Synergistic control of storage pest rice weevil using Hypericum japonicum and deltamethrin combinations: a key to combat pesticide resistance

The augmented rates of pest infestation in stored grains have forced humans to rely on pesticide application in stored food grains even in developed countries. The greater incidence and alarming rate of pesticide resistance and safety concerns about their use in the food industry also contribute to ill-being of grain consumers and environment, thereby alluring constructive attempts to reduce the levels of agrochemical use. The current research elucidated the synergistic role of Hypericum japonicum (a medicinal plant) and pyrethroid deltamethrin in controlling the most common storage pest rice weevil, Sitophilus oryzae even at low concentrations than recommended by FAO. The screening of pesticidal property of methanolic extract of H. japonicum, pyrethroid deltamethrin, and their combinatorial assay was evaluated by standard procedures under laboratory conditions and mortality was gauged after 24 h of exposure. The LC50 and LC90 concentrations of deltamethrin alone (0.725 mg/l and 3.577 mg/l respectively) and in combination with Hypericum methanolic extract (LC50 0.119 mg/l and LC90 1.27 mg/l respectively) were found to be potent. The study revealed that the supplementation of plant extract in the pest controlling formulation substantially reduced the effective individual LC90 concentration of the pesticide required for pest control. The plant extracts showed synergy towards deltamethrin with SF 6.09. This is the foremost report on the synergistic effect of H. japonicum with deltamethrin against rice weevil, which could serve as an effective and more safer storage pest control method against the indiscriminate pesticide use and abuse.