**6. Probiotics' role in stress mitigation**

### **6.1 Stress related to long-term mass-rearing and irradiation procedures**

The biological quality of sterile males can be affected by a variety of significant stressors, including handling, artificial conditions for rearing, and radiation exposure. The ability of male medflies' to fly, attract females, compete for mates, and maintain longevity are all negatively impacted by sterilizing irradiation techniques used for SIT, which are also a significant source of microbiome perturbation [16, 61]. As a result, more focus has been placed on evaluating the impact of irradiation on the survival and mating abilities of the medfly sterile males in order to identify and pinpoint the primary drawbacks of these treatments. The changes in the diversity of the gut microbiota and the decline in the physical quality of sterile males are related. According to Ben-Ami et al. [16], industrial strains exhibit an increase in potentially pathogenic species like *Pseudomonas* and *Providencia*, which are known to harm insects, while levels of dominant gut bacteria (such as *Klebsiella* spp.) decrease after sterilization. It is interesting to note that adding *K. oxytoca* to the post-irradiation diet promotes colonization of these bacteria in the gut while lowering *Pseudomonas* spp. levels. The same authors, Ben Ami et al. [16], indicate that copulatory success tests show that the addition of these bacteria to male diets significantly improved sterile male performance. Similarly, a probiotic adult diet enriched with *E. agglomerans* and

*K. pneumonia* significantly improved the gut environment of medflies whose alimentary canal had been damaged by the radiation used in the sterilization process of medfly [61]. A more recent study on the effect of irradiation on medfly immunity discovered that molecular changes occur at different time points via regulation of stress and immunity genes such as *Hsp* 70, *Hsp* 83, *cecropin*, *attacin*, and *PGPR*. The expression of *attacin* and *PGPR-LC* was increased, whereas *cecropin* was decreased. *Hsp* genes, on the other hand, showed decreased levels between 0 and 18 h, peaking at 72 h. Only the *attacin* was induced after supplementation with the probiotic *Enterobacter* sp. [35].

### **6.2 Environmental stress**

Along with the increase in agrochemicals, climate change and modifications in land use can all lead to unfavorable stress conditions for sterile males in agroecosystems. Sterile males are regularly exposed to unfavorable environments, including cold, heat, ultraviolet stress, lack of food resources, insecticide exposure, parasites, and infectious diseases or pathogens. Stress conditions can impair sterile males, physiology, biochemistry, and gene regulation, as well as the interaction between medfly and microorganisms, which lowers male performances. Given the range of beneficial functions provided by microbiota, it may also shape the ability of hosts to tolerate environmental stress [62]. Beneficial bacteria can help sterile males maintain their inherent resistance to these challenges; thus, adding these bacteria to the medfly diet can help reduce the negative impact of environmental stress conditions on sterile males. However, novel approaches are needed to explore medfly–bacteria and bacteria–bacteria interactions under abiotic and biotic stress conditions to identify potential stress-tolerant or -resistant bacteria to improve medfly performance.

### *6.2.1 Temperature tolerance*

Among multiple stress factors, the temperature has profound effects on the physiology, behavior, and performance of insects [63]. There is evidence supporting that the ongoing climate change is expected to impose strong selection pressures on the heat tolerance of insects [64], and that gut microbiota can contribute to host thermal tolerance [65–67]. Alteration of energy reserves, metabolism, or gene expression by microbiota may indirectly affect thermal tolerance, which strongly depends on these traits [68]. Since the global surface annual temperature has increased at an average rate of 0.1°C, almost double compared to 20 years ago, and increases of 1.5°C and 2–4°C are expected by 2050 and 2100, respectively [69], rising temperatures can severely affect an AW-IPM program because temperature changes can influence the longevity, flight ability, and mating performance of sterile males. An elevated temperature could lead to the death of sterile males released during SIT [70]. Numerous studies have recently suggested that the gut microbiota is sensitive to environmental temperature, which induces changes in its composition and diversity, and may have significant consequences on host phenotype and fitness [71–73]. For instance, it has been shown that *K. michiganensis* was implicated in promoting insect resistance to long-term lowtemperature stress in the tephritid fly *B. dorsalis*. The mechanisms by which gut symbionts modulate host physiologies and the molecules involved in these changes have been reported as follows: Gut symbionts, particularly *K. michiganensis*, help the host *B. dorsalis* upregulate the levels of "cryoprotectant" transcripts and metabolites,

### *Probiotics as a Beneficial Modulator of Gut Microbiota and Environmental Stress… DOI: http://dx.doi.org/10.5772/intechopen.110126*

which increases its resistance to long-term low-temperature stress by stimulating the host arginine and proline metabolism pathway [74]. It has also been noted in *Drosophila melanogaster*, the disruption of its gut microbiota leads to decreased cold tolerance [75] that can be rescued by supplementing a single member of its natural microbiota, the yeast *Lachancea kluyveri*. Similarly, increases in temperature have been associated with increased relative abundances of *Proteobacteria*. Developmental temperature has been shown to impact the composition of the gut microbiota of fruit flies, with higher temperatures (31°C) leading to increased abundances of *Acetobacter*, a genus of *Proteobacteria*, relative to lower temperatures (13°C) [76]. Additionally, in aphid, obligatory endosymbionts contribute to host performance at high temperatures [77, 78], whereas facultative endosymbionts also confer tolerance to high temperature in aphids [79, 80] and *Drosophila* [81]. Although *C. capitata's* acute tolerance of extreme temperatures, under ecologically relevant conditions, and the relative costs and benefits of acclimation have attracted significant attention [82–87], little is known about how microbial symbionts affect medfly sensitivity to toxins, desiccation resistance, and thermal tolerance.

Medflies are exposed to a variety of environmental stresses in the wild. The wild flies seem to be remarkably temperature-variation resistant [83, 84]. Even if this is true, it does not follow that laboratory sterile medfly males will be the same once released. The performance of released sterile males could be improved by enhancing their phenotypic characteristics with probiotic bacteria that confer thermal tolerance. This might be a simple and affordable way to improve the effectiveness of an SIT program. The role of the gut microbiota in the adaptive response to climate change is a new area of study, and future research must balance mechanistic approaches to understand host-microbiota interactions with holistic approaches to understanding the role of the gut microbiota in insect ecology and evolution.

### *6.2.2 Pesticides tolerance*

The management of *C. capitata* is currently based on the implementation of an integrated pest management (IPM) program that employs a variety of techniques, including insecticides [88, 89], mass trapping [90], the sterile insect technique [91, 92], and also biological control using parasitoids [93]. However, the area under IPM includes a large number of cultivated plant species that are attacked by other pests [94]. Pesticides are usually used when these pests exceed their economic thresholds. The compatibility of the existing programs will be determined by the interaction between SIT and other pest management strategies when SIT is used [95]. The impact of pesticides and their residues on sterile Vienna-8 males has been investigated in citrus-integrated pest management. San Andrés et al., [96] observed high mortality of sterile Vienna-8 males on proteinaceous malathion and spinosad baits under laboratory conditions. Additionally, Juan-Blasco et al., [97] showed that both chlorpyrifos and spinosad formulations at authorized concentrations against other citrus pests were toxic by contact with Vienna-8 males, resulting in significant mortality. Pesticides have deleterious effects on Vienna-8 males. Thus, a solution is needed to limit these off-target effects. Naturally, reducing pesticide use would expose Vienna-8 males to fewer pesticides, but this solution may reduce crop yield and burden the food supply. The use of alternative, non-chemical control methods, particularly against serious pests, is another suggestion. However, these approaches are subject to the legislative process and competing interests and do not give growers the ability to address the pesticide issue on their own.

According to recent findings, the insect-associated microbial community, that is exposed to pesticides, as a source of selection pressure, may help the host metabolize these substances by enhancing enzyme activity through a wide range of metabolic pathways able to break down and/or modify xenobiotics [98–100]. It might also act as a source of variation, which would make the host less vulnerable to pesticides [101]. In some model organisms, it has been demonstrated that administering bacteria as probiotics lowers toxicity and has protective effects on the host. Future studies can use this foundation to explore the possibility of enhancing SIT to control medfly [102– 104]. It might be a novel idea to include probiotics in the diet of sterile medfly males to lessen the effects of pesticides. Recently, some authors have drawn attention to the capacity of bacteria, such as lactic acid bacteria, to be developed into probiotic products capable of reducing the oxidative damage brought on by pesticides *in vivo* [105, 106]. These authors also emphasized how bacterial strains differ in their resistance to organophosphorus pesticides and their capacity to degrade them [107].

Pesticide-degrading bacteria are common in nature and have been found in a variety of insect orders, including Lepidoptera [108, 109], Hemiptera [110], Diptera [18, 111], and Coleoptera [101]. The surface communities of the Tephritid fruit fly *Rhagoletis pomonella* contained the first bacteria with this characteristic to be identified [112] (**Table 4**). It has been demonstrated that this bacterial symbiont degrades up to six different insecticides from three major groups (chlorinated hydrocarbons, organophosphates, and carbamates). Since then, evidence has shown that various other bacterial microbiota, such as those in the guts of herbivores, are capable of degrading insecticides [113]. For instance, it was found that in *Bactrocera tau*, bacteria were involved in the degradation of the toxic substances the host insect ingested, leading to insecticide resistance [111]. *Bactrocera dorsalis*, an oriental fruit fly, detoxifies trichloroethylene as another fascinating example of symbiont-mediated detoxification in Tephritid fruit flies [18]. The findings of this study showed that a bacterium


### **Table 4.**

*List of tephritidae gut microbiota involved in pesticide degradation.*

*Probiotics as a Beneficial Modulator of Gut Microbiota and Environmental Stress… DOI: http://dx.doi.org/10.5772/intechopen.110126*

called *Citrobacter freundii*, isolated from the gut of the *B. dorsalis*, can break down the toxin trichlorphon into less toxic compounds called chloral hydrate and dimethyl phosphite, possibly by activating genes called organophosphorus hydrolase (OPHlike) genes and conferring host resistance in the oriental fruit fly [18]. Higher trichlorphon resistance was seen when isolated *Citrobacter* species were inoculated with *B. dorsalis*, whereas flies treated with antibiotics exhibited lower resistance. Based on this evidence, it is possible to reduce pesticide uptake and increase pathogen resistance by supplementing the diet of larval and adult sterile medfly males with suitable bacteria that degrade insecticide (multiple strains or single strain). This would reduce the sublethal effects of pesticides. The ability to supplement sterile medfly males with probiotics could aid the insects in combating the unintended pernicious effects and improving the SIT application while chemical agents are still being used in agriculture.
