4:66 SUMMARY OF CUKRENT RESEARCHES RELATING TO 



INVERTEBRATA. 



Arthropoda. 

 a. Insecta. 



Insects in Relation to Disease.* — R. M. Buchanan discusses the 

 role of insects in spreading diseases. Mosquitoes have checked 

 civilisation by disseminating malaria and yellow fever ; the tsetse-flies 

 have carried sleeping sickness over the tropical area of Africa ; other 

 insects have to do with plague, typhus, and relapsing fever ; the 

 house-fly is credited with a share in the transmission of typhoid fever, 

 infantile diarrhcEa, dysentery, and -cholera. Mechanical transmission is 

 illustrated by the house-fly, and inoculation by means of biting mouth- 

 parts by the tsetse-fly. The egg of Musca domestica takes from 8 hours 

 to 3 days to develop, the maggot from 5-8 days to 6-8 weeks, the pupa 

 3-4 to 5-7 days or 2—4 weeks, the imago to become mature 14-18 days. 

 The shortest time required for an ovum to give rise to a winged fly 

 is 8^-15 days, the longest time taken is 8-12 weeks. The shortest 

 time for the whole life-cycle is 3-4 weeks, the longest 10-15 weeks. 

 The structure, habits, and enemies of the house-fly are discussed. The 

 fungus Etnpusa miiscse and the mite Gamasus musci are dealt with. 

 Attention is also directed to the lesser house-fly {Fannia canicularis), 

 the latrine-fly {F. scalaris), and the stable-fly {Stomoxys calcitrans), and 

 other flies. In some detail the author treats of the transmission of 

 trypanosomes by tsetse-flies. 



Study of Lac Insect.f — A. I). Imms and N. C. Chatterjee have 

 made a study of Tachardia lacca, the Coccid which produces the Indian 

 lac. The lac is a resinous secretion or exudation, from yellow to reddish 

 brown, produced in large quantities by the female, in very small 

 quantities by the male. It appears to be a product of the epidermis. 

 The insect is double-brooded. The larvse issue from the resinous 

 incrustations of the females in large numbers and search for succulent 

 twigs, in which they insert their mouth-parts. They become gradually 

 covered with lac. About a mouth after the fixation of the larvai of 

 the first brood, the male insects emerge. In the case of the second 

 brood the males emerge about three and a half to five months after fixa- 

 tion. Those of the first brood may consist of both winged and wingless 

 individuals, while those of the second brood are wingless. After 

 the females have been fertilized by the male the secretion of lac 

 becomes much greater. From two to three months after the emergence 

 of the males the young larvae appear. The parent female then rapidly 

 dies, and her shrivelled skin is left in the central cavity of the incrusta- 

 tion which enveloped her. As in most Coccidffi there is a pupal stage 

 in the life-history of the male and a highly evolved insect emerges, 

 while in the case of the female there is only degeneration. The 



* Glasgow Med. Journ., Jan. 1916, p. 1-28 (5 pis. and 29 figs.), 

 t Indian Forest Memoirs, iii. (1915) Calcutta, pp. 1-42 (3 pis.). 



