DEVELOPMENT RATES OF SOME PRE-ADULT STAGES IN BLOWFLIES WITH REFERENCE TO LOW-TEMPERATURES

Duration of some pre-adult stages of Calliphora vicina Robineau-Desvoidy, C.alpina Zett., C.vomitoria Linn., Phormia terraenovae R.-D. and Lucilia sericata Meig. were determined at 3.5-26-degrees-C, in the context of use of these insects in forensic estimates of post-mortem intervals. Egg development in C.vicina occurs down to at least 3.5-degrees-C, larval growth to 4-degrees-C and puparial formation, development and perfect adult emergence to 5-degrees-C. Growth curves by successive weighing of individual larvae showed specific differences in rates of development of the above species at constant temperatures. Alternating temperatures for 12 h periods (such as 10-degrees-C and 20-degrees-C) to simulate diurnal changes, usually, but not at all temperature pairs tested, caused acceleration of growth relative to the corresponding constant temperature (15-degrees-C in the above case), in C.vomitoria, P.terraenovae and L.sericata, but usually caused retardation of larval growth in C.vicina. In this species, larvae as single individuals on beef liver in small tubes grew on average at the same rates as those (50-100 larvae) growing communally. All species showed variation in larval growth between individuals, more marked in C.vicina, and slower-growing larvae showed increased unexplained mortality. Because of this and to avoid complication by fast-growing larvae from later laid egg batches on a carcass, growth curves given are those of mean weights of the heaviest 25% (upper quartile) of groups of 40-90 feeding larvae. Variation in growth rates, and acceleration or retardation of growth in different species under alternating temperatures, thus affect suggested procedures in obtaining estimates of post-mortem intervals using these insects.