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OBSERVATIONS ON THE LIFE-HISTORIES AND 

 BIONOMICS OF SOME TACHINID^. 



By H. S. Leigh. 



DiPTERA — although not generally a favourite group with 

 entomologists — forms one of the largest and most important 

 orders of insects. Their economic significance is very great, 

 some of them being capable of conveying the most serious 

 diseases, whilst others act as scavengers by devouring all kinds 

 of waste products. 



Many species live parasitically on various lepidopterous 

 larvse, and thus, together with the ichneumons, help to keep the 

 numbers of certain Lepidoptera within bounds. This is of great 

 importance to man, for some species of caterpillars are very 

 troublesome pests, and at times occur in such countless numbers 

 on cultivated plants as to strip them of all foliage. 



In several districts around Manchester the larvae of Abraxas 

 grossulariata, Linn., have been very common during the last few 

 years ; I have on one occasion collected 1500 from one garden, 

 and taken about 3000 altogether during 1906 and 1907. This 

 shows how very prevalent the species frequently becomes in 

 some localities, and anything that can help to lessen its numbers 

 will be extremely beneficial. 



The Tachinidae, one of the families comprising the Muscidse 

 Calyptratas, contains very many species of flies which are 

 parasitic on Lepidoptera and Hymenoptera. These flies look — 

 at first sight — so like the ordinary house fly, Miisca domestica, 

 Linn., that they are no doubt often mistaken for such. 



One species of Tachinid, Blepharidea vidgaris, Fin , which 

 attacks the larvae of A. grossidariata, is often very abundant 

 during the latter part of June and beginning of July. I have 

 bred many of these flies from caterpillars collected in May, and 

 Mr. Wainwright says it is "one of our commonest species, with 

 many known hosts." The proportion of parasites to hosts was 

 about eighty-five of the former to one thousand of the latter, so 

 that rather more than eight per cent, of the caterpillars were 

 parasitised. 



Mr. Hewitt* has found that the infected A. grossulariata 

 larvae contain newly-hatched Tachinid larvae during early May, 

 when the former are about half-grown. About the middle of 

 June both are matured, and the parasite breaks through the 

 body-wall of the host just prior to pupation. The Tachinid 

 larva pupates a few hours after leaving the body of the host, 

 and under natural conditions the pupae are probably formed on 

 or just below the surface of the soil. 



* " Bionomics of certain Calyptrate Muscidse and their Economic Signi- 

 ficance," Journ. Econ. Biol., vol. 2, No. 3. 



ENTOM. — MAY, 1908. K 



