The Effects of Age and Weather on Egg-Laying in Pieris rapae L.

Abstract

P. rapae egg production in large field cages varied with age, temperature and solar radiation. Adult age was measured in cumulative degree-days (D.degree.) above the larval developmental threshold of 10.degree. C. Egg production peaked at about 60 D.degree. of age, then slowly declined. Daily temperature was measured as D.degree., and egg production increased linearly with temperature. Solar radiation had both immediate and delayed effects. Few eggs were laid on overcast days, and more eggs than expected were laid on sunny days which followed overcast days. Larval rearing conditions affected fecundity, but not the timing of egg production. An algorithm including all these factors accounted for 67% of the observed variation in daily egg production per surviving female. Butterflies survived on average 156 D.degree., but may live more than 220 D.degree.