DDT-resistance in West African and Asian strains of Aedes aegypti (L.)

The yellow fever mosquito Aedes aegypti has developed resistance to DDT in the Caribbean region and in South-East Asia, but not in West Africa. Therefore West African strains were compared with South-East Asian strains for their response to laboratory selection with DDT. It was found that West African strains were much slower to respond initially, but eventually could build up a high degree of DDT-resistance. By crossing and backcrossing with a susceptible marker-gene strain, it was found that this resistance was due to a single gene linked with the gene y (yellow) on chromosome 2 at a cross-over distance of approximately 35 units in an Upper Volta strain as in a Bangkok strain; interstrain crosses indicated that the gene was the same as that in a Trinidad strain and in one from Penang. Dieldrin-resistance could be readily induced in the Upper Volta strain and proved to be due to a gene also linked with y but at a crossover distance of approximately 25 units, comparable to that in Caribbean strains previously studied. Material from Karachi, West Pakistan, developed a dieldrin-resistance also showing 25% crossing over with y, and a DDT-resistance also linked with this chromosome-2 marker gene.

Toxicity of Alpholate to Cattle

Although Apholate is used as a sexual sterilant of both sexes of houseflies (Musca domestica L.) it can not be used for ;systemic' chemosterilization of the prehypodermic larvae of the warble flies Hypoderma bovis (L.) and H. lineatum (De Vill.) because of its high toxicity to 4- to 5-month-old calves. An intramuscular dose of 2.5 mg./Kg. killed the calves in 5 to 7 days. The pathognomonic clinical signs were impaction of the rumen, anorexia, depression, and general weakness. The hematopoietic system was affected. There was marked leukocytopenia characterized by lymphocytopenia within 24 hours of Apholate injections.

Organophosphate Poisoning in Cattle with Particular reference To Co-Ral

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Immunization and Parenteral Chemotherapy for the Control of Cattle Grubs Hypoderma Lineatum

Immunization with two types of warble larvae antigens A and B, the latter treated with tannic acid, and injections of dimethoate, an organic phosphate, were tried for the control of prehypodermic larvae of Hypoderma lineatum De Vill., and H. bovis L., in range calves. In test groups of 20 calves, given intramuscularly, antigen A had no effect, but combined treatment with antigens A and B reduced the number of H. bovis L., larvae by 81 per cent (P<.001), and proved as effective as dimethoate subcutaneously or intramuscularly. H. lineatum De Vill., did not respond to any treatment. Antigen B and dimethoate were free from harmful effects on the host, but antigen A caused anaphylaxis and irritation at the site of injection.