The biological and ecological factors discussed here constantly interact to impact the risk of resistance development. Life cycle and population factors are important biological parameters.

Life cycle: An overriding aspect of insect biology that impacts an insect’s ecological interactions and the development of pesticide resistance is the insect’s life cycle (Sudo et al., 2018). Through a pest’s life cycle, there are changing interactions with its host and environment. Optimal resistance management practices rely on an understanding of these interactions. The life cycle of the insect pest is the primary factor affecting the development of insecticide resistance; in particular, the long life processes in bugs (Saulich, 2010) and short life cycle with the abundant progeny of mosquitoes which has all the properties suitable to swiftly developing resistance (Karunamoorthi and Sabesan, 2013).

The insects have different reproductive phases that influence resistance development through behavioral and genetic effects. Moreover, some ecological factors, such as environmental or host quality, will affect the reproduction phase (Helps et al., 2017). Most insects undergo sexual reproduction, involving a male and female union, and the resulting genetic recombination increases the genetic variability in a population. For example, sexual reproduction in two-spotted spider mites (Tetranychus urticae) enhanced the genetic variability in its population. It allowed for an increased potential for the development of resistance (Sun J. et al., 2022). On the other hand, asexual reproduction involves no male-female union, with the best example found in aphids (Stöck et al., 2021) (Figure 1). This will increase the reproduction rate, but it will also limit the genetic variability in a population. Multiple generations of asexually reproducing aphids, such as the green peach aphid (Myzus persicae Sulzer), are produced each year. Still, only a single sexual generation is likely to occur (Guillemaud et al., 2003). Among these reproductive phases, the insects undergo the development phase, which is a maturation process. Organisms vary a great deal in how these occur. Selection pressure can often occur throughout this life cycle phase. For example, the Housefly goes through distinct development stages (e.g., egg, pupa, adult fly) as it grows (de Jonge et al., 2020). Moreover, the sweet potato white fly, B. tabaci, has been shown to be resistant to neonicotinoids. The effects of thiamethoxam resistance selection on the life histories of B. tabaci B-biotype strains were studied by comparing those of selected and non-selected strains over multiple generations (Feng et al., 2009). The resistant individuals had shorter life spans and lower fecundity than the susceptible unselected strain. On the other hand, the nymphal stages took longer to mature in the resistant strain. Further phenotypic changes were seen in the resistant strain, with reduced body size across all instars and pupal stages compared to the susceptible strain (Feng et al., 2009). So, the life span of the insect pest, its reproductive capacity, and its surrounding habitat are crucial elements in the evolution of resistance (Naqqash et al., 2016). An insect’s lifecycle and developmental period play a crucial part in the growth of insecticide resistance (Figure 1).

Population growth: The growth of insect populations influences resistance development by determining the most successful individuals. Intense selection pressures from insecticide use, short generation time, and readily available host crops have resulted in diamondback moth (P. xylostella) resistance to almost all groups of insecticides (Taha, 2022; Venkatesan et al., 2022). The intrinsic rate of increase is the rate that an insect population will increase without external constraints. When populations are affected by biological or environmental constraints, the growth rate slows as it approaches a carrying capacity (large population size that is sustainable) (Holt, 2009). Insect populations are regulated by multiple factors, e.g., environmental conditions, host quality, and natural enemies. In the example shown, insect predator populations lag behind prey populations, but prey population decline after predator populations build up (Culshaw-Maurer et al., 2020). The invasive insects invade a new place where they do not have a natural enemy, and the environmental condition is suitable for their survival, consequently, reasons for their success. For example, Solenopsis invicta invades many countries, can increase their population, and dominates the local fauna (Morrison et al., 2004; Siddiqui et al., 2021) (Figure 1).

Generation time is also important in the time required for individuals to complete their life cycle. This ranges from multiple years per life cycle, as in the case of large pine weevil (Hylobius abietis) (Inward et al., 2012), to numerous life cycles per year in Mosquitoes (Mendoza, 2016). This allows for more genetic recombination, increasing genetic diversity and the probability of selecting resistant alleles. The population with multiple generations per year would more likely develop resistance to a pesticide because there would be more selection cycles (chances) to select for or to raise the percentage of resistant ones in the final population. For example, mosquitoes have multiple generations in short periods, which increases the possibility of the transfer of resistance alleles to the next generations and increases their genetic diversity, leading to the resistant generation (Mendoza, 2016). Another invasive species, Diamondback moths, can undergo multiple generations annually, increasing the potential for selection pressure across the population (Kliot and Ghanim, 2012) (Figure 1).

Carboxylesterases (CarEs) are an adaptable class of lipolytic enzymes that catalyze the hydrolysis of esters into alcohol and acid molecules. Widespread biocatalysis, drug metabolism, and endobiotic and xenobiotic degradation rely on these enzymes (Sood et al., 2016). CarEs enzymes also detoxify environmental toxicants such as pyrethroids, a major insecticide class used worldwide (Staudinger et al., 2010). Recent studies on invasive species indicated that a greater AChE and CarE esterase activity was seen in resistant populations compared to vulnerable ones such as S. invicta (Siddiqui et al., 2022b; 2022c), H. armigera (Young et al., 2005; Wu et al., 2011), C. tarsalis (Whyard et al., 1994), and Aonidiella aurantia (Grafton-Cardwell et al., 2004) (Figure 2).

Biochemical methods using S. litura resistant strains from Korea and India have shown the role of acetylcholinesterases in pesticide resistance (Yonggyun et al., 1998; Kranthi et al., 2002; Muthusamy et al., 2011). In the same way, a carbamate-resistant strain of S. exigua from California had an AChE enzyme that was about 30 times less sensitive to methomyl than the enzyme from a sensitive laboratory strain (Byrne and Toscano, 2001). However, molecular information on the AChE point mutation exists for a number of species of Spodoptera, while it is mostly available for S. frugiperda. When comparing two strains of this species, Yu et al. (2003) found that acetylcholinesterase from a field strain taken from Florida corn fields was up to 85-fold less responsive to inhibition by CBs and Ops (Hilliou et al., 2021).

The CarE activity reported by various studies, such as alpha and beta esterase production, when exposed to fipronil, was greater in a resistant strain of the mosquito (Culex quinquefasciatus) than in a susceptible strain (Sarkar et al., 2009). Increased activity of CarE was detected in beta-cypermethrin-resistant M. domestica when compared to beta-cypermethrin-susceptible ones (Zhang et al., 2007). Moreover, elevated esterases activity was reported after insecticides exposure to the peach potato aphid (M. persicae) (Bass and Field, 2011; Venkatesan et al., 2022) and the brown planthopper (Nilaparvata lugens) (Tang et al., 2022). This means that elevated esterases can detoxify the insecticides. Gene amplification is the cause of the increased production of these enzymes (Şengül Demirak and Canpolat, 2022). In mosquitoes, amplified esterase molecules are more reactive with insecticides than non-amplified esterases (Gan et al., 2021).

Insecticide detoxification by CarE has also been reported in other insect species. For example, some previous studies have indicated an increase in the activity of CarE in honeybees following exposure to fipronil (Carvalho et al., 2013; Roat et al., 2017). Similarly, the grassland locust, Epacromius coerulipes Ivanov (Orthoptera: Acrididae), showed a significantly higher CarE activity in a strain that had evolved resistance against fipronil than in a susceptible strain (Jin et al., 2020). Insecticide metabolism studies indicated that esterases are involved in resistance mechanisms. Increased accumulation of esterase hydrolytic products in insecticide-resistant insects compared to susceptible gives evidence for the involvement of these enzymes (Jensen, 2000; Silva et al., 2012; Khan et al., 2021b; Siddiqui et al., 2022b).

Glutathione transferases (GSTs) are a broad and diversified family of enzymes that are present in almost all organisms. GST is a class of multifunctional proteins that are extremely important in the biological transformation of exogenous compounds, drug metabolism, and protection from peroxidation (Hollman et al., 2016; Dasari et al., 2018). It was discovered that the house fly M. domestica contains DDT-dehydrochlorinase as a glutathione S-transferase (Clark, 1989). They are crucial for the detoxification of both internal and external substances, intracellular movement, the generation of hormones, and the prevention of oxidative stress (Hassan et al., 2019). GST is one of the foremost detoxifying enzymes of insecticides in insects. Insecticides can be metabolized either by reductive dehydrochlorination, which is facilitated by GSTs, or by conjugation reactions with reduced glutathione, which result in water-soluble metabolites that are more easily eliminated. Additionally, they help to remove dangerous oxygen-free radical species that are formed as a result of the use of insecticides (Panini et al., 2016). Neonicotinoid resistance in the B. tabaci is correlated with constitutive overexpression of several ESTs, GSTs, UGTs, CYPs, and ABC transporters (Vassiliou et al., 2011) (Figure 2).

Several major insecticide types, such as boric acid, carbamates, organophosphorus, organochlorine, and pyrethrin-resistant in German cockroaches, have increased their GST expression levels to varying degrees (Gentz and Grace, 2006; Nasirian, 2010; Rinkevich et al., 2013). Studies on invasive fire ants show that exposure to indoxacarb, beta-cypermethrin, and fipronil causes a substantial alteration in GST activity. Additionally, the outcomes demonstrate that population resistance and sublethal concentrations substantially impact enzyme activity (Siddiqui et al., 2022c; Siddiqui et al., 2022b). OP and DDT resistance mechanisms were reported in houseflies (Ranganathan et al., 2022). In a resistant strain of M. domestica, Zhang et al. (2007) discovered that GST activity was also markedly elevated. According to Sarkar et al. (2009), the GST activity of all populations tested was greater than that of a susceptible laboratory strain. Studying orthopterans, researchers found that a particular strain of E. coerulipes had much higher GST activity than susceptible insects (Jin et al., 2020). Insecticide treatments for maize rootworms have already been linked to an increase in GST activity, according to a recent study (Souza et al., 2020). Pest resistance has already been reported in different insects against DDT and OP.

An essential supergene family, cytochrome P450 (P450 or CYP), is responsible for the metabolism or attenuation of toxicity of numerous potentially harmful substances (Zhu et al., 2017; Hafeez et al., 2022b) (Figure 2). There are four clades in insects where the CYP gene can be placed, including CYP2, CYP3, CYP4, and the mitochondrial CYP clade (Nelson, 2011; Zhang et al., 2018). Numerous insect cytochrome P450s (CYPs) have been split into eleven families (Hafeez et al., 2022b). Numerous insect CYPs make up the CYP3 clan of cytochrome P450s, which is further divided into numerous CYP9 family members known to take part in detoxifying processes linked to pesticide resistance (Schuler, 2011; Hafeez et al., 2019). P450 enzymes play an important part in the phase I process of detoxification of many different types of hazardous chemicals, including insecticides, due to their genetic diversity, broad substrate specialization, and catalytic adaptability (Kim et al., 2022). For herbivorous insects, the main mechanism of pesticide resistance is the overexpression of cytochrome P450 detoxifying enzymes (Hafeez et al., 2020b; Wu et al., 2021).

Different P450 enzymes serve different purposes in insects, such as hormone synthesis and regulation, growth and development control, or the digestion of xenobiotic substances (Zhou et al., 2010; Nelson et al., 2013). Due to their central function in pesticide metabolism, cytochrome P450s are frequently implicated in the development of insect resistance to these chemicals (Guo et al., 2012; Panini et al., 2016). One of the most prevalent processes by which insect pests develop resistance to synthetic insecticides is the upregulation of certain detoxifying P450 enzymes within the insect (Nelson, 2011; Hafeez et al., 2022a; Luo et al., 2022). Because of this, insecticide resistance may develop as a result of changes in the activity of detoxifying enzymes in insects in response to exposure to pesticides. Many insect orders, including Coleoptera, Diptera, Hemiptera, Hymenoptera, and Lepidoptera, have shown evidence of P450 overexpression leading to increased resistance to pesticides (Bass et al., 2011; Johnson et al., 2012; Liang et al., 2015; Wang et al., 2015; Chen et al., 2017; Khan et al., 2021a; Khan et al., 2021c; Hafeez et al., 2022a; Siddiqui et al., 2022b).

Invasive species, including B. tabaci, S. exigua, S. invicta, P. xylostella, etc., have been demonstrated to exhibit extremely high levels of resistance to several kinds of insecticides, and this resistance has been linked to CYP detoxifying enzymes (Lai and Su, 2011; Yu et al., 2015; Chen and Zhou, 2017; Ahmad et al., 2018; Wang et al., 2018b; Xie et al., 2018; Hafeez et al., 2019; 2020a; 2020b; 2022c; Siddiqui et al., 2022b). Increased transcriptional levels of CYP6AE97, CYP321A9, CYP9A105, CYP321A16, and CYP459 in the midgut of S. exigua larvae treated with different insecticides are just some examples of how S. exigua has developed a high level of resistance against several types of insecticides (Wang et al., 2018a; Hu et al., 2019). Moreover, the detoxification mechanism by P450 was reported in various studies. For instance, in S. invicta belonging to the order Hymenoptera, CYP was involved in the detoxification of fluralaner (Xiong et al., 2022) (Xiong et al., 2022), fipronil and beta cypermethrin (Siddiqui et al., 2022b). Similarly, in the order Diptera, D. melanogaster, C. quinquefasciatus and Anopheles funestus (Giles) (Daborn et al., 2002; Wondji et al., 2009; Itokawa et al., 2010), in the order Hemiptera, M. persicae were all reported for the amplification of P450 and insecticide resistance (Puinean et al., 2010). The lambda-cyhalothrin detoxification studies reported the overexpression of P450 in H. zae and H. armigera (order Lepidoptera) (Li et al., 2000a; 2000b; Chen et al., 2017; Hafeez et al., 2020b). Based on these results, it appears that invasive insects rely heavily on the overexpression of P450 genes in order to detoxify xenobiotics from their bodies.

Insects host a diverse microbial population that responds to environmental stresses in a dynamic way (Zhang J. et al., 2022). Similar to the insect, the associated microbiota are shaped by the process of natural selection. Changes in food scarcity and diet chemical exposure can all affect its makeup (Adair and Douglas, 2017; Akami et al., 2022). Host microbiota may help the host metabolise pesticides if the host is subjected to selection pressure from these chemicals. It is possible that this mutation is what makes the host less vulnerable to pesticides (Akami et al., 2019a; 2019b). Bacteria capable of breaking down pesticides have been found in numerous natural environments and in several insect orders, including Coleoptera (Akami et al., 2019b), Hemiptera (Kikuchi et al., 2012), Diptera (Cheng et al., 2017; Hassan et al., 2020), and Lepidoptera (Ramya et al., 2016; Almeida et al., 2017). There has been evidence that resistant strains of bacteria from the gut of P. xylostella (Xia et al., 2018) and S. frugiperda (Almeida et al., 2017) can break down many pesticides (Gomes et al., 2020). Strains of S. frugiperda were chosen because of their ability to degrade pesticides; however, these bacteria were lacking in the microbiota of susceptible, unselected larvae (Almeida et al., 2017) (Figure 2).

Insects have a complex defense system built into their digestive tracts, and this system is most likely the driving force behind the organization of gut microbiota (Siddiqui et al., 2022a). Various processes in this defense system influence the host’s tolerance and resistance to bacteria in the insect gut. Though tolerance refers to the capacity to mitigate the detrimental effects of a particular bacterial burden on the host’s health, resistance refers to the capability to lower the bacterial burden to the point where it is no longer a threat to the host’s vigor (Schneider and Ayres, 2008). Insects harboring more bacteria in their digestive systems are more tolerant to other foreign microbes and have less resistance to them than those with less diverse bacterial communities. Because of this, the systems governing gut immunity in various insects might be personalized to the host’s individual needs. Little is known about the systems that mediate tolerance, despite the fact that resistance mechanisms have been the primary focus of immunology studies (Figure 2) (Engel and Moran, 2013). However, digestive tract microbe-host interactions are frequently mutualistic or commensalism in nature. These may be of special importance to the host in terms of minimizing any harmful effects of the resident microbiota on the host.

The insects have a symbiotic microbiome in their guts that aids detoxification (Jing et al., 2020). The enzymatic detoxification method, used by invading insects and the intestinal microbiota responsible for secreting such digestive enzymes, may be used to establish a viable resistance development strategy (Figure 2). Developing resistance in a collection of organisms at the same time is undoubtedly difficult (Barbosa and Levy, 2000). Mutualistic symbiosis plays a significant role in this process because of its synergy and combined powers; the mutualistic alliance formed by two or more species adjusts to adverse conditions (such as pesticide exposure) more quickly than the individual partners of the mutualistic partnership do (Nobre and Aanen, 2012). Accordingly, any beneficial directional flow of resistance development in the system is mitigated or reversed by this adaptability.

The generation turnover of symbiotic microorganisms may overcome the barrier of invasive ants’ extended generation time, allowing for more favorable mutations or gene regulation/alteration, which could lead to pesticide resistance development. Few studies on invasive ants have provided evidence of the ants’ ability to metabolize xenobiotic compounds such as lignin, plant allele chemicals, and pesticides (Engel and Moran, 2013; Siddiqui et al., 2022b; c). Three partiti-like viruses isolated from the African armyworm (Spodoptera exempta) have been shown to increase resistance to nucleopolyhedrovirus, while the polydnavirus from parasitoid wasps can disrupt the host insect’s immune system to make sure the survivability of wasp progeny (Strand and Burke, 2013; Xu et al., 2020). Lower termites, which feed primarily on wood, require symbiotic flagellates to break down lignocelluloses and methanogenic archaea to produce methane (Ohkuma, 2008; Shi et al., 2015).

Insect microorganisms can modulate insect resistance to synthetic insecticides through direct breakdown and by stimulating the host’s detoxifying enzymes or immune system (Liu and Guo, 2019; Zhao et al., 2022). For example, the 16S rRNA gene sequencing data demonstrated a decrease in the number of the genera Enterococcus and Stenotrophomonas following polymyxin B therapy, which affected the survival rate of Bombyx mori subjected to chlorpyrifos. The host tolerance to chlorpyrifos was improved when germ-free silkworms were given S. maltophilia. This bacteria increases host acetylcholinesterase activity but cannot directly break down chlorpyrifos in the stomach (Du et al., 2020). Aeromonas hydrophila, an intestine bacteria, was found in substantially greater abundance in deltamethrin-resistant individuals of Culex pipiens. After antibiotics were used to clear the stomach of the resistant strains, the resistance level dropped by 66%, and the host’s cytochrome P450 monooxygenase (CYP450) enzyme function dropped by 58%. The resistance and CYP450 enzyme activities were recovered when A. hydrophila was supplied, suggesting that A. hydrophila promotes host resistance to deltamethrin by boosting CYP450 activity (Xing et al., 2021). Further, P. xylostella intestinal Enterococcus sp. Upregulates the appearance of an antimicrobial peptide called gloverin, which contributes to the insect’s resistance to the pesticide chlorpyrifos (Xia et al., 2018). Wolbachia proliferated in N. lugens after treatment with imidacloprid, and their removal decreased CYP450 enzyme activities and NlCYP4CE1 transcript levels. This finding supported the hypothesis that Wolbachia increases host resistance to imidacloprid by increasing the expression of the gene encoding the enzyme responsible for its metabolism, NlCYP4CE1 (Cai et al., 2021). The gut microbiome of pollinators like the honeybee (Apis mellifera) increases tolerance to pesticides like thiacloprid, tau-fluvalinate, and flumethrin by promoting the expression of genes involved in immunity and detoxification (Wu et al., 2020; Yu et al., 2021). When creating novel pest control methods or reducing pests’ vector competence, it is important to keep an eye on the role of the pests’ microbial partners. Bioremediation and the reduction of xenobiotic toxicity may be greatly aided by the discovery of insect-associated microorganisms capable of detoxifying hazardous chemicals (Mahapatro, 2017).