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.

Extremely Low-Frequency Electromagnetic Fields Entrain Locust Wingbeats.

Extremely low-frequency electromagnetic fields (ELF EMFs) have been shown to impact the behavior and physiology of insects. Recent studies have highlighted the need for more research to determine more specifically how they affect flying insects. Here, we ask how locust flight is affected by acute exposure to 50 Hz EMFs. We analyzed the flights of individual locusts tethered between a pair of copper wire coils generating EMFs of various frequency using high-speed video recording. The mean wingbeat frequency of tethered locusts was 18.92 ± 0.27 Hz. We found that acute exposure to 50 Hz EMFs significantly increased absolute change in wingbeat frequency in a field strength-dependent manner, with greater field strengths causing greater changes in wingbeat frequency. The effect of EMFs on wingbeat frequency depended on the initial wingbeat frequency of a locust, with locusts flying at a frequency lower than 20 Hz increasing their wingbeat frequency, while locusts flying with a wingbeat frequency higher than 20 Hz decreasing their wingbeat frequency. During the application of 50 Hz EMF, the wingbeat frequency was entrained to a 2:5 ratio (two wingbeat cycles to five EMF cycles) of the applied EMF. We then applied a range of ELF EMFs that were close to normal wingbeat frequency and found that locusts entrained to the exact frequency of the applied EMF. These results show that exposure to ELF EMFs lead to small but significant changes in wingbeat frequency in locusts. We discuss the biological implications of the coordination of insect flight in response to electromagnetic stimuli. © 2021 Bioelectromagnetics Society.

Riding on the wind: volatile compounds dictate selection of grassland seedlings by snails.

Background and Aims: Seedling herbivory is an important selective filter in many plant communities. The removal of preferred food plants by both vertebrate and, more commonly, invertebrate herbivores can destroy entire seedling cohorts, and consequently dictate plant community assembly. Nevertheless, our understanding of how and why some seedlings are more prone to herbivore attack than their neighbours remains limited. For seedlings, where even minor tissue damage is fatal, avoiding contact with herbivores is probably advantageous and, on this basis, volatile organic compounds (VOCs) are strong candidates to fulfil a primary defensive role. Methods: We quantified seedling selection by snails (Cornu aspersum) for 14 common, European grassland species. Seedling acceptability was subsequently compared with species-specific expression of constitutive secondary defence metabolites (CSDMs), and VOCs to determine their relative influence on seedling selection. Results: We found no relationship between seedling acceptability and CSDMs, but seedling selection was strongly associated with VOC profiles. Monoterpenes (specifically ß-ocimene) were identified as likely attractants, while green leaf volatiles (GLVs) (3-hexen-1-ol acetate) were strongly associated with low seedling acceptability. Conclusions: By elucidating a relationship between VOCs and seedling acceptability, we contradict a long-held, but poorly tested, assumption that seedling selection by herbivores in (semi-)natural plant communities centres on CSDMs. Instead, our results corroborate recent work showing how GLVs, including 3-hexen-1-ol acetate, deter crop seedling selection by molluscs. Although our failure to establish any early-ontogenetic relationship between VOCs and CSDMs also suggests that the former do not 'advertise' possession of the latter, we nevertheless reveal the role that VOCs play in defending seedlings against herbivory before lethal damage occurs.

Pre-processing and transfer entropy measures in motor neurons controlling limb movements.

Directed information transfer measures are increasingly being employed in modeling neural system behavior due to their model-free approach, applicability to nonlinear and stochastic signals, and the potential to integrate repetitions of an experiment. Intracellular physiological recordings of graded synaptic potentials provide a number of additional challenges compared to spike signals due to non-stationary behaviour generated through extrinsic processes. We therefore propose a method to overcome this difficulty by using a preprocessing step based on Singular Spectrum Analysis (SSA) to remove nonlinear trends and discontinuities. We apply the method to intracellular recordings of synaptic responses of identified motor neurons evoked by stimulation of a proprioceptor that monitors limb position in leg of the desert locust. We then apply normalized delayed transfer entropy measures to neural responses evoked by displacements of the proprioceptor, the femoral chordotonal organ, that contains sensory neurones that monitor movements about the femoral-tibial joint. We then determine the consistency of responses within an individual recording of an identified motor neuron in a single animal, between repetitions of the same experiment in an identified motor neurons in the same animal and in repetitions of the same experiment from the same identified motor neuron in different animals. We found that delayed transfer entropy measures were consistent for a given identified neuron within and between animals and that they predict neural connectivity for the fast extensor tibiae motor neuron.

Predictive control of intersegmental tarsal movements in an insect.

In many animals intersegmental reflexes are important for postural and movement control but are still poorly undesrtood. Mathematical methods can be used to model the responses to stimulation, and thus go beyond a simple description of responses to specific inputs. Here we analyse an intersegmental reflex of the foot (tarsus) of the locust hind leg, which raises the tarsus when the tibia is flexed and depresses it when the tibia is extended. A novel method is described to measure and quantify the intersegmental responses of the tarsus to a stimulus to the femoro-tibial chordotonal organ. An Artificial Neural Network, the Time Delay Neural Network, was applied to understand the properties and dynamics of the reflex responses. The aim of this study was twofold: first to develop an accurate method to record and analyse the movement of an appendage and second, to apply methods to model the responses using Artificial Neural Networks. The results show that Artificial Neural Networks provide accurate predictions of tarsal movement when trained with an average reflex response to Gaussian White Noise stimulation compared to linear models. Furthermore, the Artificial Neural Network model can predict the individual responses of each animal and responses to others inputs such as a sinusoid. A detailed understanding of such a reflex response could be included in the design of orthoses or functional electrical stimulation treatments to improve walking in patients with neurological disorders as well as the bio/inspired design of robots.

Something in the air? The impact of volatiles on mollusc attack of oilseed rape seedlings.

BACKGROUND AND AIMS: Mounting concerns about balancing food security with the environmental impacts of agro-chemical use underpin the need to better understand the mechanisms by which crop plants, particularly during the vulnerable seedling stage, attract or repel herbivores. METHODS: The feeding preferences of the mollusc Helix aspersa were determined for several oilseed rape (Brassica napus) cultivars and a rank order of acceptability was established. This was compared with glucosinolate concentrations and volatile organic compound (VOC) profiles to determine whether seedling acceptability to molluscs was linked to either form of defence. KEY RESULTS: While VOC profiles for each oilseed rape cultivar could be separated by canonical discriminant analysis and associated with mollusc feeding preferences, glucosinolate profiles were unrelated to snail feeding behaviour. A mixture of monoterpenes (α-pinene, ß-myrcene and δ-3-carene) was identified as a putative attractant, while a blend of the green leaf volatiles 3-hexen-1-ol, 3-hexen-1-ol acetate and the monoterpene α-terpinene was identified as a putative repellent mix. Added to the VOC profile of oilseed rape seedlings, the 'repellent' mix reduced mollusc selection, while the 'attractant' mix had no effect. CONCLUSIONS: Despite the widespread assumption that seedling selection by generalist herbivores is governed by chemical defence and taste, we show that olfactory cues may be more important. Oilseed rape may be atypical of wild plants, but our ability to identify repellent volatile organic compounds that can influence snail olfactory selection points to new methods for crop protection using modified VOC profiles during the vulnerable seedling stage.

Exposure to static electric fields leads to changes in biogenic amine levels in the brains of Drosophila.

Natural and anthropogenic static electric fields are commonly found in the environment and can have both beneficial and harmful effects on many animals. Here, we asked how the fruitfly responds to these fields and what the consequences of exposure are on the levels of biogenic amines in the brain. When given a choice in a Y-tube bioassay Drosophila avoided electric fields, and the greater the field strength the more likely Drosophila were to avoid it. By comparing wild-type flies, flies with wings surgically removed and vestigial winged flies we found that the presence of intact wings was necessary to produce avoidance behaviour. We also show that Coulomb forces produced by electric fields physically lift excised wings, with the smaller wings of males being raised by lower field strengths than larger female wings. An analysis of neurochemical changes in the brains showed that a suite of changes in biogenic amine levels occurs following chronic exposure. Taken together we conclude that physical movements of the wings are used by Drosophila in generating avoidance behaviour and are accompanied by changes in the levels of amines in the brain, which in turn impact on behaviour.

Delayed mutual information infers patterns of synaptic connectivity in a proprioceptive neural network.

Understanding the patterns of interconnections between neurons in complex networks is an enormous challenge using traditional physiological approaches. Here we combine the use of an information theoretic approach with intracellular recording to establish patterns of connections between layers of interneurons in a neural network responsible for mediating reflex movements of the hind limb of an insect. By analysing delayed mutual information of the synaptic and spiking responses of sensory neurons, spiking and nonspiking interneurons in response to movement of a joint receptor that monitors the position of the tibia relative to the femur, we are able to predict the patterns of interconnections between the layers of sensory neurons and interneurons in the network, with results matching closely those known from the literature. In addition, we use cross-correlation methods to establish the sign of those interconnections and show that they also show a high degree of similarity with those established for these networks over the last 30 years. The method proposed in this paper has great potential to elucidate functional connectivity at the neuronal level in many different neuronal networks.

Intracellular nitric oxide mediates neuroproliferative effect of neuropeptide y on postnatal hippocampal precursor cells.

Neuropeptide Y (NPY) is widely expressed in the central and peripheral nervous systems and is proliferative for a range of cells types in vitro. NPY plays a key role in regulating adult hippocampal neurogenesis in vivo under both basal and pathological conditions, although the underlying mechanisms are largely unknown. We have investigated the role of nitric oxide (NO) on the neurogenic effects of NPY. Using postnatal rat hippocampal cultures, we show that the proliferative effect of NPY on nestin(+) precursor cells is NO-dependent. As well as the involvement of neuronal nitric-oxide synthase, the proliferative effect is mediated via an NO/cyclic guanosine monophosphate (cGMP)/cGMP-dependent protein kinase (PKG) and extracellular signal-regulated kinase (ERK) 1/2 signaling pathway. We show that NPY-mediated intracellular NO signaling results in an increase in neuroproliferation. By contrast, extracellular NO had an opposite, inhibitory effect on proliferation. The importance of the NO-cGMP-PKG signaling pathway in ERK1/2 activation was confirmed using Western blotting. This work unites two significant modulators of hippocampal neurogenesis within a common signaling framework and provides a mechanism for the independent extra- and intracellular regulation of postnatal neural precursors by NO.

A system identification analysis of neural adaptation dynamics and nonlinear responses in the local reflex control of locust hind limbs.

Nonlinear type system identification models coupled with white noise stimulation provide an experimentally convenient and quick way to investigate the often complex and nonlinear interactions between the mechanical and neural elements of reflex limb control systems. Previous steady state analysis has allowed the neurons in such systems to be categorised by their sensitivity to position, velocity or acceleration (dynamics) and has improved our understanding of network function. These neurons, however, are known to adapt their output amplitude or spike firing rate during repetitive stimulation and this transient response may be more important than the steady state response for reflex control. In the current study previously used system identification methods are developed and applied to investigate both steady state and transient dynamic and nonlinear changes in the neural circuit responsible for controlling reflex movements of the locust hind limbs. Through the use of a parsimonious model structure and Monte Carlo simulations we conclude that key system dynamics remain relatively unchanged during repetitive stimulation while output amplitude adaptation is occurring. Whilst some evidence of a significant change was found in parts of the systems nonlinear response, the effect was small and probably of little physiological relevance. Analysis using biologically more realistic stimulation reinforces this conclusion.