The discovery of indazapyroxamet: a novel 3-pyridinyl insecticide targeting piercing/sucking insectsa.

In recent years, the registrations for a number of commercial insecticides utilized for piercing/sucking insects have been cancelled or restricted. To meet this growing need for new hemipteran controlling agrochemicals, we discovered a 2-(pyridin-3-yl)-thiazole compound, with limited insecticidal activity against cotton/melon aphid (Aphis gossypii). The 2-(pyridin-3-yl)-thiazole moiety offered us a basis to pursue the bicyclic 2-(pyridin-3-yl)-2H-indazole carboxamides. Evaluation of such 2-(pyridin-3-yl)-2H-indazole carboxamides revealed that even analogs containing only simple alkyl amides attached at the 4 or 5 positions possess promising insecticidal activity. Extensive optimization of this novel class of 2-(pyridin-3-yl)-2H-indazole carboxamides led to identifying indazapyroxamet for commercial development. © 2024 Society of Chemical Industry.

Mode of action of triflumezopyrim: A novel mesoionic insecticide which inhibits the nicotinic acetylcholine receptor.

Triflumezopyrim, a newly commercialized molecule from DuPont Crop Protection, belongs to the novel class of mesoionic insecticides. This study characterizes the biochemical and physiological action of this novel insecticide. Using membranes from the aphid, Myzus persicae, triflumezopyrim was found to displace (3)H-imidacloprid with a Ki value of 43 nM with competitive binding results indicating that triflumezopyrim binds to the orthosteric site of the nicotinic acetylcholine receptor (nAChR). In voltage clamp studies using dissociated Periplaneta americana neurons, triflumezopyrim inhibits nAChR currents with an IC50 of 0.6 nM. Activation of nAChR currents was minimal and required concentrations ≥100 µM. Xenopus oocytes expressing chimeric nAChRs (Drosophila α2/chick ß2) showed similar inhibitory effects from triflumezopyrim. In P. americana neurons, co-application experiments with acetylcholine reveal the inhibitory action of triflumezopyrim to be rapid and prolonged in nature. Such physiological action is distinct from other insecticides in IRAC Group 4 in which the toxicological mode of action is attributed to nAChR agonism. Mesoionic insecticides act via inhibition of the orthosteric binding site of the nAChR despite previous beliefs that such action would translate to poor insect control. Triflumezopyrim is the first commercialized insecticide from this class and provides outstanding control of hoppers, including the brown planthopper, Nilaparvata lugens, which is already displaying strong resistance to neonicotinoids such as imidacloprid.

Influence of Rice Seeding Rate on Efficacies of Neonicotinoid and Anthranilic Diamide Seed Treatments against Rice Water Weevil.

Rice in the U.S. is frequently seeded at low rates and treated before sowing with neonicotinoid or anthranilic diamide insecticides to target the rice water weevil. A previous study of the influence of seeding rate on rice water weevil densities showed an inverse relationship between seeding rates and immature weevil densities. This study investigated interactive effects of seeding rate and seed treatment on weevil densities and rice yields; in particular, experiments were designed to determine whether seed treatments were less effective at low seeding rates. Four experiments were conducted over three years by varying seeding rates of rice treated at constant per seed rates of insecticide. Larval suppression by chlorantraniliprole was superior to thiamethoxam or clothianidin, and infestations at low seeding rates were up to 47% higher than at high seeding rates. Little evidence was found for the hypothesis that seed treatments are less effective at low seeding rates; in only one of four experiments was the reduction in weevil densities by thiamethoxam greater at high than at low seeding rates. However, suppression of larvae by neonicotinoid seed treatments in plots seeded at low rates was generally poor, and caution must be exercised when using the neonicotioids at low seeding rates.

Oviposition behavior of Diatraea saccharalis (Lepidoptera: Crambidae) on different rice cultivars in Louisiana.

The sugarcane borer, Diatraea saccharalis (F.), is a pest of a variety of graminaceous crops in the southern United States, including sugarcane, maize, and rice in Louisiana. This study examined several aspects of D. saccharalis oviposition behavior on rice (Oryza sativa). The vertical distribution of egg masses on four phenological stages of rice in the field showed that D. saccharalis prefers to oviposit on the uppermost portions of rice plants, regardless of plant stage. In greenhouse choice experiments, females strongly preferred plants at the boot and panicle differentiation stages over plants at the tillering stage for oviposition. Greenhouse studies were also conducted to quantify the oviposition preference of D. saccharalis for different cultivars of. When plants were at the tillering stage, cultivars Cocodrie, Priscilla, Bengal, Cheniere, and CL161 were more preferred than cultivars Jupiter, XL723, and XP744. When plants reached the panicle initiation stage, cultivars Cocodrie, CL161, and Priscilla were more preferred than Bengal, Cheniere, Jupiter, XL723, and XP744. Females also oviposited significantly more egg masses on the adaxial surfaces of rice leaves than on the abaxial surfaces. These results will facilitate scouting and management of sugarcane borer and can be used as a foundation for the development of sugarcane borer resistant cultivars.

Herbivore- and elicitor-induced resistance in rice to the rice water weevil (Lissorhoptrus oryzophilus Kuschel) in the laboratory and field.

Feeding by herbivores can change plants in ways that make them more resistant to subsequent herbivory. Such induced responses are better-studied in a number of model dicots than in rice and other cereals. In a series of greenhouse and field experiments, we assessed the effects of prior herbivory by the fall armyworm, Spodoptera frugiperda (J.E. Smith) and of exogenous applications of jasmonic acid (JA) on the resistance of rice plants to the rice water weevil, Lissorhoptrus oryzophilus (Kuschel), the major pest of rice in the United States. Prior feeding by S. frugiperda and treatment of plants with exogenous JA resulted in increases in the resistance of plants to the weevil. Increases in resistance were manifested as reduced numbers of eggs and first-instars associated with armyworm-injured or JA-treated plants relative to control plants. In field experiments, there was a transient but significant reduction in the number of immature L. oryzophilus on JA-treated plants relative to untreated plants. To our knowledge, this is the first example of direct induced resistance in rice demonstrated in small-plot field experiments. We discuss the potential for the use of elicitor induced resistance in rice.