Temporal resource partitioning mitigates interspecific competition and promotes coexistence among insect parasites

Psyllid-mite interactions promote psyllid fecundity by selecting for a different life history

BACKGROUND

In interspecific competitive interactions at the same trophic level, herbivores are often hypothesized to exhibit a fast life-history strategy characterized by early reproduction and a short lifespan. Here, we analyzed the shift in life history of the psyllid Bactericera gobica when it interacts with the aphid Aphis gossypii, the thrips Frankliniella occidentalis, or the mite Aceria pallida in similar ecological niches because all of them cause damage to goji berry leaves.

RESULTS

We found that psyllids displayed a typical fast life history when interacting with aphids and thrips. Psyllids that interacted with mites also reproduced earlier than those without any interactions, but later than those interacting with aphids and thrips. Trophic competition typically led to a loss of fecundity in psyllids. To mitigate this loss, psyllids that interacted with mites allocated more resources to reproduction compared to those interacting with aphids and thrips, resulting in their reproduction being spread over a longer lifespan. This life history can be best described as a bet-hedging strategy.

CONCLUSION

Our study suggests that interspecific interactions cannot be solely explained by invoking faster life histories. Instead, the shift in life history may converge towards a finely-tuned match between interacting species. Interactions between psyllids and mites increase psyllid fecundity, potentially promoting the persistence of both species. © 2024 Society of Chemical Industry.

Environmental influence and species occurrence of yellowjacket drones in an invaded area

During the mating season, reproductive individuals of numerous insect species gather in rendezvous areas, which increases mating opportunities. Male hymenopterans often have to move considerable distances during a particular season, searching or waiting for receptive females. Such behavior is likely driven by a complex combination of individual and species-specific traits, environmental influence, and landscape cues. Our field study aimed to determine factors affecting the occurrence of Vespula spp. drones, focusing on the influence of vegetation traits, atmospheric factors and diel effects, and the species occurrence proportion in an invaded area in Patagonia. Our results indicate that the probability of drone presence over different types of vegetation is affected both by plant species and height. Also, weather and time of day influence the number of individuals simultaneously gathering, as higher abundances of flying drones are found in early hours, warmer days and at low cloud cover. Lastly, through mid-flight drone captures, we determined that both V. germanica and V. vulgaris drones are found concurrently in the same rendezvous areas. This constitutes the first exploratory field study reporting the heterospecific occurrence of Vespula spp. drones and overall, our results contribute to the understanding of yellowjackets mating systems.

Floral resource partitioning of coexisting bumble bees: Distinguishing species-, colony-, and individual-level effects

Resource partitioning is considered a key factor in alleviating competitive interactions, enabling coexistence among consumer species. However, most studies have focused on resource partitioning between species, ignoring the potentially critical role of intraspecific variation in resource use. We investigated floral resource partitioning across species, colonies, and individuals in a species-rich bumblebee community in the diversification center of bumblebees. We used a total of 10,598 bumblebees belonging to 13 species across 5 years in the Hengduan Mountains of southwest China. First, we evaluated the influence of a comprehensive set of floral traits, including both those related to attractiveness (flower color and shape) and rewards (pollen, sugar ratio, nectar volume, sugar concentration, and amino acid content) on resource partitioning at the species level in bumblebee-plant networks. Then, we explored intraspecific resource partitioning on the colony and individual levels. Our results suggest that bumblebee species differ substantially in their use of the available floral resources, and that this mainly depends on flower attractiveness (floral color and shape). Interestingly, we also detected floral resource partitioning at the colony level within all commonest bumblebee species evaluated. In general, floral resource partitioning between bumblebee individuals decreased with species- and individual-level variation in body size (intertegular span). These results suggest that bumblebee species may coexist via the flexibility in their preferences for specific floral traits, which filters up to support the co-occurrence of high numbers of species and individuals in this global hotspot of species richness.

Cold tolerance and diapause within and across trophic levels: Endoparasitic wasps and their fly host have similar phenotypes

Low temperatures associated with winter can limit the survival of organisms, especially ectotherms whose body temperature is similar to their environment. However, there is a gap in understanding how overwintering may vary among groups of species that interact closely, such as multiple parasitoid species that attack the same host insect. Here, we investigate cold tolerance and diapause phenotypes in three endoparasitoid wasps of the apple maggot fly Rhagoletis pomonella (Diptera: Tephritidae): Utetes canaliculatus, Diachasma alloeum, and Diachasmimorpha mellea (Hymenoptera: Braconidae). Using a combination of respirometry and eclosion tracking, we found that all three wasp species exhibited the same three diapause duration phenotypes as the fly host. Weak (short duration) diapause was rare, with <5 % of all three wasp species prematurely terminating diapause at 21 °C. Most D.mellea (93 %) entered a more intense (longer duration) diapause that did not terminate within 100 d at this warm temperature. The majority of U.canaliculatus (92 %) and D. alloeum (72 %) averted diapause (non-diapause) at 21 °C. There was limited interspecific variation in acute cold tolerance among the three wasp species: wasps and flies had similarly high survival (>87 %) following exposure to extreme low temperatures (-20 °C) as long as their body fluids did not freeze. The three wasp species also displayed little interspecific variation in survival following prolonged exposure to mild chilling of 8 or more weeks at 4 °C. Our study thus documents a remarkable conservation of cold tolerance and diapause phenotypes within and across trophic levels.

The ephemeral resource patch concept

Ephemeral resource patches (ERPs) - short lived resources including dung, carrion, temporary pools, rotting vegetation, decaying wood, and fungi - are found throughout every ecosystem. Their short-lived dynamics greatly enhance ecosystem heterogeneity and have shaped the evolutionary trajectories of a wide range of organisms - from bacteria to insects and amphibians. Despite this, there has been no attempt to distinguish ERPs clearly from other resource types, to identify their shared spatiotemporal characteristics, or to articulate their broad ecological and evolutionary influences on biotic communities. Here, we define ERPs as any distinct consumable resources which (i) are homogeneous (genetically, chemically, or structurally) relative to the surrounding matrix, (ii) host a discrete multitrophic community consisting of species that cannot replicate solely in any of the surrounding matrix, and (iii) cannot maintain a balance between depletion and renewal, which in turn, prevents multiple generations of consumers/users or reaching a community equilibrium. We outline the wide range of ERPs that fit these criteria, propose 12 spatiotemporal characteristics along which ERPs can vary, and synthesise a large body of literature that relates ERP dynamics to ecological and evolutionary theory. We draw this knowledge together and present a new unifying conceptual framework that incorporates how ERPs have shaped the adaptive trajectories of organisms, the structure of ecosystems, and how they can be integrated into biodiversity management and conservation. Future research should focus on how inter- and intra-resource variation occurs in nature - with a particular focus on resource × environment × genotype interactions. This will likely reveal novel adaptive strategies, aid the development of new eco-evolutionary theory, and greatly improve our understanding of the form and function of organisms and ecosystems.

Sensitivities to Chill Durations and No-Chill Temperatures Regulating Eclosion Responses Differ Between Rhagoletis zephyria (Diptera: Tephritidae) and its Braconid Parasitoids (Hymenoptera: Braconidae)

Seasonal temperatures select for eclosion timing of temperate insects and their parasitoids. In western North America, the fruit fly Rhagoletis zephyria Snow (Diptera: Tephritidae) is parasitized by the hymenopterous wasps Utetes lectoides (Gahan), an egg parasite, and Opius downesi Gahan, a larval parasite (both Braconidae). Eclosion of wasps should be timed with the presence of susceptible fly stages, but reports indicate U. lectoides ecloses in the absence of flies under no-chill conditions. Based on this, we tested the hypotheses that chill durations and no-chill temperatures both differentially regulate eclosion times of R. zephyria and its parasitic wasps. When fly puparia were chilled at ~3°C for 130-180 d, U. lectoides and O. downesi always eclosed on average later than flies. However, after 180-d chill, flies eclosed on average earlier than after 130- and 150-d chill, whereas eclosion times of U. lectoides and O. downesi were less or not affected by chill duration. When fly puparia were exposed to 20-22°C (no chill), U. lectoides eclosed before flies, with 88.9% of U. lectoides versus only 0.61% of flies eclosing. Taken together, findings show that eclosion times of flies are more sensitive to changes in chill duration than those of wasps. Flies are less sensitive than wasps to no-chill in that most flies do not respond by eclosing after no-chill while most wasps do. Our results suggest that shorter winters and longer summers due to climate change could cause mismatches in eclosion times of flies and wasps, with potentially significant evolutionary consequences.