Life in the Pits Part Two
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LIFE HISTORY

Deinocerites cancer females lay their eggs singly on moist substrate just above the water surface in land crab burrows. Egg hatch occurs a few days after oviposition. Following eclosion first stage larvae crawl down into the water where development proceeds through a total of 4 larval stages. Low temperatures, crowding and suboptimal food levels extend the duration of the larval stages. Yet, even with summertime temperatures and other favorable conditions, it usually takes the crabhole mosquito at least 2- 3 weeks to complete larval development.
Waste products from land crabs probably enhance mosquito production by providing a food source for the larvae. By removing excessive debris and soil from their burrows land crabs also help to maintain an aquatic habitat for the crabhole mosquito. Without a resident land crab, old burrows rapidly become unsuitable for crabhole mosquitoes. Cardisoma guanhumi are herbivorous and normally remain in the burrows during the daylight hours, venturing out to feed only after sunset. This daily pattern of activity is interrupted when land crabs occasionally seal the entrance to their burrows with an earthen plug which may remain in place for several weeks or months. Crabhole mosquitoes may be trapped in these capped burrows.
Land crabs occasionally seal the entrance to their burrows with an earthen plug. Photo by David Mook.
Another inhabitant of land crab burrows is the killifish Rivulus marmoratus, which is particularly common in burrows that are more likely to be inundated by storm or seasonally high tides. Rivulus marmoratus can survive in the low oxygen and high hydrogen sulfide concentrations characteristic of the small, isolated aquatic habitats in land crab burrows, and it will readily devour Deinocerites cancer larvae. Other unusual traits enhancing the capacity of Rivulus marmoratus to prey on crabhole mosquito larvae include: the ability to move from one crabhole to another one by scooting over damp soil; the capacity to lay eggs with delayed hatching under drought conditions; and the self-fertilizing hermaphroditic mode of reproduction which enables a single fish to colonize new habitats.
Rivulus marmoratus. Photo by Michele Cutwa.
During the late summer and fall, estuarine water levels along Florida's southeast coast typically are much higher than they are during the rest of the year. These high water conditions invariably flood and submerge many land crab borrows near the estuarine intertidal zone, making the Deinocerites cancer larvae easy prey not only for Rivulus marmoratus but also for several other fish species. Nevertheless, land crabs adjust to these major floods by relocating further inland, and their new burrows are rapidly colonized by Deinocerites cancer.
The transformation from an aquatic to a terrestrial creature takes place in the non-feeding pupal stage. Deinocerites cancer pupae, like those of all mosquito species, are motile but tend to be inactive unless disturbed by other organisms. The pupal stage lasts just a few days.
Deinocerites cancer pupa. Photo by Michele Cutwa.
Newly emerged Deinocerites cancer females are sexually receptive to males, whereas the females of several other mosquito species will not mate for one or more days following emergence. Male Deinocerites cancer spend a considerable amount of time on the surface of the water where they exhibit a behavior called pupal attendance. The exceptionally long antennae of male Deinocerites have fewer sound collecting fimbrillae but more olfactory and mechanoreceptive sensilla than the males of other mosquito species. Using their highly specialized antennae, they search for female pupae.
Pupal attendance. Photo by Joe O'Neal.
Once a pupa is located, the male attaches to the pupa's air trumpet with the tarsal claw of its foreleg, while the other legs will be used to fend off other males. Somehow male Deinocerites cancer can distinguish between male and female pupa, especially in the final hour before eclosion. An attending male will initiate the mating process even before an emerging female is free of her pupal case. Copulating pairs may remain together for 30 minutes or more. Pupal attendance is known to occur in only one other mosquito, Opifex fuscus.
The male attaches to the pupa's air trumpet with the tarsal claw of its foreleg. Photo by Joe O'Neal.

Deinocerites cancer females normally do not blood feed until after the first egg clutch, which produced with carry-over reserves from the larval stage, is deposited. Birds, particularly ciconiiforms, serve as the primary blood source, but feeding also occurs on various mammalian and reptilian species. No evidence has been obtained to support the assertion that land crabs serve as a blood source for Deinocerites cancer. Both males and females obtain sugar meals from floral and other plant sources.

IMPORTANCE AS A PEST OR VECTOR:

Deinocerites cancer populations seldom annoy humans with their blood feeding activity, and Florida's crabhole mosquito has not been implicated in the transmission of any human pathogen.
   

SELECTED REFERENCES

Adames, A. J. 1971. Mosquito Studies (Diptera, Culicidae). XXIV. A revision of the crabhole mosquitoes of the genus Deinocerites. Contr. Amer. Entomol. Instit. 7(2): 1- 154.

Conner, W. E. and H. Itagaki. 1984. Pupal attendance in the crabhole mosquito Deinocerites cancer: the effects of pupal sex and age. Physiol. Entomol. 9: 263-267.

Edman, J. D. 1974. Host-feeding patterns of Florida mosquitoes. IV. Deinocerites. J. Med. Entomol. 11: 105-107.

O'Meara, G. F. and D. H. Mook. 1990. Facultative blood-feeding in the crabhole mosquito, Deinocerites cancer. Med. Vet. Entomol. 4: 117-123.

O'Meara, G. F. and J. L. Petersen. 1985. Effects of mating and sugar feeding on the expression of autogeny in crabhole mosquitoes of the genus Deinocerites (Diptera, Culicidae). J. Med. Entomol. 22: 485-490.

Provost, M. W. and J. S. Haeger. 1967. Mating and pupal attendance in Deinocerites cancer and comparisons with Opifex fuscus (Diptera: Culicidae). Ann. Entomol. Soc. Am. 60: 565-574.

Taylor, D. S. 1989. Room without a view. Natural History. 9/89: 26-33

Taylor, D. S. 1990. Adaptive specializations of the cyprinodont fish Rivulus marmoratus. Florida Sci. 53:239-248.

Wolcott, T. G. and D. L. Wolcott. 1990. Wet behind the gills. Natural History 10/90: 46-55.
   
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