Insecticidal Seed Treatments in Rice

Rice is the staple food for the majority of the world’s population. Globally, rice is cultivated on an estimated 160 m ha annually [1]. Although the U.S contributes only 2% of world rice production from less than 1% of world’s acreage, the U.S is one of top five global exporters of rice [2]. Insect pests pose a major biotic threat to rice production throughout the world. In the U.S, the rice water weevil (RWW), Lissorhoptrus oryzophilus Kuschel (Coleoptera: Curculionidae), is the most destructive insect pest of rice [3]. In addition to the RWW, a number of other pests can attack rice during the seedling, vegetative and early reproductive phases of rice development. The importance of these pests varies regionally. In Arkansas, for example, Colaspis sp. can be important pests of young rice and can severely reduce early season stands [4]. In Louisiana and Texas, several Lepidopterans are important, including the fall armyworm, Spodoptera frugiperda (Lepidoptera: Noctuidae), and the sugarcane borer, Diatraea saccharalis (Lepidoptera: Crambidae). While these pests are not consistently important constraints on yield, they can occasionally cause heavy losses. In contrast, losses from the RWW would probably average 5% or more if fields were not treated and this insect is a key driver of early season pest management decisions [5]. Application of foliar pyrethroid insecticides for weevil management, a practice used since the late 1990’s, has been problematic due to high toxicity of this group of insecticides to aquatic invertebrates, primarily to red swamp crawfish, the major aquaculture commodity cocultivated with rice in rotation systems in Louisiana [6-8]. As alternatives to pyrethroids, two groups of insecticides have been labeled since the mid-2000s as seed treatments in ricethe anthranilic diamide group (active ingredient: chlorantraniliprole; Dermacor X-100®) and the neonicotinoid group (active ingredietns: thiamethoxam; Cruiser Maxx®; clothianidin; Nipsit INSIDE®). These seed treatment insecticides have longer residual activity on RWWs than pyrethroids and are two to three orders of magnitude less acutely toxic to crawfish than pyrethroids [6,7]. The two groups of seed treatment insecticides differ in their activities on their sporadic insect pest complex [9] and in their potency against weevils [10]. The growers’ choice of treatment with neonicotinoid or anthranilic diamide is influenced by the threat of sporadic pests, the relative safety of these insecticide classes on crawfish, and the cost of treatment.