Sympatric occurrence of homozygotes for two electromorphs controlled by a locus for octanol dehydrogenase, and the absence of heterozygotes, at two localities, indicates two isomorphic species within the taxon Anopheles minimus Theobald in Thailand. This view is supported by significant, relative deficiencies of heterozygotes at other electromorphic loci. Gene frequency data are reported for seven electromorphic loci in An. minimus sensu lato from eleven localities: one of the newly recognized species predominated in all but one locality and the second was confined to two localities. This species pair of An. minimus s.l. was clearly distinguished from An. aconitus Dönitz, An. pampanai Büttiker & Beales and An. varuna Iyengar, three species closely related to An. minimus s.l. in the series Myzomyia of Anopheles subgenus Cellia.

Development of third-stage larvae of Dipetalonema viteae within subcutaneously implanted micropore chambers proceeded in all hosts tested up to the fourth-stage larvae and occasionally to adolescent worms. In the jird the timing of development was comparable to a natural infection. Although the mouse is an insusceptible host, larval development could take place, but was very slow. Two intraperitoneal inoculations of living third-stage larvae into mice induced the production of antibodies against the larval cuticle and against common antigens. In such immune mice the development of third- and fourth-stage larvae within micropore chambers was significantly inhibited, larval mortality was increased, and the larval motility was impaired.

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Females of Anopheles minimus Theobald at a site in northern Thailand that were caught on man or domestic bovids and were released showed a significant tendency to return to the type of host upon which they were first caught (F = 0-03). From a total of 3526 individuals marked and released, 51 were recaptured. A simple explanation is that the taxon is in fact a mixture of two or more morphologically cryptic species, a suggestion already indicated by previous studies.