Prevailing abiotic conditions may positively or negatively impact insects at both the individual and population levels. For example while moderate rainfall and wind velocity may provide conditions ...that favour development, as well as movement within and between habitats, high winds and heavy rains can significantly decrease life expectancy. There is some evidence that insects adjust their behaviours associated with flight, mating and foraging in response to changes in barometric pressure. We studied changes in different mating behaviours of three taxonomically unrelated insects, the curcurbit beetle, Diabrotica speciosa (Coleoptera), the true armyworm moth, Pseudaletia unipuncta (Lepidoptera) and the potato aphid, Macrosiphum euphorbiae (Hemiptera), when subjected to natural or experimentally manipulated changes in atmospheric pressure. In response to decreasing barometric pressure, male beetles exhibited decreased locomotory activity in a Y-tube olfactometer with female pheromone extracts. However, when placed in close proximity to females, they exhibited reduced courtship sequences and the precopulatory period. Under the same situations, females of the true armyworm and the potato aphid exhibited significantly reduced calling behaviour. Neither the movement of male beetles nor the calling of armyworm females differed between stable and increasing atmospheric pressure conditions. However, in the case of the armyworm there was a significant decrease in the incidence of mating under rising atmospheric conditions, suggesting an effect on male behaviour. When atmospheric pressure rose, very few M. euphorbiae oviparae called. This was similar to the situation observed under decreasing conditions, and consequently very little mating was observed in this species except under stable conditions. All species exhibited behavioural modifications, but there were interspecific differences related to size-related flight ability and the diel periodicity of mating activity. We postulate that the observed behavioral modifications, especially under decreasing barometric pressure would reduce the probability of injury or death under adverse weather conditions.
Fire is a major force acting on the structure and dynamics of the Cerrado (Brazilian savanna). Post‐fire conditions can be severe for soil‐dwelling organisms, such as dung beetles, which play ...essential roles in the Cerrado ecosystem. This study evaluated whether ash residues affect the ecological functions of dung burial and soil bioturbation by the Cerrado‐native beetle Phanaeus palaeno Blanchard (Coleoptera: Scarabaeidae, Phanaeini), and how its sex and weight influence the performance of ecological functions under post‐fire conditions. The beetles were collected from open natural grasslands and pastures in the Cerrado biome, and the functions performed by the individuals were evaluated in the laboratory. The response of beetles was measured by quantifying the amount of buried dung and soil by both females and males in buckets filled with soil, half covered or fully covered with ash, or in buckets without ash. The amount of buried dung or bioturbated soil did not differ among treatments, demonstrating that ash does not influence P. palaeno in performing these functions. Females bioturbated more soil and buried more dung than males, but neither were affected by ash. As dung beetles perform essential ecosystem functions, this information may be helpful in developing novel fire management practices to conserve Cerrado biodiversity.
We tested whether fire ash deposited on the soil influences the ecological functions performed by the Cerrado‐native dung beetle Phanaeus palaeno (Coleoptera: Scarabaeidae). The ash did not influence dung burial nor bioturbation of soil by dung beetles. However, both functions were influenced by sex, females being more active than males. These results contribute to the understanding of the resilience of the native fauna to fire in savanna ecosystems such as the Brazilian Cerrado.
The transition from a perennial to an annual life cycle, as well as domestication, are expected to increase plant growth and reproduction at the same time that anti-herbivore defences are reduced. ...Here, we investigated the effects of the life-history transition (the perennial teosinte
Zea diploperennis
to the annual teosinte
Z. mays
ssp.
mexicana
) and domestication of
Zea
(annual teosinte to the modern maize
Z. mays
ssp.
mays
) on direct and indirect defences against the fall armyworm
Spodoptera frugiperda
. The direct defence of
Zea
was assessed by larval survival and nutritional indices based on food intake and utilisation. Indirect defence was measured in terms of the olfactory preference of the night-active predatory earwig
Doru luteipes
for nocturnal herbivore-induced plant volatiles (HIPVs) from the teosintes and maize. Larval growth and survival were reduced on teosintes relative to maize. Whilst larvae fed on perennial teosinte had lower food intake indices, those on annual teosinte showed lower food utilisation indices relative to maize. The earwig preferred HIPVs emitted by teosintes over those by maize, but it did not discriminate between odours of herbivore-damaged annual and perennial teosinte. The nocturnal HIPV blend from maize contained the lowest total amount of fatty acid derivatives, while it had higher total amounts of terpenes compared to teosintes. Our study shows that the teosintes are better defended than maize in terms of direct and indirect defences; however, the perennial teosinte have stronger direct defences against the fall armyworm than the annual teosinte.
Plants attacked by herbivores have evolved different strategies that fend off their enemies. Insect eggs deposited on leaves have been shown to inhibit further oviposition through visual or chemical ...cues. In some plant species, the volatile methyl salicylate (MeSA) repels gravid insects but whether it plays the same role in the model species Arabidopsis thaliana is currently unknown. Here we showed that Pieris brassicae butterflies laid fewer eggs on Arabidopsis plants that were next to a MeSA dispenser or on plants with constitutively high MeSA emission than on control plants. Surprisingly, the MeSA biosynthesis mutant bsmt1-1 treated with egg extract was still repellent to butterflies when compared to untreated bsmt1-1. Moreover, the expression of BSMT1 was not enhanced by egg extract treatment but was induced by herbivory. Altogether, these results provide evidence that the deterring activity of eggs on gravid butterflies is independent of MeSA emission in Arabidopsis, and that MeSA might rather serve as a deterrent in plants challenged by feeding larvae.
Supplementation with Silicon (Si) is well-known for increasing resistance of grasses to insect herbivores. Although the exact underlying mechanism remains unknown, Si accumulation interacts with the ...jasmonic acid-signalling pathway, which modulates herbivore-induced plant defences. We examined whether Si supplementation alters direct and induced indirect defences in maize plants in ways that deter the initial infestation by the fall armyworm
Spodoptera frugiperda
(JE Smith). We assessed the herbivore’s oviposition preference, neonate and third-instar larval performance as well as the recruitment of a predator of young larvae, the flower bug
Orius insidiosus
(Say), by herbivore-induced plant volatiles (HIPVs). In choice tests,
S. frugiperda
deposited about two times more eggs on −Si than on +Si maize. The mortality of neonate
S. frugiperda
larvae was about sixfold higher in +Si compared to −Si plants, even though they consumed similar leaf area on both treatments. Although there were no mortality differences, Si supplementation also impacted third-instar larvae that gained about twofold less weight than those fed on −Si maize. In olfactometer assays,
O. insidiosus
was not attracted to volatiles of uninfested maize plants with or without Si supplementation, but it was attracted to those emitted by fall armyworm-infested plants, irrespective of whether plants received Si supplementation. However, when the flower bug could choose between the volatiles released from −Si and +Si fall armyworm-infested plants, it preferentially oriented to +Si fall armyworm-infested plant. Our results show that Si supplementation in maize may deter fall armyworm colonization because of greater direct defences and attractiveness of HIPVs to the flower bug.
Plants are under constant threat from insect herbivores that can consume all types of plant tissue, both aboveground and belowground. Because plants connect aboveground and belowground environments, ...they are uniquely positioned to mediate indirect herbivore interactions between the two ecosystems. The effects of this mediation may change over time with cascading consequences both aboveground and belowground. We used a system involving the larval belowground (BG) herbivore Diabrotica speciosa (Coleoptera: Chrysomelidae), corn, and the aphid aboveground (AG) herbivore Rhopalosiphum maidis to answer three questions: (1) What effects does belowground herbivory by D. speciosa have on feeding preferences and distributions of the aboveground R. maidis? (2) How do these preferences and distributions change over time? And (3) what are the longer term consequences for R. maidis populations? Adult alate aphids initially preferred corn seedlings with root feeding by D. speciosa, but preference declined over time driven by aphids leaving corn seedlings with root herbivory. Similarly, observations of aphid performance and colony growth indicated negative effects of root herbivory in contrast to previous studies. These results suggest that shifts in plant‐mediated aboveground–belowground interactions can have important consequences for long‐term distributions of aboveground herbivores.
According to the theory of optimal foraging and preference–performance hypothesis, herbivores usually select plant hosts that benefit themselves or their offspring. We investigated the hypothesis ...that gravid females of the cucurbit beetle
Diabrotica speciosa
use volatiles derived from non-infested maize plants and herbivore-infested plants under attack by their conspecific immatures and adults in selecting a host for oviposition. The response of
D. speciosa
females to volatiles was quantified for the following treatments: (i) non-infested plants; (ii) plants infested by larvae (root-infested); (iii) plants infested by adults (leaf-infested); and (iv) plants infested by larvae and adults (leaf + root-infested). We also assessed if females were able to identify conditions of competition and host adequacy for offspring by means of chemical cues emitted by these plants. The results indicated that the presence of
D. speciosa
conspecifics on maize plants triggered the emission of volatiles, which influenced host selection for oviposition. Gravid females avoided both plants infested by larvae and plants infested by larvae and adults. Leaf-infested plants did not affect the host-selection behavior of females. Weight gain was higher in larvae kept on non-infested and leaf-infested plants than on root-infested or root + leaf-infested plants, indicating that female preference is related to its offspring performance.
Graphical Abstract
Synthesis of the effects of volatile organic compounds (VOCs) produced by uninfested, leaf-infested, root-infested and leaf+root-infested corn plants on the host-choice behavior of adults and performance of
Diabrotica speciosa
larvae
Few systems have been described in which herbivore-induced root volatiles mediate attraction of entomopathogenic nematodes (EPNs), and they only concern root damage inflicted by chewing insects. ...EPNs, especially Heterorhabditis indica and Steinernema carpocapsae, are potential biological control agents of sugarcane spittlebug (Mahanarva fimbriolata) populations. Here, we investigated the response of these two species of EPNs to sugarcane root volatiles damaged by M. fimbriolata nymphs in a belowground six-arm olfactometer. We also examined changes on root volatile profile in response to herbivory of sugarcane spittlebug nymphs. Results showed that both EPN species did not discriminate between odors of undamaged sugarcane and moistened sand (blank). However, when EPNs were exposed to odors of spittlebug-damaged and undamaged sugarcane roots, both species significantly preferred odors of spittlebug-damaged roots. Headspace collection followed by GC–MS analyses showed no qualitative difference (total of 11 compounds) between volatile profiles of spittlebug-damaged and undamaged sugarcane roots. In contrast to the previous studies involving feeding by root chewing insects, our root volatile analysis did not reveal any up-regulation resulting from sugarcane spittlebug damage, but the down-regulation of the terpenes dihydromyrcenol and β-isomethyl ionone when compared with the profile of undamaged sugarcane roots. Here, we propose alternative explanations for the EPN attraction to spittlebug-damaged roots as it is unlikely that reduced concentrations of the volatiles play a role in this interaction. Further studies are necessary to determine the key compounds of the root volatile emission to enhance biological control efficacy with EPNs against M. fimbriolata in sugarcane.
Harvestmen (Arachnida, Opiliones) are arachnids that rely on chemicals for communication and are particularly dependent on high humidity. The harvestman Jussara spec. (Sclerosomatidae) clearly ...prefers to rest on the stem and leaves of Psychotria suterella Muell. Arg. (Rubiaceae), a plant having a complex architecture of overlapping branches. So far, few studies have focused on understanding how harvestmen find their host plant and the benefits associated with the selected plant. Here, we investigated cues harvestmen may exploit to find P. suterella and the potential benefits for harvestmen of this interaction. To address how harvestmen find the plant, we tested two non‐exclusive hypotheses: harvestmen use chemicals from conspecifics, and/or harvestmen use chemicals from plants. For the first hypothesis, we assessed the number of harvestmen choosing P. suterella with or without chemicals of Jussara spec. on the main stem. We did not find evidence that Jussara spec. uses chemicals from conspecifics to select P. suterella, at least in isolation, without any mechanical stimuli such as stem texture or size. For the second hypothesis, we tested harvestman behavior exposed to volatiles from P. suterella, a non‐preferred host plant – Impatiens walleriana Hook.f. (Balsaminaceae) – and a blank treatment, both in a triangular arena and in a Y‐tube olfactometer. We also found no evidence that the harvestmen use plant volatiles to find it. We also tested two non‐exclusive hypotheses regarding the benefits of selecting P. suterella for harvestmen. The first hypothesis is that P. suterella offers a higher humidity than other plants in the micro‐environment surrounding the leaves because of a high leaf transpiration rate. Harvestmen could benefit from this because they rest with the body in contact with the leaf or at less than 5 mm from it. We did not find evidence that leaf transpiration rate is important for Jussara spec., as P. suterella did not present high rates compared to other local species. The second hypothesis is that the leaves of P. suterella provide a better shadow than other plants, acting as a sun shade due to its complex architecture with overlapping leaves. We measured light passage through the leaves of P. suterella and three other local species and found that less light passes through the leaves of P. suterella, which therefore provides darker shadow. This potentially provides a favorable micro‐climate for harvestmen, which might help to explain the micro‐habitat preference of Jussara spec.
Ants are known to function as reliable biological indicators for habitat impact assessment. They play a wide range of ecological roles depending on their feeding and nesting habits. By clustering ...ants in guilds, it is possible both to assess how agriculture and forest fragmentation can disturb ant communities and to predict the ecological impacts due to losses of a specific guild. This study aimed at determining the impact of non-shaded coffee and pasture agriculture on predatory and omnivorous guilds of leaf-litter ants of Atlantic Forest fragments in Minas Gerais, Brazil. Both coffee and pasture agriculture influenced leaf-litter ant community, although coffee was more disruptive than pasture. Coffee agriculture not only disturbed the diversity of predatory ants, but also negatively affected the number of predatory and omnivorous ants when compared to forest fragments. In contrast, pasture agriculture only disrupted the abundance of predatory ants. Fragment edges skirting crops were negatively affected in terms of leaf-litter ant abundance, but not diversity. Cluster analysis showed that forest fragments were similar irrespective of the cultivation, but the borders were similar to the crop. The study assessed agriculture impact by surveying ant guilds, and revealed that the predatory guild is more susceptible than omnivorous ants.
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