Eran Gefen

Aerobic capacity in arachnids is closely linked with considerable structural variation in their respiratory systems. However, although all scorpions are non-tracheated and possess four pairs of book lungs, they vary greatly in their locomotor activity patterns. Many non-burrowing species express short bursts of activity whereas other species dig deep burrows within hours, suggesting more aerobically fueled exercise. We hypothesized that locomotion in surface dwellers is more dependent on anaerobic ATP synthesis, and that this would be reflected in their exercise performance and functional adaptation to potential disturbance of resting-state homeostasis. We used an experimental design consisting of two surface-dwelling Buthidae species (Hottentotta judaicus and Leiurus hebraeus), a burrowing buthid (Buthus israelis) and two burrowing Scorpionidae (Scorpio fuscus and Scorpio palmatus). Maximum running speeds were higher for buthids, which were also more prone to fatigue than scorpionids. Higher respiratory exchange ratios recorded for buthids during activity and subsequent recovery indicated a higher reliance on anaerobically fueled locomotion compared with scorpionids. Our data show that quicker removal of excess CO2 resulting from anaerobic exercise and hemolymph buffering in buthids is associated with significantly higher carbonic anhydrase activity in their hemolymph, compared with that of scorpionids. Efficient CO2 emission may also contribute to the lower respiratory water losses of buthids, and thus assist in facing both biotic and abiotic challenges of surface existence, from which the scorpionid burrows provide refuge.

The mango stem borer Batocera rufomaculata is a large beetle (Cerambycidae) exhibiting a high intra-specific variation in adult body size because of differing environmental conditions during larval growth. Previous studies revealed that smaller individuals can fly longer distances than larger ones before reaching exhaustion, a surprising fact considering that the cost of transport is expected to increase with decreased body size. We tested the flight propensity and metabolic rhythms of these beetles as a function of sex and body size. The intrinsic flight-initiating behaviour and the daily fluctuations in metabolic rate (MR) were measured over 48 h in closed arenas and in metabolic chambers, respectively. Beetles displayed a strong circadian pattern of nocturnal activity in both locomotion and MR. Smaller conspecifics were significantly more active both metabolically and behaviourally than larger ones with sex having no effect on the size-related difference. The results suggest a stronger innate drive to disperse by flight in smaller conspecifics, providing a behavioural–physiological link between environmental conditions during the larval growth period and the dispersal potential of the adults.

Summary: A hallmark of the desert locust's ancient and deserved reputation as a devastating agricultural pest is that of the long‐distance, multi‐generational migration of locust swarms to new habitats. The bacterial symbionts that reside within the locust gut comprise a key aspect of its biology, augmenting its immunity and having also been reported to be involved in the swarming phenomenon through the emission of attractant volatiles. However, it is still unclear whether and how these beneficial symbionts are transmitted vertically from parent to offspring. Using comparative 16S rRNA amplicon sequencing and direct experiments with engineered bacteria, we provide evidence for vertical transmission of locust gut bacteria. The females may perform this activity by way of inoculation of the egg‐pod's foam plug, through which the larvae pass upon hatching. Furthermore, analysis of the composition of the foam revealed chitin to be its major component, along with immunity‐related proteins such as lysozyme, which could be responsible for the inhibition of some bacteria in the foam while allowing other, more beneficial, strains to proliferate. Our findings reveal a potential vector for the transgenerational transmission of symbionts in locusts, which contributes to the locust swarm's ability to invade and survive in new territories.

As one of the world’s most infamous agricultural pests, locusts have been subjected to many in-depth studies. Their ability at one end of their behavioral spectrum to live as solitary individuals under specific conditions, and at the other end of the spectrum to form swarms of biblical scale, has placed them at the focus of vast research efforts. One important aspect of locust ecology is that of their interactions with the bacteria that reside in and on them. Although this aspect of locust ecology has been little studied relative to the mainstream locust research, these bacteria have been shown both to affect locust immunity and to participate in maintaining swarm integrity through the secretion of attractant volatiles. The interaction between locusts and their bacteria seems, however, to be bi-directional, with the bacteria themselves, as recently shown, being influenced by their host’s swarming tendencies. This seems to be a consequence of the bacterial composition in the locust’s gut, reproductive organs, and integument undergoing change with the change in their host’s behavior. In this review we describe the current state of knowledge of the locust–bacteria interactions (data exists mainly for the desert and the migratory locusts), as well as highlighting some newly-gained understanding; and offer perspectives for future research.

Locust plagues are an ancient phenomenon, with references going back to the Old Testament. These swarming pests are notorious for their tendency to aggregate and perform long migrations, consuming vast amounts of vegetation and decimating the cultivated fields on their path. However, when population density is low, locusts will express a solitary, cryptic, non-aggregating phenotype that is not considered as an agricultural pest. Although transition of locusts from the solitary to the gregarious phase has been well studied, the shifts in the locust microbiome composition associated with this phase-transition have yet to be addressed. Here, using 16S rRNA amplicon sequencing, we compared the bacterial composition of solitary desert locusts before and after a crowding-induced phase-transition. Our findings reveal that the microbiome is altered during the phase transition. We also show that this significant change in bacterial composition includes the acquisition of a specific bacterial species - Weissella cibaria (Firmicutes), which has been previously shown to induce aggregation in cockroaches. Our findings led us to hypothesize that the locust microbiome may play a role in inducing aggregation behavior, contributing to the formation and maintenance of a swarm. Employing a mathematical model, we demonstrate the potential evolutionary advantage of inducing aggregation under various environmental conditions; and specifically, when the aggregation-inducing microbe exhibits a relatively high horizontal transmission rate. This is a first description of a previously unknown and important aspect of locust phase transition, demonstrating that the phase shift includes a shift in the gut and integument bacterial composition.

A hallmark of the desert locust’s ancient and deserved reputation as a devastating agricultural pest is that of the long-distance, multi-generational migration of locust swarms to new habitats. The bacterial symbionts that reside within the locust gut comprise a key aspect of its biology, augmenting its immunity and having also been reported to be involved in the swarming phenomenon through the emission of attractant volatiles. However, it is still unclear whether and how these beneficial symbionts are transmitted vertically from parent to offspring. Using comparative 16S rRNA amplicon sequencing and direct experiments with engineered bacteria, we provide here evidence of the vertical transmission of locust gut bacteria. The females perform this activity by way of inoculation of the egg-pod’s foam plug, through which the larvae pass upon hatching. Furthermore, analysis of the biochemical structure of the foam revealed chitin to be its major component, along with immunity-related proteins such as lysozyme, which could be responsible for the inhibition of some bacteria in the foam while allowing other, more beneficial, strains to proliferate. Our findings reveal a potential vector for the transgenerational transmission of symbionts in locusts, which contributes to the locust swarm’s ability to invade and survive in new territories.

Large insects actively ventilate their tracheal system even at rest, using abdominal pumping movements, which are controlled by a central pattern generator (CPG) in the thoracic ganglia. We studied the effects of respiratory gases on the ventilatory rhythm by isolating the thoracic ganglia and perfusing its main tracheae with various respiratory gas mixtures. Fictive ventilation activity was recorded from motor nerves controlling spiracular and abdominal ventilatory muscles. Both hypoxia and hypercapnia increased the ventilation rate, with the latter being much more potent. Sub-threshold hypoxic and hypercapnic levels were still able to modulate the rhythm as a result of interactions between the effects of the two respiratory gases. Additionally, changing the oxygen levels in the bathing saline affected ventilation rate, suggesting a modulatory role for haemolymph oxygen. Central sensing of both respiratory gases as well as interactions of their effects on the motor output of the ventilatory CPG reported here indicate convergent evolution of respiratory control among terrestrial animals of distant taxa.Summary statement: Tight control over respiratory gas supply to the isolated locust CNS reveals interactions of oxygen and carbon dioxide effects on central ventilatory output.