Weather Forecasting by Insects: Modified Sexual Behaviour in Response to Atmospheric Pressure Changes

<div><p>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, <i>Diabrotica speciosa</i> (Coleoptera), the true armyworm moth, <i>Pseudaletia unipuncta</i> (Lepidoptera) and the potato aphid, <i>Macrosiphum euphorbiae</i> (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 <i>M. euphorbiae</i> 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.</p></div

A Novel Interaction between Plant-Beneficial Rhizobacteria and Roots: Colonization Induces Corn Resistance against the Root Herbivore <i>Diabrotica speciosa</i>

<div><p>A number of soil-borne microorganisms, such as mycorrhizal fungi and rhizobacteria, establish mutualistic interactions with plants, which can indirectly affect other organisms. Knowledge of the plant-mediated effects of mutualistic microorganisms is limited to aboveground insects, whereas there is little understanding of what role beneficial soil bacteria may play in plant defense against root herbivory. Here, we establish that colonization by the beneficial rhizobacterium <i>Azospirillum brasilense</i> affects the host selection and performance of the insect <i>Diabrotica speciosa</i>. Root larvae preferentially orient toward the roots of non-inoculated plants versus inoculated roots and gain less weight when feeding on inoculated plants. As inoculation by <i>A. brasilense</i> induces higher emissions of (<i>E</i>)-β-caryophyllene compared with non-inoculated plants, it is plausible that the non-preference of <i>D. speciosa</i> for inoculated plants is related to this sesquiterpene, which is well known to mediate belowground insect-plant interactions. To the best of our knowledge, this is the first study showing that a beneficial rhizobacterium inoculant indirectly alters belowground plant-insect interactions. The role of <i>A. brasilense</i> as part of an integrative pest management (IPM) program for the protection of corn against the South American corn rootworm, <i>D. speciosa</i>, is considered.</p></div

Insect Behaviour under different barometric pressure conditions.

<p>Frequency of different behaviours exhibited by three different insect species when subjected to stable, decreasing and increasing barometric pressure. A: The proportion of active <i>D. speciosa</i> males in Y-tube olfactometer to sex pheromone stimuli; B: The proportion of <i>P. unipuncta</i> and <i>M. euphorbiae</i> females exhibiting calling behaviour; C: The proportion of <i>P. unipuncta</i> and <i>M. euphorbiae</i> couples mating. **Indicates significant difference among treatments at 1%.</p

Effect of <i>Azospirillum brasilense</i> on <i>Diabrotica speciosa</i> larval host choice.

<p><i>Diabrotica speciosa</i> larval choice between inoculated plants and the blank treatment (non-inoculated soil), inoculated and non-inoculated corn, and the plant-beneficial rhizobacterium (PBR) inoculant and the blank. Bars represent the mean number of larvae ± SE. Pie charts on the right represent non-responsive (no choice) and responsive (choice) larvae. Asterisks indicate a significant difference between treatments according to a quasi-Poisson glm (n = 10, <i>P</i><0.05).</p

Effect of <i>Azospirillum brasilense</i> on <i>Diabrotica speciosa</i> performance.

<p><i>Diabrotica speciosa</i> larval performance when fed on inoculated and non-inoculated corn plants. Bars represent the mean larval weight ± SE. Asterisks indicate a significant difference between treatments according to according to a glmm (n = 10, <i>P</i><0.05).</p

Scanning electron microscopy images of inoculated and non-inoculated corn roots.

<p>Scanning electron microscopy images showing the colonization of corn roots by the plant-beneficial rhizobacterium <i>Azospirillum brasilense</i>. (A) Inoculated corn roots and (B) non-inoculated corn roots.</p

Identification of compounds in the root volatile profile.

<p>Retention time (Rt), Kovats Index (KI), peak area (%) and identification of compounds emitted by inoculated and non-inoculated corn roots through combined GC-MS analysis.</p><p>Identification of compounds in the root volatile profile.</p

Root volatile profile induced by <i>Azospirillum brasilense</i> colonization.

<p>Emissions of volatile compounds from inoculated and non-inoculated corn roots. Bars represent the mean ± SE. Different letters indicate a significant difference between treatments according to <i>One-Way</i> ANOVA followed by Tukey’s HSD test (n = 4, <i>P</i><0.05).</p