Natural products are and always will be an inexhaustible source of complex and diverse structures (Laurençon 2013). Several authors have shown that plants are capable of producing a wide variety of active substances involved in the defense against pests (Deravel et al. 2013). These substances usually come as cocktails of metabolic compounds with different activities (Alexenizer and Dorn 2007). In this context, this preliminary study aims to look for methods to improve the effectiveness of new bioactive molecules with biocidal activity by incorporating synergistic products.
Assessment of the insecticidal potential of phytopreparations and of the active ingredient on the abundance of Chaitophorus leucomelas
The results of biological treatments by applying aqueous extracts of the whole plant Dittrichia viscosa, aqueous extract ratio Dittrichia viscosa / Silene fuscata and the active ingredient Thiamethoxam/Lambda-cyhalothrin showed an explicit knock-down effect on the abundance of Chaitophorus leucomelas sexuparae compared to the control group. This reported shock effect on abundances shows an upward rating of toxicity starting from the aqueous extract of the whole plant Dittrichia viscosa, then the aqueous extracts to the Dittrichia / Silene ratio and finally the active ingredient. Considering the results obtained by the cross-correlation test, we find that the aphid populations settle first in the block treated with the aqueous extracts and then in the block treated with the active ingredient. In accordance with these results, it can be assumed as a hypothesis that the synthetic product generates a moderately persistent repressive shock effect on the population of Chaitophorus leucomelas, which is ephemeral under the effect of phytopreparations.
Studies have shown that chemicals have the ability to disrupt the normal functioning of exposed organisms (Jean and Benmarhnia 2011). In other words, the impact of pesticides on harmful organisms targets the integrity of the individual, therefore a dysfunction of all of his biological parameters where each parameter plays a role in his survival.
Very satisfactory results have been found following the use of the aqueous extract of the entire plant Dittrichia viscosa on the population structure of Chaitophorus leucomelas. These results allow us to suggest that the obtained aqueous extracts contain a wide variety of bioactive components that have been released during the extraction process and that act in synergy. This hypothesis is supported by a fairly rich literature which states that Dittrichia viscosa contains natural defensive substances that have been used as a very diverse therapy and have been known for a long time (Cafarchia et al. 2002; Kattouf et al. 2009). D. viscosa is known for its antihypertensive (Kattouf et al. 2009), anti-inflammatory and antioxidant (Lounis et al. 2009), antidiabetic, antipyretic, wound healing, antiseptic and antiphlogistic activities (Lauro and Rolih 1990; Omezzine et al. 2011) and its antiulcerogenic action is attributed to its flavonic composition. Moreover, extracts of D. viscosa were tested for thier antiviral (Abad et al. 2000), antifungal (Mamoci et al. 2011), antimicrobial (Maoz and Neeman, 1998), antibacterial (Squalli et al. 2007), herbicidal (Muehlchen et al. 1990) nematicidal (Oka et al. 2006), acaricidal (Mansour et al. 2004) and insecticidal activities (Alexenizer and Dorn 2007).
The aqueous extract ratio Dittrichia viscosa / Silene fuscata expressed a remarkable toxic action compared to unformulated aqueous extracts. The use of ratios increased the insecticidal efficacy of Dittrichia viscosa and reduced the incidence of side effects on population recovery. Presuming that the bio-adjuvant Silene fuscata accelerated the penetration of the bioactive molecule, this assumes that the distribution of the biomolecules to the sensitive sites of the pest is done in a relatively short period of time. These results are consistent with the results of other researchers such as Hayes et al. (2006), who also showed that the adjuvant is used primarily to increase the quantity and penetration speed of the product into organisms, therefore to increase its speed of action, to expand its functions and to offer it a better adhesion. According to Hernandez Ochoa (2005), adjuvants improve the performance of active ingredients by notably allowing a reduction in the usable doses, thus limiting their impact on the flora and fauna and helping protect the environment.
Evaluation of the insecticidal potential of Dittrichia viscosa aqueous extract-based phytopreparations on the demographic parameters
The results relating to the application of the different treatments on C. leucomelas allowed us to clearly see that fecundity is remarkably disturbed following the action of the active ingredient Thiamethoxam/Lambda-cyhalothrin compared to aqueous extracts. These results are comparable to those discussed by Jean and Benmarhnia (2011) expressing that xenobiotic substances have the capacity to act on a broad spectrum of animal or plant species and interrupt their normal functioning. Bernard (1992), had shown that most pesticides act on the fecundity of contaminated organisms through partial or total sterilization and by reducing the number of eggs laid. Dallaire (2003), shows that tebufenozide affects the development as well as some aspects of chemical communication and of the reproductive success of insects such as Lepidoptera. This product causes a deceleration in ovarian maturation and consequently a decrease in the fecundity of females. In addition, the effects of tebufenozide on fecundity and fertility were found to vary widely depending on the development stage at the time of treatment. In the same aspect, bioproducts have insecticidal and anti-appetizing effects, thus affecting the growth, moulting, development and fecundity of insects (Konstantopoulou et al. 1992; Keane and Ryan 1999).
The net reproductive rate (R0) of C. leucomelas females exposed to phytopreparations and to Thiamethoxam/Lambda-cyhalothrin underwent a notable decline compared to the control, this decline is very clear under the homologous dose of the active ingredient Thiamethoxam/Lambda-cyhalothrin compared to the aqueous extracts applied. Our results are confirmed by those found by Tron et al. (2015), that showed an important link between exposure to pesticides and some reproductive and developmental disorders. According to Forbes and Forbes (1997), reproduction is often closely related to environmental variables that delay the reproductive period, which can impair reproductive success. The same author indicates that the impact of pollutants at the individual level is more often related to growth and reproduction than to population abundance. Studies have shown that insecticides can have subtle effects, particularly in impairing recognition of the breeding partner and identification of the spawning site. Therefore, the products cause an alteration in the expression of genes important for reproduction. This work has demonstrated a considerable susceptibility of the effects of insecticides on the ability of insects to reproduce (Amichot 1999). Devault (2007), shows that the behavior, reproduction and survival of adults as well as the number and properties of their offspring can be affected by exposure to pesticides.
Furthermore, the results obtained allowed us to perceive that the aqueous extract exerts a moderately important pressure effect on the reproduction rate of C. leucomelas. This result reminds us of the statements of Delimi et al. (2013), who found that the biopesticide can disturb adult reproduction by extending the preoviposition period and reducing the egg deposition period given that fertilized females cannot live longer than one or two days, which reduces the number of eggs laid.
Regarding the growth rate (rm) of C. leucomelas cohorts, the results demonstrate a significant increase between the treated and the controls. This increase is much pronounced following the action of the active ingredient Thiamethoxam/Lambdacyhalothrin compared to that of the aqueous extracts. The results show that the prescribed dose of the active ingredient Thiamethoxam/Lambdacyhalothrin and the aqueous extract of D. viscosa / S. fuscata ratio cause a significant decrease in the multiplication rate (λ) of the populations studied. A strong decrease in the mean life time (T) is reported in the population of C. leucomelas following the use of the homologous dose of the active ingredient compared to other treatments that remain close to the control. At the end, the various treatment systems hardly affect the doubling time (DT) of the populations. Toxic effects of pesticides on the demographic parameters are scarce in the scientific literature.
Evaluation of the insecticidal potential of phytopreparations and of the active ingredient on the biochemical life traits of Chaitophorus leucomelas
Studies show that chemicals can reach all the intracellular organelles and change their number, structure and location in the cell and that they can also act on intracellular energy reserves (lipids and glycogen) (Gernhöfer et al. 2001; Triebskorn et al. 2002). Calow (1991) proves that energy reserves are mobilized following stress. The aim of this investigation is to show the role of energy biomarkers in understanding the behavioral or physiological strategies that allow C. leucomelas females to partially or totally circumvent bioactive or active materials. This study describes the metabolic reactions and weight measurements of C. leucomelas under the effect of phytopreparations and the synthetic product Thiamethoxam/Lambda-cyhalothrin. The results reveal a significant quantitative change between lipid and carbohydrate reserves stored in the tissues of biological model females, where lipid reserves are clearly distinguished from carbohydrate reserves. Moreover, it is very important to coordinate the strong positive correlations existing between the reorganization of lipid reserves and the chemical treatment under the different applied doses (homologous dose or half-dose). The dominance of energetic lipid biomarkers can probably be explained by a change in the biochemical life traits of females exposed to the different applications, especially the active ingredient Thiamethoxam/ Lambda-cyhalothrin. This hypothesis can be explained by the fact that the synthetic product has a stimulating effect on the physiology or the behavior of an organism after exposure. The weight measurements show a slight disturbance under the effect of the two treatment types compared to the control.
Several authors point out that exposure to chemical stress can disrupt the energy balance of living organisms as a direct consequence of the tolerance means adopted (e.g. defense mechanisms, damage repair) and this at the expense of the energy allocated to reproduction and to growth (Amiard and Amiard-Triquet 2008; Palais et al. 2011). This energy balance can also be negative under certain environmental conditions, generating consumption of energy reserves to activate and/or set up tolerance and defense mechanisms.
Our results are consistent with the results of other studies showing that organisms exposed to chemical contamination will use energy to limit the physiological alteration caused by substances present in the environment. Thus, the amount of energy available to ensure the body's vital functions will be lower than that in unexposed organisms. The dosage of energy reserves (proteins, glycogen and lipids) allocated to the various functions of the body will then provide information on the overall physiological state of living organisms (Poisson et al. 2011). The results demonstrate a strong accumulation of lipid reserves in the cohort exposed to the synthetic product. This lipid accumulation indicates that the treated females are in fact subjected to a stressful action which could stimulate a high production and a greater accumulation of lipids. The explanation most often described in the literature is that lipids generally accumulate in organisms exposed to organic contaminants (Köhler 1989; Pelosse 2008). Hence, an increase in lipid metabolites promotes the storage of the toxic substance. According to Abdoulaye (2007), lipids are necessary for maintaining good health, they contribute to the formation of cell membranes, to the synthesis of hormones; without disregarding that they represent a concentrated source of energy that is twice as much as carbohydrates or proteins. The lipid content is closely related to survival, which means that the decrease in lipid stores could be responsible for the death of individuals. However, it should be noted that the measured lipid level corresponds to the amount of lipids contained in the entire body of the insect. Lipids are involved in various functions in insects, which may play a role in the survival, dispersal or even constitute a crucial source of energy for egg production (Pelosse 2008).
The results show a relatively significant disturbance of the carbohydrate energy balance of C. leucomelas females after applying the dose of the active ingredient Thiamethoxam/ Lambda-cyhalothrin. Carbohydrate biomarkers are very low but stable, which suggests that the low amount of sugar is related to the detoxification action (Amiard and Amiard-Triquet 2008).
Finally, many stresses (physical and/or chemical) can lead to the mobilization of energy reserves. In addition to variations related to exposure to toxicants, the variability of the energy reserve concentrations in organisms depends on several biotic and/or abiotic factors. These energy reserves can be mobilized to supply defense mechanisms (Storage, elimination, detoxification of contaminants). In this toxic situation, energy reserves can provide vital information on the maintenance, growth and reproduction capacities of individuals (Amiard and Amiard-Triquet 2008).