed variation in daily egg production per surviving female. The adults lived for an average of 156 day-degrees C, but some survived for over 220 day-degrees C.