Thomas Meade

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.

Discovery and Characterization of Sulfoxaflor, a Novel Insecticide Targeting Sap-Feeding Pests

The discovery of sulfoxaflor [N-[methyloxido[1-[6-(trifluoromethyl)-3-pyridinyl]ethyl]-λ(4)-sulfanylidene] cyanamide] resulted from an investigation of the sulfoximine functional group as a novel bioactive scaffold for insecticidal activity and a subsequent extensive structure-activity relationship study. Sulfoxaflor, the first product from this new class (the sulfoximines) of insect control agents, exhibits broad-spectrum efficacy against many sap-feeding insect pests, including aphids, whiteflies, hoppers, and Lygus, with levels of activity that are comparable to those of other classes of insecticides targeting sap-feeding insects, including the neonicotinoids. However, no cross-resistance has been observed between sulfoxaflor and neonicotinoids such as imidacloprid, apparently the result of differences in susceptibility to oxidative metabolism. Available data are consistent with sulfoxaflor acting via the insect nicotinic receptor in a complex manner. These observations reflect the unique structure of the sulfoximines compared with neonicotinoids.

Insect resistance conferred by 283-kDa Photorhabdus luminescens protein TcdA in Arabidopsis thaliana

The tcdA gene of Photorhabdus luminescens encodes a 283-kDa protein, toxin A, that is highly toxic to a variety of insects, including some agriculturally important pests. We tested the efficacy of transgenic toxin A in Arabidopsis thaliana for control of feeding insects. Plants with toxin A expression above about 700 ng/mg of extractable protein were highly toxic to tobacco hornworm (Manduca sexta). Toxin A isolated from transgenic plants also strongly inhibited growth of the southern corn rootworm (Diabrotica undecimpunctata howardi). Addition of 5′ and 3′ untranslated regions of a tobacco osmotin gene (osm) increased toxin A production 10-fold and recovery of insect-resistant lines 12-fold. In the best line, high toxin A expression and insect resistance were maintained for at least five generations in all progeny. The intact tcdA mRNA represents the largest effective transgenic transcript produced in plants to date. These results may open a new route to transgenic pest control in agriculture.

Binary Insecticidal Crystal Protein from Bacillus thuringiensis, Strain PS149B1: Effects of Individual Protein Components and Mixtures in Laboratory Bioassays

Abstract A family of novel binary insecticidal crystal proteins, with activity against western corn rootworm, Diabrotica virgifera virgifera LeConte, was identified from Bacillus thuringiensis Berliner. A binary insecticidal crystal protein (bICP) from B. thuringiensis strain PS149B1 is composed of a 14-kDa protein (Cry34Ab1) and a 44-kDa protein (Cry35Ab1). These proteins have been co-expressed in transgenic maize plants, Zea mays L., and effectively control western corn rootworm larvae under field conditions. Laboratory experiments were conducted to better understand the contribution of each component protein to the in vivo activity of the bICP. The 14-kDa protein is active alone against southern corn rootworm, Diabrotica undecimpunctata howardi Barber, and was synergized by the 44-kDa protein. In mixtures, the concentration of the 14-kDa protein had a greater impact on efficacy than the 44-kDa component. Although both proteins are clearly required for maximal insecticidal activity, laboratory results did not support the formation of a stable, fixed-ratio complex of the two component proteins.

Discovery and Development of Insect-Resistant Crops Using Genes from Bacillus thuringiensis

Abstract Bacillus thuringiensis (Bt) is a ubiquitous, spore-forming soil bacterium that is well known for production of insecticidal proteins that are active on a wide range of pest insects. The potential of Bt to be used as an insecticide was recognized in the early twentieth century and since that time many Bt-based biopesticides have been commercialized. The advent of modern molecular biology tools made it possible to engineer plants to express the genes coding for Bt insecticidal proteins as a safe, convenient and highly effective means to protect plants from insect damage. The first Bt crop was commercialized in 1995, and today Bt corn, cotton and soybean are cultivated on ca. 76 million hectares in 27 countries. First generation products containing single Bt genes were followed by broader spectrum products containing multiple Bt genes with the most recent generation of products contain multiple Bt genes encoding proteins that target the same pest(s) but with differences in their mechanism of action (i.e. gene pyramids) as a means of increasing product durability. Developing Bt crops is a long and expensive process that by recent estimates averages 13 years at a cost of

A method to control insects resistant to common insecticides

136 million. The process of obtaining approvals by government regulatory agencies is among the most critical in the later stages of the development process and represents ca. 25% of the total cost in bringing a Bt crop to the market. Multiple factors drive the search for novel insect resistance (IR) traits and Bt remains a significant focus of new IR trait discovery.