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Larvae of Culex pervigilans can be obtained in Auckland and the surrounding districts throughout the whole year, and in every conceivable type of water container, as mentioned above in the section dealing with the eggs. They maintain themselves even in streams flowing at one and a half miles per hour, by holding on 10 stones and debris near the banks. I have also found them in wheel ruts on clay roads, although motor and horse-drawn vehicles would splash through the ruts from time to time, and close observation has shown that most of the larvae in such a wheel-rut survive the passage of a car through it. There is no water puddle so small or so foul but that these larvae can be found in it, and water-holding rubbish of any kind provides breeding places for almost incredible numbers.
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The larval period of this species varies a great deal in accordance with the temperature; in the summer months it occupies from 8 to 14 days. Individuals live through the winter in either the adult or larval stage, but should a period of warm weather occur, the larvae of the fourth instar will complete their development and emerge as adults within a week. In the laboratory I have bred this species through all stages from egg to adult, although the water was never above 60° F. and often as low as 48° F., which indicates that brief spells of low temperature will not unduly retard development. I have also bred adults successfully from larvae taken from ice-covered water, and I have obtained active larvae from troughs (at Mangere) where 15° of frost were registered for three days in succession.
Experiments have shown that these larvae are capable of living in water containing a considerable salt proportion; while the sudden addition of two parts of sea-water to one of stream water will kill them at once, they will survive in water which has been brought gradually up to this salt content. They will live for several days in soft mud, rapidly regaining their activity when rain falls. At the same time they are quickly killed by oiling, with either kerosene or light lubricating oil: observations in the laboratory have shown that they die within an hour under an oil film, as might be expected. This is in marked contrast to what happens in the case of the next described species.
Finally it may be mentioned that they are far less susceptible to sound or disturbances than the larvae of Aedes notoscriptus. When I have purposely disturbed the larvae of both these species together and caused them to sink to the bottom of the pool or laboratory jar, those of C. pervigilans. have invariably been the first to rise to the surface again.
It is probably worth mentioning that of the hundreds of breeding groups I have had under observation only one failed to develop. These were kept under the same conditions as to water, food and temperature as all the others, but grew very slowly, taking a month to attain the fourth instar at which stage they remained for six months, when they died without reaching the pupal stage. This unaccountable inhibition of development is recorded in the hope that some other observer may be able to offer a comparative case, or a possible explanation.