Vol.:(0123456789) 1 3 Environmental Sustainability https://doi.org/10.1007/s42398-019-00086-w ORIGINAL ARTICLE Synergistic control of storage pest rice weevil using Hypericum japonicum and deltamethrin combinations: a key to combat pesticide resistance Sreedev Puthur 1  · A. N. Anoopkumar 1  · Sharrel Rebello 1  · Embalil Mathachan Aneesh 1 Received: 31 October 2018 / Revised: 28 August 2019 / Accepted: 29 August 2019 © Society for Environmental Sustainability 2019 Abstract 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 japoni- cum (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 labora- tory conditions and mortality was gauged after 24 h of exposure. The LC 50 and LC 90 concentrations of deltamethrin alone (0.725 mg/l and 3.577 mg/l respectively) and in combination with Hypericum methanolic extract (LC 50 0.119 mg/l and LC 90 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 efective individual LC 90 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 efect of H. japonicum with deltamethrin against rice weevil, which could serve as an efective and more safer storage pest control method against the indiscriminate pesticide use and abuse. Keywords Hypericum japonicum · Sitophilus oryzae · Deltamethrin · Combinatorial bioassay Introduction The escalating population rates, as well as increased lev- els of plant raw material utility in industries, has always demanded the need for increased agricultural outputs world- wide (Ribeiro et al. 2003). Grain damage by pests has been a major test to the agricultural sector and the stored grain products being infested from the time of harvest to consump- tion. Majority of these pests belong to the coleopteran family and the most damaging candidates include Sitophilus Genus members (commonly called weevils) (Huignard et al. 2011; Tennyson et al. 2012). Rice weevil (Sitophilus oryzae) a serious pest of stored grains has a worldwide distribution especially in temperate areas, critically afecting the qual- ity and quantity of the stored grains (Agarwal et al. 1979; Batta 2004). The damages caused by the pest alone accounts to 40% of the worldwide stored grain production (Mishra et al. 2013), as the adult weevils consume the endosperm of the grain and diminish its carbohydrate and protein content (Belloa et al. 2000). In such a scenario, synthetic pesticides, especially contact insecticides are traditionally used to prevent and eliminate various insect pests (Cengiz et al. 2016). Deltamethrin is one such synthetic pyrethroid-based pesticide widely used in agriculture and veterinary applications for the man- agement of rice weevils (Bekele et al. 2010; Vélez et al. 2017). Regardless of its benefts in pest control, the great- est resultant problem is that the continued application of synthetic pesticides leads to physiological resistance and undesirable ecological efects (Suresh et al. 2017). Moreo- ver, the increasing pyrethroid resistance in grain weevils * Embalil Mathachan Aneesh aneeshembalil@gmail.com 1 Communicable Disease Research Laboratory, Department of Zoology, St. Joseph’s College, Irinjalakuda, Thrissur, India