RESUMO
Stored product beetles that are resistant to the fumigant pesticide phosphine (hydrogen phosphide) gas have been reported for more than 40 years in many places worldwide. Traditionally, determination of phosphine resistance in stored product beetles is based on a discriminating dose bioassay that can take up to two weeks to evaluate. We developed a diagnostic cleaved amplified polymorphic sequence method, CAPS, to detect individuals with alleles for strong resistance to phosphine in populations of the red flour beetle, Tribolium castaneum, and the lesser grain borer, Rhyzopertha dominica, according to a single nucleotide mutation in the dihydrolipoamide dehydrogenase (DLD) gene. We initially isolated and sequenced the DLD genes from susceptible and strongly resistant populations of both species. The corresponding amino acid sequences were then deduced. A single amino acid mutation in DLD in populations of T. castaneum and R. dominica with strong resistance was identified as P45S in T. castaneum and P49S in R. dominica, both collected from northern Oklahoma, USA. PCR products containing these mutations were digested by the restriction enzymes MboI and BstNI, which revealed presence or absence, respectively of the resistant (R) allele and allowed inference of genotypes with that allele. Seven populations of T. castaneum from Kansas were subjected to discriminating dose bioassays for the weak and strong resistance phenotypes. Application of CAPS to these seven populations confirmed the R allele was in high frequency in the strongly resistant populations, and was absent or at a lower frequency in populations with weak resistance, which suggests that these populations with a low frequency of the R allele have the potential for selection of the strong resistance phenotype. CAPS markers for strong phosphine resistance will help to detect and confirm resistant beetles and can facilitate resistance management actions against a given pest population.
Assuntos
Besouros/efeitos dos fármacos , Marcadores Genéticos , Resistência a Inseticidas/genética , Fosfinas/farmacologia , Tribolium/efeitos dos fármacos , Alelos , Sequência de Aminoácidos , Animais , Besouros/genética , DNA Complementar , Genótipo , Dados de Sequência Molecular , Homologia de Sequência de Aminoácidos , Tribolium/genética , Estados UnidosRESUMO
In laboratory experiments, a flameless catalytic infrared emitter, fueled by propane, was used to disinfest hard red winter wheat, Triticum aestivum L., containing different life stages of the lesser grain borer, Rhyzopertha dominica (F.), an economically important insect species associated with stored wheat in Kansas. The emitter generates infrared radiation in the 3-7-microm range. The life stages of R. dominica exposed to infrared radiation included eggs, larvae in different stages of development, pupae, and 2-wk-old adults. A noncontact infrared thermometer measured grain temperatures continuously during exposures of infested wheat to infrared radiation. The grain temperatures attained were influenced by wheat quantity; distance from the emitter; and exposure time, which in turn influenced effectiveness against various life stages of H. dominica. In general, higher grain temperatures were attained in 113.5 g of wheat as opposed to 227.0 g, and at 8.0 cm from the emitter surface rather than at 12.7 cm, and during a 60-s exposure compared with a 45-s exposure. Logistic regression indicated the probability of death of various life stages of R. dominica was temperature dependent. The log odds ratios showed old larvae were less susceptible to infrared radiation than young larvae. Approximately > or = 94% mortality of all R. dominica life stages occurred when using 113.5 g of wheat, exposed for 60 s at a distance of 8.0 cm from the emitter, resulting in mean +/- SE wheat temperatures that ranged between 107.6 +/- 1.4 and 113.5 +/- 0.5 degrees C. Our results with small grain quantities show flameless catalytic infrared technology to be a promising tool for disinfestation of stored wheat.
Assuntos
Besouros/fisiologia , Raios Infravermelhos , Controle de Insetos/métodos , Animais , Contaminação de Alimentos , Estágios do Ciclo de Vida , Sementes , Triticum/parasitologiaRESUMO
A series of tests was conducted to characterize differences in the mortality of the lesser grain borer, Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae), and rice weevil, Sitophilus oryzae (L.) (Coleoptera: Curculionidae), exposed to three commodities treated with a liquid and dry spinosad formulation. In laboratory bioassays, adults of the two insect species were exposed to untreated wheat, Triticum aestivum L., corn, Zea mays L., and sorghum, Sorghum bicolor (L.) Moench., and to commodities treated with 1 mg (AI)/kg of liquid and dry spinosad formulations. Mortality was assessed from independent samples examined at specific time intervals to determine immediate mortality and after 24 h of recovery on untreated grain at 28 degrees C and 65% RH to determine delayed mortality. Comparison of the time required for 50% (LT50) and 95% (LT95) mortality indicated that R. dominica adults were consistently and significantly more susceptible (died quickly) than S. oryzae adults when exposed to spinosad-treated commodities. In general, the toxicity of liquid and dry spinosad formulations was similar against R. dominica or S. oryzae. The toxicity of spinosad to each species varied slightly among the three commodities, and there were no consistent trends to suggest that spinosad was more effective on one commodity versus another. LT50 values based on immediate mortality for R. dominica on all commodities ranged from 0.45 to 0.74 d; corresponding values based on delayed mortality ranged from 0.04 to 0.23 d, suggesting delayed toxic action of spinosad in R. dominica. LT50 values based on immediate and delayed mortality for S. oryzae on all three commodities treated with the two spinosad formulations were essentially similar and ranged from 2.75 to 4.56 d. LT95 values for R. dominica based on immediate mortality on spinosad-treated commodities ranged from 1.75 to 3.36 d, and those based on delayed mortality ranged from 0.49 to 1.88 d. There were no significant differences in LT95 values based on immediate and delayed mortality for S. oryzae on spinosad-treated commodities, and the LT95 values ranged from 7.62 to 18.87 d. The toxicity of spinosad was enhanced during a 24-h holding period after removal from spinosad-treated commodities only against R. dominica adults, and possible reasons for increased postexposure mortality of R. dominica adults after brief exposures to spinosad warrant further study.