Author Institution: Department of Zoology and Entomology, The Ohio State University, Columbus 1

Hintz, Howard W.

The Ohio Journal of Science

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THE ROLE OF CERTAIN ARTHROPODS IN REDUCINGMOSQUITO POPULATIONS OF PERMANENTPONDS IN OHIOHOWARD W. HINTZDepartment of Zoology and Entomology, The Ohio State University, Columbus 10An examination of the literature shows that transient rather than permanentbodies of water are most favorable to the production of mosquitoes, and furtherthat there is little data explaining why this is so. Part of the answer may lie in(1) the fact that the mosquito fauna of permanent ponds is different from that oftemporary ponds and pools, although Mead (1949) has shown that species such asAnopheles quadrimaculatus, Aedes vexans, and Culex pipiens breed in both typesof habitat, and (2) the fact that there is higher mortality among the larvae inpermanent ponds.The predatory activity of the arthropod fauna doubtless causes much of thislarval mortality. However, most general works dealing with mosquitoes onlybriefly discuss arthropod predation and thus leave the impression that it is un-important. Arthropods other than insects have seldom aroused the interest of inves-tigators, and relationships other than predation have been given little consideration.The writer has conducted an inquiry into these problems and here reportssome observations which he made concerning predation and competition in per-manent ponds. The work was carried out during the summers of 1947 and 1948,and the principal facility used was the Ohio State University farm pond. Thispond was inspected several times each week. Supplementary aquarium studieswere carried on concurrently. In addition, a number of other ponds and poolswere observed at irregular intervals for the purpose of making comparisons.LIMITS TO POPULATIONS OF MOSQUITO LARVAEMany insects and some other arthropods prey upon mosquito larvae. Further-more, the arthropods can limit mosquito breeding in other ways. Thus a largereservoir of predators is supported by the herbivores, such as mayflies and midges,which are present throughout the year. Whenever mosquito larvae are introducedinto the pond, predators are already present and will begin to take a toll. Sincethe midges and other herbivores provide a series of alternate hosts for the predators,the mosquito population will not build up ahead of a lagging predator increase.Secondly, the arthropods compete with the mosquito larvae for the availablefood. Little is known about this competition. Weed (1924) made a very briefreport of a pond in which he thought cladocerans completely prevented mosquitobreeding by utilizing all of the food.Finally, the larger arthropods can create an unfavorable physical environmentfor mosquito larvae by their movements. This is because the larvae and pupaeof many mosquito species move rapidly when they are disturbed and constantescape reactions can slow down their development and expose them to predation.When Aedes aegypti larvae were kept in an aquarium with hydrophilid adults,many of them died because the beetles were constantly moving. Such mortalitydoubtless rarely if ever occurs naturally. In ponds hydrophilid adults spend mostof the time feeding and resting on the bottom with occasional trips to the surfacewhere they obtain air. Since there are several beetles per lineal foot of shore inthe Ohio University pond in July, they would continuously disturb any immaturemosquitos in the vicinity. The constant motions of notonectids and gyrinidswould also produce a pronounced disturbance of larvae in their paths.THE OHIO JOURNAL OF SCIENCE 51(5): 277, September, 1951.278 HOWARD W. HINTZ Vol. LISOME IMPORTANT PREDATORS: COPEPODS AND INSECTSHaub (1930) in a review of the literature does not mention copepods. Thepresent author has not discovered any report of their predacious activity sincethat time. However, some species of these microcrustaceans readily feed uponfirst and second instar mosquito larvae when they are kept in aquaria.Several species of Cyclops are common inhabitants of shore water and thewater among the plants in ponds and lakes. Mosquito larvae probably occur intheir normal diet. Members of the genus can capture moving larvae and retaina grasp throughout vigorous movements of the prey even though this prey is oftenlarger than the captor. These copepods attack both culicine and anophelinetype larvae, but they capture culicines much more often.During 1948 a group of Cyclops was kept in a small dish and provided dailywith Aedes aegypti larvae. The copepods seized the larvae seconds after theywere added. Individual copepods consumed about five first and second larvae perday. Aedes aegypti larvae placed in a large aquarium with a mixed populationof small invertebrates, including copepods, disappeared, and they were probablytaken by the Cyclops which were the only predacious metazoan species present.The relatively large aquatic insect predators of many species probably consumemany more larvae than do the copepods. Odonatan nymphs are among the mostnumerous predators in many ponds and the habits of a number of species are suchthat they would encounter mosquito larvae. For instance, damselfly nymphscling to stems along which mosquito larvae feed. The long-legged nymphs of thedragonfly Erythemis simplicicolis wander about in the vegetation and in the littlepools within the surface blanket of algae. Bottom dwelling forms such as Libellulaspp. probably move to shallow water at night, as they are sometimes seen movingback to central parts of the pond from the shore between midmorning and noon.Other insects including notonectids, dytiscid larvae and adults, naucorids,hydrometrids, some neuropterons, and hydrophilid larvae prey on immaturemosquitos. On the average, according to aquarium studies made by the author,a centimeter long insect predator can destroy ten third and fourth instar mosquitolarvae per day. A large anisopteran nymph will consume as many as one hundredlarge larvae in a day.The larvae of hydrophilid beetles of the genus Tropisternus are especiallyimportant predators. Hixson (1943) presented data indicating that in Floridalarvae of Tropisternus spp. were the principal predators of anopheline larvae in anassociation in which no minnows were present.The present author found that Tropisternus larvae have structures and feedinghabits which make them efficient in destroying mosquito pupae. These beetlelarvae obtain air through posterior spiracles which are kept in contact with thewater surface. Therefore they walk about on vegetation or along the shore wherethe water is a half inch or so deep in places where mosquito pupae tend to collect.Furthermore, the hydrophilid larvae move continuously and they will leave thewater and travel overland and possibly reach small isolated puddles containingmosquito larvae.When Tropisternus larvae ingest food they hold the head out of the water andspend considerable time macerating their prey. This manner of eating furtherconfines them to the top half inch of water.These beetle larvae when kept in an aquarium captured mosquito pupaeeasily, but they had difficulty in catching the larvae. Field observations of feedingwere difficult to make. In one instance a beetle larva and a mosquito pupa weredipped together from a ditch. The larva immediately captured the pupa. Afarm water tank examined in late August contained anopheline larvae and hydro-philid larvae and numerous smaller invertebrates. No mosquito pupae werepresent so it is probable that the hydrophilids were destroying them as they formed.No. 5 ARTHROPODS AND MOSQUITO POPULATIONS 279THE IMPORTANCE OF ARTHROPOD PREDATIONArthropod predators are abundant and have a great diversity of structureand habit. Throughout the year various species inhabit open water and vegetatedareas, shore and bottom areas, and regions of low and high oxygen concentration.The soft-bodied mosquito larvae which swim conspicuously and which spend apupal period exposed at the water surface, would seem to be susceptible to thesepredators.These predators, therefore, very likely help prevent a large production ofmosquitoes in permanent bodies of water. This is indirectly indicated by Herms,Hackett, and others who list ecological provinces in order of importance of mosquitoproduction as: (1) floodwater remnants, (2) artificial containers, (3) woodland pools,(4) swamp-ponds, and (5) streams and ditches.This is roughly in inverse order to habitats listed according to the abundanceof predacious arthropods. Similarly, Mead (1949) states that the worst pests incentral Ohio are temporary pool breaders such as Aedes vexans (Meigen), A.stimulans (Walker), A. trivittatus (Coquillet), and species of Culex and Psorophora.A survey in the Columbus area will disclose small temporary pools of waterwith a surface area of a few square feet which contain more mosquito larvae thanlarge permanent ponds. Mead's records of mosquito larvae in the Universitypond show Anopheles quadrimaculatus larvae or pupae present on August 1, 8,and 25, and Sept. 21, 1948. But on the 25th of August, even though a dense algalmat was present, there was only a total of 17 larvae and two pupae in 75 dips.These low pond populations are probably often the result of the rich insect andcopepod fauna present.SUMMARYArthropods prey upon mosquito larvae and maintain reservoirs of predators.They compete with mosquito larvae for food and space.Copepods of the genus Cyclops, which are abundant in quiet water, feed uponfirst and second instar larvae of mosquitoes. Hydrophilid larvae of the genusTropisternus have habits which make them important mosquito pupal predators.Permanent ponds produce fewer mosquitoes than do transient ponds and pools.Arthropod predation is probably an important cause of mosquito larval mortalityin permanent ponds.LITERATURE CITEDHaub, J. G. 1931. The Gyrinidae and other predators of mosquito larvae. Master's Thesis,Ohio State University.Hixson, H. 1943. Data and observations on the natural reduction of Anopheles mosquitolarvae in certain environments. Florida Ent. 26: 17-24.Mead, F. W. 1949. Ecology of central Ohio mosquitoes. Master's Thesis, Ohio StateUniversity.Weed, A. C. 1924. Another factor in mosquito control. Ecology 5: 110-111.

The Role of Certain Arthropods in Reducing Mosquito Populations of Permanent Ponds in Ohio

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The Role of Certain Arthropods in Reducing Mosquito Populations of Permanent Ponds in Ohio

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