Bottom‐up and top‐down forces in plant‐gall relationships: testing the hypotheses of resource concentration, associational resistance, and host fitness reduction

Abstract

1. The abundance of insect galls may be influenced by the local host abundance as well as by the structure of the surrounding plant community, while insect galls may reduce host fitness. So far, few studies have been done in order to understand the relationship between galling insect abundance and the surrounding non-host plant community.2. In the present study, we explored the relationship between galling insect abundance and plant community structure and diversity. We tested the bottom-up forces of host and non-host plant density and non-host diversity on gall abundance. We also tested the top-down force of gall abundance on host fitness.3. We sampled all trees, measured their basal area, and estimated gall abundance in 25 plots (1 ha in total) located in a Brazilian savanna. In addition, we recorded the presence of flowers and fruits in all trees studied. 4. We found a positive relationship between host basal area per plot and gall abundance and a negative relationship between non-host basal area and species diversity with gall abundance. We also observed a negative association between gall abundance and the probability of the host plant to have flowers or fruits.5. Our data provide evidence that plant communities in which one host species dominates can be more susceptible to herbivore pressures than communities with less host dominance and more non-host neighbours, and that the non-host species create disruptive cues limiting galling insect infestation.

Unsuitability of the gall‐inducing fly Eutreta xanthochaeta for biological control of Lantana camara in presence of other native hosts in nature

“…Thus, the galls modified the structural complexity of the plant, generating new meristems potentially suitable for oviposition of female flies. Therefore, plant–gall interactions involve changes in plant structure, physiology, and chemistry, and this redifferentiation of host tissues may cause negative effects, such as a reduction of leaf area and photosynthetic rates (Oliveira et al, 2016; Martini et al, 2021).…”

Sexually dimorphic galls induced on leaflets of Matayba guianensis (Sapindaceae): a rare phenomenon occurring in Diptera (Cecidomyiidae)

“…Usually, each insect species induces only one gall morphotype in a host plant (Rohfritsch and Shorthouse 1982;Price 2005). In a rare report, the same insect species (Pseudophacopteron longicaudatum) was shown to induce morphologically similar galls on distinct host plant species (Aspidosperma macrocarpon and Aspidosperma tomentosum) (Malenovský et al 2015;Martini et al 2021). Therefore, a single species of galling insect can induce different gall morphotypes on the same host plant depending on its own life cycle or sex (e.g., Gonçalves et al 2005;Dorchin et al 2009;Kurzfeld-Zexer et al 2015;Pfeffer et al 2018;Silva et al 2019).…”