Efficacy of Phosphine Gas Against the Darkling Beetle (Alphitobius diaperinus)

Background: The darkling beetle, Alphitobius diaperinus is the most commonly beetle found in poultry sheds and causes economic and sanitary impact in the poultry industry. The life cycle of the mealworm can vary from one to three months depending on environmental conditions, and adults can survive for up to one year. The insect lives in the poultry litter where it eats feed and organic waste. The temperature in the poultry house and the accumulation of feed and organic matter promote ideal conditions for beetle infestation. The consumption of beetles affects feed conversion in poultry, especially in the first days of life and it is often cited as a vector of viral, bacterial and parasitic pathogens. The control of its populations is generally achieved by insecticide application on the walls and floor, but resistant populations of beetles are often reported. Phosphine gas is used as a fumigant to control insects in stored grain. In this study the efficacy of phosphine gas against this beetle was evaluated. Materials, Methods & Results: Two experiments were conducted: one in vitro trial, and a trial simulating field conditions. The in vitro trial aimed to evaluate the exposure time required (ETR) to obtain 100% insect mortality, in the presence and absence of wood shavings. Adults and larvae were tested separately. In treatment T1, 100 adult beetles were placed in a petri dish without poultry litter; treatment T2, had 100 adult beetles per plate and filled with sterilized poultry litter. Treatments T3 andT4 had 100 A. diaperinus larvae per plate, in absence and presence of poultry litter, respectively. Three repetitions were performed for each treatment. Insect mortality in plates was monitored at 5 min intervals. The absence of beetle movements after shaking the plate was considered an indicator of insect mortality. The field evaluation was carried out in a poultry house with litter infested with A. diaperinus. [...](AU)

Efficacy of Phosphine Gas Against the Darkling Beetle (Alphitobius diaperinus)

Background: The darkling beetle, Alphitobius diaperinus is the most commonly beetle found in poultry sheds and causes economic and sanitary impact in the poultry industry. The life cycle of the mealworm can vary from one to three months depending on environmental conditions, and adults can survive for up to one year. The insect lives in the poultry litter where it eats feed and organic waste. The temperature in the poultry house and the accumulation of feed and organic matter promote ideal conditions for beetle infestation. The consumption of beetles affects feed conversion in poultry, especially in the first days of life and it is often cited as a vector of viral, bacterial and parasitic pathogens. The control of its populations is generally achieved by insecticide application on the walls and floor, but resistant populations of beetles are often reported. Phosphine gas is used as a fumigant to control insects in stored grain. In this study the efficacy of phosphine gas against this beetle was evaluated. Materials, Methods & Results: Two experiments were conducted: one in vitro trial, and a trial simulating field conditions. The in vitro trial aimed to evaluate the exposure time required (ETR) to obtain 100% insect mortality, in the presence and absence of wood shavings. Adults and larvae were tested separately. In treatment T1, 100 adult beetles were placed in a petri dish without poultry litter; treatment T2, had 100 adult beetles per plate and filled with sterilized poultry litter. Treatments T3 andT4 had 100 A. diaperinus larvae per plate, in absence and presence of poultry litter, respectively. Three repetitions were performed for each treatment. Insect mortality in plates was monitored at 5 min intervals. The absence of beetle movements after shaking the plate was considered an indicator of insect mortality. The field evaluation was carried out in a poultry house with litter infested with A. diaperinus. [...]

Detection and characterisation of strong resistance to phosphine in Brazilian Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae).

As failure to control Rhyzopertha dominica (F.) with phosphine is a common problem in the grain-growing regions of Brazil, a study was undertaken to investigate the frequency, distribution and strength of phosphine resistance in R. dominica in Brazil. Nineteen samples of R. dominica were collected between 1991 and 2003 from central storages where phosphine fumigation had failed to control this species. Insects were cultured without selection until testing in 2005. Each sample was tested for resistance to phosphine on the basis of the response of adults to discriminating concentrations of phosphine (20 and 48 h exposures) and full dose-response assays (48 h exposure). Responses of the Brazilian R. dominica samples were compared with reference susceptible, weak-resistance and strong-resistance strains from Australia in parallel assays. All Brazilian population samples showed resistance to phosphine: five were diagnosed with weak resistance and 14 with strong resistance. Five samples showed levels of resistance similar to the reference strong-resistance strain. A representative highly resistant sample was characterised by exposing mixed-age cultures to a range of constant concentrations of phosphine for various exposure periods. Time to population extinction (TPE) and time to 99.9% suppression of population (LT(99.9)) values of this sample were generally similar to those of the reference strong-resistance strain. For example, at 0.1, 0.5 and 1.0 mg L(-1), LT(99.9) values for BR33 and the reference strong-resistance strain were respectively 21, 6.4 and 3.7 days and 17, 6.2 and 3.8 days. With both strains, doubling phosphine concentrations to 2 mg L(-1) resulted in increased LT(99.9) and TPE. High level and frequency of resistance in all population samples, some of which had been cultured without selection for up to 12 years, suggest little or no fitness deficit associated with phosphine resistance. The present research indicates that widespread phosphine resistance may be developing in Brazil. Fumigation practices should be monitored and resistance management plans implemented to alleviate further resistance development.

Effect of exposure period on degree of dominance of phosphine resistance in adults of Rhyzopertha dominica (Coleoptera: Bostrychidae) and Sitophilus oryzae (Coleoptera: Curculionidae).

Degree of dominance of phosphine resistance was investigated in adults of Rhyzopertha dominica F and Sitophilus oryzae L. Efficacy of the grain fumigant phosphine depends on both concentration and exposure period, which raises the possibility that dominance levels vary with exposure period. New and published data were used to test this possibility in adults of R dominica and S oryzae fumigated for periods of up to 144 h. The concentrations required for control of homozygous resistant and susceptible strains and their F1 hybrids decreased with increasing exposure period. For both species the response lines for the homozygous resistant and susceptible strains and their F1 hybrids were parallel. Therefore, neither dominance level nor resistance factor was affected by exposure period. Resistance was incompletely recessive and the level of dominance, calculated at 50% mortality level, was -0.59 for R dominica and -0.65 for S oryzae. The resistant R dominica strain was 30.9 times more resistant than the susceptible strain, compared with 8.9 times for the resistant S oryzae strain. The results suggest that developing discriminating doses for detecting heterozygote adults of either species will be difficult.

The response of phosphine-resistant lesser grain borer Rhyzopertha dominica and rice weevil Sitophilus oryzae in mixed-age cultures to varying concentrations of phosphine.

The response of Rhyzopertha dominica and Sitophilus oryzae (both phosphine-resistant) in mixed-age cultures to phosphine at fixed concentration-time products (CT) of 10,500 to 168,000 microliters litre 1 h (ppm h) with either constant, rising or falling concentrations for 7 days was studied at 27 (+/- 2) degrees C. At lower CT products, rising concentrations of phosphine led to significantly fewer survivors of R dominica and S oryzae. Conversely, exposure to falling concentrations of phosphine resulted in significantly more survivors. The influence of changing concentrations of phosphine was more pronounced in S oryzae than in R dominica. In the latter, at the lower CT products of 21,000 and 42,000 microliters-1 h, the adult stage proved to be most tolerant, contrary to the accepted belief that the egg or pupal stage are always more tolerant to phosphine. The results indicate that application of phosphine in rising concentrations is more effective than in constant or falling concentrations.