Development of a controlled release formulation of an indigenous insect growth regulator, DPE-28, a substituted diphenylether, for controlling the breeding of Culex quinquefasciatus.

Background & objectives: DPE-28, a substituted diphenyl ether (2,6-ditertiarybutyl phenyl-2’,4’-dinitro phenyl ether) was reported to exhibit promising insect growth regulating activity against Culex quinquefasciatus, the vector of lymphatic filariasis. A controlled release formulation (CRF) of DPE-28 has been developed to control Cx. quinquefasciatus in its breeding habitats. Toxicity of DPE-28, safety to non-target mosquito predators and the release profile of the CRF of DPE-28 are studied and discussed. Methods: The acute oral and dermal toxicity was tested in male and female Wistar rats as per the Organization for Economic Cooperation and Development (OECD) guidelines 425 and 402 respectively. The toxicity of DPE-28 to non-target predators was tested as per the reported procedure from this laboratory. The CRF of DPE-28 was prepared by following the reported procedure developed at this laboratory earlier. The concentration of DPE-28 released from the CRF was monitored by HPLC by constructing a calibration graph by plotting the peak area in the Y-axis and the concentration of DPE-28 in the X-axis. Results: DPE-28 has been tested for acute oral toxicity and found to be moderately toxic with LD50 value of 1098 mg/kg body weight (b.w). The results of the acute dermal toxicity and skin irritation studies reveal that DPE-28 is safe and non-irritant. DPE-28 when tested at 0.4 mg/litre against non-target mosquito predators did not produce any mortality. The release profile of the active ingredient DPE-28 from the CRF by HPLC technique showed that the average daily release (ADR) of DPE-28 ranged from 0.07 to 5.0 mg/litre during first four weeks. Thereafter the matrix started eroding and the ADR ranged from 5 to 11 mg/litre during the remaining 5 wk. The cumulative release of active ingredient showed that > 90 per cent of the active ingredient was released from the matrix. Interpretation & conclusions: The controlled release matrix of DPE-28 was thus found to inhibit the adult emergence (>80%) of Cx. quinquefasciatus for a period of nine weeks. The CRF of DPE-28 may play a useful role in field and may be recommended for mosquito control programme after evaluating the same under field conditions.

Lethal and Sublethal Effects of Methoxyfenozide on the Development, Survival and Reproduction of the Fall Armyworm, Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae)

The lethal and sublethal effects of the ecdysone agonist methoxyfenozide on the fall armyworm, Spodoptera frugiperda (J. E. Smith), were investigated by feeding a methoxyfenozide-treated diet to fifth instars until pupation in doses corresponding to the LC10 and LC25 for the compound. Larval mortality reached 8 percent and 26 percent in the low and high concentration groups, respectively, on the seventh day of the experiment. A progressive larval mortality of 12 percent for the LC10 and 60 percent for the LC25 was observed before pupation. Treated larvae exhibited lower pupal weights, higher pupal mortality, presence of deformed pupae, and more deformed adults than untreated larvae. The incorporation of methoxyfenozide into the diet had a significant effect on the timing of larval development. The development period for males and females was about seven days longer than the controls for both concentrations tested. In contrast, the compound affected neither pupae nor adult longevity. Finally, S. frugiperda adults that resulted from fifth instars treated with methoxyfenozide were not affected in their mean cumulative number of eggs laid per female (fecundity), nor percentages of eggs hatched (fertility), or the sex ratio. Our results suggest that the combination of lethal and sublethal effects of methoxyfenozide may have important implications for the population dynamics of the fall armyworm.

Efficacy of IGR compound Starycide 480 SC (Triflumuron) against mosquito larvae in clear and polluted water.

BACKGROUND AND OBJECTIVES: An environmental friendly formulation Starycide 480 SC (Triflumuron-OMS-2015 ), a new insect growth regulator with chitin synthesis inhibitor type mode of action was evaluated against mosquito larvae in laboratory and small-scale field trials carried out in and around Delhi. METHODS: The formulation was tested in laboratory for its bio-efficacy against late III instar mosquito larvae of different species using WHO bioassay procedure. In the field formulation was sprayed at doses of 0.3, 0.5 and 1 ppm (g/m3) in the natural breeding habitats of Anopheles and Culex mosquitoes. The impact was assessed by monitoring densities of larvae by dipper and observing the reduction in larval density and inhibition of adult emergence. RESULTS: In the laboratory, formulation was more effective against larvae of Anopheles stephensi and Aedes aegypti than Culex quinquefasciatus, but it produced 100% inhibition of adult emergence for all mosquito species at a concentration of 0.02 ppm. In the field trials, formulation did not produce 100% reduction in the density of late stage larvae even at 1 ppm (g/m3), the highest dose tested, but it resulted in 100% inhibition of pupal formation of both Anopheles and Culex spp in different types of habitats for 3-7 weeks even at a lower dose of 0.5 ppm. INTERPRETATION AND CONCLUSION: Application of triflumuron in the natural breeding habitats in both clean and polluted water @ 0.5 ppm (g/m3) resulted in complete inhibition of adult emergence of both Anopheles and Culex spp for 3-7 weeks. This formulation may be tested in large-scale field trials for further use in the vector control programme.

Efecto de los inhibidores del desarrollo en insectos contra Culex quinquefasciatus (Diptera: Culicidae) / Effect to insect development inhibitors against Culex quinquefasciatus (Diptera: Culicidae)

Se realizó un estudio en condiciones de laboratorio donde se evaluó la efectividad de 2 reguladores del crecimiento de insectos, diflubenzuron y metopreno, contra larvas de Culex quinquefasciatus, un mosquito indicador de la presencia de aguas contaminadas, persistente picador nocturno en zonas urbanas y transmisor de filariasis humana. El diseño experimental contempló la realización de 3 bioensayos para cada cepa y producto, y la utilización de grupos controles y factores abióticos controlados. Los principales resultados mostraron que ambos productos fueron efectivos contra esta especie, destacándose el diflubenzuron por una mayor actividad biológica (p < 0,01). estos resultados posibilitan mejorar el saneamiento ambiental contra este mosquito mediante la inclusión de estos compuestos de programas de lucha integrada