Methods of Mosquito Control (Unless otherwise notated, all information provided by the American Mosquito Control Association) IDENTIFICATION Mosquitoes are insects belonging to the order Diptera, the True Flies. Like all True Flies, they have two wings, but unlike other flies, mosquito wings have scales. There are over 2500 different species of mosquitoes throughout the world; about 200 species occur in the United States with 77 species occurring in Florida. A new species, Anopheles grabhamii, was reported from the Florida Keys in 2001 (Darsie et al. 2002). Mosquito adults are small, flying, midge-like insects. Female mosquitoes can be differentiated from similar insects by the presence of a long slender proboscis that is adapted for piercing skin and sucking blood, and long slender wings that are covered with small scales. Male mosquitoes have scale-covered wings, but their proboscis, or beaks, are shorter and thicker than the females’, and are adapted for sucking plant juices and other sources of sugar rather than blood. In the immature stages, called larvae or wigglers, mosquitoes are usually black or dark brown and occur in nonmoving or nearly still water. Most mosquito larvae have a distinctive siphon or air tube at the rear of their bodies. The next stage is the pupal stage; pupae, called tumblers, are also aquatic and are small, somewhat round forms, usually black in color.2 Mosquitoes can be an annoying, serious problem in man’s domain. They interfere with work and spoil hours of leisure time. Their attacks on farm animals can cause loss of weight and decrease milk production. Some mosquitoes are capable of transmitting diseases such as malaria, yellow fever, dengue, filariasis, and encephalitis [St. Louis encephalitis (SLE), Western Equine encephalitis (WEE), LaCrosse encephalitis (LAC), Japanese encephalitis (JE), Eastern Equine encephalitis (EEE) and West Nile virus (WNV)] to humans and animals. © 2014 All Star Training, Inc. 1 LIFE CYCLE The life cycles of mosquitoes vary widely from species to species. Some female mosquitoes lay single eggs on water surfaces; others lay single eggs on moist soil where later flooding is likely. Still other species lay batches of eggs, called rafts, 100 or more at a time on water surfaces. Eggs deposited on water surfaces usually hatch within a day or so, but eggs laid on soil surfaces do not hatch until flooding occurs, which may be months or even years later. Larvae, which are nearly invisible to the naked eye, hatch from eggs. Larvae molt three times to become 4th-stage larvae. Several days later, this larval form molts again to become a pupa. Adult mosquitoes emerge from pupae 1 to 2 days after that, with male mosquitoes always emerging first. In summer, the entire life cycle, from egg to adult, may be completed in a week or less.2 The mosquito goes through four separate and distinct stages of its life cycle: Egg, Larva, Pupa, and Adult. Each of these stages can be easily recognized by its special appearance. Egg: Eggs are laid one at a time or attached together to form “rafts.” They float on the surface of the water. In the case of Culex and Culiseta species, the eggs are stuck together in rafts of up to 200. Anopheles, Ochlerotatus and Aedes, as well as many other genera, do not make egg rafts, but lay their eggs singly. Culex, Culiseta, and Anopheles lay their eggs on the water surface while many Aedes and Ochlerotatus lay their eggs on damp soil that will be flooded by water. Most eggs hatch into larvae within 48 hours; others might withstand subzero winters before hatching. Water is a necessary part of their habitat. Larva: The larva (plural - larvae) lives in the water and comes to the surface to breathe. Larvae shed (molt) their skins four times, growing larger after each molt. Most larvae have siphon tubes for breathing and hang upside down from the water surface. Anopheles larvae do not have a siphon and lie parallel to the water surface to get a supply of oxygen through a breathing opening. Coquillettidia and Mansonia larvae attach to plants to obtain their air supply. The © 2014 All Star Training, Inc. 2 larvae feed on microorganisms and organic matter in the water. During the fourth molt, the larva changes into a pupa. Pupa: The pupal stage is a resting, non-feeding stage of development, but pupae are mobile, responding to light changes and moving (tumble) with a flip of their tails towards the bottom or protective areas. This is the time the mosquito changes into an adult. This process is similar to the metamorphosis seen in butterflies when the butterfly develops - while in the cocoon stage - from a caterpillar into an adult butterfly. The Culex species takes about two days to do this during summer in the southern United States. When development is complete, the pupal skin splits and the adult mosquito (imago) emerges. Adult: The newly emerged adult rests on the surface of the water for a short time to allow itself to dry and all its body parts to harden. The wings have to spread out and dry properly before it can fly. Blood feeding and mating does not occur for a couple of days after the adults emerge. How long each stage lasts depends on both temperature and species characteristics. For instance, Culex tarsalis, a common California mosquito, might go through its life cycle in 14 days at 70° F and take only 10 days at 80° F. On the other hand, some species have naturally adapted to go through their entire life cycle in as little as four days or as long as one month. © 2014 All Star Training, Inc. 3 MOSQUITO EGG RAFT Many mosquitoes, such as Culex quinquefasciatus, lay their eggs on the surface of fresh or stagnant water. The water may be in tin cans, barrels, horse troughs, ornamental ponds, swimming pools, puddles, creeks, ditches, catch basins, or marshy areas. Mosquitoes prefer water sheltered from the wind by grass and weeds. Culex mosquitoes usually lay their eggs at night over a period of time sticking them together to form a raft of from 100 to 300 eggs. A raft of eggs looks like a speck of soot floating on the water and is about 1/4 inch long and 1/8 inch wide. A female mosquito may lay a raft of eggs every third night during its life span. Anopheles and many other mosquitoes lay their eggs singly on the water surface. Aedes and Ochlerotatus mosquitoes lay their eggs singly, usually on damp soil. Aedes and Ochlerotatus eggs are more resistant to drying out (some require complete drying out before the eggs will hatch) and hatch only when flooded with water (salt water high tides, irrigated pastures, treeholes flooded by rains, flooded stream bottoms). Anopheles, Culex, and Mansonia eggs are susceptible to long periods of drying out. Tiny mosquito larvae (1st instar) emerge from the eggs within 24 - 48 hours almost in unison. MOSQUITO LARVA Mosquito larvae, commonly called “wigglers,” live in water from 4 to 14 days depending on water temperature. Larvae must come to the surface at frequent intervals to obtain oxygen through a breathing tube called a siphon. They are constantly feeding since maturation requires a huge amount of energy and food. They hang with their heads down and the brushes by their mouths filtering anything small enough to be eaten toward their mouths to nourish the growing larvae. They feed on algae, © 2014 All Star Training, Inc. 4 plankton, fungi, bacteria, and other microorganisms. They breath at the water surface with the breathing tube up breaking the water surface tension. One mosquito species larva feeds on larvae of other mosquitoes: Toxorhynchites, the largest mosquito known, are predators of other mosquito larvae sharing their habitat. Their larvae are much larger than other mosquito larvae. During growth, the larva molts (sheds its skin) four times. The stages between molts are called instars. At the fourth instar, the usual larva reaches a length of almost 1/2 inch and toward the end of this instar ceases feeding. When the fourth instar larva molts, it becomes a pupa. MOSQUITO PUPA Mosquito pupae, commonly called “tumblers,” live in water from 1 to 4 days, depending upon species and temperature. The pupa is lighter than water and therefore floats at the surface. It takes oxygen through two breathing tubes called “trumpets.” The pupa does not eat, but it is not an inactive stage. When disturbed, it dives in a jerking, tumbling motion toward protection and then floats back to the surface. The metamorphosis of the mosquito into an adult is completed within the pupal case. The adult mosquito splits the pupal case and emerges to the surface of the water where it rests until its body dries and hardens. MOSQUITO ADULT Only female mosquitoes require a blood meal and bite animals – warm or cold-blooded – and birds. Stimuli that influence biting (blood feeding) include a combination of carbon dioxide, temperature, moisture, smell, color, and movement. Male mosquitoes do not bite, but feed on the nectar of flowers or other suitable sugar source. Acquiring a blood meal (protein) is essential for egg production, but mostly both male and female mosquitoes are nectar feeders. Female Toxorhynchites actually can’t obtain a bloodmeal and are restricted to a nectar diet. Of those © 2014 All Star Training, Inc. 5 female mosquitoes capable of blood feeding, human blood meals are seldom first or second choices. Horses, cattle, smaller mammals, and/or birds are preferred. Aedes and Ochlerotatus mosquitoes are painful and persistent biters. They search for a blood meal early in the morning, at dusk (crepuscular feeders) and into the evening.