Robert G. Orth

Fitness Cost of Resistance to Bt Cotton Linked with Increased Gossypol Content in Pink Bollworm Larvae

Fitness costs of resistance to Bacillus thuringiensis (Bt) crops occur in the absence of Bt toxins, when individuals with resistance alleles are less fit than individuals without resistance alleles. As costs of Bt resistance are common, refuges of non-Bt host plants can delay resistance not only by providing susceptible individuals to mate with resistant individuals, but also by selecting against resistance. Because costs typically vary across host plants, refuges with host plants that magnify costs or make them less recessive could enhance resistance management. Limited understanding of the physiological mechanisms causing fitness costs, however, hampers attempts to increase costs. In several major cotton pests including pink bollworm (Pectinophora gossypiella), resistance to Cry1Ac cotton is associated with mutations altering cadherin proteins that bind this toxin in susceptible larvae. Here we report that the concentration of gossypol, a cotton defensive chemical, was higher in pink bollworm larvae with cadherin resistance alleles than in larvae lacking such alleles. Adding gossypol to the larval diet decreased larval weight and survival, and increased the fitness cost affecting larval growth, but not survival. Across cadherin genotypes, the cost affecting larval growth increased as the gossypol concentration of larvae increased. These results suggest that increased accumulation of plant defensive chemicals may contribute to fitness costs associated with resistance to Bt toxins.

Relative distribution of 2,3,7,8-tetrachlorodibenzo-p-dioxin human hepatic and adipose tissues

Paired human hepatic and adipose tissues from 26 people were assayed for 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). On a whole tissue weight basis, TCDD concentration in the liver was about one-tenth that in the adipose tissue. When expressed in total tissue lipid basis, the TCDD concentrations in the liver and adipose tissue were about equal. At low levels of exposure, presumably below those necessary to cause hepatic enzyme induction, TCDD appeared to be partitioning into the human liver predominantly on the basis of its lipid solubility in that tissue store. The partitioning behavior of TCDD in the livers of humans exposed to higher levels of TCDD is currently unclear.

Synergistic interactions between Cry1Ac and natural cotton defenses limit survival of Cry1Ac-resistant Helicoverpa zea (Lepidoptera: Noctuidae) on Bt cotton.

Larvae of the bollworm Helicoverpa zea (Boddie) show some tolerance to Bacillus thuringiensis (Bt) Cry1Ac, and can survive on Cry1Ac-expressing Bt cotton, which should increase resistance development concerns. However, field-evolved resistance has not yet been observed. In a previous study, a population of H. zea was selected for stable resistance to Cry1Ac toxin. In the present study, we determined in laboratory bioassays if larvae of the Cry1Ac toxin-resistant H. zea population show higher survival rates on field-cultivated Bt cotton squares (= flower buds) collected prebloom—bloom than susceptible H. zea. Our results show that Cry1Ac toxin-resistant H. zea cannot complete larval development on Cry1Ac-expressing Bt cotton, despite being more than 150-fold resistant to Cry1Ac toxin and able to survive until pupation on Cry1Ac toxin concentrations greater than present in Bt cotton squares. Since mortality observed for Cry1Ac-resistant H. zea on Bt cotton was higher than expected, we investigated whether Cry1Ac interacts with gossypol and or other compounds offered with cotton powder in artificial diet. Diet incorporation bioassays were conducted with Cry1Ac toxin alone, and with gossypol and 4% cotton powder in the presence and absence of Cry1Ac. Cry1Ac toxin was significantly more lethal to susceptible H. zea than to resistant H. zea, but no difference in susceptibility to gossypol was observed between strains. However, combinations of Cry1Ac with gossypol or cotton powder were synergistic against resistant, but not against susceptible H. zea. Gossypol concentrations in individual larvae showed no significant differences between insect strains, or between larvae fed gossypol alone vs. those fed gossypol plus Cry1Ac. These results may help explain the inability of Cry1Ac-resistant H. zea to complete development on Bt cotton, and the absence of field-evolved resistance to Bt cotton by this pest.

Measurement of the photoinduced loss of vapor phase TCDD

Abstract The photoloss of vapor 2,3,7,8-TCDD was observed to occur in the UV region of the light spectrum from 250 nm to 340 nm with an average quantum yield of 0.033-0.046.

Dibenzofuran in diphenyl oxide and the relationship to brominated dibenzofurans in brominated diphenyl oxide

Abstract A method was developed for the ppb level analysis of dibenzofuran (DBF) in diphenyl oxide (DPO). Complimentary analytical techniques for the analysis of polybrominated dibenzofurans (PBDFs) in polybrominated diphenyl oxides (PBDPOs) were also developed. The PBDFs in PBDPOs were found to be related to the presence of DBF in the original DPO.

An evaluation of the molecular structure of octachlorodibenzofuran

Abstract Several properties of halogenated dibenzofurans indicated unusual behavior when the 1 and 9-positions were halogenated. This behavior was thought to be due to steric crowding causing the molecule to twist out of planarity to relieve the crowding. In a more definitive study, the molecular structure of octachlorodibenzofuran was determined by x-ray diffraction and was found to be planar with crowding of all chlorines, particularly those at the 1 and 2-positions rather than the expected 1 and 9-positions.

Thiol protected platinum black and palladium black catalysts in oxidation catalysis

Platinum and palladium metals are common catalysts for formic acid wet oxidation, exhibiting high activity and good stability. However, in the presence of some reactive organic substances, even in low concentrations, they suffer severe deactivation. This paper demonstrates the feasibility of protecting metal catalysts from aggressive media by creating a tertiary structure over the active sites. The approach is based on the known principle of metal surface modification by self-assembled organic monolayer films. We have found that self-assembled monolayers (SAMs) fabricated from heterocyclic thiols containing nitrogen, e.g., 6-mercaptopurine (6MP), can protect platinum and palladium black catalysts for formic acid oxidation in the presence of iminobis[methylenephosphonic acid] (IDMPA). IDMPA was chosen as a model inhibitor because it displays strong chelating properties. Catalysts protected with 6MP demonstrate higher activity and stability and have significantly lower metal leaching (up to 15 times in case of palladium black) than their unprotected counterparts. The surface structure of the catalysts and their surface composition were characterized using X-ray photoelectron spectroscopy (XPS) and Scanning Tunneling Microscopy (STM).

Methodology for the analysis of 2,3,7,8-tetrachlorodibenzo-p-dioxin in feces

Abstract A methodology for the analysis of 2378-TCDD in feces is presented. This method involves complete digestion of lyophilized feces, extraction and cleanup by routine column chromatography. Analysis is performed by high resolution GC/MS to detect 2378-TCDD concentrations in the sub part-per-trillion range. Successful analysis allows for the estimation of the adipose 2378-TCDD concentration as well as an estimation of dosage.