Suboptimal Larval Habitats Modulate Oviposition of the Malaria Vector Mosquito Anopheles coluzzii.

Selection of oviposition sites by gravid females is a critical behavioral step in the reproductive cycle of Anopheles coluzzii, which is one of the principal Afrotropical malaria vector mosquitoes. Several studies suggest this decision is mediated by semiochemicals associated with potential oviposition sites. To better understand the chemosensory basis of this behavior and identify compounds that can modulate oviposition, we examined the generally held hypothesis that suboptimal larval habitats give rise to semiochemicals that negatively influence the oviposition preference of gravid females. Dual-choice bioassays indicated that oviposition sites conditioned in this manner do indeed foster significant and concentration dependent aversive effects on the oviposition site selection of gravid females. Headspace analyses derived from aversive habitats consistently noted the presence of dimethyl disulfide (DMDS), dimethyl trisulfide (DMTS) and 6-methyl-5-hepten-2-one (sulcatone) each of which unitarily affected An. coluzzii oviposition preference. Electrophysiological assays across the antennae, maxillary palp, and labellum of gravid An. coluzzii revealed differential responses to these semiochemicals. Taken together, these findings validate the hypothesis in question and suggest that suboptimal environments for An. coluzzii larval development results in the release of DMDS, DMTS and sulcatone that impact the response valence of gravid females

Flight attraction of Spodoptera littoralis (Lepidoptera, Noctuidae) to cotton headspace and synthetic volatile blends

The insect olfactory system discriminates odor signals of different biological relevance, which drive innate behavior. Identification of stimuli that trigger upwind flight attraction toward host plants is a current challenge, and is essential in developing new, sustainable plant protection methods, and for furthering our understanding of plant-insect interactions. Using behavioral, analytical and electrophysiological studies, we here show that both females and males of the Egyptian cotton leafworm,Spodoptera littoralis(Lepidoptera, Noctuidae), use blends of volatile compounds to locate their host plant, cotton,Gossypium hirsutum(Malvales, Malvaceae). FemaleS. littoraliswere engaged in upwind orientation flight in a wind tunnel when headspace collected from cotton plants was delivered through a piezoelectric sprayer. Although males took off toward cotton headspace significantly fewer males than females flew upwind toward the sprayed headspace. Subsequent assays with antennally active synthetic compounds revealed that a blend of nonanal, (Z)-3 hexenyl acetate, (E)-β-ocimene, and (R)-(+)-limonene was as attractive as cotton headspace to females and more attractive to males. Two compounds, 4,8-dimethyl-1,3(E),7-nonatriene (DMNT) and (R)-(−)-linalool, both known plant defense compounds may have reduced the flight attraction of both females and males; more moths were attracted to blends without these two compounds, however, other compounds such as benzaldehyde may also be behavioral antagonists. Our findings provide a platform for further investigations on host plant signals mediating innate behavior, and for the development of novel insect plant protection strategies againstS. littoralis

Mate recognition and reproductive isolation in the sibling species Spodoptera littoralis and Spodoptera litura

Mate recognition is crucial for reproductive isolation and for maintaining species integrity. Chemosensory-mediated sexual communication with pheromones is an essential component of mate recognition in moths. Confronted with sex pheromone stimuli released from conspecific and closely related heterospecific females, which partially overlap in chemical composition, male moths are under strong selection to recognize compatible mates. Here, we investigated the role of pheromone signals in premating communication in the sibling species Spodoptera littoralis and S. litura (Lepidoptera, Noctuidae). Further, we measured the reproductive consequence of conspecific vs. heterospecific matings. Both species use Z9,E11–14:Ac as the major pheromone compound, and the 11-component blend found in pheromone glands of S. littoralis comprises the compounds found in S. litura. Accordingly, S. littoralis and S. litura males readily responded to conspecific and heterospecific calling females in no-choice behavioral tests. In contrast, in a dual-choice test, S. littoralis males choose conspecific calling females, whereas S. litura males did not discriminate between conspecific and heterospecific females. In S. littoralis females, heterospecific matings had a negative fitness effect as compared to conspecific matings. Female longevity, egg-laying and hatching of larvae were significantly reduced by matings with heterospecific males. Reciprocal crossings, between S. litura females and S. littoralis males, were prevented by genital morphology, which is consistent with reduced heterospecific attraction of S. littoralis males in a dual-choice assay. On the other hand, matings between S. littoralis females and S. litura males, under a no-choice situation, show that interspecific matings occur in zones of geographical overlap and corroborate the idea that mate quality, in these closely related species, is a continuous and not a categorical trait

Floral to green: mating switches moth olfactory coding and preference

Mating induces profound physiological changes in a wide range of insects, leading to behavioural adjustments to match the internal state of the animal. Here, we show for the first time, to our knowledge, that a noctuid moth switches its olfactory response from food to egg-laying cues following mating. Unmated females of the cotton leafworm (Spodoptera littoralis) are strongly attracted to lilac flowers (Syringa vulgaris). After mating, attraction to floral odour is abolished and the females fly instead to green-leaf odour of the larval host plant cotton, Gossypium hirsutum. This behavioural switch is owing to a marked change in the olfactory representation of floral and green odours in the primary olfactory centre, the antennal lobe (AL). Calcium imaging, using authentic and synthetic odours, shows that the ensemble of AL glomeruli dedicated to either lilac or cotton odour is selectively up- and downregulated in response to mating. A clear-cut behavioural modulation as a function of mating is a useful substrate for studies of the neural mechanisms underlying behavioural decisions. Modulation of odour-driven behaviour through concerted regulation of odour maps contributes to our understanding of state-dependent choice and host shifts in insect herbivores

Pest categorisation of Spodoptera litura

The EFSA Panel on Plant Health (PLHP) performed a pest categorisation of Spodoptera litura (Lepidoptera: Noctuidae) for the EU. S. litura is widely distributed across South and East Asia and Oceania. It is established in tropical and subtropical regions where there are no, or few, frost days each year. It can extend its range into cooler temperate regions during summer months. S. litura is highly polyphagous feeding on hosts within at least 40 botanical families, including economically important crops within Brassicaceae, Cucurbitaceae, Fabaceae, Malvaceae, Poaceae and Solanaceae. Larvae are primarily leaf feeders and can cause complete defoliation. At high population densities almost all plant parts are eaten. S. litura is a serious pest in the Asia-Pacific region where it causes losses to many economically important cultivated field crops and crops such as eggplants, sweet peppers and tomatoes in protected cultivation. As a species that appears limited by winter temperatures, only a small area of the EU provides climatic conditions where establishment outdoors may be possible although cultivated and wild hosts are distributed across the EU. S. litura has been intercepted in the EU many times on ornamentals and leafy vegetables. Outbreaks have occurred in EU glasshouses and have been eradicated. Phytosanitary measures are available to inhibit entry. S. litura satisfies the criteria that are within the remit of EFSA to assess for it to be regarded as a potential Union quarantine pest. S. litura does not meet the criteria of occurring in the EU, and plants for planting being the principal means of spread for it to be regarded as a potential Union regulated non-quarantine pest

A novel lineage of candidate pheromone receptors for sex communication in moths

Sex pheromone receptors (PRs) are key players in chemical communication between mating partners in insects. In the highly diversified insect order Lepidoptera, male PRs tuned to female-emitted type I pheromones (which make up the vast majority of pheromones identified) form a dedicated subfamily of odorant receptors (ORs). Here, using a combination of heterologous expression and in vivo genome editing methods, we bring functional evidence that at least one moth PR does not belong to this subfamily but to a distantly related OR lineage. This PR, identified in the cotton leafworm Spodoptera littoralis, is highly expressed in male antennae and is specifically tuned to the major sex pheromone component emitted by females. Together with a comprehensive phylogenetic analysis of moth ORs, our functional data suggest two independent apparitions of PRs tuned to type I pheromones in Lepidoptera, opening up a new path for studying the evolution of moth pheromone communication

Use of habitat odour by host-seeking insects

Locating suitable feeding or oviposition sites is essential for insect survival. Understanding how insects achieve this is crucial, not only for understanding the ecology and evolution of insect–host interactions, but also for the development of sustainable pest-control strategies that exploit insects' host-seeking behaviours. Volatile chemical cues are used by foraging insects to locate and recognise potential hosts but in nature these resources usually are patchily distributed, making chance encounters with host odour plumes rare over distances greater than tens of metres. The majority of studies on insect host-seeking have focussed on short-range orientation to easily detectable cues and it is only recently that we have begun to understand how insects overcome this challenge. Recent advances show that insects from a wide range of feeding guilds make use of ‘habitat cues’, volatile chemical cues released over a relatively large area that indicate a locale where more specific host cues are most likely to be found. Habitat cues differ from host cues in that they tend to be released in larger quantities, are more easily detectable over longer distances, and may lack specificity, yet provide an effective way for insects to maximise their chances of subsequently encountering specific host cues. This review brings together recent advances in this area, discussing key examples and similarities in strategies used by haematophagous insects, soil-dwelling insects and insects that forage around plants. We also propose and provide evidence for a new theory that general and non-host plant volatiles can be used by foraging herbivores to locate patches of vegetation at a distance in the absence of more specific host cues, explaining some of the many discrepancies between laboratory and field trials that attempt to make use of plant-derived repellents for controlling insect pests

Recognition and modulation of olfactory signals in the noctuid moth spodoptera littoralis

Food, mates and host plants are essential resources for plant-feeding insects. Optimal resource localization that fulfils the physiological need and reproductive goals of an insect is of utmost importance. Insects, like most animals, rely largely on the sense of smell to locate and evaluate potential resources that enhance their reproductive fitness. Confronted with a multitude of stimuli ranging from food to conspecifics, insects execute behavioural strategies that are strongly modulated by internal physiological factors such as hunger and reproductive status. In this thesis, I address how an insect’s reproductive state modulates olfactory perception and ultimately behaviour towards adult food, female sex pheromone and larval host plant odours. The cotton leafworm Spodoptera littoralis is an appropriate species for studying modulation of olfactory perception and behaviour, since the chemical ecology and olfactory physiology of mate finding and host seeking is being thoroughly studied. Here, I show that mating in female S. littoralis causes transient reduction in the sexual receptivity, and a reduction in longevity. Mating induces physiological changes that strongly influence olfactory coding and preference in males and females that match their current physiological need. Following mating, female S. littoralis switches olfactory preference from adult food to egg-laying cues. Unmated female S. littoralis are highly attracted to lilac flowers (Syringa vulgaris). After mating, females switch their olfactory preference to the host plant cotton (Gossypium hirsutum). Remarkably, the behavioural switch from floral to green odours is also mirrored in the primary olfactory centre, the antennal lobe (AL). Further, I have identified odorants from cotton that elicit robust upwind flight responses in gravid female S. littoralis. In male S. littoralis, mating transiently abolishes attraction to pheromone-releasing females and cotton volatiles that signal larval habitat and mating sites. This behavioural modulation is reflected in the peripheral and central olfactory system, the antenna and the AL. In contrast, behavioural and neuronal responses to lilac flowers that signal an adult food source are not influenced by mating status. These findings provide an excellent substrate to examine how neuronal circuits integrate external sensory information with physiological state to shape behaviour

Probing the structural, mechanical, phonon, thermal, and transport properties of magnetic halide perovskites XTiBr3 (X = Rb, Cs) through ab-initio results

Abstract Herein, we have first reported the intrinsic properties, including structural, mechanical, electronic, magnetic, thermal, and transport properties of XTiBr3 (X = Rb, Cs) halide perovskites within the simulation scheme of density functional theory as integrated into Wien2k. First and foremost, the structural stability in terms of their ground state energies has been keenly evaluated from their corresponding structural optimizations, which advocate that XTiBr3 (X = Rb, Cs) has a stable ferromagnetic rather than the competing non-magnetic phase. Later on, the electronic properties have been computed within the mix of two applied potential schemes like Generalized Gradient Approximation (GGA) along with Trans-Bhala modified Becke Johnson (TB-mBJ), which thoroughly addresses the half-metallic behaviour with spin-up as metallic and in contrast to opposite spin-down channel signatures the semiconducting behaviour. Furthermore, the spin-splitting seen from their corresponding spin-polarised band structures offers a net magnetism of 2 µB which lends their opportunities to unlock the application branch of spintronics. In addition, these alloys have been characterised to show their mechanical stability describing the ductile feature. Moreover, phonon dispersions decisively certify the dynamical stability within the density functional perturbation theory (DFPT) context. Finally, the transport and thermal properties predicted within their specified packages have also been forwarded in this report