Alphitobius diaperinus is often referred to as the darkling beetle, with the larvae known as the lesser mealworm. The species is believed to have originated in the tropical east Africa region. It occurs naturally in bird and bat nests, where it feeds on droppings and animal parts such as feathers and carcasses (Lambkin, 2011). It is a common insect pest of meat chicken sheds, where it is mostly found in the litter. This is an ideal environment for this tropical species because the environment is warm and humid. Compacted earth floors provide a haven for the larvae after clean-out (Poultry Hub, 2020).
Compacted earth floors of meat chicken sheds provide an ideal haven for lesser mealworms between growth cycles.
The life cycle of the darkling beetle depends on a variety of environmental factors but is usually 40–100 days. Fifteen days after initial mating, females can lay 200–400 eggs every 1–5 days, with eggs taking less than one week to hatch as larvae. This means populations can increase rapidly without effective control (The Poultry Site, 2020).
All stages of the pest can act either as reservoirs or external carriers for serious avian/poultry diseases, including leucosis, Marek’s disease, infectious bursal disease, reovirus, enterovirus, fowl pox, Newcastle disease and infectious laryngotracheitis. The pest can also act as an intermediate host for tapeworms and protozoans (Lambkin, 2011; Poultry Hub, 2020). It can cause serious economic losses in the chicken meat industry because it not only acts as a reservoir for the above avian diseases and parasites, it also destroys compacted earth floors and insulation materials within sheds. The pest is also known to transmit food-borne diseases and pathogens such as rotavirus, Escherichia coli and Salmonella enterica (serovar typhimurium), and has been implicated in the transmission of Campylobacter spp. (Lambkin, 2011).
Economic loss can occur through the pest consuming chicken feed, and when chickens feed on lesser mealworms in preference to provided feed. In this instance, the chickens’ optimal nutritional requirements are compromised. In addition, if chickens feed on beetle larvae directly, it increases the likelihood of them ingesting disease organisms or parasites. (Poultry Hub, 2020). They will also reduce feed conversion rates by physically irritating chickens and generating skin lesions that could lead to downgrades at the processing plant.
Darkling beetles tunnel into the compacted earth floors of sheds, which reduces the effectiveness of cleanout (particularly if they tunnel under feed lines). They also tunnel into insulation, reducing its insulating value. This tunnelling behaviour causes the compacted earth floors to become perforated and hollowed. These hollows then retain spent litter at clean-out out time (Poultry Hub, 2020), reducing the effectiveness of clean-out and sanitisation.
The application of residual insecticides onto the floors and lower walls of sheds is the standard management method used in Australia. Three insecticides are mostly used: Fenitrothion (since the 1970s), Cyfluthrin (since about 1995), and Spinosad (registered for use in meat chicken sheds in early 2007) (Lambkin, 2001). Further work by this researcher revealed that the darkling beetle has become widespread and has developed high levels of resistance to fenitrothion and cyfluthrin in eastern Australia. He concluded that, because of the inadequacies of long-standing control practices and the prevalence of insecticide resistance, novel agents for their management are required. This has led to new and seemingly effective treatments that are formulated from Australian native essential oils.
Control of darkling beetle can be difficult as no acceptable field control strategies have been developed, and there has been little long-term success in controlling them. Research in Australia has shown that the current standard industry insecticide is not effective when applied to meat chicken shed floors. This situation is exacerbated by strong and widespread insecticide resistance that occurs in meat chicken shed beetle populations (Poultry Hub, 2020). McGahan et al. (2014) reported that litter beetles are likely to cause increased problems when multi-use litter practices are used. Thus, good pasteurisation of multi-use litter is required to reduce populations between growth cycles. As with many pests, an integrated pest management approach is likely to be the most effective strategy. This would include effective insecticide application, pasteurisation of litter before reuse, total clean-out, or a combination of these.
Control of darkling beetles can be difficult, as no ‘magic bullet’ has been developed to fully control them.
