Correlation between the reproductive potential and the pyrethroid resistance in an Indian strain of filarial vector, Culex quinquefasciatus Say (Diptera: Culicidae).

The laboratory studies were conducted to uncover the correlation between the levels of pyrethroid resistance and the reproductive potential of parent (SS) and resistant strains of Culex quinquefasciatus (RR) originating from Delhi, India and selected with deltamethrin (RDL) or the combination of deltamethrin and PBO (1:5) (RDP) at the larval stage and selected with deltamethrin at the adult stage (RDA). The reproductive potential was evaluated in terms of fecundity, fertility, egg hatchability and longevity of gonotrophic cycles. The RR strains exhibited 68-74% reduced duration of the gonotrophic cycles when compared with that of SS strain. The considerable decrease in the egg production, ranging from 45.4% to 61.6%, observed in the selected strains as compared to the SS strain, indicates the possible positive correlation between the levels of deltamethrin resistance and the reproduction disadvantage. This correlation was further confirmed by 24.6% to 53.6% decrease in the hatchability of eggs of the selected strains with respect to that of the parent strain. A worth-mentioning observation of the reduced reproductive fitness in RDP strains suggests the effectiveness of synergized deltamethrin selections in reducing the frequency of resistant individuals. The reproductive disadvantage in adult-selected strains possessing negligible resistance to deltamethrin implicates the efficacy of deltamethrin as an adulticide rather than as a larvicide against Cx. quinquefasciatus. The results suggest that the reduced reproductive fitness of resistant genotypes in the population can eliminate heterozygotes and resistant homozygotes by implementing different resistance-management strategies against Cx. quinquefasciatus.

Diminished reproductive fitness associated with the deltamethrin resistance in an Indian strain of dengue vector mosquito, Aedes aegypti L.

The susceptible (SS) and resistant (DLR) strains of Aedes aegypti selected with deltamethrin and combination of deltamethrin and PBO (1:5) at the larval/adult stage were studied in the laboratory for their reproductive fitness in terms of fecundity, hatchability and longevity of gonotrophic cycles. The DLR strains exhibited 73-88% reduction in the duration of gonotrophic cycles as compared to their SS counterparts. There was a considerable decrease in egg production and hatchability rates in the selected strains of Ae. aegypti, as compared to that of the SS strain. Data indicate deltamethrin being an effective insecticide against Ae. aegypti and a possible correlation between the deltamethrin resistance and disadvantages during reproduction. The most drastic and significant effect was observed in DLR1b strains exhibiting 36.7% decrease in fecundity and 32.4% reduction in hatchability. Another important observation was diminished reproductive fitness in DLR2 strains. This suggests the usefulness of synergized deltamethrin selections in reducing the frequency of resistant individuals. A significant finding was to observe the reproductive disadvantage in adult-selected strains having negligible resistance to deltamethrin implicating the efficacy of deltamethrin as an adulticide rather than as a larvicide. Various probable reasons for the reduction in the reproductive potential and the possible resistance-management strategies of Ae. aegypti are discussed.

Variations in the insecticide-resistance spectrum of Anopheles stephensi after selection with deltamethrin or a deltamethrin-piperonyl-butoxide combination.

When the larvae of Anopheles stephensi, a malaria vector, were selected with deltamethrin for 40 successive generations, there was a 60-fold increase in larval resistance to deltamethrin but no increase in the resistance of the adult mosquitoes. This result, and the observation that deltamethrin selection of adults for 40 generations resulted in only a six-fold increase in adult resistance to deltamethrin, indicated some stage specificity. When F(24) deltamethrin-resistant larvae were selected with 1:5 deltamethrin-piperonyl butoxide (deltamethrin-PBO), instead of deltamethrin alone, for 16 generations, the level of resistance to deltamethrin in the F(40) larvae was reduced by 6%-21%. Similarly, selection with deltamethrin-PBO of adults of the parental strain for 20 generations reduced the speed of the development of resistance to deltamethrin, compared with that seen using selection with deltamethrin alone. Deltamethrin selection appears to select initially a monooxygenase-based mechanism. When the monooxygenase-based mechanism is blocked, by treatment with PBO, selection of a kdr-type mechanism is accelerated, as is evident from increased cross-resistance to 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT) in the adults selected with deltamethrin-PBO. The implications of these results are discussed in terms of the management of the larval and adult stages of An. stephensi .

Organochlorine and organophosphorus pesticide residues in breast milk from Bhopal, Madhya Pradesh, India.

HCH isomers, endosulfan, malathion, chlorpyrifos, and methyl-parathion were monitored in human milk samples from Bhopal, Madhya Pradesh. The endosulfan concentrations were highest and exceeded the sigma-HCH, chlorpyrifos, and malathion concentrations by 3.5-, 1.5-, and 8.4-fold, respectively. Through breast milk, infants consumed 8.6 times more endosulfan and 4.1 times more malathion than the average daily intake levels recommended by the World Health Organization. A correlation analysis (r values) between mothers' age and the content of the chemicals accumulated in breast milk indicated a substantial degree of correlation for malathion (r = 0.5). The other chemicals showed low to negligible correlation with donor age.

Effect of the synergist, piperonyl butoxide, on the development of deltamethrin resistance in yellow fever mosquito, Aedes aegypti L. (Diptera: Culicidae).

The larvae and adults of Aedes aegypti were tested for the potential to develop resistance to the synthetic pyrethroid, deltamethrin, alone or a combination of deltamethrin with the synergist, piperonyl butoxide (PBO). Although continuous larval selection for 40 generations resulted in 703-fold resistance, the resistance ratio in the adults was only 1.3. Similarly, adult selections with deltamethrin showed a resistance ratio of less than four after 40 generations, indicating differential response to deltamethrin selection in the two developmental stages of the insect. When the susceptible larvae were subjected to selection pressure of deltamethrin and PBO in the ratio of 1:5 for 20 generations, the speed of selection for deltamethrin resistance slowed down by 60%. The F24 larvae obtained from the strain selected with deltamethrin alone were further subjected to selection pressure with synergized deltamethrin, which resulted in 89% reversal in deltamethrin resistance in just one generation. However, long-term selection with the insecticide-synergist combination returned resistance close to original levels in 15 generations. The data indicate the involvement of cytochrome P450-dependent detoxification as the primary mechanism of development of resistance to deltamethrin in the larvae. Implications of the results on the management of larval and adult stages of Ae. aegypti are discussed.

Trends in ambient levels of DDT and HCH residues in humans and the environment of Delhi, India.

Monitoring of DDT and HCH residues in abiotic and biotic components of the environment of Delhi during 1988 to 1989 revealed low to moderate levels of these insecticides in soil, earthworms, birds, buffalo milk, water, freshwater clams, fish, human fat, human blood and breast milk samples. Total HCH residues were less than those of DDT in all the samples. This survey indicates (in spite of the continued use of DDT and HCH in the country) a general decline in the levels of DDT residues in most of the samples studied when compared to previous surveys. Although the levels of DDT and HCH residues in fish and river water were below the permissible limits, those in human samples remained fairly high.

Differential selection of malathion resistance in Anopheles culicifacies A and B (Diptera: Culicidae) in Haryana State, India.

In November 1989, for the first time after the introduction of malathion spray in 1982, increased densities of Anopheles culicifacies Giles s.l. were observed in Chhatera and Barota, two villages in Halalpur block in Sonepat District, Haryana State, India. In bioassay tests against the diagnostic dose of malathion (5% for 1 h), 41-47% of mosquitoes survived. An culicifacies populations in this area comprise two sibling species, A and B. Differential malathion resistance was observed; in species A it was 2-9% and in species B 62-66%. Likewise, species A was found to be more susceptible to DDT than was species B. The possible use of DDT spray to delay the onset of malathion resistance is discussed.

Aldrin and dieldrin residues in human fat, milk and blood serum collected from Delhi.

1. Aldrin and dieldrin residues were monitored in the fat, breast milk and blood serum from female residents of Delhi. 2. The average aldrin and dieldrin contents were 0.048 and 0.099 ppb in adipose tissue, 0.003 and 0.060 ppb in breast milk and 0.004 and 0.002 ppb in blood serum, respectively. 3. The older donors contained higher levels of aldrin and dieldrin in their adipose tissue. 4. Primagravidae contained more of these chemicals in their breast milk. 5. A positive correlation was observed between the aldrin concentration in adipose tissue and breast milk, and that in adipose tissue and blood serum. Similarly, a significant correlation was found between dieldrin in adipose tissue and blood serum. 6. The levels of aldrin and dieldrin were low in samples from residents of Delhi when compared to those in developed countries.

Levels of aldrin and dieldrin in environmental samples from Delhi, India.

Aldrin and dieldrin residues in soil, earthworms, water, fish and clams from different sites in Delhi were monitored. Concentrations of aldrin and dieldrin were found to be higher in earthworms than in soil. Concentrations of dieldrin were higher in fish than the ambient water, but the concentration of aldrin in the ambient water was the same as that in fish and clams.

Resistance in Anopheles culicifacies sibling species B and C to malathion in Andhra Pradesh and Gujarat States, India.

Studies conducted in Warangal, Khammam and Mahabubnagar districts in Andhra Pradesh and Surat district in Gujarat have revealed that Anopheles culicifacies sensu lato (s.l.) populations were resistant to malathion. In the absence of indoor spraying of malathion in public health programs in the 3 districts of Andhra Pradesh, resistance is attributed to the extensive use of pesticides in agriculture. Species B and C were sympatric in all areas surveyed, and both the species were resistant to malathion. In most of the surveys carried out in Mahabubnagar, Khammam and Warangal, levels of resistance were higher in species C than in B. In Mahabubnagar district an increase in resistance from 5.5 to 64% was observed from 1985 to 1987 in An. culicifacies s.l. The proportion of species C was low in the initial 2 surveys, and in the later surveys the proportion was almost equal to that of species B; the resistance level was also significantly higher than in species B. In Surat district, where resistance ranged from 74 to 93%, the level of resistance in the 2 species was almost the same.

Involvement of mono-oxygenases as a major mechanism of deltamethrin-resistance in larvae of three species of mosquitoes.

Role of mono-oxygenases as a mechanism of resistance to the synthetic pyrethroid, deltamethrin in the larvae of Culex quinquefasciatus Say, Aedes aegypti L. and Anopheles stephensi Liston developed by laboratory selections with deltamethrin, DDT or deltamethrin and the synergist, piperonyl butoxide (PBO) in the ratio of 1:5, was investigated. There was a significant correlation with mono-oxygenase activity and larval LC50 to deltamethrin in various strains of all the three species. In addition, the activity of glucose-6-phosphate dehydrogenase (G6PD), the main NADPH generating enzyme for mono-oxygenases, also showed enhanced activity in deltamethrin and DDT-selected strains. The present data, therefore, clearly suggest that deltamethrin resistance in the larvae of Cx. quinquefasciatus, Ae. aegypti and An. stephensi is mainly due to the detoxification of deltamethrin by microsomal mono-oxygenases. High activity of G6PD observed in DDT-selected strains seems to be related to its role as a rate-limiting enzyme in GSH-dependent dehydrochlorination of DDT.

Impact of repeated application on the binding and persistence of [14C]-DDT and [14C]-HCH in a tropical soil.

An Indian sandy loam soil was initially treated with 1 kg a.i. ha(-1) of either [(14)C]-p,p'-DDT or [(14)C]-gamma-HCH during winter. DDT concentration after 30 days declined to 75.3%, which included 2.1% soil-bound residues. After 150 days, DDT levels further decreased to 42.4% with a concomitant increase in bound residues amounting to 5.9%. Identical treatment with HCH caused the residue levels to be reduced to 67.4 and 23.6%, after 30 and 150 days, respectively. During this period, the soil-bound residues of HCH increased from 5.2 to 12.8%. Repeat application to pre-treated soils in summer and subsequent field exposure for 30 days reduced the concentration of DDT to 52.1% and that of HCH to 42.4% of the total concentration following the second treatment. In parallel control experiments, which received only a single treatment, DDT levels declined to 61.3%, while HCH slumped to 45.3%, indicating a slower dissipation rate than in the corresponding repeated treatments. In repeat experiments, the soil-bound residues of DDT and HCH showed only a 1.07 to 1.08-fold increase in 30 days, as compared to three to ten-times increase in the control experiments. The results amply demonstrate that pre-treatment of tropical soils with DDT or HCH enhances their rate of dissipation and significantly reduce the formation of their soil-bound residues.

Dry aerial fallout of organochlorine insecticide residues in Delhi, India.

Monitoring of airborne dust in Delhi during May to July 1985 revealed residues of DDT varying from 1.3 to 7.14 ng mg(-1) (4.06-22.31 ng m(-2) day(-1)) with an average of 3.32 ng mg(-1) (10.38 ng m(-2) day(-1)), and HCH which ranged from 0.46 to 2.35 ng mg(-1) (1.44-7.34 ng m(-2) day(-1)) with a mean of 1.16 ng mg(-1) (3.63 ng m(-2) day(-1)). The concentration of total DDT was almost 3 times greater than that of HCH.

The effect of temperature and solar radiations on volatilisation, mineralisation and degradation of [14C]-DDT in soil.

The influence of temperature and solar radiations on the rapid dissipation of DDT from tropical soils was studied by quantifying volatilisation, mineralisation, binding and degradation of ((14)C)-p,p'-DDT in a sandy loam soil. The bulk of the DDT loss occurred by volatilisation, which increased fivefold when the temperature changed from 15 to 45 degrees C. Degradation of DDT to DDE was also faster at higher temperatures. Mineralisation of DDT, though minimal, increased with temperature and time. Higher temperatures also enhanced binding of DDT to soil. Flooding the treated soil further increased volatilisation and degradation, although mineralisation was greatly reduced. Exposure of flooded and unflooded soils treated with DDT to sunlight in quartz, glass and dark tubes for 42 days during summer resulted in significant volatile losses. Volatilisation in the quartz tubes was nearly twice as great as that in the dark tubes The volatilised organics from the quartz tubes contained larger amounts of p,p'-DDE than the glass and dark tubes. Higher rates of volatilisation and degradation were found in flooded soils. Also significant quantities of p,p'-DDD were detected in addition to DDE. The data clearly show that volatilisation is the major mechanism for the rapid dissipation of DDT from Indian soils.

Pesticide pollution of soil, water and air in Delhi area, India.

In India organochlorine insecticides such as DDT and HCH constitute more than 70% of the pesticides used at present. Its continued use has given interest to monitor for the last few years the extent of organochlorine insecticide residues in soil, water, air and rain water in Delhi area. Out of the 50 samples each of soil and earthworms collected from different parts 48 samples showed that soil and earthworms contained 0-2.61 and 0-37.74 mg Kg-1 of total DDT residues respectively. The area near the vicinity of the DDT factory showed high levels of DDT residues. A two-year survey of the Yamuna river in Delhi showed that water contained an average of 0.24 ug L-1 and the bottom sediment had 0.24 mg Kg-1 of total DDT residues. The fishes collected from the Yamuna river showed very high bioaccumulation of DDT residues. The air and rainwater samples monitored from 3 different areas for two years indicated that DDT was more near the DDT factory area while HCH was more near a commercial complex. These results indicate that the overall organochlorine-residue levels in Delhi is not alarming. It probably indicates that DDT and HCH are more rapidly dissipated and degraded in a tropical country like India.