Mosquito larvae, toxicity

Malaria affects an estimated 270 million people and causes 2—3 million deaths annually, approximately one million of which occur in children under the age of five. While primarily an affliction of the tropics and subtropics, it has occurred as far north as the Arctic Circle. The disease essentially has been eradicated in most temperate-zone countries, but some 1100 cases of malaria in U.S. citizens returning from abroad were reported to the Centers for Disease Control during 1990. Malaria is seen today in Southeast Asia, Africa, and Central and South America. It is on the increase in Afghanistan, Brazil, China, India, Mexico, the Philippines, Sri Lanka, Thailand, and Vietnam. Escalation of the disease is because of the discontinued use of the insecticide DDT which effectively kills mosquito larvae, but has been found to be toxic to Hvestock and wildlife. Also, chloroquine (6), a reUable dmg for the prophylaxis and treatment of falcipamm malaria, is ineffective in many parts of the world because of the spread of dmg-resistant strains. 

The edible parts of parsnips (Pastimea sativa L.), which have been consumed for centuries by humans without causing any obvious harm, were found to contain a chemical of insecticidal and strong synergistic nature (1). The insecticidal constituent, present at about 200 p.p.m., was isolated and identified as 5-allyl-l-methoxy-2, 3-methylenedioxybenzene or myristicin. Its toxicity to various insects [vinegar flies, houseflies, Mediterranean fruit flies, mosquito larvae, Mexican bean beetles, and pea aphids] was established and compared with pyrethrum and aldrin (Tables I and II). The knockdown effect, although definite, was not as great as that of pyrethrum. In tests... 

The purpose of this work was to determine the toxicity to mosquito larvae of insecticide spray residues. That certain insecticides are translocated in plants (4, 5) adds impetus to this study. Fresh orchard fruit sprayed or dusted with preparations containing parathion (0,0-diethyl O-p-nitrophenyl thiophosphate), tetraethyl pyrophosphate (TEPP, HEPP), DDD [2,2-bis(p-chlorophenyl)-l,l-dichloroethane], DDT [2,2-bis(p-chlorophenyl)-l,l,l-trichloroethane], chlorinated camphene, and basic lead arsenate were shipped from California to Yonkers, N. Y., by air express for bioassay. 

As mosquito larvae are relatively easy to kill with insecticides, any toxic spray residue is likely to be detected. Two species of mosquito larvae were used, the yellow fever mosquito (Aedes aegypti L.) and the southern house mosquito (Culex quinquefasdatus Say). Tests with the southern house mosquito were made essentially according to the method of Campbell, Sullivan, and Smith (I), except for the kind of food supplied and size of containers used. 

In addition to the tests made on peaches and apricots, samples of prunes from trees that had been sprayed with parathion, DDT, DDD, basic lead arsenate, and toxaphene at the rate of from 1 to 2 pounds of these insecticides per 100 gallons of water were tested on larvae of Aedes aegypti. The trees had been sprayed on April 20 and June 16, 1948. The fruit was harvested on or about September 10. Prunes from trees that had been treated with 1 quart of tetraethyl pyrophosphate and 12 pounds of sulfur dust per acre on June 15, and harvested about July 6, were tested on larvae of the above named species. None of the prune samples tested in this study exhibited any significant toxicity to mosquito larvae as compared with the unsprayed check. 

An aqueous solution containing 1 part in 200,000,000 of parathion gave 50% kill to southern house mosquito larvae (Culex quinquefasdaius Say). Parathion solutions did not lose any toxicity on standing for a month at room temperature (Figure 1). At the end of 2 months, however, the solutions lost their toxicity to mosquito larvae. 

The data used are given in Table I. The elimination rate constants included were determined at 20° C. (5). The toxicity to mosquito larvae, given as median lethal dosages (concentration in parts per million of water required to cause 50% mortality in 48 hours), was estimated from the data of Deonier et al. (9) and is probably reproducible to within 30%. 

Table I. Toxicity of Thiocarbamate Derivatives of Carbofuran to House Flies, Mosquito Larvae and Mice...

Polyacetylenes are toxic to a broad range of organisms (39) but are especially toxic to insects. At 0.5 ppm, 9 of 14 compounds tested were toxic to first instar mosquito larvae (Aedes aegypti) in 30 min treatments with sources of near UV (15 W/m ) (40). The compounds were more active in sunlight. For example CX-T killed second instar larvae Instantaneously at 4 ppm. Compounds VTI, Ct-T and PHT were especially active and were selected for further testing in dose response experiments (41). For similar near UV treatments, the LC50 for a-T was 19 ppb,... 

In an effort to reduce costs, civic organizations have from time to time gathered waste crankcase oil for use in controlling mosquito larvae. Usually such mosquito control programs have failed, because waste crankcase oils are low in toxicity to mosquito larvae, they contain dirt and other materials that clog spray nozzles, and the collection and supply are imdependable. 

Lindquist (34) and his associates have applied Diesel oil containing DDT or other chlorinated hydrocarbons as a prehatching treatment for controlling snow-water mosquitoes. Late in the fail Lindquist applied several oil formulations containing chlorinated hydrocarbon insecticides to swales and depressions that had produced mosquitoes in season. These oil formulations remained on the ground during the winter and when flooded with snow water proved toxic to the newly hatched mosquito larvae. A dosage of 2 pounds of DDT per acre (10 quarts of a 5% DDT-oil solution) prevented mosquito development in some instances for 2 years. 

Crystal solubilization is facilitated by an alkaline pH of susceptible insects. The typical midgut pH is between pH 9-11 in lepidopteran larvae [37-39]. In mosquito larvae, the pH inside the posterior midgut/gastric caeca is between 7-8, while the pH inside the anterior midgut is close to 11 [40]. Thus alkaline buffers are usually used for in vitro solubilization of lepidopteran and dipteran active B. thuringiensis crystals. Differential crystal solubility can be useful in partial separation of toxins. For example, CrylA toxins are fully soluble at pH 9.5, while the Cry2 proteins require a pH of 12 for complete solubilization [41]. Moreover, pH has different effects on Cry toxin pore-formation activities [42], and differences in the level of solubilization can contribute to toxicity differences... 

B9-1327, isolated by Anagnostopoulos et al. [71] and later assigned as Toxicant C, was four times more toxic in the Musca domestica test than technical toxaphene [71]. Chandurkar et al. found B9-1679 (P-50) to be four times more toxic to fish and as harmful to mosquito larvae as the technical mixture [80]. Furthermore, B8-806/B8-809 (P-42) was more potent than B9-1679 (P-50) [80]. Olson et al. found a difference in the toxicity of B7-515 (P-32) and B8-806/9 (P-42) for lake trout compared to technical toxaphene by studying behavioral parameters such as inferior swimming ability and delayed righting reflex [245]. 

Toxicity to house fly is obviously quite good. Moderate efficacy is demonstrated against the corn rootworm beetles and mosquito larvae. For an insecticide of the prolan/DDT class, the potency demonstrated against the wild strain German cockroach is quite remarkable. Preliminary tests on the larval stage corn rootworm revealed soil activity of a monochloro compound, unlike most previously reported chemicals in this class. Overall, the spectrum of activity is quite broad, although other categories of insect pests must still be tested (e.g., lepidopteran larvae). 

In addition to many early examples, biological response has been found to be quantitatively linearly dependent on log P or it in the inhibition of the Hill reaction >activity of penicillins, toxicity of benzoic acids to mosquito larvae , phenol coefficients , cholinesterase inhibitors , and catechol-amine activity . 

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