A solitary ground‐nesting wasp truncates its parental investment in response to detection of parasites

Abstract

1. Parental investment by solitary nest-building wasps and bees is predicted to be plastic, responding to variation in the sex of the offspring, the availability of food used as provisions ('resource limitation'), the female's inventory of mature oocytes ('egg limitation'), and risk imposed by nest parasites. 2. I observed nest provisioning by Ammophila dysmica, a solitary, ground-nesting wasp that provisions its nest with one or two caterpillar prey to evaluate the hypotheses that provisioning is shaped by caterpillar size, offspring sex, the hunting time required to capture prey, a female's egg load, and penetration of nests by the parasites Argochrysis armilla and Hilarella hilarella. 3. Ammophila dysmica were more likely to add a second provision to the nest when the first prey item was relatively small and when provisioning daughters. 4. Neither the hunting time required to capture the first caterpillar prey nor the female's inventory of oocytes predicted a female's likelihood of adding a second caterpillar to a nest. Variation in oocyte inventory across females was minimal; all females examined had a mature or nearly mature oocyte remaining in the ovaries immediately after laying an egg. 5. Ammophila dysmica were much less likely to add a second caterpillar to nests that were penetrated by parasites during the first provisioning. 6. Although many nest parasites have evolved adaptations to avoid detection by their hosts, oviposition by A. armilla often appears to reveal its presence, eliciting an abrupt truncation of investment by the host in that nest.

A double-edged sword: parental care increases risk of offspring infection by a maternally vectored parasite

“…Single-prey provisioning produces just one point of contact between the mother and offspring before the nest is sealed for the larva's development, whereas multiple-prey provisioning produces multiple points of contact [ 1 , 8 ]. Female Ammophila do clean the nest during their provisioning trips, and cleaning trips have been shown to remove some parasite larvae or adults from the nest [ 19 , 20 ]. We hypothesize that multiple contacts between the Ammophila mother and her offspring may still increase parasitism risk for the offspring if the increased parasite exposure more than offsets the increased nest cleaning activity associated with multiple provisioning visits.…”