Reference to Table 5 will show that while Enithares destroyed a large number of larvae of both anophelines and culicines, almost twice as many of the latter were eaten. This fact can perhaps be explained by the circumstance that anophelines, lying parallel to the water-surface, are not so readily seen by back-swimmers as culicine larvae which hang head downwards from the surface. Few pupae were destroyed by this predator during the laboratory investigation. Wladimirow and Smirnov (1932) report that a species of Notonecta which they studied ate up to twenty-five mosquito larvae a day. They carried out experiments on several species of notonectids, most of which destroyed more culicines than anophelines. Graham (1939) states that the New Zealand back-swimmer Anisops assimilis White, devours mosquito larvae readily, but only eats pupae in the absence of larvae.

Text-fig. 5.—Enithares bergrothi.

At Palmalmal, ten adults of E. bergrothi were introduced into an uncovered water drum heavily populated with larvae of Aëdes scutellaris. The numbers of the latter declined very sharply, and a search five days later resulted in the finding of only nine late instar larvae of A. scutellaris in this drum.

Dempwolff (1904), working in what was then German New Guinea, observed that waters which contained many notonectids harboured no mosquito larvae. Within a week this investigator brought about the destruction of all the mosquito larvae in seventeen water tanks by introducing Notonecta into them.

E. bergrothi was seldom sufficiently plentiful in nature to act as a really efficient check on the breeding of mosquitoes in ground pools. As Hale (1923) has pointed out, this species leads a solitary rather than a gregarious existence. Its usefulness as a mosquito enemy under natural conditions is thus curtailed. However, like many other notonectids, E. bergrothi can be put to good use in the control of mosquito larvae in artificial containers.