Studies on insecticide-resistant anophelines. I. Chromosome arrangements in a dieldrin-selected strain of Anopheles atroparvus.

The authors present the results of a cytological examination, carried out by the technique developed by Frizzi, of the larvae of a normally susceptible and a dieldrin-selected strain of Anopheles atroparvus, both laboratory-reared. A very high percentage (77.4) of heterozygous inversions was observed in the larvae of the 28th generation of the dieldrin-resistant strain, whereas only 20.8% occurred in the normally susceptible strain, in which the standard chromosomal arrangement predominated (74.2%). These results are similar to those obtained recently by other workers in the case of larvae of the 12th generation of a DDT-selected strain of A. atroparvus (74.8% heterozygous inversions observed).