Efficacy of Combinations of Methoprene and Deltamethrin as Long-Term Commodity Protectants

Abstract

Wheat, corn, and brown rice were treated with different combinations of a deltamethrin suspension concentrate (SC) formulation and a new emulsifiable concentrate (EC) formulation, at rates of either 0.5 or 1.0 ppm alone or in combination with 1.25 and 2.5 ppm methoprene (10 treatments in all, including an untreated control). Treated commodities were stored at ambient conditions on the floor of an empty grain bin in Manhattan, KS, USA, in 5-kg lots for individual replicates. The commodities were sampled and bio-assayed every three months for 15 months by exposing 10 mixed-sex parental adults of selected adult stored product insects on 70–80 g of the commodity. For all treatments, there was no regression of declining efficacy with respect to the month. Therefore, the data were combined for analysis. On wheat and brown rice, there was no reproduction of Rhyzopertha dominica (Fabricius) in any of the treatments, and there was no weight loss in either commodity that was caused by feeding of the parental adults or developing progeny. There was reproduction of Sitophilus oryzae (L.) on wheat but, for several combinations, the EC formulation gave better suppression of progeny compared to the standard SC. However, on brown rice, only the combination of 1.0 ppm deltamethrin EC and 2.5 ppm methoprene was different than other treatments with respect to progeny development, sample weight loss caused by feeding, and weight of the feeding damage itself. Progeny production was correlated with grain damage. No progeny of Tribolium castaneum (Herbst) developed on the treated corn, but there was some variation in insect damage, with less damage in those treatments involving the EC formulation. Progeny production of Sitophilus zeamais (Motschulsky) was at the lowest in the combination of 1.0 ppm deltamethrin EC and 2.5 ppm methoprene. The resulting insect damage was the lowest in this combination as well. Results of this study were used by the registrant (Central Life Sciences) in the United States (US) to modify the commercial formulation to replace the deltamethrin SC with the EC, at label rates of either 0.5 ppm EC+ 1.25 ppm methoprene, or 1.0 ppm EC + 2.5 ppm methoprene, on wheat, corn, and rice.

Residual efficacy of methoxyfenozide applied on different grain commodities for the control of three stored-product insect pests

“…The results of methoxfenozide persistence are in contrast to those obtained by Liu et al (2016) who found that methoprene (a juvenoid IGR) was effective up to 40 weeks at 1 ppm due to its residual activity in treated wheat. Similarly, Arthur (2019) reported that efficacy of the IGR increased with different combinations of deltamethrin and methoprene were applied to grain, all treatments were effective against T. castaneum for 15 months on maize.…”

Synthetic and Natural Insecticides: Gas, Liquid, Gel and Solid Formulations for Stored-Product and Food-Industry Pest Control

“…However, the usage and registration of various carbamates (carbaryl) and organophosphates (e.g., malathion, dichlorvos, pirimiphos-methyl, chlorpyrifos methyl, diazinon, fenitrothion, fenthion) has been in decline over the last several decades. At present, the remaining pyrethroids (deltamethrin, cypermethrin, and bifenthrin, eventually mixed with piperonyl butoxide—PBO—as a synergist) are the neurotoxic insecticide active compounds most commonly used as grain protectant formulations [ 209 , 214 ]. The prevalent reliance on pyrethroid protectants may result in decreased sensitivity or resistance of storage arthropods [ 215 ] as already found in some pest species, populations, and geographical areas [ 40 , 216 ].…”

“…Among IGRs/IGDs, methoprene (r/s-methoprene, a mixture of r- and s- enantiomers) and s-methoprene (s- enantiomer) are the few compounds that have not only been tested but have also reached the registration and commercial usage stages [ 234 , 238 , 239 ]. As grain protectants, r/s methoprene (USA—1980s) and s-methoprene (USA—2002) were first registered in the USA and Australia [ 214 , 238 , 239 ]. The biological efficacy of r/s methoprene and s-methoprene as protectants of various commodities against storage pests has been evaluated by several authors [ 214 , 235 , 240 , 241 , 242 ].…”

Detection of Phosphine Resistance in Field Populations of Four Key Stored-Grain Insect Pests in Pakistan

“…Control tactics applied in grain commodities before storage include the removal of grain debris and the application of insecticides [ 1 ]. Although synthetic insecticides act as efficient management tools that provide quick control of insect pests, they can have negative impact on humans’ health and the environment [ 2 , 3 ].…”