Field-based evaluation of novaluron EC10 insect growth regulator, a chitin synthesis inhibitor against dengue vector breeding in leaf axils of pineapple plantations in Gampaha District, Sri Lanka

Efficacy of the insect growth regulator novaluron in the control of dengue vector mosquitoes Aedes aegypti and Ae. albopictus

Insect Growth Regulator (IGR) novaluron is an alternative to synthetic neuro-inhibitory insecticides. Present study was designed to assess appropriate dosages of novaluron for dengue vector control. Larvae of Aedes aegypti and Ae. albopictus were exposed to a concentration series of novaluron (Rimon EC10) for two fixed exposure periods of 7-days and 14-days to determined LC50 and LC99 values. Inhibition of adult emergence (IE50 and IE99) was determined by a 14-day exposure. Semi-field experiments were conducted by exposing cohorts of Ae. aegypti larvae to IE99, 2 × IE99 and 10 × IE99 novaluron concentrations in water storage buckets (10 L) and plastic barrels (200 L). For the 7-day exposure, LC50 values were 0.047-0.049 ppm and LC99 were 0.144-0.151 ppm. For 14-day exposure, these values were 0.002-0.005 ppm and 0.006-0.01 ppm respectively. For both species, IE99 was 0.001 ppb under semi-field conditions, and was effective for nearly 2 months. Novaluron concentration 0.01 ppb was effective up to 3 months, with an IE of 89-95%. Authorities should critically review a reduction of the presently recommended field dosage of 200 ppm novaluron by × 100 or more. This would provide the same efficacy but mitigate environmental pollution, development of vector resistance, and financial losses.

Evaluation of Insect Growth Regulators (IGRs) as biological pesticides for control of Aedes aegypti mosquitoes

BACKGROUND OBJECTIVES

Insect growth regulators (IGRs) are biological hormone analogue or mimics used as pesticides to inhibit the growth of larva during their molting and skin shedding. This study aimed to test the effect of IGRs on the eggs hatching and post-hatching inhibition of Aedes mosquitoes and understanding its effect in the mosquito breeding habitats for reduction in adult emergence.

METHODS

Experiments on the evaluation of three insect growth regulators (IGRs) for the control of different stages of Aedes aegypti was carried out during 2020-21. Each experiment consisted of four treatments viz., Pyriproxyfen, Novaluron, and Larvicol at 1.0 ppm and distilled water as a control. All experiments were carried out in completely randomized design (CRD) except eggs which were carried out in factorial design each with three replications.

RESULTS

All tested IGRs performed better in affecting eggs, larval and pupal stages of Ae. aegypti. Highest eggs hatching inhibition (80%) of fresh eggs occurred in Pyriproxyfen followed by Novaluron (66%) and lowest in Larvicol (62%). Eggs hatch inhibition of embryonated eggs was lower than fresh eggs. Pyriproxyfen caused 69%, Novaluron 59% and Larvicol 39% eggs hatch inhibition of embryonated eggs. Both Pyriproxyfen and Novaluron performed better in causing 98-100% larval mortality followed by Larvicol (39%). Larval development to pupal stage was completely prevented by both Pyriproxyfen and Novaluron. Although Larvicol resulted in lowest eggs hatch and larval inhibition but prevented pupae to emerge as adults. Results further showed 70-89% mortality of 3rd instar larvae of Ae. aegypti when exposed to Pyriproxyfen and Novaluron solutions after 30 days storage at lab. temperature (27±2°C), RH 70±5.

INTERPRETATION CONCLUSION

None of the IGRs was more effective at the pupal stage but showed carry-on activity of growth inhibition and mortality of the successive stages of development when used against eggs stages. Therefore, we recommend early application of IGRs at mosquito habitats during the beginning and onset of the season when very early stages of mosquitoes are available in the field.

The Laboratory and Semi-Field Larvicidal Effects of Essential Oil Extracted from Feronia limonia against Anopheles arabiensis Patton

This study intended to evaluate the larvicidal activity of Feronia limonia leaf essential oil against the wild population of Anopheles arabiensis Patton larvae in laboratory and semi-field environments. Larvae mortality was observed after 12, 24, 48, and 72 hours of exposure. In laboratory condition, the essential oil showed good larvicidal activity against An. arabiensis (LC₅₀ = 85.61 and LC₉₅ = 138.03 ppm (after 12 hours); LC₅₀ = 65.53 and LC₉₅ = 117.95 ppm (after 24 hours); LC₅₀ = 32.18 and LC₉₅ = 84.59 ppm (after 48 hours); LC₅₀ = 8.03 and LC₉₅ = 60.45 ppm (after 72 hours), while in semi-field experiments, larvicidal activity was (LC₅₀ = 91.89 and LC₉₅ = 134.93 ppm (after 12 hours); LC₅₀ = 83.34 and LC₉₅ = 109.81 ppm (after 24 hours); LC₅₀ = 66.78 and LC₉₅ = 109.81 (after 28 hours); LC₅₀ = 47.64 and 90.67 ppm (after 72 hours). These results give an insight on the future use of F. limonia essential oils for mosquitoes control.

Statewide Efficacy Assessment of Insect Growth Regulators Against Aedes albopictus (Diptera: Culicidae) in Sabah, Malaysia: An Alternative Control Strategy?

The efficacy of three groups of insect growth regulators, namely juvenile hormone mimics (methoprene and pyriproxyfen), chitin synthesis inhibitors (diflubenzuron and novaluron), and molting disruptor (cyromazine) was evaluated for the first time, against Aedes albopictus Skuse (Diptera: Culicidae) larvae from 14 districts in Sabah, Malaysia. The results showed that all field populations of Ae. albopictus were susceptible towards methoprene, pyriproxyfen, diflubenzuron, novaluron, and cyromazine, with resistance ratio values ranging from 0.50-0.90, 0.60-1.00, 0.67-1.17, 0.71-1.29, and 0.74-1.07, respectively. Overall, the efficacy assessment of insect growth regulators in this study showed promising outcomes and they could be further explored as an alternative to conventional insecticides.

Residual Efficacy of Novaluron Applied on Concrete, Metal, and Wood for the Control of Stored Product Coleopteran Pests

Simple Summary

Insect pests of stored commodities cause harm not only to bulk grains but also to many value-added food products in mills, processing plants, and other facilities where these products are stored. In this study, the residual efficacy of an Insect Growth Regulator (IGR), novaluron, was evaluated under laboratory conditions against larvae of three stored product insects, Oryzaephilus surinamensis (L.), Triboliumcastaneum (Herbst), and Trogoderma granarium Everts, on concrete, metal, and wood surfaces to which IGRs are typically applied for pest control in such facilities. Statistically significant reductions in emergence percentages of adults compared to a distilled water control occurred for up to 12 weeks when novaluron was sprayed on concrete, metal, and wood at rates between 0.053 and 0.209 mg/m², the highest of which induces 100% mortality at 0 weeks after treatment. Residual efficacy decreased with increasing time after treatment due to degradation and sorption of novaluron into the surfaces. Novaluron residues were most persistent on metal and least persistent on wood surfaces. Knowledge of novaluron residual efficacy on storage facility surfaces can be helpful guidance for timing of postharvest insect pest management treatments as the costs of commonly used pesticides increase along with insect resistance to such pesticides.

Abstract

The residual efficacy of novaluron on concrete, metal and wood was evaluated against last-instar larvae of Oryzaephilus surinamensis (L.), Triboliumcastaneum (Herbst), and Trogoderma granarium Everts. The larvae and food provided for survival were exposed to surfaces pretreated at rates of 0.053, to 0.209 mg/m² and bioassays were conducted from 0- to 16-weeks post-treatment. Percentage emergence of adults was recorded after 30 days (d). On all surfaces at week 0, no O. surinamensis or T.castaneum adults emerged, and ≤3.3% emergence of T. granarium was found at 0.209 mg/m². Novaluron significantly reduced the percentage emergence of adults of the three species compared to a distilled water control for the first 12 weeks on all the tested surfaces as the residual efficacy declined at a low rate during initial weeks and then at a high rate in the final weeks of the 16-week study. Reductions to emergence were most persistent on metal surfaces, with mean percentages of adult emergence of ≤18.3 in week 12, followed by concrete (≤32.5) and wood (≤45.0) for all species at novaluron application rates of 0.209 mg/m². For >4-weeks protection, higher application rates would be needed to avoid buildup of pest populations and reductions in profitability. Such results can be helpful for the management of O. surinamensis, T.castaneum, and T. granarium as the costs of commonly used insecticides against postharvest insect pests and the resistance of these insects to the pesticides gradually increase in mills, warehouses, and food storage facilities.