Gary D. Thompson

Discovery and Characterization of Field Resistance to Bt Maize: Spodoptera frugiperda (Lepidoptera: Noctuidae) in Puerto Rico

ABSTRACT Transgenic maize, Zea mays L., event TC1507 produces the Cry1F protein to provide protection from feeding by several important lepidopteran pests, including Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae). Reports of reduced field performance against this species in Puerto Rico were investigated, and laboratory bioassays showed that S. frugiperda collected from the affected area exhibited lower sensitivity to the Cry1F protein compared with typical colonies from other regions. The resistance was shown to be autosomally inherited and highly recessive. The Puerto Rico colony was shown to be moderately less sensitive than susceptible laboratory strains to Cry1Ab and Cry1Ac, but the differences in sensitivity were dramatically smaller than for Cry1F. Potential contributory factors to the emergence of resistance to Cry1F in Puerto Rico populations of S. frugiperda include the tropical island geography, unusually large population sizes in 2006, and drought conditions reducing the availability of alternative hosts. In response to this resistance incident, the technology providers have stopped commercial sales of TC1507 maize in Puerto Rico pending potential reversion to susceptibility.

Spinosad – a case study: an example from a natural products discovery programme†

The discovery and characterization of the soil actinomycete, Saccharopolyspora spinosa, and the insecticidal metabolite spinosad is presented as a case history of a successful project emerging from a natural products crop protection discovery programme. A who, what and how approach is utilized to communicate the events around the discovery and development of the project. The companies and departments involved are listed with insight into their structure and philosophy. A detailed description of spinosad and its properties is also provided. Finally an overview is given of the various tasks required and hurdles that were overcome to bring the project to a commercial success. © 2000 Society of Chemical Industry

Status of resistance to Bt maize in Spodoptera frugiperda: Lessons from Puerto Rico

In 2006, reports of potential Spodoptera frugiperda resistance to TC1507 maize in Puerto Rico were received. Subsequent investigation confirmed that pest populations collected from several sites in Puerto Rico were largely unaffected by the Cry1F protein in bioassays, with resistance ratios likely in excess of 1000. Since then, we have continued monitoring populations in Puerto Rico and in southern areas of the mainland US. The majority of the collections from Puerto Rico continue to show high levels of Cry1F resistance whereas populations collected from the southern US mainland continue to show full susceptibility to Cry1F and TC1507 maize. It does not appear that resistant populations have spread to any measurable extent from Puerto Rico to mainland US, nor that local selection pressure from Cry1F-expressing maize or cotton production in the southern US has caused a measurable change in population susceptibility. Lessons learned from Puerto Rico are being applied in other parts of the Americas where TC1507 maize is grown and additional steps being taken to protect the long-term durability of Cry1F in maize in areas where similar selection pressure may be expected. Tactics include using locally-adapted germplasm that contain native Spodoptera resistance, a robust education program to teach end-users about the potential for resistance to develop appropriate crop stewardship, resistance monitoring, and the use of insecticides under high S. frugiperda pressure. Perhaps most importantly, pyramided trait products that produce two or more different Bt proteins are being introduced to further delay resistance development to Cry1F.

A Review of Spinosad as a Natural Product for Larval Mosquito Control

Abstract The effectiveness of spinosad for larval mosquito control is summarized based on available published literature and some heretofore unpublished studies. Spinosad is highly active against larvae of all mosquito species tested thus far. It is effective at similar dosages for all larval mosquito instars, with peak cumulative mortality occurring at 72 h posttreatment. More studies are needed to fully define spinosads ovicidal properties and its impact on the pupal stage. High levels of organic matter and full sunlight are both factors that can negatively impact spinosad efficacy and longevity and should be considered when making use rate and retreatment decisions. Studies clearly show that spinosad technical active ingredient and current crop formulations are suboptimal for larval mosquito control and underrepresent spinosads true activity. A series of spinosad formulations specialized for larval mosquito control will be sold commercially. Prior to its launch and widespread use, there is a need for additional baseline studies to clarify the natural geographic variation in susceptibility of field mosquito populations. Spinosad represents a new and effective natural product for the integrated management of larval mosquitoes. It possesses a unique mode of action not shared by any other insecticide and is shown to be minimally disruptive to most nontarget species tested thus far at its proposed field use rates.

Spinosad Toxicity to Pollinators and Associated Risk

Spinosad is a natural insecticide derived from an actinomycete bacterium species, Saccharopolyspora spinosa (Mertz and Yao 1990), that displays the efficacy of a synthetic insecticide. It consists of the two most active metabolites, designated spinosyn A and D. Both spinosyns are readily degraded in moist aerobic soil, and field dissipation, which is quite rapid (half-life, 0.3-0.5 d) can be attributed to photolysis or a combination of metabolism and photolysis. Spinosad causes neurological effects in insects that are consistent with the general activation of nicotinic acetylcholine receptors but by a mechanism that is novel among known insecticide compounds. Spinosad has a high level of efficacy for lepidopteran larvae, as well as some Diptera, Coleoptera, Thysanoptera, and Hymenoptera, but has limited to no activity to other insects and exhibits low toxicity to mammals and other wildlife. Although spinosad has low toxicity to most beneficial insects, initial acute laboratory tests indicated that spinosad is intrinsically toxic to pollinators. The hazard of spinosad to bees was evaluated using a tiered approach. Initial acute laboratory exposures were conducted, followed by toxicity of residues of spinosad on treated foliage, greenhouse studies to assess acute as well as chronic toxicity, confined field assessments, and finally full field studies using a variety of crops under typical use conditions. These data were used to assess the potential of adverse effects on foraging bees following the use of spinosad. This research has clearly demonstrated that spinosad residues that have been allowed to dry for 3 hr are not acutely harmful to honeybees when low-volume and ultralow-volume sprays are used. Further, glasshouse and semifield studies have demonstrated that dried residues are not acutely toxic, and although pollen and nectar from sprayed plants may have transient effects on brood development, the residues do not overtly affect hive viability of either the honeybee or the bumblebee. Field studies in which typical application methods of spinosad were used on a variety of crops have demonstrated that spinosad has low risk to adult honeybees and has little or no effect on hive activity and brood development. The collective evidence from these studies indicates that once spinosad residues have dried on plant foliage, generally 3 hr or less, the risk of spinosad to honeybees is negligible.

Insecticide Resistance Action Committee (IRAC)

Gary D. Thompson and Bob Dutton from Dow AgroSciences at Indianapolis, IN and Abington, U.K. respectively, give a 2003 update on the activities on a committee which seeks to provide a coordinated crop protection industry response to prevent or delay the development of resistance in insect and mite pests.