Pathogen‐mediated modulation of host metabolism and trophic interactions in Spodoptera littoralis larvae

Abstract

The success and sustainability of entomopathogens in insect control depend on their stress potential and ability to modulate certain physiological aspects of their insect hosts. In the present study, newly moulted fourth instars of Spodoptera littoralis (Boisduval) (Lepidoptera: Noctuidae) were incubated for 24 h with the median lethal dose (LD 50) of Steinernema riobrave, Heterorhabditis bacteriophora, or Beauveria bassiana to determine their effects on certain metabolic activities and nutritional physiology compared to those of uninfected (control) larvae. Infection decreased total protein, lipid, and carbohydrate contents. Carbohydrase activity was found to be pathogen and enzyme dependent, with S. riobrave and H. bacteriophora infection increasing amylase, invertase, and trehalase activities. Beauveria bassiana infection decreased amylase and invertase activities but increased that of trehalase. Infection with the three pathogens also enhanced phosphatase activity. All pathogens reduced transaminase activity. Changes in the nutritional indices varied not only with the variation in the candidate entomopathogen and surviving instar but also with the variation in the age of the same instar, with a profound change in late last instars (3-day-old sixth instars). The link between the metabolic activities and nutritional indices was discussed. Overall, the entomopathogen-host interaction appears to be primarily nutritional. The pleiotropic effects of the median lethal infections on the insect pest might eventually help in the biological control potential of the entomopathogens tested.

Enzymatic Disturbance in Larvae of The Black Cut Worm, Agrotis ipsilon (Lepidoptera: Noctuidae), by Infection with The Entomopathogenic Nematodes, Steinernema carpocapsae and Heterorhabditis bacteriophora

“…As reported by many authors (Abdel-Razek et al, 2004;Shaurub et al, 2015;Ibrahim et al, 2015;Shairra et al, 2016;Vidhya et al, 2016;Shaurub et al, 2020;Ghoneim et al, 2022), some EPNs influenced certain metabolic activities of a number of insects, including some enzymes and the main body metabolites.…”

“…riobrave and H. bacteriophora (Ahmed et al, 2014); A. ipsilon 6 th instar larvae at 6 hr post-infection with Steinernema glaseri or H. bacteriophora (Hassan et al, 2016); the 5 th nymphs of the desert locust Schistocerca gregaria after infection with 1000 IJs of H. bacteriophora (Gaber et al, 2018); the 3 rd instar larvae of S. littoralis after infection with EPNs H. bacteriophora and S. carpocapsae (Gomaa et al, 2020); and the 4 th instar larvae of S. littoralis after infection with LD50 values of S. riobrave or H. bacteriophora for 24 hr (Shaurub et al, 2020). Also, increased ACP activity in the haemolymph of some insects after infection with entomopathogens have been reported (Xia et al, 2001;Mirhaghparast et al, 2013;Vidhya et al, 2016).…”

Review of entomopathogenic fungi and nematodes as biological control agents of tephritid fruit flies: current status and a future vision

“…As young, sexually mature, gravid female fruit flies are more susceptible to fungal infection than older flies (Dimbi et al, 2003b), any control strategy that targets this age group (<1‐ to 7‐day‐old flies) and reduces the oviposition level in field populations should contribute to the overall management of the insect. Entomopathogenic fungi reduce digestive enzyme activities and main nutrient contents (Shaurub et al, 2020; Sharma & Sharma, 2021). At a sublethal level, such effects coupled with toxin production may have negative impacts on the reproductive system of the fruit flies, reducing fecundity and fertility.…”

“…The relationship of fruit fly mortality to concentrations of IJ nematodes is complex, sometimes showing increased mortality from low to moderate densities (Minas et al, 2016; Godjo et al, 2018; Usman et al, 2020b; Jean‐Baptiste et al, 2021; Shaurub et al, 2021; Aryal et al, 2022), followed by decreases at very high densities (Mokrini et al, 2020; Rohde et al, 2020). Variable factors act in combination to induce EPN pathogenicity to hosts, including suppression of the immune system, nutrient depletion, enzyme inhibition, reduction of nutritional metabolism, and toxin production by symbiotic bacteria (Poinar, 1990; Ayad et al, 2001; Shaurub et al, 2015, 2020). The decrease in nematode infectivity at very high densities may be due to the intraspecific competition of nematodes.…”

Genome‐wide identification and characterization of basic helix‐loop‐helix transcription factors in Spodoptera litura upon pathogen infection

“…Entomopathogens, such as S. litura nucleopolyhedrovirus (SpltNPV), Nomuraea rileyi , and Bacillus thuringiensis (Bt), have been used as biocontrol agents to control S. litura and other pests. Pathogen infection leads to changes in metabolism, immune defense, and energy consumption, which affect the survival and development of hosts (Freyberg & Harvill, 2017; Shaurub et al ., 2020). Although bHLH proteins are mainly involved in controlling developmental processes, regulating the cell cycle, and sensing environmental signals (Jones, 2004; Meng et al ., 2020), they are also involved in plant defense against pathogens (Song et al ., 2013; Fan et al ., 2014; Xu et al ., 2014; Meng et al ., 2020), and several bHLH members have also been found to be crucial for immune responses in mammals (Kim et al ., 2002; Xu et al ., 2014; Meng et al ., 2020).…”