Fitness, parasitoids and biological control: an opinion

Fitness, defined as the per capita rate of increase of a genotype with reference to the population carrying the associated genes, is a concept used by biologists to describe how well an individual performs in a population. Fitness: is rarely measured directly and biologists resort to proxies more easily measured but with varying connection to fitness. Size, progeny survival, and developmental rate are the most common proxies used in the literature to describe parasitoid fitness. The importance of the proxies varies between papers looking at evolutionary theories and those assessing ecological applications. The most direct measures of fitness for parasitoids are realised fecundity for females and mating ability for males, although these proxies are more difficult to measure under natural conditions. For practical purposes, measure of size, through body size or mass, is the proxy easiest to use while providing good comparative values; however, care must be taken when using a single proxy, as proxies can be affected differently by rearing conditions of the parasitoid. [KEYWORDS: LARVAL COMPETITION; QUALITY-CONTROL; CLUTCH SIZE; HOST; HYMENOPTERA; FIELD; SELECTION; WASP; SUPERPARASITISM; ICHNEUMONIDAE]

Seasonal dynamic shifts in patch exploitation by a parasitic wasp

We developed and tested predictions of a dynamic life history model that is concerned with how temperate-zone parasitic wasps adjust patch residence time and tendency to superparasitize when expectation of life and habitat quality varies. The theory predicts that wasps with short life expectancy should continue to search longer and superparasitize more frequently than similar wasps with long life expectancy. Similarly, wasps with long life expectancy that forage in habitats where patches are already heavily exploited should continue to search longer and superparasitize more frequently than similar wasps foraging in habitats where patches are relatively unexploited. In contrast, the theory predicts that wasps with short life expectancy will be insensitive to habitat quality. We tested the predictions on Drosophila parasitoids (Lep-topilina heterotoma) by (1) rearing wasps under fall and summer photoperiod (i.e., short versus long life expectancy) and (2) giving wasps foraging experience on different quality patches (i.e., exploited versus unexploited habitats). Results of the experiments corroborated our predictions. We discuss how parasitic wasp behavior can be shaped by globally predictable and locally unpredictable events.

When nesting involves two sequential, mutually exclusive activities: What's a mother to do?

Background: Parents can invest in offspring through a variety of behaviours, some of which trade off against each other, such as investment in the current brood versus investment in a future one. Question: When should hymenopteran parents stop provisioning the current nest and decide whether to seal the entrance to the nest (e.g. with a number of leaf pieces)? Method and key assumptions: A dynamic state variable model. We assume that mothers alter reproductive decisions based on their perception of costs and benefits of brood cell and nest construction. Some of these construction behaviours allocate investment at one or a few offspring in a brood but others affect the entire brood. Conclusions: Several factors impact the decisions of when to cease provisioning new offspring and whether to seal the nest. Higher current nest value and greater risk of mortality increase the likelihood of both ceasing provisioning earlier and sealing the nest. The greater the benefit of sealing, either because of increased benefits or decreased negative impacts, the earlier and the more frequently it occurs

Seasonal dynamic shifts in patch exploitation by parasitic wasps.

We developed and tested predictions of a dynamic life history model that is concerned with how temperate-zone parasitic wasps adjust patch residence time and tendency to superparasitize when expectation of life and habitat quality varies. The theory predicts that wasps with short life expectancy should continue to search longer and superparasitize more frequently than similar wasps with long life expectancy. Similarly, wasps with long life expectancy that forage in habitats where patches are already heavily exploited should continue to search longer and superparasitize more frequently than similar wasps foraging in habitats where patches are relatively unexploited. In contrast, the theory predicts that wasps with short life expectancy will be insensitive to habitat quality. We tested the predictions on Drosophila parasitoids (Lep-topilina heterotoma) by (1) rearing wasps under fall and summer photoperiod (i.e., short versus long life expectancy) and (2) giving wasps foraging experience on different quality patches (i.e., exploited versus unexploited habitats). Results of the experiments corroborated our predictions. We discuss how parasitic wasp behavior can be shaped by globally predictable and locally unpredictable events. [Behav Ecol 3:156-165 (1992)] Recent advances in the development of dy-namic life-history models (Houston e