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

Abstract

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.

Galling insect communities mediate the effects of fire on their associated parasitoid communities

“…As previously reported, we found that the parasitoid communities were mostly composed of few very abundant generalist parasitoid species, whereas the specialist parasitoid species occurred in higher number, but in low abundance (De Araújo & Maia, 2021;Luz et al, 2021;Paniagua et al, 2009). Most of the generalist parasitoid species occurred in burned scenarios, as we expected, but we failed to detect any changes directly related to fire effects.…”

“…Some studies have found that parasitoid richness varies among galling insect communities that differ in species richness and composition (Dawah et al, 1995; Nyman et al, 2015; Paniagua et al, 2009). Moreover, according to the studies addressed in the Neotropical region, most of the galling insects appear to be attacked by specialist parasitoid species (De Araújo & Maia, 2021; Luz et al, 2021; Paniagua et al, 2009). Therefore, changes in galling insect species composition may be strongly reflected in the specific composition of the associated parasitoids (László & Tóthmérész, 2013; Nyman et al, 2015).…”

Host-enemy interactions provide limited biotic resistance for a range-expanding species via reduced apparent competition

“…For each parasitoid morphospecies, we measured 1-3 individuals per region per host morphotype. We measured body size from the tip of the thorax to the end of the abdomen, the area of the wing, length of external ovipositor, width of thorax, and size of tibia (all in mm) (45). Since body size correlates with all other traits, we divided trait measurements by body size.…”

“…At the same time selection favors traits in parasitoids that help them evade host defenses (42)(43)(44)(45). Traits include morphological features such as body size that can facilitate host defense or ovipositor size that can facilitate parasitoid attack (44)(45)(46). Phenology is also essential to interactions between insect hosts and parasitoids, as successful development for parasitoids requires that they attack hosts during discrete time windows, outside of which their development will not correspond with host resources (43,47).…”

“…Selection favors the evolution of defensive traits that reduce the success of parasitoid attacks in insect hosts. At the same time selection favors traits in parasitoids that help them evade host defenses (42)(43)(44)(45). Traits include morphological features such as body size that can facilitate host defense or ovipositor size that can facilitate parasitoid attack (44)(45)(46).…”