Deltamethrin toxicity and impaired swimming behavior of two backswimmer species

Descriptions of new species and new records of water bugs (Hemiptera: Heteroptera: Gerromorpha & Nepomorpha) from southeastern Brazil

Although most of the diversity of true bugs (Hemiptera: Heteroptera) is terrestrial, over 550 species of water bugs (Heteroptera: Gerromorpha, Leptopodomorpha & Nepomorpha) have been recorded from Brazil alone. Southeastern Brazil, composed of the states of Esprito Santo, Minas Gerais, Rio de Janeiro and So Paulo, is the best studied region of the country, but there are still knowledge gaps in the area. Here, two new species are described from Esprito Santo: Hydrometra ruschii Cordeiro, Rodrigues & Moreira, sp. nov. and H. tuberculata Cordeiro, Rodrigues & Moreira, sp. nov. (Gerromorpha: Hydrometridae). Furthermore, new records from southeastern Brazil are provided for 78 species of water bugs, of which 19 are firstly recorded from Esprito Santo, four from Minas Gerais, eight from Rio de Janeiro, and seven from So Paulo.

Characterization in Potent Modulation on Voltage-Gated Na+ Current Exerted by Deltamethrin, a Pyrethroid Insecticide

Deltamethrin (DLT) is a type-II pyrethroid ester insecticide used in agricultural and domestic applications as well as in public health. However, transmembrane ionic channels perturbed by this compound remain largely unclear, although the agent is thought to alter the gating characteristics of voltage-gated Na⁺ (Na_V) channel current. In this study, we reappraised whether and how it and other related compounds can make any further modifications on voltage-gated Na⁺ current (I_Na) in pituitary tumor (GH₃) cells. Cell exposure to DLT produced a differential and dose-dependent stimulation of peak (transient, I_Na(T)) or sustained (late, I_Na(L)) I_Na; consequently, the EC₅₀ value required for DLT-stimulated I_Na(T) or I_Na(L) was determined to be 11.2 or 2.5 μM, respectively. However, neither the fast nor slow component in the inactivation time constant of I_Na(T) activated by short depolarizing pulse was changed with the DLT presence; conversely, tefluthrin (Tef), a type-I pyrethroid insecticide, can accentuate I_Na with a slowing in inactivation time course of the current. The I_Na(L) augmented by DLT was attenuated by further application of either dapagliflozin (Dapa) or amiloride, but not by chlorotoxin. During pulse train (PT) stimulation, with the Tef or DLT presence, the cumulative inhibition of I_Na(T) became slowed; moreover, following PT stimuli, a large tail current with a slowly recovering process was observed. Alternatively, during rapid depolarizing pulse, the amplitude of I_Na(L) and tail I_Na (I_Na(Tail)) for each depolarizing pulse became progressively increased by adding DLT, not by Tef. The recovery time constant following PT stimulation with continued presence of Tef or DLT was shortened by further addition of Dapa. The voltage-dependent hysteresis (Hys_(V)) of persistent I_Na was differentially augmented by Tef or DLT. Taken together, the magnitude, gating, frequency dependence, as well as Hys_(V) behavior of I_Na exerted by the presence of DLT or Tef might exert a synergistic impact on varying functional activities of excitable cells in culture or in vivo.

Deltamethrin-Induced Respiratory and Behavioral Effects and Adverse Outcome Pathways (AOP) in Short-Term Exposed Mozambique Tilapia, Oreochromis mossambicus

Disrupted behavior and respiratory distress effects of 96-h acute deltamethrin exposures in adult Mozambique tilapia, Oreochromis mossambicus, were investigated using behavioral indices and opercular movement, respectively. Deltamethrin concentrations were found to be associated with toxicological (lethal and sublethal) responses. At 24, 48, 72, and 96 h, the LC50 values and 95% confidence limits were 12.290 (11.174-14.411 µg/L), 12.671 (11.334-15.649 µg/L), 10.172 (9.310-11.193 µg/L), and 8.639 (7.860-9.417 µg/L), respectively. The GUTS-model analysis showed that GUTS-SD (stochastic death) with a narrow tolerance distribution in deltamethrin exposed O. mossambicus populations was more sensitive than the GUTS-IT (individual tolerance) model. Prior to death, exposed fish demonstrated concentration-dependent mortality and disturbed behavioral responses, including uncoordinated swim motions, increased mucus secretion, unbalanced and unpredictable swimming patterns, and inactivity. The altered behavioral patterns and increased opercular movement with increased deltamethrin levels and exposure time are strongly suggestive of neurotoxicity and respiratory distress, respectively. Adverse Outcome Pathways (AOPs), describing biological mechanisms and plausible pathways, highlighted oxidative stress and cholinergic effects as intermediate steps linked to respiratory distress and behavioral toxicity.

Sublethal exposure to pyriproxyfen does not impair the abilities of the backswimmer Buenoa amnigenus to prey upon Aedes aegypti larvae

Pyriproxyfen is a juvenile hormone analogue that is commonly used to control the immature stages of mosquitoes in both artificial and natural water reservoirs. Recently, concerns have been raised regarding the community effectiveness of pyriproxyfen in preventing vector-transmitted diseases. Such concerns have been based on the unintended effects on non-target organisms and the selection of resistant mosquito populations. This investigation was, therefore, conducted to evaluate the toxicity of pyriproxyfen to Aedes aegypti (Diptera: Culicidae) larvae and the backswimmer Buenoa amnigenus (Hemiptera: Notonectidae), a naturally occurring mosquito larvae predator. We also assessed the abilities of backswimmers exposed to sublethal levels of pyriproxyfen to prey upon mosquito larvae (L2) under three larval densities (3, 6, or 9 larvae/100 mL of water) using artificial containers. Our results revealed that pyriproxyfen killed backswimmers only at concentrations higher than 100 μg active ingredient [a.i.]/L, which is 10 times higher than that recommended for larvicidal field application (i.e, 10 μg a.i./L). The abilities of backswimmers exposed to sublethal levels of pyriproxyfen (100 μg a.i./L) to prey upon mosquito larvae were not affected. Harmful effects on the backswimmer predatory abilities were detected only at concentrations of 150 μg a.i./L and when there was a higher prey availability (i.e., 9 larvae/100 mL of water). Together, our findings indicate that the reduced community effectiveness of this insecticide derives from factors other than its detrimental effects on non-target organisms such as backswimmers.

Exposures to deltamethrin on immature Chironomus columbiensis drive sublethal and transgenerational effects on their reproduction and wing morphology

Sublethal exposure to insecticides can trigger unintended responses in non-target insects that may disrupt reproductive and developmental performances of these organisms. Here, we assessed whether sublethal exposure to the pyrethroid insecticide deltamethrin in early life had sublethal and transgenerational effects on the reproduction (i.e., fecundity and fertility) and wing morphology of Chironomus columbiensis, an aquatic insect used as a water quality indicator. We first conducted concentration-response bioassays to evaluate the susceptibility of C. columbiensis larvae to deltamethrin. Our results revealed that deltamethrin toxicity was approximately 7-fold higher when C. columbiensis larvae where exposed to 96 h (LC₅₀ = 0.17 [0.15-0.20] μg/L) than to 24 h (LC₅₀ = 1.17 [0.97-1.43] μg/L). Furthermore, the sublethal exposures (at LC₁ = 0.02 μg/L or LC₁₀ = 0.05 μg/L) of immature C. columbiensis resulted in lower fecundity (e.g., reduced eggs production) and morphometric variation wing shapes. Further reduction in fertility rates (quantity of viable eggs) occurred at deltamethrin LC₁₀ (0.05 μg/L). Almost 80% of the fecundity was recovered with only a single recovery generation; however, two subsequent recovery generations were not sufficient to fully recover fecundity in C. columbiensis. Specimens recovered from 98.5% of wing morphometric variation after two consecutive generations without deltamethrin exposure. Collectively, our findings demonstrates that sublethal exposure to synthetic pyrethroids such as deltamethrin detrimentally affect the reproduction and wing shape of C. columbiensis, but also indicate that proper management of these compounds (e.g., concentration and frequency of application) would suffice for these insects' population recovery.

Pyrethroid bioaccumulation in wild fish linked to geographic distribution and feeding habit

The accumulation of pyrethroid insecticides in aquatic food webs has attracted increased research attention. Fish are key species in aquatic food webs, directly connecting invertebrates and human consumption. However, little is known about the bioaccumulation of pyrethroids in wild fish species. In this study, 19 species of wild fish were collected from 11 sites in the Pearl River, China, and the levels of seven pyrethroids in the fish were determined. Linear mixed-effects models were applied to estimate the means of pyrethroid concentrations, in which sample site and fish species were set as random effects. The concentrations of Σ₇ pyrethroids in fish ranged from 4.99 to 50.82 ng/g. Permethrin and bifenthrin were present at the highest concentration (8.89 ± 1.47 ng/g) and frequency (100%) in fish muscle, respectively. The composition patterns of pyrethroids varied in fish organs. Fish species contributed a higher proportion of the variance than geographic distribution (28.6% vs. 26.4%). The pyrethroids in carnivorous fish (23.5 ± 2.9 ng/g) were significantly higher than in omnivorous (14.6 ± 1.9 ng/g) and phytophagous fish (16.0 ± 4.7 ng/g). To our knowledge, this is the first report examining the effect of feeding habits on pyrethroid bioaccumulation in wild fish. The results can provide evidence for the risk of pyrethroid pollution in aquatic ecosystems.

Pollution impacts on water bugs (Nepomorpha, Gerromorpha): state of the art and their biomonitoring potential

As water pollution poses an increasing risk worldwide, it is timely to assess the achievements of the aquatic macroinvertebrate ecotoxicology to provide a sound basis for the discipline's future and support the development of biomonitoring. Aquatic and semi-aquatic bugs (Hemiptera: Nepomorpha, Gerromorpha) are ubiquitous in almost all water types, sometimes in high densities, and play a significant role in organic material turnover and energy flow. Nevertheless, they are ignored in the water pollution biomonitoring schemes. Here, based on 300 papers, we review and evaluate the effects of chemical pesticides, microorganism-derived pesticides, insecticides of plant origin, heavy metals, eutrophication, salinisation and light pollution which are summarised for the first time. Our review encompasses the results of 100 laboratory and 39 semi-field/field experiments with 47 pesticides and 70 active ingredients. Pyrethroids were found to be more toxic than organochlorine, organophosphate and neonicotinoid insecticides to water bugs, like other macroinvertebrate groups. Additionally, in 10 out of 17 cases, the recommended field concentration of the pesticide was higher than the LC50 values, indicating potential hazards to water bugs. The recommended field concentrations of pesticides used in mosquito larvae control were found non-toxic to water bugs. As very few replicated studies are available, other findings on the effects of pesticides cannot be generalised. The microorganism-derived pesticide Bti appears to be safe when used at the recommended field concentration. Data indicates that plant-derived pesticides are safe with a high degree of certainty. We have identified three research areas where water bugs could be better involved in water biomonitoring. First, some Halobates spp. are excellent, and Gerris spp. are promising sentinels for Cd contamination. Second, Micronecta and, to a certain extent, Corixidae species composition is connected to and the indicator of eutrophication. Third, the species composition of the Corixidae is related to salinisation, and a preliminary method to quantify the relationship is already available. Our review highlights the potential of water bugs in water pollution monitoring.

Effects of Some Insecticides (Deltamethrin and Malathion) and Lemongrass Oil on Fruit Fly (Drosophila melanogaster)

<b>Background and Objective:</b> The continuous use of pesticides in the ecosystem is of great concern, as some of them are highly stable and impact non-target organisms. The effect was tested of different concentrations of insecticides such as (Deltamethrin and Malathion) and natural products, Including, lemongrass oil on Fruit Fly (<i>Drosophila melanogaster</i>), to calculate the concentration at which the highest mortality occurred and death half the number of individuals after 96 hrs, as well as calculating the half-lethal time for individuals. <b>Materials and Methods:</b> This study, which evaluated the toxicity of five different concentrations (0.75, 1.00, 1.25, 1.50 and 1.75 mg L<sup>1</sup>) of Malathion, (0.05, 0.10, 0.21, 0.53 and 1.48 mg L<sup>1</sup>) of Deltamethrin and lemongrass oil (0.25, 0.50, 0.75, 1.00 and 1.50 mg L<sup>1</sup>) on the insect of <i>Drosophila melanogaster</i> after 96 hrs of treatment. <b>Results:</b> From the results of this study, the concentration (LC<sub>50 </sub>= 2.938 mg L<sup>1</sup>) of Malathion leads to kills half of the individuals, compared to Deltamethrin a higher concentration (LC<sub>50 </sub>= 4.8673 mg L<sup>1</sup>) that leads to killing half of the individuals. While lemongrass oil the concentration (LC<sub>50 </sub>= 9.7478 mg L<sup>1</sup>) leads to kills half of individuals. Also, when used Deltamethrin it takes (LT<sub>50 </sub>= 660.277) hours to kill half of the individuals compared to Malathion, which takes approximately (LT<sub>50</sub> = 321.862) hours to death half of the individuals. But lemongrass oil (LT<sub>50 </sub>= 819.745) hours to kill half of the individuals. <b>Conclusion:</b> In conclusion, the lemon plant and its components have excellent potential for being used in the control of <i>Drosophila melanogaster</i>, which had an effective role in biological control.

Detrimental effects of pyriproxyfen on the detoxification and abilities of Belostoma anurum to prey upon Aedes aegypti larvae

Despite being effective in controlling mosquito larvae and a few other target organisms, the application of insecticides into aquatic systems may cause unintended alterations to the physiology or behavioral responses of several aquatic non-target organisms, which can ultimately lead to their death. Here, we firstly evaluated whether the susceptibility of the giant water bug, Belostoma anurum (Hemiptera: Belostomatidae), a predator of mosquito larvae, to pyriproxyfen would be similar to that of its potential prey, larvae of Aedes aegypti (Diptera: Culicidae). Secondly, we recorded the nominal concentrations of pyriproxyfen in water and evaluated whether sublethal exposures would lead to physiological or behavioral alterations on the B. anurum nymphs. We characterized the activities of three major families of detoxification enzymes (i.e., cytochrome P450 monooxygenases, glutathione-S-transferase, and general esterases) and further evaluated the abilities of pyriproxyfen sublethally-exposed B. anurum to prey upon A. aegypti larvae at different prey densities. Our findings revealed that nominal pyriproxyfen concentration significantly decreased (approximately 50%) over the first 24 h. Furthermore, when applied at the concentration of 10 μg a.i./L, pyriproxyfen was approximately four times more toxic to A. aegypti larvae (LT₅₀ = 48 h) than to B. anurum nymphs (LT₅₀ = 192 h). Interestingly, the pyriproxyfen sublethally-exposed (2.5 μg a.i./L) B. anurum nymphs exhibited reduced enzyme activities (cytochrome P450 monooxygenases) involved in detoxication processes and preyed significantly less on A. aegypti larvae when compared to unexposed predators. Collectively, our findings demonstrate that mortality-based pyriproxyfen risk assessments are not always protective of aquatic non-target organisms.

Assessment of deltamethrin toxicity in Macrobrachium nipponense based on histopathology, oxidative stress and immunity damage

Deltamethrin (Del), a commonly used broad-spectrum insecticide, has been reported to have a toxic effect on aquatic animals, but knowledge in freshwater prawns is limited. This study revealed that Del is highly toxic to Macrobrachium nipponens with the 24 h, 48 h, 72 h, and 96 h LC₅₀ values to be 0.268, 0.165, 0.104, and 0.066 μg/L, respectively. To further investigate the toxic effect of Del in M. nipponense and the reversibility of damage, prawns were exposed to 0.05 μg/L Del for four days and then transferred into fresh water for seven days. Histopathological examination, oxidative stress, hepatopancreas function, respiration system, and immune system were analyzed through multiple biomarkers. Results showed that Del exposure caused severe histopathological damage to hepatopancreas and gill in M. nipponense, and the prominent decrease of acid phosphatase (ACP) and alkaline phosphatase (AKP) activity further enhanced the hepatopancreas damage; the accumulation of malonaldehyde (MDA) and hydrogen peroxide (H₂O₂), and the decrease of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) activity, indicated severe oxidative stress caused by Del. Besides, Del exposure also induced remarkably increased lactic acid (LD) level, decreased lactate dehydrogenase (LDH) activity, and decreased expression of immune-related genes, which demonstrated the respiration disruption and immunosuppression caused by Del. After 7-day decontamination in freshwater, the indicator of hepatopancreas function (ACP and AKP activity) and respiration (LD level and LDH activity) improved to the control group level. However, the histopathological damage and the biomarker in oxidative stress and immune system did not recover to the initial level.

Sublethal exposure to deltamethrin impairs maternal egg care in the European earwig Forficula auricularia

The application of pesticides typically leads to lethal and sublethal exposure of non-target insects. Whereas our current understanding of these sublethal effects typically focuses on reproductive and physiological parameters, recent works emphasize that sublethal effects on behaviors such as maternal care could be of major importance in non-target species. However, it remained unknown whether these sublethal effects occur in insects. Here, we tested if exposure to sublethal doses of deltamethrin - a pyrethroid insecticide commonly used in crops - alters the expression of maternal egg care in females of the European earwig Forficula auricularia, a predator insect and pest control. Our results first reveal that deltamethrin exposure impaired the expression of three forms of maternal egg care: It decreased the likelihood of mothers to gather their otherwise scattered clutch of eggs, increased the time during which the female abandoned the clutch after a predator attack and reduced egg grooming duration. These sublethal effects did not reflect a lower activity of deltamethrin-exposed females, as these females increased their expression of self-grooming, and deltamethrin exposure did not affect females' exploration and mobility. Finally, we found that the negative effects of deltamethrin on egg care did not modify egg development, hatching rate and juvenile weight, possibly due to the transient effects of deltamethrin on maternal behaviors. Overall, our results reveal that sublethal exposure to a pesticide may diminish maternal egg care in a natural pest control and call for the integration of this measurement in assays on pesticides application.

Life History Traits and Predatory Performance of Belostoma anurum (Hemiptera: Belostomatidae), a Biological Control Agent of Disease Vector Mosquitoes

Understanding the life cycle and dietary requirements of laboratory-reared insects is critical for optimizing resources (including time) and can provide more reliable ecological basis for using such biological control agents in realistic programs. Here, we evaluated the complete development and the predatory abilities of Belostoma anurum (Herrich-Schäffer, 1848) (Hemiptera: Belostomatidae), an aquatic predator widely distributed in Neotropical region, when reared at different diets. We firstly investigated the predatory performance of B. anurum nymphs upon mosquito larvae (i.e., larvae of Aedes aegypti (Linnaeus, 1758) or Culex sp. (Diptera: Culicidae)) and, second, whether the immature diets (i.e., arthropod-based diet (mosquito larvae and adults of Notonectidae) or vertebrate (fish larvae)-based diet) affect the predatory behavior of B. anurum adults. The B. anurum egg-to-adult developmental time was 85.1 days in an arthropod-based diet. However, when a fish-based diet was offered after nymphs reached 3rd instar, we recorded up to 50% reductions on the B. anurum developmental time. Interestingly, B. anurum adults could live more than 1 year under laboratory conditions, independently of the immature diet regime. Furthermore, the fish diet-experienced B. anurum adults spent less time feeding on fish larvae when compared with adults that never experienced this type of diet. Predatory results revealed that 2nd instar B. anurum were more efficient to catch and consume larvae of A. aegypti than of Culex sp. Collectively, our findings show that B. anurum is long-lived aquatic predators, and demonstrate the impacts of dietary regime on the life history traits and predatory performance of these insects.

Resistance to a chemical pesticide increases vulnerability to a biopesticide: Effects on direct mortality and mortality by predation

Pesticide mixtures are increasingly used to fight pest species that developed resistance to pesticides. To assess the pesticide control efficiency and to reduce ecological damage to non-target species, it is important to quantify the effect of these mixtures and compare them with the effect of their single pesticides on pest species, non-target species and their predator-prey interactions. We studied the effects of the chemical pesticide chlorpyrifos (CPF), the biopesticide Bacillus thuringiensis israelensis (Bti) and their mixture both on the direct mortality and on the mortality by predation. We focused on larvae of a CPF-resistant and a non-resistant strain of the vector mosquito Culex quinquefasciatus and its predator, the pygmy backswimmer Plea minutissima. In the CPF-Bti mixture, both pesticides interacted antagonistically for direct mortality. Exposure to the mixture caused equal direct mortality and equal mortality by predation in both strains. As expected, exposure to CPF resulted in less direct mortality and less mortality by predation in the CPF-resistant mosquito strain compared to the non-resistant strain. Notably, Bti caused a higher mortality in the mosquito larvae of the CPF-resistant strain compared to the non-resistant strain. Furthermore, the predator killed more mosquito larvae of the resistant strain compared to the non-resistant strain when exposed before to Bti alone. These observations identify a novel cost of resistance to a chemical pesticide in terms of increased vulnerability to a biopesticide.

Acute toxicity testing of TiO2-based vs. oxybenzone-based sunscreens on clownfish (Amphiprion ocellaris)

Given the prevalence of skin cancer, sunscreens are recommended by dermatologists including the American Academy of Dermatology to protect skin from harmful ultraviolet rays. Unfortunately, this leads to an estimated 14,000 tons of sunscreen entering waterways each year. Many of the chemicals in sunscreens, such as oxybenzone and benzophenone-2, are indicated to have adverse effects on corals and other aquatic life. As an eco-conscious alternative, physical barrier sunscreens, such as non-nano-titanium dioxide (TiO₂), have been suggested as a replacement. This study examines the impact of a non-nano-TiO₂-based sunscreen over a nationally sold brand of sunscreen containing oxybenzone, on clownfish (Amphiprion ocellaris). Animals were evaluated for mortality, swimming behavior, and feeding behavior. Our data indicate that at an exposure level of 100 mg/L oxybenzone-containing sunscreen had a negative impact on mortality, leading to 25% death by the end of the 97-h testing period. Negative impacts on behavior were even more dramatic for the 100 mg/L oxybenzone-containing sunscreen, with 100% of the animals failing to feed over the first 49 h of testing and 100% of animals demonstrating abnormal swimming behavior over the entire testing period. By comparison, the non-nano-(TiO₂) sunscreen at 100 mg/L had little (6.7%) negative impact on mortality and feeding. While swimming behavior was disrupted during the first 25 h of testing (26.7% abnormal movement), animals recovered well over the remainder of the testing period (out to 97 h).

"Armed to the teeth": The multiple ways to survive insecticidal and predatory challenges in Aedes aegypti larvae

Environmental pollutants, such as insecticides, can alter the equilibrium of aquatic ecosystems, particularly those closely located to human occupations. The use of such anthropogenic compounds frequently results in the selection of resistant individuals. However, how the underlying insecticide resistance mechanisms interplay with the abilities of the resistant individuals to cope with other environmental challenges (e.g., predators) has not received adequate attention. Here, we evaluated whether resistance to pyrethroid insecticides in larvae of the yellow fever mosquito, Aedes aegypti (Diptera: Culicidae), would affect their abilities to survive other environmental challenges. We assessed the susceptibilities of the pyrethroid-resistant larvae to other insecticides (i.e., the oxadiazine indoxacarb and juvenile hormone mimic pyriproxyfen) and determined the activities of potential detoxification enzymes. Finally, we also recorded potential alterations in larva swimming behavior in the presence of predators, such as the water bug Belostoma anurum (Hemiptera: Belostomatidae). Our results revealed that high pyrethroid resistance was associated with moderate resistance to the other two insecticides. Furthermore, this multiple resistance was associated with higher detoxification activity by glutathione-S-transferases and general esterases. Interestingly, in comparison with insecticide-susceptible larvae, the pyrethroid-resistant larvae not only swam for longer periods and distances, but also took longer to be captured by B. anurum nymphs. Collectively, our findings revealed increased abilities to survive natural environmental challenges (e.g., predatory attacks) in mosquito larvae that express physiological and behavioral changes associated with multiple resistance to insecticides.

Non-target toxicity of novel insecticides

Humans have used insecticides since ancient times. The spectrum and potency of available insecticidal substances has greatly expanded since the industrial revolution, resulting in widespread use and unforeseen levels of synthetic chemicals in the environment. Concerns about the toxic effects of these new chemicals on non-target species became public soon after their appearance, which eventually led to the restrictions of use. At the same time, new, more environmentally-friendly insecticides have been developed, based on naturally occurring chemicals, such as pyrethroids (derivatives of pyrethrin), neonicotinoids (derivatives of nicotine), and insecticides based on the neem tree vegetable oil (Azadirachta indica), predominantly azadirachtin. Although these new substances are more selective toward pest insects, they can still target other organisms. Neonicotinoids, for example, have been implicated in the decline of the bee population worldwide. This review summarises recent literature published on non-target toxicity of neonicotinoids, pyrethroids, and neem-based insecticidal substances, with a special emphasis on neonicotinoid toxicity in honeybees. We also touch upon the effects of pesticide combinations and documented human exposure to these substances.

Diversity and convergence of mechanisms involved in pyrethroid resistance in the stored grain weevils, Sitophilus spp

Target-site mutations and changes in insect metabolism or behavior are common mechanisms in insecticide-resistant insects. The co-occurrence of such mechanisms in a pest strain is a prominent threat to their management, particularly when alternative compounds are scarce. Pyrethroid resistance among stored grain weevils (i.e., Sitophilus spp.) is an example of a long-standing concern, for which reports of resistance generally focus on a single mechanism in a single species. Here, we investigated pyrethroid resistance in maize and rice weevils (i.e., Sitophilus zeamais and S. oryzae), exploring potential knockdown resistance (kdr) mutations in their sodium channels (primary site for pyrethroid actions) and potential changes in their detoxification and walking processes. Resistance in pyrethroid-resistant rice weevils was associated with the combination of a kdr mutation (L1014F) and increases in walking and detoxification activities, while another kdr mutation (T929I) combined with increases in walking activity were the primary pyrethroid resistance mechanisms in maize weevils. Our results suggest that the selection of pyrethroid-resistant individuals in these weevil species may result from multiple and differential mechanisms because the L1014F mutation was only detected in Latin American rice weevils (e.g., Brazil, Argentina and Uruguay), not in Australian and Turkish rice weevils or Brazilian maize weevils.

Sublethal dose of deltamethrin damage the midgut cells of the mayfly Callibaetis radiatus (Ephemeroptera: Baetidae)

In insects, the midgut performs multiple physiologic functions (e.g., digestion and nutrients absorption) and serves as a physical/chemical barrier against pathogens and chemical stressors such as deltamethrin, a pyrethroid insecticide, commonly used in insect control that are agricultural pests and human disease vectors. Here, we described the midgut cell ultrastructure of Callibaetis radiatus nymphs, which are bioindicators of water quality and the ultrastructural alterations in midgut under sublethal exposure to deltamethrin at three different periods (1, 12, 24 h). The digestive cells of deltamethrin-unexposed nymphs had long microvilli, many mitochondria in the apical cytoplasm, a rough endoplasmic reticulum, a basal labyrinth with openings for hemocele, and the midgut peritrophic matrix which is classified as type I. Nymphs exposed to deltamethrin exhibited digestive cells rich in autophagic vacuoles, basal labyrinth loss, and microvilli disorganization since the first hour of contact with deltamethrin. However, these midgut tissues underwent to autophagic cellular recovery along the 24 h of exposure to deltamethrin. Thus, the sublethal exposure to deltamethrin is sufficient to disturb the ultrastructure of C. radiatus midgut, which might reduce the abilities of these insects to survive in aquatic environments contaminated by pyrethroids.

Sublethal exposure to deltamethrin reduces the abilities of giant water bugs to prey upon Aedes aegypti larvae

Freshwater ecosystems provide environmental conditions for many arthropod species, including pests like mosquitoes and beneficial insects. Giant water bugs, Belostoma anurum (Hemiptera: Belostomatidae), are aquatic insects that provide biological control of mosquitoes and small vertebrates in freshwater environments. However, the application of insecticides aiming to control mosquitoes can lead to insecticide exposures of aquatic predators that can result in their death or significant reductions in their behavioral abilities. Here, we assessed the susceptibilities of B. anurum to the pyrethroid insecticide deltamethrin and evaluated whether sublethal exposure to deltamethrin would change the abilities of B. anurum to prey upon larvae of Aedes aegypti (Diptera: Culicidae). Bioassays of predator performance were conducted at three prey densities (i.e., 3, 6 and 9 larvae/100 mL of water) just after insecticide exposure and on the three following days. Our results revealed that B. anurum (LC₅₀ = 90.9 μg a. i./L) was approximately 32-fold less susceptible to deltamethrin than A. aegypti larvae (LC₅₀ = 2.8 μg a. i./L). However, the number of larvae eaten by B. anurum sublethally exposed to deltamethrin (at 13 μg a. i./L for 24 h) was significantly (P < 0.05) smaller than that recorded for unexposed predators. Furthermore, the deltamethrin-mediated behavioral changes were higher at the highest availability of prey and, as expected, just after insecticide exposure. Thus, sublethal exposure to deltamethrin reduces the ability of B. anurum to capture and prey upon A. aegypti larvae, compromising the efficacy of these insects as naturally occurring mosquito control agents.

Repeated pulse exposures to lambda-cyhalothrin affect the behavior, physiology, and survival of the damselfly larvae Ischnura graellsii (Insecta; Odonata)

Damselflies form an essential part of the aquatic and terrestrial food web. Pesticides may, however, negatively affect their behavior, physiology, and survival. To assess this, a 42-day-lasting bioassay was conducted, during which damselfly larvae (Ischnura graellsii; n = 20) were repeatedly exposed to lambda-cyhalothrin (3 days at; 0, 10, 50, 250, 1250, and 6250ng LCH L^-1), followed by recovery phases (4 days) in pesticide-free medium for six weeks. This exposure design was used to simulate frequent runoff events in the field. Variables related to the behavior (strikes against prey and capture success), growth, physiology (lipid content and fatty acid composition), as well as mortality were assessed throughout the experiment. The two highest LCH concentrations induced 100% mortality within the first 48h, whereas 85% of the test organisms survived 28 days under control conditions. The number of strikes against prey was not affected by LCH. In contrast, prey capture success decreased significantly (up to ~50% at 250ng LCH L^-1, for instance, after the third pulse exposure) following LCH-exposures compared to the control. This difference was not observed after recovery phases, however, which did not counteract the enhanced energy demand for detoxification and defense mechanisms indicated by a lower growth rate (up to ~20%) and lipid content (up to ~30%) of damselflies at 50 and 250ng LCH L^-1. In addition, two essential fatty acids (eicosapentaenoic acid and arachidonic acid) and two precursors (linolenic acid and α-linolenic acid) decreased in their concentrations upon exposure towards 250ng LCH L^-1. Thus the results of this study indicate that long-term exposure towards LCH pulses can affect damselfly behavior, physiology and survival. Given the essential role of damselflies in food web dynamics, these effects may potentially translate into local population impairments with subsequent bottom-up directed effects within and across ecosystem boundaries.

Bti-based insecticide enhances the predatory abilities of the backswimmer Buenoa tarsalis (Hemiptera: Notonectidae)

The backswimmer Buenoa tarsalis (Hemiptera: Notonectidae) is a naturally occurring predator of immature stages of mosquitoes. These aquatic predators can suffer from non-targeted exposure to insecticides that are commonly used in aquatic environments to control mosquitoes. Here, we evaluated whether insecticide formulations containing the bacterium Bacillus thuringiensis var. israelensis (Bt_i) or the organophosphate pirimiphos-methyl would affect the survival and the predatory abilities of B. tarsalis. First, we conducted survival bioassays to estimate the median survival time (LT₅₀) of B. tarsalis when exposed to Bt_i-based insecticide (at 0.25 and 25 mg a.i./L) and pirimiphos-methyl (at 1, 10 and 1000 mg a.i./L). The highest concentrations of the insecticides were equivalent to the label-recommended field rates. Second, the predatory abilities of B. tarsalis exposed to insecticides were evaluated at three prey densities (3, 6 and 9 mosquito larvae/100 mL water) just after insecticide exposure or after a 24 h recovery time. While the survival of B. tarsalis was significantly reduced with pirimiphos-methyl concentrations ≥10 mg a.i./L, the Bt_i-exposed predators exhibited similar survival as unexposed predators. Interestingly, after a recovery time of 24 h, B. tarsalis sublethally exposed to pirimiphos-methyl or Bt_i-based insecticide consistently killed more A. aegypti larvae (at the intermediate density) than unexposed predators. However, for the without-recovery bioassays, the pirimiphos-methyl-exposed predators exhibited reduced predatory abilities at the lowest prey density. Because they do not reduce the survival or the predatory abilities of B. tarsalis, Bt_i-based insecticides can be considered a safe insecticide to use in the presence of backswimmers.