The polyphagous Drosophila suzukii is a highly invasive species that causes extensive damage to a wide range of berry and stone fruit crops. A better understanding of its biology and especially its behaviour will aid the development of new control strategies. We investigated the locomotor behaviour of D. suzukii in a semi-natural environment resembling a typical summer in northern England and show that adult female D. suzukii are at least 4-fold more active during daylight hours than adult males. This result was reproduced in several laboratory environments and was shown to be a robust feature of mated, but not virgin, female flies. Both males and virgin females kept on a 12 h light:12 h dark (12LD) cycle and constant temperature displayed night-time inactivity (sleep) followed by weak activity in the morning, an afternoon period of quiescence (siesta) and then a prominent evening peak of activity. Both the siesta and the sharp evening peak at lights off were severely reduced in females after mating. Flies of either sex entrained in 12LD displayed a circadian pattern of activity in constant darkness confirming the importance of an endogenous clock in regulating adult activity. This response of females to mating is similar to that elicited in female Drosophila melanogaster by the male sex peptide (SP). We used mass spectrometry to identify a molecular ion (m/z, 5145) corresponding to the poly-hydroxylated SP of D. suzukii and to show that this molecule is transferred to the female reproductive tract during copulation. We propose that the siesta experienced by male and virgin female D. suzukii is an adaptation to avoid unnecessary exposure to the afternoon sun, but that mated females faced with the challenge of obtaining resources for egg production and finding oviposition sites take greater risks, and we suggest that the change in female behaviour is induced by the male SP.
Adult longevity and lifetime fecundity, but not fertility, of northern (Maine, USA) Wyeomyia smithii (Coquillet) increase with female pupal weight. Mean egg size does not vary with pupal weight, but the standard deviation in egg size shows a marginally significant increase with pupal weight. Egg sizes are not skewed but are leptokurtic in their distribution; neither skewness nor kurtosis changes with female pupal weight. Mean egg size is not correlated with weight-specific adult longevity or with weight- and longevity-specific lifetime fecundity. Reproductive effort early in adult life does not affect longevity, reproductive effort late in life, or reproductive rate late in life. Finally, there is no significant correlation late in adult life between weight-specific rate of egg production and the size of eggs being produced. Egg size does vary within females but is not a variable entered into the physiological allocation of resources among survivorship, fecundity, or rate of egg production.
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