Field mating rate of female meadow grasshoppers, Chorthippus parallelus, estimated from sperm counts

1. Female mating frequency is an important life-history component in many insect species. It has been suggested that its laboratory measurement may frequently represent an overestimation of the natural situation because laboratory females have little opportunity to avoid matings. Here, numbers of sperm stored by field-collected females are investigated in order to address whether this method is suitable for estimating field mating frequencies. 2. Data on sperm numbers stored by females and their estimated age based on mandible abrasion were fitted to a simple mechanistic model to obtain estimates of: (i) remating interval; (ii) ejaculate size, and (iii) the rate of sperm loss from the female sperm store. Females were calculated to remate every 5.9-7.0 days. By contrast, sperm numbers of field-collected females did not exceed ejaculate size, which would have resulted in the false conclusion that females mate only once. 3. In the laboratory, females first mated when aged 4-11 days and remated approximately every 2.6 days. Because females are not restricted by mate encounters under these conditions, this confirms the notion that female mating rates are likely to be lower in the field than in the laboratory. Such reduced field mating rates should be taken into account when predicting ecological or evolutionary parameters based on laboratory observed mating rates.