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 and T4 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. The evaluation was made in areas of 1 m2 where 2 gm-3 of aluminum phosphide was applied, according to manufactures recommendation. The area of product application was covered with a plastic cover to seal the litter. Under in vitro conditions the ETR for total mortality of insects in plates with presence of litter was 15 min for larvae and 20 min for adults. In plates without poultry litter the ETR for A. diaperinus mortality was 25 and 35 min, for larvae and adults, respectively. It was observed that the presence of poultry litter in the plates reduced the volume and so increased the phosphine gas concentration, causing more rapid inset death. The mortality of adults and larvae insects occurred approximately 30 s after the exposure to the product. All the insects exposed to the phosphine gas died, resistant insects were not observed. In the field test the ETR to obtain 100% of mortality was 90 min for larvae and adults. Discussion: The phosphine gas showed good potential to be used in strategic control of A. diaperinus. The product was effective in the killing adults and larvae beetles on in vitro and in field trials. However, more studies are needed to establish the issues related to safe use of PH3 in poultry facilities.