Floodwater Mosquitoes Research Articles

Development, Structure, and Function of Coverings of Eggs of Floodwater Mosquitoes. III. Functions of Coverings1

In Aedes aegypti (L.), on which this paper is largely based, the envelopes composing the egg shell have different functions. The exochorion imbibes water from saturated atmospheres and releases it slowly while drying. An annular line of weakness, from which a cap later dehisces, is determined by a structural change in the chorion at or about the time when embryogenesis is completed. The chorion, by changes in stratification, tanning, and infiltration by water-repellent chemicals, combines with the endochorion to create a barrier to movement of water. Hatching is brought about when the embryo is activated to elevate its hatching spine against the fracture line while applying pressure toward the water, the larva rapidly expands and soon swims a ventral depression of the cap. Once exposed to sway.

Eggs of Floodwater Mosquitoes (Diptera: Culicidae) V. Effect of Oxygen on Hatching of Intact Eggs1

Conditioned embryos of floodwater mosquitoes in intact eggs change from a latent to an active state and hatch when placed in a medium from which at least part of the dissolved oxygen has been removed. Replacement of oxygen by nitrogen in atmospheres of closed systems permitted a study of effects of differences in levels of oxygen. Species capable of completing several generations each year in nature will hatch immediately after completion of morphogenesis. When kept at room temperature eggs of Aedes trivittalus continued to hatch readily for some 80 days. Many of the embryos between the ages of 100 and 140 days of age could not be conditioned. Embryos from 100 to 300 days of age again hatched well even at fairly high percentages of oxygen. Embryos in eggs on dry surfaces could be stimulated to crack the shells of their eggs by lowering the oxygen in the atmosphere about them. Eggs within a closed system of small volume hatched without outside stimulation, presumably by reducing the oxygen tension by metabolism of enclosed embryos.

Development, Structure, and Function of Covering of Eggs of Floodwater Mosquitoes. I. Ovarian Development1

There are a number of readily observed phenomena associated with the eggs of floodwater mosquitoes that suggest the shell to be a structure with unusual properties. In North America these eggs are produced by mosquitoes in the genera Aedes and Psorophora. They are laid in situations where conditions of transient water occur, retaining their viability out of water in nature for a year or longer. Inasmuch as a fully developed embryo is within the egg during such extended periods (in contrast to the partially developed embryo within diapause eggs of grasshoppers), it seems obvious that factors tied up with successful hatching are connected with the egg coverings. It has been shown that oxygen must be removed from the surrounding medium before hatching will take place, but even when such a condition exists the hatching will be irregular if certain other conditions have not been met first (Horsfall, 1956). These environmental conditions differ among species, and have been collectively termed “conditioning” by Borg and Horsfall, 1953. While the determination of structure and composition of the chorion may not clarify factors responsible for the observed phenomena, such findings are a desirable adjunct to further study.

Eggs of floodwater mosquitoes (Diptera: culicidae). VI. Effect of metabolites on latent embryos in uncapped eggs.

SummaryLatency in both intact and manually uncapped eggs of floodwater mosquitoes may be continued or terminated at will. Conditioned embryos in uncapped eggs become active in a modified Ringer's solution. Latency may be continued in such embryos by adding metabolites such as glucose, fructose and salts of organic acids which are recognized substrates in oxidative metabolism to the basic Ringer's solution.

Eggs of Flood Water Mosquitoes III (Diptera, Culicidae). Conditioning and Hatching of Aedes Vexans1

Eggs of floodwater mosquitoes are capable of withstanding adversities such as drought, cold and unfavorable submersion. Once the eggs of a species have been subjected to adversity, a sequence of events called “conditioning” is required to predispose them to respond to the final stimulus. This sequence of events necessary for conditioning varies according to the species. Accordingly some may hatch shortly after the onset of any period of inundation in spring and summer; others respond to a hatching stimulus only as the ice breaks up late in the winter or early in the spring. Eggs of both groups refrain from hatching whenever they are flooded before they have been conditioned or prepared for hatching. Once eggs are conditioned, the ultimate stimulus to hatching of any of the species is a decreasing gradient of oxygen dissolved in the water under which the eggs are submerged (Borg and Horsfall, 1953).

Eggs of Floodwater Mosquitoes. I. Species of Psorophora (Diptera: Culicidae)1

Eggs of mosquitoes have been known to provide important characters for segregating smaller categories ever since the work of Falleroni, 1926, but little has been done on groups other than anophelines. That his work permitted much of our knowledge of subspeciation of Anopheles maculipennis Meigen of the Old World suggests this stage of other groups might be profitably examined more carefully for characters. Numerous descriptions of eggs of various species of floodwater mosquitoes exist, but little effort has been directed toward systematizing the knowledge. Such knowledge would be helpful in certain groups particularly because only females are usually collected, and often they are difficult to determine. Optical systems in the form of phase microscopes now provide convenient means for much more minute examinations of surface features of the chorion than were formerly available. The observations reported herewith serve to show how distinct are the characters that may be seen by such devices for lighting the surfaces.

Studies on Aedes Vexans (Meig.) and Aedes Sticticus (Meig.), Flood-Water Mosquitoes, in the Lower Columbia River Valley

The annual spring floods of the Columbia River usually inundate thousands of acres of open and wooded lowlands along its borders below Bonneville Dam for a distance of about 60 miles or more up and down the river from Vancouver, Wash., and Portland, Oreg. The Willamette River floods smaller areas for about 15 miles above the point where it joins the Columbia, and considerable backing up of water occurs near the mouths of smaller tributaries in this region. The area that flooded above the site of the Bonneville Dam before it was built is now permanently covered with water (Stage, 1943).

Hatching eggs of floodwater mosquitoes in media that promote plant growth.

Hatching eggs of floodwater mosquitoes in media that promote plant growth.

Pre-Hatching Treatment of Irrigated Lands with DDT, Dichlorodiphenyl Dichloroethane, and Gamma-Benzene Hexachloride for Control of Flood-Water Mosquitoes

Pre-Hatching Treatment of Irrigated Lands with DDT, Dichlorodiphenyl Dichloroethane, and Gamma-Benzene Hexachloride for Control of Flood-Water Mosquitoes

Flight Range and Longevity of Flood-water Mosquitoes in the Lower Columbia River Valley

Flight Range and Longevity of Flood-water Mosquitoes in the Lower Columbia River Valley

OBSERVATIONS ON SOME AQUATIC ANIMAL AND PLANT ENEMIES OF MOSQUITOES

Animal and plant enemies undoubtedly play an important part in controlling mosquitoes, but it is fully recognized that a study of these organisms forms only one phase of a very complex subject spoken of generally as natural control. Climate, weather conditions, topography, etc., all have an important bearing on mosquito abundance. Precipitation, whether in the form of rain or snow, and temperatures, exert a vital influence on mosquito populations. If the winter accumulation of snow is heavy, the spring infestation of snow pool and floodwater mosquitoes may be expected to be heavy too.