Pheromone release and perception, and fertility of insecticide-exposed cotton boll weevils (Anthonomus grandis grandis)

doi:10.21203/rs.3.rs-5277839/v1

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Pheromone release and perception, and fertility of insecticide-exposed cotton boll weevils (Anthonomus grandis grandis)

https://doi.org/10.21203/rs.3.rs-5277839/v1

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The objective of this work was to evaluate the effects of sublethal exposure to the insecticides malathion and beta-cyfluthrin on the pheromone perception and emission by the cotton boll weevil (Anthonomus grandis grandis Boheman (Coleoptera: Curculionidae)). The potential impact of such sublethal exposure on this species population growth was also determined using fertility table parameters. Males and females were exposed to malathion at 10% of the label rate for 1 min, and to beta-cyfluthrin either at the full or 20% label rate also for 1 min. The response of insects exposed and non-exposed to pesticides to their aggregation pheromone (grandlure) was evaluated in Y-tube olfactometer and the pheromone production was evaluated. In order to evaluate the possible reproductive effects, the couples remained individualized for 48 hours and the females were subsequently evaluated until their death. The treatments were: 1) insecticide-exposed male and female; 2) exposed male; 3) exposed female; and 4) non-exposed males and females. Insects exposed to both insecticides did not show a response to their aggregation pheromone during the first 24 hours after the exposition. However, insecticide-exposed males did not have their pheromone production affected compared to non-exposed males. Sublethal insecticide exposure compromised the net reproductive rate (Ro) compromising the intrinsic rate of population growth (rm) of the cotton boll weevil.

Insecticide

pheromone

reproductive fitness and sublethal concentration

The use of insecticides for pest control is the basis for the management and control of several insect species of economic importance (Matthews 2008), including the boll weevil, Anthonomus grandis grandis Boheman (Coleoptera: Curculionidae). Among the most used insecticides in Brazil for control this pest the organophosphorus molecules, malathion, and the pyrethroid beta-cyfluthrin are prevalent. These chemicals are applied with a high periodicity, every 3 to 5 days during the reproductive phase of cotton crops¹, to reach successful control of A. grandis. The negative consequences of this practice are known, but often overlooked (Köhler 2013). Among these consequences, the development of resistance to insecticides and the impact on non-target species, such as natural enemies, pollinators and detritivorous insects, can be mentioned (Bernardes et al. 2022).

Traditionally, the toxicity of insecticides to arthropods is assessed by determining the median lethal dose or concentration (LD₅₀ or LC₅₀) (Stack Mills 2022). However, the constant application of insecticide in crop areas and its consequent degradation allows insects, pests or beneficial ones, to be continuously subjected to sublethal exposure of these compounds (Bernardes et al. 2022). Despite the greater concern with natural enemies and pollinating insects (Barbosa et al. 2015), sublethal exposure to insecticides is an important and frequent condition also for pest insects (Bernardes et al. 2022; Guedes et al. 2016).

Among the sublethal effects, behavioral changes deserve special consideration as they potentially affect density-dependent relationships and population dynamics (Guedes et al. 2016). According to this study, the behavior of insects is the result of the interaction between their physiology and the environment to which they are exposed. An environment contaminated with insecticide will cause physiological changes in the insect's individual response, which may vary according to the mode of action of each chemical (Guedes et al. 2016). As a consequence of these changes, the performance of each individual may be reduced or improved, varying even with sex (Santos et al. 2018).

Insect behavior is commonly modulated by the presence of pheromones (Anton et al. 2021). In insects, the perception of pheromones involves the excitation of specific receptors that trigger the transmission of nerve impulses integrated by the central nervous system (Wang et al. 2022). Neurotoxic insecticides, which affect nerve transmission, can not only interfere with the recognition of pheromone but also with its biosynthesis (Müller 2018). The boll weevil, for example, uses the aggregation pheromone released by the male to locate the host by colonizing it, and facilitating mating (Lima et al. 2013). Thus, the effects of sublethal exposure to neurotoxic insecticides can lead to a reduction or interruption in the production of pheromone and/or difficulty in its perception, decreasing the attraction of new insects and mating. Changes in the insect's organism can also be reflected in the reproductive potential (Tuelher et al. 2016). The results observed in these studies have direct consequences for the management of the pest, as they help in controlling the population of pest insects and, consequently, in reducing the dose or the frequency of application of insecticides (Desneux et al. 2004).

Thus, this work aimed to elucidate possible behavioral changes caused by the insecticides malathion and beta-cyfluthrin in the perception and release of aggregation pheromone by the boll weevil and, possible effects on its reproductive capacity.

Insects

Anthonomus grandis grandis adults were obtained from a colony maintained at Embrapa Genetic Resources and Biotechnology, in Brasília, DF, Brazil (15° 46' 46" S, 47° 55' 46 W). Insects were maintained in plastic Petri dishes (90 x 15 mm) in controlled environmental chambers (25 ± 2°C, 65 ± 10% RH, 14:10 L:D photoperiod) and reared in an artificial diet based on a mixture of agar, yeast, wheat germ, soy protein, glucose, ascorbic acid and sorbic acid, nipagin, embryo cottonseed flour (Pharmamedia®, Traders Protein,USA), mixture of Wesson salts, Vanderzant vitamin and water (Da Silva et al. 2022). The newly emerged adults were separated by sex (Suh et al. 2020), transferred to Petri dishes (20 insects /Petri dish). And feed with an artificial diet.

Plants

Gossypium hirsutum L. (genotype Delta Opal obtained by MDM-Maeda DeltaPine Monsanto, in Uberlândia – MG) were grown individually in 1.5 L pots filled with soil and organic substrate (in proportion of 1:1). Plants were grown in a greenhouse under controlled conditions temperature 27 ± 1ºC and photoperiod 14:10 LD. Cotton plants used in experiments were 12 weeks old at the reproductive stage (presence of squares).

Concentration- and time-mortality bioassay

Time-mortality bioassays were carried out to record the median survival time for the boll weevil adults using a range of exposure times, and each subjected to a range of insecticide concentrations. The concentrations used initially were based on the maximum concentration recommended for application in the field. For malathion, the concentrations evaluated were: 1000, 500, 400, 300, 200 and 100 g (active ingredient a.i) a.i./L (emulsifiable concentrate, FMC, Uberaba, MG, Brazil). For beta-cyfluthrin, concentrations evaluated were: 125, 62.5, 50, 37.5, 25 and 12.5 g a.i./L (concentrated suspension, Bayer CropScience, Belford Roxo, RJ, Brazil). Each insecticide was diluted in distilled water and 1mL of solution was applied to a transparent glass surface (90 x 15 mm) (Yuan and Chambers 1998) homogeneously. The control treatment was carried out without the use of insecticides (only distilled water), used to assess natural mortality. After application, the water was allowed to evaporate keeping the plates at ambient temperature for 24 hours. The top of the Petri dish was brushed with petroleum jelly to prevent the insects from escaping.

For each insecticide and concentration in each time-mortality bioassay, two replicates with 30 insects each were used. Each replicate consisted of a glass Petri dish. The design used was completely randomized. Mortality assessments were made at discrete (and independent) time intervals for each insecticide and concentration. The data thus obtained were submitted to time-mortality analysis using probit (PROBIT procedure; SAS, SAS Institute, Cary, NC, USA). The endpoint estimates of median lethal time (LT₅₀) were subsequently regressed against insecticide concentration using the curve-fitting procedure of TableCurve 2D (Systat Software, San Jose, CA, USA). Model selection was based on parsimony, high F-values and steep R² increase with model complexity, indicating that the complexity chosen for the model significantly improved the explanatory capacity of the data, justifying the inclusion of the parameters in the model.

Behavioral bioassay

Adult boll weevils were exposed to 100 g a.i. / L of malathion, per 1 min, and to beta-cyfluthrin, concentration 25 g i.a./L per 1.0 min. Each Petri dish received 1 mL of insecticidal suspension at the desired concentration (Yuan and Chambers 1998). The insecticidal residue was dried in fresh air for 24 hours, after which 30 adult insects were placed into each Petri dish, with three replicates for each insecticide. The top of the Petri dish was brushed with odorless talc to prevent insects from escaping. A control treatment (with distilled water only) was used to determine the natural mortality. Insect mortality was assessed until all insects were dead. Insects were recognized as dead when they were unable to walk coordinately, even when touched with a fine hair brush. These concentrations and exposure times were established in order to allow maximum exposure with reduced mortality of individuals, providing an adequate number of surviving individuals for the experiments and quantification of the variables with maximum accuracy and precision (Oliveira-Marra et al. 2019)

Pyrethroid Insecticide can cause a marked initial knock-down effect on insects, which can remain paralyzed and, later, return to normal movements (Casida and Durkin 2013). In order to ensure the correct observation of the possible effects of exposure to insecticides after their full recovery, the responsiveness to the grandlure synthetic pheromone was assessed after 24 h and 96 h of exposure to insecticides in tests performed on an olfactometer.

For the bioassays, an olfactometer made of Y-shaped acrylic plate was used, with the central body of 7.7 x 1.3 cm and two arms of 7.0 x 1.3 cm each. The olfactometer was closed, both at the top and at the bottom, with glass plates. The air filtered through activated charcoal (4–20 mesh, Supelco) and humidified was conducted using an aquarium pump (flow of 1.0 L min^− 1), through silicone hoses, to the arms of the olfactometer. In one arm, a glass syringe containing the sex pheromone grandlure (Luretape BW-10 from Biocontrole®, Emigsville, PA, USA) was connected to thte silicone hoses. In the other arm of the olfactometer, only filter air pass across sytinge and silicone hoses, constituting the control treatment. For a clean air flow, a suction pump was connected at the opposite end to the olfactometer inlet (0.6 L min^− 1). Males and females, virgins, 7 days old (N = 40 for each sex) of cottonweed were individually placed on the olfactometer and their behavior observed for a period of up to 5.0 minutes. The measured variable was called “initial choice”, that is, the first arm of the olfactometer through which the insect enters, in more than half of its length. Every five bioassays the position of each treatment was inverted to avoid position bias.

The data of the choices made by the individuals in each treatment were analyzed by the chi-square test (at 5% significance) using the statistical program R 3.4.3 (R Statistical Software) and testing the null hypothesis of non-preference for between one of the treatments (50% of choice for pheromone or control).

Volatile collections

Ninedays-old males of the cotton weevil were exposed to malathion (N = 6 individuals) at 10% of the field concentration, 0.2 L pc. / ha (100 g ia / L), and beta-cyfluthrin (N = 9 individuals) at 20% of the field concentration (20 mL pc / ha), both for 1.0 min, following the methodology described previously. These concentrations and exposure times were predetermined according to the time-mortality curves described above. The control was exposed to a surface containing distilled water (N = 9 individuals). After exposure, the insects remained for 24 hours without feeding and subsequently placed in pairs in contact with cotton plants in reproductive stage, without previous attack, conditioned in a glass cylinder (10 L internal volume). In this system, aerations were carried out by a push-pull system with the air entering into the chambers by means of a compressor with an air flow of 1 L.min-1, connected to an activated charcoal filter. The air was exhausted through a vacuum pump, at a flow rate of 0.6 L.min^− 1, connected to a glass tube containing an adsorbent polymer, via polytetrafluoroethylene (PTFE) connections. The volatiles were collected every 24 h, for four consecutive days, in glass tubes containing 60 mg of Porapak Q (50–80 mesh, Sigma-Aldrich, Bellefonte, PA, USA). These were eluted from the adsorbent tubes using 500 µL of the organic solvent n-hexane and concentrated to 50 µL under N₂ flow. The samples obtained were stored at -20ºC until use in a gas chromatograph coupled to the flame ionization detector (CG-DIC) and CG coupled to the mass spectrometer (CG-EM).

Chemical analysis

For analysis of volatile samples, 1 µL of each solution was injected into the GC (Agilent 7890-A, non-polar column DB-5MS, 0.32 mm in diameter x 60 m in length and 0.25 µm film, Supelco, Bellefonte, PA, USA), with flame ionization detector (FID), using splitless mode and using helium as carrier gas. The initial temperature of the ramp was 50° C for 2 min, gradually increasing by 5°C.min-1 until reaching 180°C, where it was maintained for 0.1 min, followed by a second gradual increase of 10°C min ^− 1 until reaching 250°C, remaining at that temperature for 20 min. The detector temperature was 270°C and the injector temperature was 250°C.

For qualitative analysis, selected samples were injected into the CG-MS (Agilent 5975-MSD) equipped with a quadrupole analyzer, in a DB-5MS apolar column (0.25 mm in diameter x 30 m in length, with 0.25 µm film, Supelco, Bellefonte, PA, USA), with electron impact ionization (70 -eV, temperature 200°C) and injector in splitless mode. Helium was used as the carrier gas. The data were collected and analyzed with the ChemStation software. The identification of volatile compounds was performed by comparing the fragmentation pattern of the sample components with that of cataloged data in spectral libraries (NIST 2008).

For the quantitative analysis the ratio between the four pheromone components of the cotton weevil was obtained using the area obtained from the chromatography analysis (GC-FID). Pheromone components: [cis-2-isopropenyl-1-methylcyclobutane-ethanol (grandlure I), cis-2-(3,3- dimethyl)-cyclohexylidene-ethanol (grandlure II), cis-3,3-dimethylcyclohexylidene- acetaldehyde (grandlure III) and trans-3,3-dimethylcyclohexylidene-acetaldehyde (grandlure IV)]. The proportions between the components of the pheromone obtained were compared using Kruskal-Wallis (P < 0.05). The presence or absence of the four main components release by the insects inside each chamber was observed during the evaluation periods (0–24, 24–48, 48–72 and 72–96 h). The same plants and insects were used along the experimental period. The influence of the treatments on the pheromone release were tested using athe generalized linear model of repeated measures (GLM) with binomial error distribution. The mean quantities of pheromone production from insects submitted to different treatments were compared through contrast analysis. The determination of the proportion of individuals capable of releasing pheromone by treatment, as well as their confidence interval, were performed using a generalized linear model (GLM) with binomial error distribution. All analyzes were performed using the statistical program R 3.4.3 (R Statistical Software).

Fertility table bioassay

Newly emerged males and females were sexed and kept in a Petri dish containing the diet for seven days, until their complete sexual maturation (Showler et al. 2004). After this period, the insects were exposed to dry insecticide residue, as described above and at the desired concentration and exposure time (Guimarães et al. 2008). The insecticide malathion (100 g a.i./L) was used for 1.0 min and beta-cyfluthrin (25 g a.i./L) for 1.0 min. The control was treated with sterile distilled water (Yuan and Chambers 2008).

The couples stayed together for 48 hours to ensure mating. After this period, the couples were separated, and the females were observed and evaluated until their death. Each female constituted an experimental unit, totaling 15 experimental units per treatment. The tests were carried out in a completely randomized design, which were placed in an air-conditioned room, at a temperature of 26 ± 2 ° C, RH, 70 ± 5% and a photophase of 12 hours. The treatments consisted of: 1) non-exposed male and female; 2) exposed male; 3) exposed female; 4) exposed male and female. The number of eggs deposited by mated females was checked daily and they were placed in a Petri dish containing an artificial diet to determine the viability of the eggs. The pre-oviposition period (time established between the emergence of the female and the beginning of the laying), total and average fertility (number of eggs / female), the oviposition period (laying period) and the longevity of females in each treatment were determined. From the data on survival and oviposition, fertility tables were drawn up (Garcia et al. 2006). Subsequently, the average number of eggs per female (mx) was calculated on each oviposition date (x), considering the total number of females, the accumulated female survival index (lx) during the oviposition period, and the number of descendants who reached age x. These values constituted the columns of the life tables (Teodoro et al. 2014).

Based on the information condensed in the fertility table, the following parameters were estimated for each treatment (Chi et al. 2020): average generation time (days), which represents the average time between laying a generation and the posture of the next generation; net reproduction rate (Ro), which is the estimate of the average number of offspring generated per female over the oviposition period and which will reach the next generation; and intrinsic growth rate (rm), which is the factor related to the population growth rate (daily production of progeny per adult female).

The estimates of the parameters of the fertility life table were performed using the jackknife method, using a protocol developed for the R statistical program (Maia et al. 2014). The means were compared by the Tukey HSD test to P < 0,05.

Survival time under insecticidal exposure

The time-mortality curves of adult cotton boll weevils showed significant differences upon exposure to increasing concentrations of beta-cyfluthrin (c² = 117.37, df = 4, P < 0.001) and malathion (c² = 537,97, df = 6, P < 0.001). Estimates of median survival time for boll weevil adults obtained through these analyzes showed a significant decline with increased concentration of both beta-cyfluthrim and malathion (Fig. 1). These bioassays made it possible to select the concentrations of 25 and 100 mg a.i./mL for beta-cyfluthrin and malathion, respectively, but maintaining a time of 1 min just to equal mortality in the control (without insecticidal exposure). Thus, an exposure time of 1 min was defined for both insecticides in these two concentrations, which was subsequently used in the other tests because they are sublethal.

Behavioral bioassay and volatile collection

Insects exposed to malathion (100 mg ai / mL for 1 minute) did not have the ability to differentiate pheromone and control treatment after 24 hours (Male:χ2 = 2.5, df = 1, P = 0.9, female: χ2 = 2. 57, df = 1, P = 0.11) and after 96 hours of exposure (Male: χ2= 0.9, df = 1, P = 0.34, female: χ2 = 0.64, df = 1, P = 0.42). Similarly, males and females exposed to the beta-cyfluthrin insecticide (25 g ia / L for 1 minute), after 24 hours (Male: χ2 = 1,6 , df = 1, P = 0,2, female: χ2 = 0,11 , df = 1, P = 0,74) and after 96 hours (Male: χ2 = 2,6 , d f= 1, P = 0,32 , female: χ2 = 1,3 , df = 1, P = 0,65) of exposure also did not recognize the pheromone (Figure 2). In contrast to these results, the insects of the control treatment showed the ability to choose the pheromone in detriment to the control treatment after 24 hours (Male: χ2 = 5,4 , df = 1, P = 0,02, female: χ2 = 5,1 , df = 1, P = 0,02) and after 96 hours (Male: χ2 = 7,7 , df = 1, P = 0,05 , female: χ2 = 8,8, df = 1, P = 0,003). Assessments made after 96 hours of exposure indicate that the effect does not appear to be temporary (Desneux et al. 2004).

Regardless of the treatments, males showed the ability to release pheromone aggregation, not differing significantly between treatments (χ2₂=0.00, P=1) or between release periods (χ2₁=1.824, P=0.177). Although there is a significant effect on the interaction between treatments and period (χ2₁=123.9, P<0.001), the mean pheromone released by insects in each time period did not differ between treatments (contrast analyses P>0,05) (Figure 3).

The aggregation pheromone was emitted by exposed and non-exposed insects. Figure 1 in the supplementary materials shows the chromatographic profile (pA) of volatiles from males of A. grandis grandis Boh. after exposure to the tested insecticides.

The ratio between the components of the pheromone released in the unexposed insects, and malathion and beta-cyfluthrin exposed insects treatments were, respectively: 42:35:11:12; 55:36:5:4; 38:31:14:17, showing no significant variation between the treatments (H = 0.15, df = 2. P = 0.93; figure 4).

Fertility table

The parameters of the fertility life table, estimated using the Jackknife method (P <0.05), indicate that males and females exposed to sublethal dosage of the insecticides malathion and beta-cyfluthrin showed a reduction in the population growth potential. The net reproductive rate (Ro) of individuals exposed to both insecticides was significantly lower when compared to females belonging to the control treatment (Figure 5A and 5B). The generation time did not show any significant difference between the treatments, except for the male treatment exposed to beta-cyfluthrin, whose generation time was significantly shorter than the others (Figure 5C and Figure 5D). Malathion exposure affected the intrinsic population growth rate (rm) (Figure 5E).

Although the conditions of insecticides in the field are constantly changing, the main focus of toxicological studies is mortality, neglecting the effects caused by sublethal exposure and their impacts on pest management (Barbosa et al. 2015; Guedes and Cutler 2014; Guedes et al. 2016). In this work, the two most used insecticides for the control of the cotton weevil were evaluated in terms of sublethal effects related to reproductive potential (Oliveira-Marra et al. 2019).

It was hypothesized that sublethal exposure to beta-cyfluthrin and malathion would affect the ability to perceive and release aggregation (or sexual) pheromone. It was also hypothesized that these effects could be reflected in reproductive capacity, with possible differences in responses depending on the exposed gender.

According to the results observed in this study, both insecticides negatively affected the ability of males and females to recognize the aggregation (or sexual) pheromone released by the male 96 hours after the exposition. This result shows that the insect does not have a fast recovery capacity after treated with these two insecticides. However, exposure to insecticides did not affect the pheromone's ability of production and emission. The lack of effect on the pheromone production can be related to the faster recovery of insecticide exposed-insects due to these ones were allowed to remain in a bigger chamber with cotton plants, and they feed on a natural diet, ie, cotton plants.

Although some studies have shown positive responses in the perception of pheromone (Umoru et al. 1996), most of the cases reported in the literature demonstrate that insecticides negatively affect intraspecific communication, both in relation to pheromone synthesis and in the ability to respond to this (Desneux et al. 2004), corroborating with the results observed in this study.

In this sense, it was observed (Floyd and Crowder 1981) that responses of males of Pectinophora gossypiella (Lepdoptera: Gelechiidae) surviving the LD₅₀ of permethrin showed lethargy to the synthetic pheromone, reducing their ability to locate the source of sexual pheromone and, possibly, mating. Similarly, it was demonstrated (Delpuech et al. 2001) that the insecticide chlorpyrifos (DL₂₀) impaired the ability of males of Trichogramma brassicae (Hymenoptera: Trichogrammatidae) to respond to the sexual pheromone released by the female.

For the cotton weevil, these results directly affect the attractiveness of traps containing baits with aggregation pheromone, reducing their attractiveness and underestimating the population levels. Further studies should be conducted to evaluate the weekly boll weevil captures in traps, comparing areas with and without insecticide application, in order to quantify the insecticide's negative impact on trap efficiency.

In certain cases, exposure to neurotoxic insecticides can alter the proportions of the components in released pheromones (Moore and Marler 1987). Sublethal exposure of Trichogramma brassicae Bezdenko (Hymenoptera: Trichogrammatidae) to deltamethrin, for instance, was observed to affect the insect’s ability to attract using pheromones (Delpuech et al. 1999). Similar effects were reported in Heliothis virescens (F.) (Lepidoptera: Noctuidae). Therefore, monitoring the proportions of pheromone components in the sample is crucial for understanding the recipient’s behavioral response.

In the case of male cotton boll weevils exposed to the insecticides tested in this study, the proportions of pheromone components remained close to those reported in the literature. The proportions varied from (52:39:4:4) (Hedin et al. 1974) and (6:6:2:1) to (42:42:5:10), (42.5:42.5:5:10) (Spurgeon 2003), (45:42:3:10) (Spurgeon and Suh 2007), (44:43:3:10) (Spurgeon and Suh 2009), and (32:38:15:15) (Suh et al. 2013). Despite these differences, all mixtures were equally attractive. This variability is often attributed to different volatile collection methods and the age of the insects (Spurgeon 2003).

Despite the variability of proportions in the pheromone components demonstrated in the literature, the proportions found in this work are consistent with the predictions that components grandlure I and II (alcohols) are produced in greater quantities than grandlure III and IV (aldehydes) and that the proportions between I and II are more constant than the proportions between III and IV (Mitlin and Hedin 1974). The variability found between components III and IV may be related to the low stability of these compounds, since aldehydes, in general, are more unstable than alcohols in the presence of oxygen (Guimarães et al. 2008).

The reproductive potential of males and females of the cotton weevil exposed to neurotoxic insecticides was evaluated considering the effect of exposure on parameters of the fertility table. The net reproductive rate (Ro) of populations exposed to both insecticides showed a significant reduction, regardless of treatment, when compared to the control. These results indicate that exposure to insecticides, under the conditions tested, reduces the number of offspring that each female can generate, thus reducing the potential growth of the population. Malathion did not interfere with the average generation time, unlike beta-cyfluthrin, which led to a reduction in this variable. This result could indicate that new generations would occur in the field in a shorter time. However, the population growth rate, represented by the intrinsic population growth rate (r_m), was lower for insects exposed to beta-cyfluthrin, which can help to keep population growth low. Malathion, in contrast, interfered with the intrinsic (population) growth rate only in the treatment with contaminated male. These results indicate that there is a reduction in the population growth potential when males and females are sublethally exposed to malathion and beta-cyfluthrin, determined by the reduction of the net reproductive rate (Ro) and the intrinsic population growth rate (r_m).

The results presented in this study corroborate those observed in previous studies with other species (Storch 2003), in which sublethal exposure to malathion was able to reduce the fecundity and fertility of Culex quinquefasciatus Say (Diptera: Culicidae) mosquitoes. A 51.5% reduction in progeny production of Anticarsia gemmatalis Hübner (Coleoptera: Noctuidae) was observed when females were exposed sublethally to lambda-cyhalothrin (Storch et al. 2014).

Spodoptera frugiperda Smith caterpillars (Coleoptera: Noctuidae) exposed to LC₁₀ of malathion and lambda-cyhalothrin reduced the fertility of females (Abd-Elghafar and Appel 1992). Similar effects were also observed in populations of cockroaches Blattella germanica L. (Blattodea: Blattellidae) which, when exposed to sublethal doses of neurotoxic insecticides, had reduced fertility (Abd-Elghafar and Appel 1992). It is possible to hypothesize that the adverse effects caused by neurotoxic insecticides, reflected in fertility and fecundity, are likely due to interference in the coordination between the nervous and hormonal systems resulting in the interruption of behavioral and physiological events involved in the reproductive capacity of insects (Delpuech 2001).

The results observed in this study are particularly important when the objective is integrated pest management, helping to keep the insect pest population below damage levels with a significant reduction in the applied insecticide concentration or frequency of application. This possibility represents a lower cost in pest control, minimizes the risk of developing resistant populations (Wolfson and Murdock 1995), reduces environmental impacts and increases security for rural workers, corresponding to society's desires for more sustainable agriculture. However, it is important to highlight that the loss of the insect's ability to perceive the pheromone can impair the use of traps containing synthetic pheromone. Thus, new studies must be carried out in areas where neurotoxic insecticides are applied in order to avoid underestimating the damage caused by the insect in the crop.

The sublehtal exposure to the neurotoxic insecticides malathion and beta-cyfluthrin compromised the perception capacity of the aggregation (or sexual) pheromone released by males, both in males and in females. Such effects translated into fertility table parameters, where decrease in population growth was observed. Therefore, sublethal insecticide exposure affect the population growth of the insect, preventing populations from reaching densities of individuals above the desired and reducing damage to the crop, but also can compromise insect capture in pheromone-baited traps limiting the potential of this monitoring technique.

Author Contribution

Sharrine Omari carried out laboratory tests, wrote her doctoral thesis and this manuscript.Wagner F., Marinaldo L. and Paulo S. performed the statistical analysis Raul A. , Maria Carolina, Raul Guedes and Miguel Borges provided the materials and equipment to carry out the research and guided the development of the research Anderson M. is the doctoral advisorAll the authors reviewed the manuscript

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No competing interests reported.

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Pheromone release and perception, and fertility of insecticide-exposed cotton boll weevils (Anthonomus grandis grandis)

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Abstract

Figures

Introduction

Material and methods

Insects

Plants

Concentration- and time-mortality bioassay

Behavioral bioassay

Volatile collections

Chemical analysis

Fertility table bioassay

Results

Survival time under insecticidal exposure

Behavioral bioassay and volatile collection

Fertility table

Discussion

Conclusion

Declarations

Author Contribution

References

Additional Declarations

Supplementary Files

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