Geographic origin affects larval competitive ability in European populations of the blow fly, Lucilia sericata

The blow fly, Lucilia sericata (Meigen) (Diptera: Calliphoridae), is found throughout Europe. In northern areas, in addition to breeding in carrion, it can also commonly act as primary facultative ectoparasite of sheep, resulting in animal suffering and production losses. However, in the south of Europe, L. sericata is not usually implicated in myiasis and is found almost entirely in carrion. The causes of this behavioural difference are unclear. To begin to address the possible reasons for this difference, the present study examined the effects of competition on the survival and development of L. sericata populations derived from southern Spain, England, and a hybrid derived from a cross between Spanish females and UK males. Larvae were reared at a range of different initial densities and the mortality, development rate, and size of the resultant adults were measured. Mortality increased significantly with density, but the Spanish population had a significantly higher mortality rate than the UK population at all densities. Similarly, adult size declined with increased larval density, but individuals from the Spanish population were consistently larger than those from the UK population at all densities. The mortality and size of the hybrids was consistently intermediate between the Spanish and UK populations. No consistent effects on development rate were observed. This study demonstrates that insects from northwestern and southern European population have qualitatively different life history traits and competitive abilities and may contribute towards explaining the different behaviour of populations of this species in different part of its distribution range.