Phenotypic matching in ovipositor size in the parasitoid Galeopsomyia sp. (Hymenoptera, Eulophidae) attacking different gall inducers

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1. Ecological interaction networks, those built from linking interacting species in a biological community, can be structured according to neutral factors, like abundance, or depend on species distribution in space, time, or functional aspects of interacting species. 2. Gall inducers are a specialized guild of herbivores producing a structure serving as shelter, food, and defence against natural enemies. Interactions between galling insects and their parasitoids can become complex; studies analysing processes influencing how these interactions occur are uncommon. 3. We tested for ecological processes predictive of network structure: neutral (abundance), temporal, or morphological coupling factors. 4. We used a single host plant, and six Cecidomyiidae species from subtropical forests of southern Brazil. There were 14 samples across two years; out of 1762 galls, 741 parasitoids emerged (45 species). The network had high specialization (39 exclusive parasitoid species) and low connectance (21%). 5. Gall-parasitoid morphological coupling (gall thickness vs. parasitoid ovipositor length) was the best factor explaining network structure, with little effect for time, or abundances. Modularity was significant, with two modules, one with only Pisphondylia brasiliensis and its parasitoids. This insect induces thick multichambered galls with the lowest parasitism rate, attacked by parasitoids with longer ovipositors. Thinner galls had higher parasitism rates and more attacking parasitoid species, implying an important adaptive role for gall shape/size in natural enemy interactions. 6. Interaction networks are important tools to help understand how ecological function impacts community structure, but higher-scale studies may be needed to reach more encompassing conclusions about galler-parasitoid interactions.

Section: Discussionmentioning

confidence: 99%

What drives gallers and parasitoids interacting on a host plant? A network approach revealing morphological coupling as the main factor

Luz

Goetz

Mendonça

2020

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“…(Van Hezewijk & Roland, 2003). Moreover, Luz et al (2020) suggested phenotypic matching for the increased size and ovipositor length of Galeopsomyia sp. attacking the thicker galls of two cecidomyiid Bauhinia spp.…”

Section: Discussionmentioning

confidence: 99%

Bottom‐up effects shift top‐down community structure of the parasitoid guild that attacks Asphondylia borrichiae (Diptera: Cecidomyiidae) on Borrichia frutescens (Asteraceae)

Orta,

Rossi

2023

Asphondylia borrichiae induces galls at the apical meristems of its host plant, Borrichia frutescens, and the larvae develop and pupate within the gall. During development, immature stages of the midge are attacked by four species of parasitic wasps; two of these parasitoids, Galeopsomyia haemon and Torymus umbilicatus, are the most common members of the guild, and both are hyperparasitic. In the current study, plots of B. frutescens were randomly assigned to control (unmanipulated), salted or fertilised in a long‐term press experiment. Although plots initially exhibited no differences in stem length, gall and flower densities, after 3 months, they began to exhibit significant differences, suggesting stress (salted plots) and vigour (fertilised plots). Galls produced on plants from fertilised plots were approximately 20% and 31% larger than those from control and salted plots, respectively. Larger gall diameter in fertilised plots resulted in a shift of the parasitoid community towards the largest parasitoid, T. umgbilicatus, whereas smaller galls produced in salted plots became biased towards the smallest, but gregarious, G. haemon; interestingly, this pattern held for T. umbilicatus across treatments, and the effect for G. haemon was not significant when all treatments were combined. This study suggests that abiotic factors that alter host plant characteristics, such as gall diameter, affect the composition of the parasitoid guild that attacks A. borrichiae, which has implications for the acquisition of enemy‐free space during host range expansion of the midge.

“…This result differs from what is found in the literature. Luz et al (2020) found clear evidence that a model considering morphological coupling between Cecidomyiidae gall wall thickness and parasitoid ovipositor length was the best one to explain interaction network structure on the host plant Guapira opposita . For oak galls, despite parasitoid polyphagy, there is evidence that parasitoid community structure is defined by various attributes of galls such as hardness, hairiness and adhesion (some galls secrete sticky substances) (Bailey et al, 2009).…”

Section: Discussionmentioning

confidence: 99%

What shapes galling insect–parasitoid interaction networks on closely related host plants?

Prauchner,

de Souza Mendonça

2023

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Ecological networks describe community structure by focusing on how nodes are connected by links (interactions). Related species have higher probabilities of sharing links if interactions depending on phylogeny and/or species are functionally similar; however, if and how this modularity impacts higher trophic levels is still an open question. We aimed to evaluate the effect of different structuring factors on an observed bipartite network of galling insects and associated parasitoids on a system with two closely related and recently diverged plants, where host‐tracking could be underway. We hypothesized that gall structure, galler taxonomy and host plant identity could contribute, from a higher to a lower degree respectively, to network modularity by generating a selective pressure on parasitoids. Samples were collected between May 2015 and June 2017 in the forest areas of Porto Alegre, southern Brazil. Overall, we found 4629 galls of three monophagous and four oligophagous galling species; 664 parasitoid individuals were obtained and classified into 37 morphospecies. We constructed four networks with the collected data by organising nodes according to the tested factors, that is, gall structure, galler taxonomy, host plant identity and gall–plant interaction. All networks were significantly modular, and for three out of four analysed factors (gall structure, galler taxonomy and gall–plant interaction), modularity levels were at least intermediate (at about Q = 0.4). Barriers to or preferences for certain interactions appear to be responses to multiple concomitant factors. However, galler taxonomy and host plant identity are somehow stronger determinants for the parasitoids in terms of attacked hosts.