The dominance of Coleoptera in poultry house litter could be explained by several factors, such as the climatic conditions of the environment, their reproductive cycle, and the availability of nutrients in the litter. These results corroborate those obtained by Yao in Côte d'Ivoire, where Coleoptera were the most abundant order in manure with an automatic watering system (Yao et al., 2022). The high abundance of the Coleoptera Alphitobius diaperinus in the litter insect population suggests that these litters constitute favourable biotopes for this species, due to the availability of food debris, water, their reproductive system, and the atmospheric conditions conducive to their multiplication. Several authors have also shown that many Coleoptera species are associated with poultry farms, and that Alphitobius diaperinus is often the dominant species (Rowland et al. 2007; Johnson et al. 2018).
This Coleoptera is a very common polyphagous species in poultry litters, present in many countries. It can have a detrimental effect by destroying poultry structures (Rowland et al. 2007). Furthermore, it has been identified as a vector for the transmission of avian pathologies such as Newcastle disease, Gumboro disease, and Marek's disease (Johnson et al. 2018). The strong correlation between the presence of Alphitobius diaperinus in the litter and poultry mortality observed in Bingerville corroborates these findings.
Many studies have also reported a high relative frequency of Alphitobius diaperinus in poultry houses, up to 93.33% (Sanver and Tezcan, 2016) and 96.63% (Johnson et al., 2018), which is consistent with the observations of this study.
Several factors can explain the massive presence of Alphitobius diaperinus in poultry farms in southern Togo, mainly related to the age of the litter and buildings. Its high density in the alignment zones of the feeders and drinkers, as well as the presence of crushed cereals served to the poultry, could also favour. Furthermore, the presence of overflowing water from the troughs and moistening the litter provides a suitable environment for the development of this insect. In this study, other insect species were also counted in the litter, including Periplaneta americana, Periplaneta fuliginosa, Blatella germanica, Folicula decipiens, Chelifer cancroides, Attagenus pellio, and Pseudomyrmex gracilis, which did not appear in the studies of (Sanver and Tezcan, 2016 ; Johnson et al., 2018). This implies that there is a diversity of fauna in the litter of poultry houses. Studies have reported that the production system and agricultural practices influence the development and composition of the arthropod community in livestock buildings (Roy et al., 2017).
Our findinds differ from those reported by Aak and Ottesen in southern Norway, where the species Carcinops pumilio was the most abundant (Aak and Ottesen, 2002). This same species was observed in abundance, with a relative frequency of 64.09%, in a study on automatic manure irrigation in poultry houses in Côte d'Ivoire (Yao et al., 2022). This difference could be explained by factors such as humidity and freshness, which would justify the abundance of the species Carcinops pumilio in relation to the species Alphitobius diaperinus and vice versa.
The average number and average density per square metre of Alphytobius diaperinus, found are slightly higher than those respectively obtained (211.08 ± 44.97 n = 90 and 107.21 ± 45.12) by (Johnson et al. 2018). This difference could be related to the reproductive activity of the insects and their consumption by birds, which could lead to their death through the transmission of various pathogens.
The abundance of insects of the order Diptera, particularly Musca domestica and Calliphora vicina, around and inside the buildings could be explained by their attraction to the odours released by these poultry houses, as well as their search for food debris and watering. Calliphora vicina, Sarcophaga carnaria and Lucilia sericata have been described as facultative myiasis agents in birds (Bermudez et al., 2007; Dik and Kandir, 2021). From a medical and veterinary point of view, Lucilia sericata is reported as a primary and facultative myiasis agent, mainly in sheep, but also in other wild and domestic animals, as well as in humans (Hall and Wall, 1995). Forty-six (46) cases of myiasis have been confirmed in birds, in the oral cavity, the eyes, the cloaca and the phallus, caused by Lucilia sericata. Chrysomya albiceps and Chrysomya megacephala are disease vectors and are responsible for myiasis (Verves, 2007). Finally, blood-sucking species such as Culex pipiens, Culiseta longiareolata and Stomoxys calcitrans are considered a nuisance source by transmitting pathogens to humans (Baldacchino et al., 2013).
Poultry farmers could be victims of these pathogens given that they are in permanent contact with the poultry transported by these insects. Livestock buildings constitute a privileged area for these insects due to the favourable climatic conditions such as humidity and temperature. The high number of Diptera compared to other insects demonstrates their significant presence in the dwellings, particularly around the poultry buildings. Some authors have shown that Diptera such as Culicinae (mosquitoes) and Simulidae (black flies) are vectors transmitting haemoparasites to chickens (Kaufmann, 1996). (Rodhain (2015) reported that some biting flies are important vectors of human and animal diseases worldwide and can transmit them mechanically and/or biologically through their bites.
The elevated number of insects under the drinkers and feeders is linked to the increase in humidity, which favours their hatching and development. Humidity is a determining factor for the reproduction and survival of these insects. The longer the litter renewal, the higher the prevalence of Alphitobius diaperinus (poultry darkling beetle) in the feeding and watering areas. This abundance could be explained by their search for food and water for their survival, and the decomposition of the litter creates favourable microclimates for these insects.
These results corroborate those obtained by (Johnson et al., 2018) who reported that the age of the litter influences the proliferation of Alphitobius diaperinus and its predilection for the poultry feeding areas. The proliferation of this insect is facilitated by the presence of water overflowing from the drinkers and the humidity of the litter, providing it with a suitable vital environment. (Sauvage, 1993) observed that excessive drying of the litter, due to the use of nipples in farms, causes nocturnal attacks of Alphitobius diaperinus on poultry due to the lack of water, thus confirming the role of humidity in the survival and proliferation of these insects. Gupta reported that the humidity of the litter favours the presence of moulds, algae and heterotrophic bacteria (Gupta et al., 2004).
In summary, laying hen houses host a diversity of insects, with humidity and long litter renewal time being the main factors responsible for their proliferation and development. Some of these insects can threaten the life of laying hens and undermine the development of poultry farming.