Neonicotinoids suppress contact chemoreception in a common farmland spider

Lethal and sublethal effects of five common herbicides on the wolf spider, Pardosa milvina (Araneae: Lycosidae)

We tested lethal and sublethal effects of five commonly applied herbicides on the agrobiont wolf spider Pardosa milvina. Pardosa were collected from two agricultural fields; one kept under continuous crop rotation and sprayed for over twenty years, the other had no pesticide application for the last twelve years. Male and female Pardosa from each site were exposed to one of seven herbicide treatments (atrazine, glyphosate, mesotrione, S-metolachlor, rimsulfuron, a combination of all five herbicides, or a distilled water control; N = 1201) and maintained for 52 days on the treated soil substrate. We recorded mortality, prey capture behavior, weight change, courtship behavior, and egg sac production across treatments. Mesotrione and the five-herbicide combination showed significantly higher mortality than control substrates while atrazine, glyphosate and S-metolachlor showed significantly higher survival than the control. Both male spiders and spiders collected from the conventional field had reduced survival under some herbicide treatments. Prey capture behavior varied significantly by herbicide treatment, sex, and site. We observed significant weight change differences in males and differences in egg sac production in females, with, compared to the control, significant male weight loss in the rimsulfuron treatment collected from the no herbicide field, and a decrease in egg sac production in rimsulfuron and S-metolachlor treatments among females collected from the no herbicide field. Our results show some herbicides may have modest but significant fitness benefits (atrazine, glyphosate, and S-metolachlor) while others strongly increase the mortality of a generalist predator (mesotrione and the combination herbicide treatment).

Behavioral, Histological, and Physiological Evaluation of the Effect of Imidacloprid on the Spider Misumenops maculissparsus

The aim of the present study was to evaluate the effects of the neonicotinoid insecticide imidacloprid (commercial formulation) on juveniles of the spider Misumenops maculissparsus (Keyserling, 1891). We first analyzed whether spiders recognized the presence of the insecticide on surfaces and in drinking water (in the form of droplets). Next, we investigated if the insecticide generated histologic, physiologic, and/or biochemical alterations. We observed that spiders do not detect the insecticide on a surface (e.g., paper) or in the form of droplets. After the imidacloprid ingestion by droplet intake, most spiders exhibited a paralysis that reverted after 48 h. Consequently, we observed histopathologic damage (i.e., pigment accumulation, necrosis, and cuticle detachment), and an increased catalase (CAT) activity and total-protein concentration in the individuals treated. The activities of glutathione-S-transferase, glutathione peroxidase, glutathione reductase, and superoxide dismutase, however, did not undergo significant variations. The results obtained emphasize the need to consider different classes of biomarkers, such as CAT and other proteins, to identify and evaluate the histologic, biologic, and biochemical effects of imidacloprid, one of the most widely used insecticides. Environ Toxicol Chem 2022;41:2152-2161. © 2022 SETAC.

Contact exposure to neonicotinoid insecticides temporarily suppresses the locomotor activity of Pardosa lugubris agrobiont wolf spiders

Exposure to numerous chemicals disrupts the spiders' locomotion. Spiders, particularly epigeic spiders, are dependent on their locomotory activities to search for prey, hide from their enemies, and perform sexual reproduction and subsequent parental care. Among the best-known compounds that inhibit the locomotion of arthropods are neonicotinoids. Despite spiders are less affected by the neonicotinoids than insects due to the sequence differences in their acetylcholine receptors, they are not resistant to these compounds. We hypothesized that acute exposure to a broad spectrum of neonicotinoids suppresses the traveled distance, mean velocity, and maximum velocity in epigeic spiders. As a model species, we used adults of Pardosa lugubris. We tested commercial formulations of thiamethoxam, acetamiprid, and thiacloprid. We tested each of the neonicotinoids in the maximum and minimum concentrations recommended for foliar applications. We applied them under controlled conditions dorsally by spraying them directly on the spiders or exposing the spiders to the tarsal contact with neonicotinoid residues. Control groups consisted of 31 individuals; treated groups consisted of 10–21 individuals. We found that a broad spectrum of neonicotinoids temporarily suppresses the traveled distance in epigeic spiders. At 1 h after application, all the three tested neonicotinoid insecticides induced declines in the traveled distance, but this effect mostly disappeared when tested at 24 h after the application. The decrease in the traveled distance was associated with substantial temporary decreases in the mean and maximum velocities. Despite differences among modalities, all three insecticides caused multiple adverse effects on the locomotory parameters in any tested concentrations. It remains to test what would be the lowest safe concentration for the chronic exposure to neonicotinoids in epigeic spiders.

Thiamethoxam as an inadvertent anti-aphrodisiac in male bees

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There is consensus that neonicotinoids can impact non-target animal fertility.

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Thiamethoxam reduced both mating success and sperm physiology in bumblebees.

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Queens mated by exposed males had 50% less total living sperm in their spermatheca.

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Thiamethoxam may act as anti-aphrodisiac, thereby limiting conservation efforts.

Sexual reproduction is common to almost all multi-cellular organisms and can be compromised by environmental pollution, thereby affecting entire populations. Even though there is consensus that neonicotinoid insecticides can impact non-target animal fertility, their possible impact on male mating success is currently unknown in bees. Here, we show that sublethal exposure to a neonicotinoid significantly reduces both mating success and sperm traits of male bumblebees. Sexually mature male Bombus terrestris exposed to a field-realistic concentration of thiamethoxam (20 ng g⁻¹) or not (controls) were mated with virgin gynes in the laboratory. The results confirm sublethal negative effects of thiamethoxam on sperm quantity and viability. While the latency to mate was reduced, mating success was significantly impaired in thiamethoxam-exposed males by 32% probably due to female choice. Gynes mated by exposed males revealed impaired sperm traits compared to their respective controls, which may lead to severe constraints for colony fitness. Our laboratory findings demonstrate for the first time that neonicotinoid insecticides can negatively affect male mating success in bees. Given that holds true for the field, this provides a plausible mechanism contributing to declines of wild bee populations globally. The widespread prophylactic use of neonicotinoids may therefore have previously overlooked inadvertent anti-aphrodisiac effects on non-target animals, thereby limiting conservation efforts.

The sublethal effects of neonicotinoids on spiders are independent of their nutritional status

Spiders were recently shown to be adversely affected by field-realistic concentrations of a broad scale of neonicotinoid insecticides. Among the reported effects of neonicotinoids on invertebrates were declines in lipid biosynthesis and upregulation of β-oxidation, while vertebrate models suggest increased adipogenesis following treatment with neonicotinoids. Therefore, we hypothesized that there exists synergy between the effects of diet and concurrent exposure to field-realistic concentrations of neonicotinoid insecticides. To address this hypothesis, we fed first instars of the large wolf spider Hogna antelucana with two types of diets and exposed them to field-realistic concentrations of three formulations of neonicotinoids (thiamethoxam, thiacloprid and acetamiprid). We then measured the growth of the tested spiders; the lipid and protein content of their bodies; and their behavior, including ballooning, rappelling, and locomotor parameters. The two tested diets consisted of casein-treated and sucrose-treated Drosophila melanogaster. The dietary treatments affected the lipid and protein content of the spiders, their body weight and carapace length but did not affect any of the measured behavioral parameters. Surprisingly, we did not find any effects of acute exposure to neonicotinoid insecticides on the lipid or protein reserves of spiders. Exposure to neonicotinoids altered the behavior of the spiders as reported previously in other spider species; however, these effects were not affected by dietary treatments. Overall, the dietary treatments did not have any major synergy with acute exposure to field-realistic concentrations of neonicotinoid insecticides.