Eugênio E. Oliveira

Use of odours by Cycloneda sanguinea to assess patch quality

Adult ladybirds are likely to encounter various species of prey when foraging for oviposition sites. Optimal oviposition theory predicts that females should lay eggs in those sites that are the most suitable for offspring development. Therefore, factors that directly affect offspring mortality, such as the presence of predators and food, are expected to play an important role in the assessment of patch profitability by ladybird predators. Using a Y‐tube olfactometer, we tested whether the predatory ladybird Cycloneda sanguinea L. (Coleoptera: Coccinellidae) can use volatile cues to assess patch profitability and avoid predator‐rich patches. We assessed the foraging behaviour of C. sanguinea in response to odours associated with tomato plants infested with a superior prey, Macrosiphum euphorbiae Thomas (Homoptera: Aphididae), and with an inferior prey, Tetranychus evansi Baker and Pritchard (Acari: Tetranychidae), in the presence or absence of the heterospecific predator Eriopis connexa Mulsant (Coleoptera: Coccinellidae). Females of C. sanguinea significantly preferred plants infested by M. euphorbiae to plants infested by T. evansi and avoided odours emanating from plants on which E. connexa females were present. Our results show that C. sanguinea use volatile cues to assess patch profitability and to avoid patches with heterospecific competitors or intraguild predators.

Desensitization of nicotinic acetylcholine receptors in central nervous system neurons of the stick insect (Carausius morosus) by imidacloprid and sulfoximine insecticides.

Imidacloprid, sulfoxaflor and two experimental sulfoximine insecticides caused generally depressive symptoms in stick insects, characterized by stillness and weakness, while also variably inducing postural changes such as persistent ovipositor opening, leg flexion or extension and abdomen bending that could indicate excitation of certain neural circuits. We examined the same compounds on nicotinic acetylcholine receptors in stick insect neurons, which have previously been shown to desensitize in the presence of ACh. Brief U-tube application of 10(-4)xa0M solutions of insecticides for 1xa0s evoked currents that were much smaller than ACh-evoked currents, and depressed subsequent ACh-evoked currents for several minutes, indicating that the compounds are low-efficacy partial agonists that potently desensitize the receptors. Much lower concentrations of insecticides applied in the bath for longer periods did not activate currents, but inhibited ACh-evoked currents via desensitization of the receptors. Previously described fast- and slowly-desensitizing nACh currents, I(ACh1) and I(ACh2) respectively, were each found to consist of two components with differing sensitivities to the insecticides. Imidacloprid applied in the bath desensitized high-sensitivity components, I(ACh1H) and I(ACh2H) with IC(50)s of 0.18 and 0.13 pM, respectively. It desensitized the low-sensitivity slowly desensitizing component, I(ACh2L), with an IC(50) of 2.6xa0nM, while a component of the fast-desensitizing current, I(ACh1L), was least sensitive, with an IC(50) of 81xa0nM I(ACh1L) appeared to be insensitive to the three sulfoximines tested, whereas all three sulfoximines potently desensitized I(ACh1H) and both slowly desensitizing components, with IC(50)s between 2 and 7xa0nM. We conclude that selective desensitization of certain nAChR subtypes can account for the insecticidal actions of imidacloprid and sulfoximines in stick insects.

Pharmacological Analysis of Tonic Activity in Motoneurons During Stick Insect Walking

Stick insect middle leg (mesothoracic) motoneurons receive tonic excitatory input during front leg stepping on a treadmill. We studied the pharmacology of this excitatory input to the motoneurons during single-legged treadmill walking (in situ). During bath application of drugs restricted to the mesothoracic ganglion, activity in motoneurons contralateral to the stepping front leg was recorded from neuropilar processes. Application of the cholinergic antagonist atropine reduced the tonic depolarization amplitude. These results were compared with findings in acutely dissociated motoneuron cell bodies (in vitro) under whole cell voltage-clamp conditions. The presence of an acetylcholine-induced current in situ was supported by the finding of an acetylcholine evoked biphasic inward current with a sustained component that could be blocked by atropine. In situ the tonic depolarization was generally increased by application of the neuro-modulator octopamine and decreased by its antagonist mianserin. In vitro, however, octopamine reduced the inward current evoked by acetylcholine application to motoneurons. Intracellular application of bis-(o-aminophenoxy)-N,N,N,N-tetraacetic acid (BAPTA) into motoneurons in situ revealed a dependence of the tonic depolarization on Ca(2+) and application of the membrane-permeable cAMP analogue 8-bromo-cAMP increased the tonic depolarization. In contrast, 8-bromo-cAMP reduced the inward current evoked by acetylcholine application to motoneurons in vitro. We conclude that during walking, acetylcholine contributes to mediating the tonic depolarization possibly by acting on atropine-sensitive receptors on motoneurons. Octopamine that is released during walking increases the tonic depolarization. This increase, however, is not based on modulation of cholinergic action on motoneurons but rather on effects on premotor neurons. Both, Ca(2+) and cAMP are likely second messengers involved in mediating the tonic depolarization, but whereas Ca(2+) acts in motoneurons, cAMP does not appear to mediate a cholinergic depolarization in motoneurons.

Resistência vs susceptibilidade a piretróides em Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae): há vencedor?

Studies on insecticide resistance evolution usually associate the phenomenon with an adaptative cost to the individual carrying this trait. Our objective was to verify if insecticide resistance in a population of Sitophilus zeamais Motschulsky incurs in fitness cost under an insecticide-free environment. Two populations of the species (a susceptible and a pyrethroid resistant population) were submitted to competition against each other for two consecutive generations in the absence of insecticide. A factorial bivariated derivated from an additive series was used in the experimental design with two initial density levels (lower, with 50 individuals of one population and a crescent series of individuals from 0 to 50 from the other population; and higher, with 100 individuals of a population and a crescent series of individuals from 0 to 100 from the other). The total number of adult insects, mortality by deltamethrin and insect body mass for each treatment were recorded. Adaptative disadvantage was not found on the resistant population compared with the susceptible population in an insecticide-free environment since both populations showed similar growth rate. This finding brings about practical complications for insecticide resistance management in this species because management strategies based on the interruption of pyrethroid use aiming their future reintroduction may not achieve the desired effects. This may take place because even after a long period without insecticide use, the resistant populations may still maintain themselves as such since there is no perceptible adaptative disadvantage associated with this trait.

Cholinergic Currents in Leg Motoneurons of Carausius morosus

We used patch-clamp recordings and fast optical Ca(2+) imaging to characterize an acetylcholine-induced current (I(ACh)) in leg motoneurons of the stick insect Carausius morosus. Our long-term goal is to better understand the synaptic and integrative properties of the leg sensory-motor system, which has served extremely successfully as a model to study basic principles of walking and locomotion on the network level. The experiments were performed under biophysically controlled conditions on freshly dissociated leg motoneurons to avoid secondary effects from the network. To allow for unequivocal identification, the leg motoneurons were backfilled with a fluorescent label through the main leg nerve prior to cell dissociation. In 87% of the motoneurons, I(ACh) consisted of a fast-desensitizing (I(ACh1)) and a slow-desensitizing component (I(ACh2)), both of which were concentration dependent, with EC(50) values of 3.7 x 10(-5) and 2.0 x 10(-5) M, respectively. Ca(2+) imaging revealed that a considerable portion of I(ACh) ( approximately 18%) is carried by Ca(2+), suggesting that I(ACh), besides mediating fast synaptic transmission, could also induce Ca(2+)-dependent processes. Using specific nicotinic and muscarinic acetylcholine receptor ligands, we showed that I(ACh) was exclusively mediated by nicotinic acetylcholine receptors. Distinct concentration-response relations of I(ACh1) and I(ACh2) for these ligands indicated that they are mediated by different types of nicotinic acetylcholine receptors.

Desenvolvimento e Reprodução do Predador Podisus distinctus (Stal) (Heteroptera: Pentatomidae) Frente a Doses Subletais de Permetrina

Development and reproduction were studied in the predator Podisus distinctus (Stal) subjected to sublethal doses of the insecticide permethrin under laboratory conditions. Third instar nymphs were subjected to topical application of permethrin at the doses of 0, 0.0172, 0.172, 1.72, 17.2 e 172 ppb. The only parameter statisticaly different was egg viability. This parameter had the gratest increase at the dose 0.172 ppb provinding evidence for the phenomenon of hormesis.

Deltamethrin toxicity and impaired swimming behavior of two backswimmer species

Backswimmers (Hemiptera: Heteroptera: Notonectidae) are insect predators in a wide variety of freshwater habitats. These insects are well known through their role as mosquito biocontrol agents, their ability to prey on immature fishes and frogs, and because they are often the first to colonize aquatic habitats. As a consequence, these predators may face intended or unintended insecticide exposures that may lead to death or to impairment of essential behaviors (e.g., swimming and position in the water column). The toxicity of deltamethrin (a type II pyrethroid insecticide stressor) and the swimming activity of the backswimmers Buenoa tarsalis and Martarega bentoi were evaluated. Concentration-mortality and survival bioassays were conducted with the insecticide, which were compared with controls without deltamethrin. Deltamethrin was 26-fold more toxic to B. tarsalis (median lethal concentration [LC50]u2009=u20094.0u2009ng a.i./L) than to M. bentoi (LC50u2009=u2009102.5u2009ng a.i./L). The pattern of occupation of B. tarsalis, but not of M. bentoi, in the water column was also disrupted, and B. tarsalis was forced to stay near the water surface longer with exposure to deltamethrin. Thus, based on the findings, B. tarsalis was less resilient to deltamethrin exposure compared with M. bentoi, and the efficacy of swimming-dependent processes might be negatively affected (e.g., prey catching, partner encounter, and antipredator behaviors) for B. tarsalis under deltamethrin exposure. Environ Toxicol Chem 2017;36:1235-1242.

Imidacloprid resistance in the Neotropical brown stink bug Euschistus heros: selection and fitness costs

Neonicotinoid insecticides (e.g., imidacloprid) are some of the most prevalent tools used to control hemipterans that attack soybean crops worldwide. However, the emergence of neonicotinoid-resistant strains of phytosuccivorous soybean pests, such as the Neotropical brown stink bug Euschistus heros, has posed a challenge to the sustainable use of these compounds. Here, we laboratory-selected two E. heros strains for imidacloprid resistance and evaluated the activity of detoxification enzymes (e.g., cytochrome P450, esterases and glutathione-S-transferases) as well as potential adaptive costs associated with resistance (e.g., in survival, fecundity and fertility) in both strains, while laboratory selection for 13 generations in a known imidacloprid-susceptible E. heros strain (ImiSusc) resulted in an imidacloprid-resistant strain (ImiLabSel) with a resistance ratio (RR) of 11.6; similar resistance levels (i.e., RR =u200913.5) were also achieved in another imidacloprid-resistant strain, which was field-collected (ImiGoias) and laboratory-selected for only six generations (ImiRes). Regarding enzymatic activity, both resistant strains differed from the imidacloprid-susceptible strain only in the activity of cytochrome P450, where the ImiLabSel and ImiRes strains exhibited higher activity by 72.3% and 40.5%, respectively. Furthermore, severe fitness costs (reductions of 86% for ImiLabSel and 68.0% for ImiRes) were recorded in both imidacloprid-resistant strains. Collectively, our results showed that E. heros rapidly responded to laboratory selection for neonicotinoid resistance, with enhanced cytochrome P450 activity as the likely underlying mechanism, and that they exhibit associated fitness costs, which have direct implications for the management of this insect pest.