Mosquito susceptible

Table III. It is obvious from the data in Table III that the housefly and the mosquito, in both the adult and larval stage, are susceptible to insecticides of the DDT type. However, the extravagant claims that DFDT is far superior to DDT as a contact insecticide against flies are not borne out by the results of controlled laboratory tests. The Peet-Grady testing technique used by Prill (92) would indicate that in the presence of added pyrethrins DDT is definitely superior to DFDT when applied as a spray. On the other hand, DFDT gave higher percentage kills than DDT when flies were placed under a Petri dish and held in contact with deposits of the compounds on glass surfaces. A comparison of the activity of these compounds against adult mosquitoes has not been reported.

Hughes, J.M., D.A. Harrison, and J.M. Arthur. 1991. Genetic variation at the Pgj locus in the mosquito fish Gambusia affinis (Poecilidae) and a possible effect on susceptibility to an insecticide. Biol. Jour. Linnean Soc. 44 153-167. 

Table 7 shows that the dl,d-T80-allethrin 0.5% mosquito coil was effective on the susceptible SS strain of A. aegypti in the 25-m3 semi-field test, but showed low efficacy against the BS strain and colonies collected in districts A and B, their KT5o values being uncalculated. 

As shown in Table 8, mosquito colonies with KT50 values below 60 min in the 25-m3 semi-field test were classified as susceptible (Group I), those with KT50 of 60-120 min as less susceptible (Group II), and those with KT50 of over 120 min as low susceptible (Group III). 

It was found that two colonies were susceptible to allethrin, similar to the SS strain, six colonies had low susceptibility similar to the allethrin-resistant BS strain, and the remaining three colonies had susceptibility to allethrin between the SS and BS strains. The allethrin mosquito coils, even at higher concentrations, were ineffective on the six decreased susceptibility colonies, similar to the BS strain. 

Table 8 Allethrin susceptibilities of Aedes aegypti colonies in 25 -m3 room semi-field tests by using dl,d-T80-allethrin 0.5% mosquito coil...

A. aegypti colonies were found to have developed cross-resistance to even polyfluoro benzylalcohol ester pyrethroids with potent insecticidal activity. Mosquito coils of these compounds were effective against allethrin-susceptible A. aegypti colonies at ultra-low concentration, but needed several times higher concentrations for A. aegypti colonies in Group III in Table 8 (unpublished). 

Katsuda Y, Leemingsawat S, Thongmngkiat S, Prummmonkol S, Samung Y, Kanzaki T, Watanabe T, Kahara T (2008) Control of mosquito vectors of tropical infectious diseases (2) pyrethroid susceptibility of Aedes aegypti (L.) collected from different sites in Thailand. Southeast Asian J Trop Med Public Health 39(2) 229-234... 

Carboxylesterases are well-represented in insects and are sometimes important in the development of resistance to insecticides. Thus, a well-characterized carboxylesterase E4 is responsible for resistance to organophosphorus insecticides in the aphid (Myzuspersicae) [107]. In the California Culex mosquito, the esterase B1 is 500-fold more abundant in organophosphate-resistant than in susceptible insects. The increase of esterase levels is the result of gene amplification, i.e., the resistant animals have an increased number of copies of the structural esterase gene [108],... 

The development of strains resistant to insecticides is an extremely widespread phenomenon that is known to have occurred in more than 200 species of insects and mites, and resistance of up to several 100-fold has been noted. The different biochemical and genetic factors involved have been studied extensively and well characterized. Relatively few vertebrate species are known to have developed pesticide resistance and the level of resistance in vertebrates is low compared to that often found in insects. Susceptible and resistant strains of pine voles exhibit a 7.4-fold difference in endrin toxicity. Similarly pine mice of a strain resistant to endrin were reported to be 12-fold more tolerant than a susceptible strain. Other examples include the occurrence of organochlorine insecticide-resistant and susceptible strains of mosquito fish, and resistance to Belladonna in certain rabbit strains. 

Several species and populations from other Anopheles complexes have been discriminated based on CHC patterns. Examples include all five species of the An. quad-rimaculus complex (Carlson et al., 1997), some species of the An. maculipennis complex (Phillips et al., 1990a), malaria-vector and non-vector forms of the An. maculates complex (Kittayapong et al., 1990, 1993), and An. Stephensi strains susceptible or resistant to DDT and malathion (Anyanwu et al., 1993, 1997). CHCs have been used in combination with isoenzyme analysis to successfully differentiate populations of An. darlingi (Rosa-Freitas et al., 1992). All these findings demonstrate that hydrocarbon analysis is a powerful tool for distinguishing mosquito species and populations. This is particularly important for disease vectors, since it can facilitate interpretation of epidemiological data and assist implementation of control measures. 

Figure 5.10 Changes in the susceptibility of mosquito larvae with age and instar, as measured by the time for 50% inactivation to light stimulus, caused by 0.1 ppm heptachlor. (From Burchfield, H.P. et al., Contr. Boyce Thompson Inst., 17, 317,1953. With permission.)...

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... 

---