Fitness, parasitoids, and biological control: an opinion

Fitness, defined as the per capita rate of increase of a genotype with refe rence to the population carrying the associated genes, is a concept used by biologists to describe how well an individual performs in a population. Fi tness: is rarely measured directly and biologists resort to proxies more ea sily measured but with varying connection to fitness. Size, progeny surviva l, and developmental rate are the most common proxies used in the literatur e to describe parasitoid fitness. The importance of the proxies varies betw een papers looking at evolutionary theories and those assessing ecological applications. The most direct measures of fitness for parasitoids are reali sed fecundity for females and mating ability for males, although these prox ies are more difficult to measure under natural conditions. For practical p urposes, measure of size, through body size or mass, is the proxy easiest t o use while providing good comparative values; however, care must be taken when using a single proxy, as proxies can be affected differently by rearin g conditions of the parasitoid.