Recent additions to knowledge on the inheritance of insecticide resistance indicate simple inheritance (1) of dieldrin resistance in Anopheles gambiae Giles and in Lucilia cuprina Wiedeman, (2) of DDT resistance in Anopheles sundaicus (Rodenwaldt), in Aedes aegypti (L.), in at least four different strains of the house fly (Musca domestica L.) and possibly in A. stephensi Favre; and (3) of organophosphorous resistance in five unrelated strains of the house fly.

Two loci for DDT-knockdown resistance have been located in the same linkage group of the house fly. Two loci (chromosome II, 64.5 and chromosome III, 50) of Drosophila melanogaster Meigen are involved in the control of different degrees of resistance to DDT, BHC, parathion and phenylthiourea, the locus on chromosome III controlling also resistance to nicotine and to phenylura. In Drosophila factors for resistance have been found also on the X chromosome and maternal effects have been observed for parathion and DDT resistance.

The building-up of complex adaptive polygenic systems has been confirmed by gene or chromosome analysis by all workers who have adopted Drosophila melanogaster for the experimental study of population dynamics. The multifactorial type of inheritance controls also transmission of DDT, BHC, and chlordane resistance in Blattella germanica (L.).

A progressive increase in resistance to DDT without contact with the insecticide has been twice (independently) obtained by directional sib-selection and also by selection of physiological properties not directly related to resistance

Levels of dechlorinating activity and levels of resistance to DDT have indicated similar patterns of inheritance.

Low ali-esterase activity (typical of all examined organo-phosphorous-resistant strains of the house fly) has been inherited in coincidence with malathion and with one factor for parathion resistance. However, one factor for parathion resistance unrelated to low ali-esterase activity has also been isolated.

The use of genetically marked strains of the house fly and of repeated hackcrosses has allowed (a) the detection in the Orlando-R strain of a major gene for DDT resistance, (b) the location of the gene in its linkage group, and (c) the recognition of occasional gross disturbances in Mendelian segregation. A sex-limited enhancer of dominance, acting on the two known genes for knockdown resistance, is also strongly suggested.