Diet Incorporation Assay Research Articles

Dehydrothalebanin: a source of resistance from Glycosmis pentaphylla against the citrus root weevil Diaprepes abbreviatus.

Roots of a citrus relative, Glycosmis pentaphylla (orangeberry), were shown to inhibit the growth and survival of larvae of the citrus root weevil Diaprepes abbreviatus. Roots of G. pentaphyllaincorporated into the diet of D. abbreviatus increasingly inhibited the growth of neonate larvae with increased concentration of roots, while roots from citrus rootstocks produced little inhibition. The diet-incorporation assay was used to guide fractionation of an active acetone extract of G.pentaphylla roots. Three major fractions from silica open-column liquid chromatography were active, and these were purified using semipreparative normal-phase HPLC. A single active HPLC subfraction was isolated from each of the three liquid chromatography fractions, and two active compounds were isolated and identified by GC-MSD. GC-MSD and NMR identified one compound as the amide dehydrothalebanin B, and the other was identified by GC-MSD as dieldrin, a chlorinated hydrocarbon insecticide whose origin in our samples is uncertain.

The African yam bean seed lectin affects the development of the cowpea weevil but does not affect the development of larvae of the legume pod borer

Artificial feeding assays were used to study the effect of purified galactose-specific lectins from African yam beans ( Sphenostylis stenocarpa) on development of larvae of the cowpea weevil, Callosobruchus maculatus (Coleoptera: Bruchidae) and the legume pod-borer, Maruca vitrata (Lepidoptera: Pyralidae). Inhibition of development of C. maculatus was observed when larvae were fed on artificial cowpea seeds containing 0.2%, 2.0% and 5.0% (wt/wt) of dietary lectin. Larval mortality was between 30% and 88%, while delays in total developmental time ranged between 7 and 13 days. The lectin had no effect on development of larvae of M. vitrata, when tested through topical artificial diet incorporation assays, except at the extremely high dose of 35% dietary level.

Relative Activity of Commercial Formulations of Bacillus thuringiensis Against Selected Noctuid Larvae (Lepidoptera: Noctuidae)

Diet incorporation and spray chamber assays compared the activity of three commercial formulations of Bacillus thuringiensis Berliner against Heliothis virescens (F.), Helicoverpa zea (Boddie), Pseudoplusia includens (Walker), and Spodoptera exigua (Hübner). The commercial products evaluated were Condor OF® (Ecogen Inc., Langhorne, PA), Dipel ES® (Abbott Laboratories, North Chicago, IL), and Javelin WG® (Sandoz Crop Protection Corp., Des Plaines, IL). Variation in results of the diet incorporation studies illustrated the importance of including a standard reference formulation in the design of the studies and suggested that some standardization of insect strains used in such assays may be important also. Overall results of the diet incorporation studies were similar to those obtained in the spray chamber studies where insects were assayed on sprayed cotton and soybean. Dose-mortality regressions were developed for each B. thuringiensis formulation applied against each insect species on cotton and soybean over a 28-day observation period. These regressions may be helpful in the development of recommendations for the use of B. thuringiensis on cotton and soybean. They may also have value in establishing base-line levels of susceptibility for future resistance monitoring efforts. Median lethal concentrations (LC50s) tended to be slightly higher on cotton than on soybean. The most susceptible insect species was H. virescens, and the least susceptible was S. exigua. LC50s for H. zea and P. includens were similar and intermediate between those of H. virescens and S. exigua. Javelin WG tended to exhibit the highest activity per unit weight of commercial product, but the relative differences among the commercial formulations were influenced by insect species.

Population Growth of Dermatophagoides farinae Hughes (Acari: Epidermoptidae) Suppressed by Methoprene and Hydroprene

Insect growth regulators are synthetic chemicals that mimic the function of hormones that occur naturally in arthropods. Two such insect growth regulators, methoprene and hydroprene, were tested to determine effects on growth of laboratory populations of the American house dust mite, Dermatophagoides farinae Hughes. Adults and immature mites were treated with four concentrations of each chemical in contact and diet-incorporation bioassays. Data were collected after 30 and 90 d of exposure to the treatments. Both compounds significantly suppressed population growth when compared with acetone controls at concentrations of > or = 5%. Methoprene was more effective than hydroprene in diet-incorporation bioassays and was slightly more effective for the first 30 d of the contact assays. A second set of contact and diet-incorporation assays was done using one concentration (7.5%) of methoprene and hydroprene to determine the effect of these compounds on population dynamics of D. farinae. In this experiment, population numbers were evaluated at weekly intervals for 13 wk. The average number of mites in the untreated control population increased by more than 10 times the original inoculum during the experiment while the number of mites in the treated containers did not increase significantly. This trend was similar for both contact and diet-incorporation bioassays although the average number of mites per container was significantly higher when the treatments were incorporated in the house dust mite diet than when applied directly to the substrate.

Comparative toxicity of the HD-1 and NRD-12 strains of Bacillus thuringiensis subsp. kurstaki to defoliating forest Lepidoptera

Insecticidal activities of sporulated cultures of the HD-1 and NRD-12 strains of Bacillus thuringiensis subsp. kurstaki were compared against four species of defoliating forest lepidopterans in diet-incorporation assays. There was no difference in LC 50 between the two strains to larvae of spruce budworm ( Choristoneura fumiferana), gypsy moth ( Lymantria dispar), eastern hemlock looper ( Lambdina fiscellaria fiscellaria), and whitemarked tussock moth ( Orgyia leucostigma), whether expressed as total alkaline soluble protein, activated toxin protein, or International Units as determined by bioassay against Trichoplusia ni. Both strains were consistently more toxic than HD-1-S-1980 when compared on the basis of alkali-soluble protein, but not on the basis of activated toxin or International Units. Hybridization of genomic DNA after restriction with HindIII revealed the presence of all three cryIA toxin genes in each of the isolates used in this study, including HD-1-S-1980, which was previously reported to have lost the cryIA(b) gene.