The Housefly, Musca domestica is a cosmopolitan vector belong to order Diptera and family Muscidae. It creates lot of difficulties where poor sanitation exists (Khan et al. 2013). Houseflies have been known to transmit serious diseases such as anthrax, ophthalmia, typhoid fever, tuberculosis, cholera and infantile diarrhea from human-animal and vice versa (Akter et al. 2020). According to BMC Public Health, over 130 pathogens were isolated from body surface of houseflies, predominantly bacteria were identified (Khamesipour et al. 2018). This emphasizes the importance of the housefly as vector of pathogenic diseases. The habitat of M. domestica favors it to carry, disseminate human and animal pathogens such as helminth parasites, protozoan cysts, viruses and bacteria. Notably, poultry farm house provides best habitat for production of M. domestica due to high temperature and humidity (Macovei et al. 2008).
Housefly population can be managed by three methods such as cultural, biological and chemical method (Kumar et al. 2011). Amongst, chemical insecticides would effectively control houseflies. However, the insects detoxify insecticide by hydrolysis of molecules at different sites. This metabolism makes mechanism for insect resistance against insecticides (Wang et al. 2018). On the other hand, many producers now tend to avoid treating larval habitat with broad spectrum of pesticides because of its ill effects on non-target beneficial arthropods (Manzoor et al. 2021). Therefore, there is a requirement of alternative method for insect control (Tarelli et al. 2009). There are several non-chemical approaches such as botanicals, fungi, bacteria and nematodes are in practice. Researchers strived to develop new environment friendly chemicals as well as better fly pest control agents (Quesada et al. 2008). Among living organisms, fungi and bacteria are able to produce secondary metabolites with potential biological activities (Kornienko et al. 2015). These metabolites belong to all different classes of natural compounds such as terpenes, phenylpropanoids, polyketides and alkaloids (Dewick 2009). Different types of microbes, EPF evolved highly specialised mechanisms to produce secondary metabolites and enzymes with immunosuppressive or toxic functions that helps in invasion of insect host by overcoming cellular and humoral defence systems (Rohlfs and Churchill 2011). Recently, in 2018 the first insecticide, Inscalis®, based on fungal metabolite was approved in which PPA (pyripyropene A) as a key component of Inscalis® insecticide (Jeschke 2021). The known mycotoxins produced by entomopathogenic fungi include beauvericins, bassianolides, destruxins, oosporein, oxalic acid and tenellin (Xu et al. 2008). Amongst, beauvericins has more advantages as it is known to provide good insect control efficacy even if low amount of spores were used, bassianolides induce anatomical defects in insects, destruxins inhibit the insect defence system, oosporein and tenellin are known to inhibit ATP’s activity of erythrocyte membrane (Boucias and Pendland, 1991; Leland et al. 2005). The most important insect infecting fungi are Metarhizium, Hirsutella, Beauveria, Lecanicillium, Aspergillus, Paecilomyces, Tolypocladium (Huang et al. 2010).
The innate immune system of insects is divided into humoral and cellular defence responses. In which later refers to haemocyte-mediated responses like phagocytosis and encapsulation. Circulating hemocyte population undergoes a rapid change in response to the entry of foreign substances (Dun 1986). Dodecanol, a metabolite of entomopathogenic fungus Conidiobolus coronatus shown negative response on cellular immunity of Galleria mellonella and Calliphora vicina (Kazek et al. 2021). During the infection process, the fungi produce secondary metabolites which paralyse and disrupt the host’s physiological processes mainly its immune responses (Donzelli and Krasnoff 2016). This emphasizes the importance of fungal secondary metabolites in infecting insect host.
Hence, the present study was aimed to study the immunotoxicity of secondary metabolites from novel entomopathogenic fungi isolated from natural source against housefly M. domestica.