James Edwin Dripps

Recent advances in the chemistry of spinosyns

The spinosyns are a new class of fermentation-derived insect control agents that are effective against a variety of chewing insect pests. The successful introduction of spinosad into the agricultural marketplace represents an important milestone in the use of natural products for commercial pest control. The development of a natural product presents additional limitations relative to a synthetic material. While the latter affords some degree of control in building appropriate physical attributes such as photostability, a natural product, designed to function in a different environment, is often less suited for traditional spray applications. Despite its intrinsic photolability, spinosad is stable enough to perform under field conditions. In an effort to generate analogs with improved physical characteristics, we have developed a variety of conditions for selectively modifying different portions of the molecule, and we have discovered analogs with greater activity against a broader spectrum of pests. The inability to translate improved greenhouse activity to actual field conditions resulted in a detailed study of the effects of formulations and crystallinity on biological activity. Through this effort, measurably improved field performance of synthetic spinosyn analogs relative to the natural product have now been observed.

Neural network-based QSAR and insecticide discovery: spinetoram

Improvements in the efficacy and spectrum of the spinosyns, novel fermentation derived insecticide, has long been a goal within Dow AgroSciences. As large and complex fermentation products identifying specific modifications to the spinosyns likely to result in improved activity was a difficult process, since most modifications decreased the activity. A variety of approaches were investigated to identify new synthetic directions for the spinosyn chemistry including several explorations of the quantitative structure activity relationships (QSAR) of spinosyns, which initially were unsuccessful. However, application of artificial neural networks (ANN) to the spinosyn QSAR problem identified new directions for improved activity in the chemistry, which subsequent synthesis and testing confirmed. The ANN-based analogs coupled with other information on substitution effects resulting from spinosyn structure activity relationships lead to the discovery of spinetoram (XDE-175). Launched in late 2007, spinetoram provides both improved efficacy and an expanded spectrum while maintaining the exceptional environmental and toxicological profile already established for the spinosyn chemistry.

Kinetics of Uptake, Clearance, Transfer, and Metabolism of Hexaflumuron by Eastern Subterranean Termites (Isoptera: Rhinotermitidae)

Abstract The rates of uptake, clearance, insect-to-insect transfer, and metabolism of [14C]hexaflumuron [N-(((3,5-dichloro-4-(1,1,2,2-tetrafluroethoxy)phenyl)- amino)carbonyl)-2,6-diflurobenzamide] were measured in eastern subterranean termite workers, Reticulitermes flavipes (Kollar), fed cellulose diets containing either 0.1 or 0.5% (wt:wt) hexaflumuron. The rate of uptake, level of maximum uptake, and amount of insect-to-insect transfer were concentration dependent. The clearance rate constant for hexaflumuron was independent of concentration, with a mean value of 3.2 × 10−3 /h. This corresponds to a mean half-life for hexaflumuron inside termites of 9 d. No evidence of metabolism of hexaflumuron to additional products was detected when extracting and examining the radioactivity contained in the fecal and regurgitated material within the termite holding apparatus 40 d after exposure to the chemical. Hexaflumuron was efficiently transferred from treated to untreated termites, through trophallaxis, resulting in spread of the toxicant throughout the insect population. The combination of uptake and efficient transfer of hexaflumuron between treated and untreated termites ensures broad distribution of the material even to insects not directly exposed to the toxicant. The distribution of hexaflumuron by termite workers, along with their minimal ability to metabolize the compound to other metabolites, and their slow ability to clear the material from the termite population results in death of the entire group of termites contained within the holding apparatus.

Attraction and Mortality of Bactrocera dorsalis (Diptera: Tephritidae) to STATIC Spinosad ME Weathered under Operational Conditions in California and Florida: A Reduced-Risk Male Annihilation Treatment

ABSTRACT Studies were conducted in 2013–2014 to quantify attraction, feeding, and mortality of male oriental fruit flies, Bactrocera dorsalis (Hendel) (Diptera: Tephritidae), to STATIC SpinosadME a reduced-risk male annihilation treatment (MAT) formulation consisting of an amorphous polymer matrix in combination with methyl eugenol (ME) and spinosad compared with the standard treatment of Min-U-Gel mixed with ME and naled (Dibrom). Our approach used a behavioral methodology for evaluation of slow-acting reduced-risk insecticides.MEtreatments were weathered for 1, 7, 14, 21, and 28 d under operational conditions in California and Florida and shipped to Hawaii for bioassays. In field tests using bucket traps to attract and capture wild males, and in toxicity studies conducted in 1-m3 cages using released males of controlled ages, STATIC Spinosad ME performed equally as well to the standard formulation of Min-U-GelMEwith naled for material aged up to 28 d in both California and Florida. In laboratory feeding tests in which individual males were exposed for 5 min to the different ME treatments, mortality induced by STATIC Spinosad ME recorded at 24 h did not differ from mortality caused by Min-U-Gel ME with naled at 1, 7, 14, and 21 d in California and was equal to or higher for all weathered time periods in Florida during two trials. Spinosad has low contact toxicity, and when mixed with an attractant and slow release matrix, offers a reduced-risk alternative for eradication of B. dorsalis and related ME attracted species, without many of the potential negative effects to humans and nontargets associated with broad-spectrum contact insecticides such as naled.

CHAPTER 6:The Bisacylhydrazine Insecticides

The bisacylhydrazine (BAH) insecticides are a class of green chemistry compounds very specific to the target insect pests that induce a premature molting process in the affected insects. The BAH insecticides bind to the ecdysone receptors in the target pests with a greater affinity than that observed for the natural hormone, 20-hydroxyecdysone. This confers a greater level of selectivity towards most non-target organisms present in the ecosystems where the BAH insecticides are used. The BAH insecticides act directly on immature stages of the target insects (eggs and larvae) and cause some sublethal effects, such as delayed developmental rates and reduced fecundity and fertility on the adult stage of the pests. These insecticides have very good ecotoxicological profile, having virtually no impact on most non target organisms including beneficial insects and pollinators, (bees, predators and parasitoids), birds, fish and terrestrial invertebrates. The BAH insecticides also have low-toxicity to mammals making them reduced risk materials for humans handling the products. The most widely registered BAH is methoxyfenozide, which has registrations in more than 50 countries in a variety of crops ranging from vegetables to specialty uses such as forestry and tea. Due to their characteristics, the BAH insecticides can be incorporated in insecticide resistance and integrated pest management programs. Data related to these aspects of BAH insecticides are presented.