Anopheles arabiensis and An. gambiae s.s. were equally and highly susceptible to Sumilarv®0.5G under laboratory and standardized field conditions. Sumilarv®0.5G inhibited over 80% of the total adult emergence over a period of six weeks at both application dosages. However, weekly emergence rates increased steadily over the six-week test period at the lower dosage that corresponded with the EI99 in the laboratory and weekly emergence inhibition was frequently lower than the 80% that is recommended by WHOPES for successful immature control . Laboratory tests were conducted under standardized conditions without major abiotic and biotic influences and therefore EI values represent only minimum dosages. Application rates frequently have to be increased up to several times the minimum dose to obtain sufficient immature control under field conditions [57, 63]. The higher dosage of 5 mg ai per m2 or 0.09 ppm ai inhibited well over 80% of adult emergence in all but one test week. This dosage was 4.5 times the average EI99 in the laboratory. Further field tests to establish the optimum dose for operational control in a variety of different habitats are necessary but based on the results presented here it is likely that the optimum dosage lies between the two tested here and therefore coincides with the maximum dosage recommended by the manufacturer (0.05 ppm ai) for operational control of other mosquito species .
The estimated emergence inhibition rates from the dose–response tests were four times higher than those previously reported by Kawada and his colleagues  for An. gambiae, but within the range of rates estimated for Culex and Aedes species [66–70]. These differences may arise from the different pyriproxyfen formulations used in separate studies , but also from the material of the test containers . Kawada and colleagues used a 5% emulsifiable concentrate formulation while in the present study a granular formulation was used and had to be crushed in a mortar for the laboratory tests, which might have not led to an equal amount of active ingredients being released into the stock solution. Also, in the present study plastic cups were used for bioassays while Kawada and his colleagues used aluminium cups. There is a concern that the active ingredient pyriproxyfen adheres to plastic  leading to a longer residual effect from such treated containers due to a continuous slow release from the plastic . In the short term however, plastic might reduce the amount of active ingredient in the water, which could be responsible for the higher estimates of EI concentrations found in this study. The extremely low concentrations of active ingredient needed for the control of mosquitoes with Sumilarv®0.5G is worth noting. The estimated effective dose of pyriproxyfen is approximately 10 times lower than those reported for microbial larvicides [20, 21]. This is not surprising since pyriproxyfen is a juvenile hormone analogue, and insect hormones, like all hormones, operate at extremely low concentrations as chemical messengers [70, 73]. Thus, far smaller quantities of Sumilarv®0.5G would be required for larviciding programmes compared to microbial larvicides, thereby helping to lower costs associated with transporting and storing larvicides .
The residual impact of Sumilarv®0.5G on An. gambiae s.l. emergence observed here corresponds well with reports from previous studies on other mosquito species [44, 67, 74] but application dosages required to achieve the same effect seem slightly higher for An. gambiae s.l. Sumilarv®0.5G at 0.02 ppm ai and 0.05 ppm ai provided almost complete emergence inhibition of Aedes aegypti, Aedes albopictus and Aedes taeniorhynchus, Culex nigripalpus and Anopheles quadrimaculatus for six weeks under standardized field conditions . This slow-release formulation has even been shown to exhibit prolonged residual activity for control of Aedes larvae even when the treatments were diluted by using replacement of treated water with untreated water in the treated containers [44, 75]. Similarly, here it was observed that rainfall did not negatively affect the impact of the treatments. Exceptional performance of Sumilarv®0.5G was reported for the control of Anopheles culicifacies in confined gem pits in Sri Lanka  where a single application of pyriproxyfen at 0.01 ppm ai was sufficient to inhibit adult emergence for approximately six months. Similarly, Sihuincha and colleagues  reported complete emergence inhibition of Ae. aegypti for five months from water tanks in Peru at an application rate of Sumilarv®0.5G of 0.05 ppm ai. Overall it can be concluded from previous work that the efficacy and residual activity of different pyriproxyfen-containing products depends on the formulation, dose, habitat types treated, prevailing weather conditions and target mosquito species [53, 67, 74].
The current study showed that the efficacy of Sumilarv®0.5G is reduced in turbid water and water with a pH ≥8. Water is turbid because it carries a suspension of fine particles of both organic and inorganic matter in the water column. Some of the turbidity observed here might have been due to algae and bacteria growth in the established habitats, which in turn might have increased the water pH. It is possible that the active ingredient, pyriproxyfen, is adsorbed onto particles in the water column and was less accessible to larvae. Turbidity and pH of aquatic habitats are important parameters that are associated with the abundance, development and survival of Anopheles larvae . Anopheles larvae are known to exploit aquatic habitats with varying degrees of water turbidity and pH [76, 77]. Suspended particles including algae in the water column in turbid ponds provide mosquitoes with food that enhances their development and survival thus increase emergence from turbid ponds [78, 79]. Mulligan and Schaefer  found pyriproxyfen to adsorb onto organic matter which might have been responsible for larvae to be exposed to reduced doses. This needs to be considered and monitored in field operations where it might be necessary to increase the application dose or reduce retreatment intervals to ensure a consistent emergence inhibition above 80% as recommended by WHOPES .
An added benefit to the direct effect of Sumilarv®0.5G on immature stages were the sub-lethal effects that affected the offspring of adult females that successfully emerged from treated ponds. At 5 mg ai per m2 the reproduction of females was reduced by well over 90%. Similar effects of insect growth regulators have been shown for Aedes and Culex[46, 47, 81]. The laying of non-viable eggs by female An. gambiae s.s. emerging from treated ponds might further extend the efficacy and residual effect of pyriproxyfen, and may help further reduce intervention costs by extending the retreatment intervals. It would be particularly helpful in the context of an auto-dissemination strategy  of Sumilarv®0.5G where potentially only sub-lethal doses are transferred to a habitat by female gravid mosquitoes. The delayed sub-lethal effects of insect growth regulators were also shown to affect the sex ratio and to reduce blood-feeding rates in exposed mosquitoes [47, 83]. Similar effects were shown for adults exposed to pyriproxifen [48, 49, 84]. Ohashi and colleagues  demonstrated that An. gambiae s.s. was completely sterilized, with no female laying eggs after exposure to pyriproxyfen-treated nets. Insect growth regulators have been shown to suppress ovarian development and egg development in mosquitoes [85, 86]. Judson and de Lumen  showed that exposure of Ae. aegypti females to juvenile hormone analogues suppressed egg development by inhibiting development of ovarian follicles. Fournet and colleagues  similarly showed that the ovarian development of Ae. aegypti females that emerged from larvae exposed to insect growth regulators was affected.
As with every insecticide it is important to be cautious about using pyriproxyfen formulations as a stand-alone intervention since tolerance to pyriproxyfen has been found in Diptera [87, 88]. It is also of concern to know whether the progeny of gravid females that are exposed to sub-lethal level doses of pyriproxyfen and survive have greater tolerance to pyriproxyfen than other mosquitoes. If this is the case, resistance may spread.
Pyriproxyfen exhibits favourable characteristics for utilization as a larvicide for mosquito control. The recommended application rate in drinking water limit of 300 ppb (0.3 ppm)  is several folds higher than the recommended dose of 0.01-0.05 ppm  for mosquito control and also has minimal environmental impacts at recommended rates for mosquitoes [52, 53].