Effect of pyriproxyfen on larvae of the Mediterranean flour moth, Ephestia kuehniella (Zeller) (Lepidoptera: Pyralidae)

The widespread Mediterranean flour moth, Ephestia kuehniella (Zeller), causes economic damage by feeding on stored products, particularly cereal flour. Pyriproxyfen is one of the most significant insect growth regulators widely used in controlling stored-product insect pests due to its low toxicity to mammals and lack of dangerous residues in food. By imitating the action of juvenile hormone, pyriproxyfen causes insect pests to experience prolonged larval development, failure to emerge as pupae or malformed pupae, absence of embryo development, and in some cases, a reduction in fecundity.
This study examined the toxicity of pyriproxyfen on E. kuehniella fifth instar larvae at 25 ± 1°C, 65 ± 5% relative humidity, and a photoperiod of 16:8 (L:D) h. The 50% lethal concentration (LC50) of the insecticide was calculated as 7.39 and 5.68 ppm at 72 and 96 h post-treatment, respectively. After preparing the desired concentrations based on the preliminary test using acetone solvent, the effect of sublethal concentrations (LC20 = 2.87, LC30 = 4.10, and LC40 = 5.56 ppm) of pyriproxyfen on mortality and survival period of fifth instar larvae was investigated.
The results of this study demonstrated that the survival period of larvae treated with LC20 (35.05 days) was significantly longer than the control group (18.85 days). One week after exposure to sublethal concentrations of pyriproxyfen, the larvae's survival rate was significantly lower than the control group. However, the survival percentage of larvae at two- and three-weeks post-treatment was not significantly different from the control.
One of the possible explanations for the shorter survival period of larvae treated with LC30 and LC40 is the greater toxicity of these concentrations against the pest and, consequently, the increase in the percentage of larval mortality in the second- and third-weeks following treatment. This study found that sublethal concentrations of pyriproxyfen could be used to control the Mediterranean flour moth under storage conditions.