Martín Videla

A tritrophic analysis of host preference and performance in a polyphagous leafminer

The optimal oviposition theory predicts that oviposition preferences of phytophagous insects should correlate with host suitability for their offspring. As plant host suitability depends not only on its quality as food, but also on its provision of enemy‐free space, we examined the relationship between adult host preference and offspring performance for the leafminer Liriomyza huidobrensis (Blanchard) (Diptera: Agromyzidae) on various host plants, considering also the interaction with natural enemies. Preference and offspring performance were assessed through observational field data and laboratory experiments in central Argentina. Field data suggested a positive host preference – performance linkage, as the leafminer attained larger body size on the crops where it was more abundant. Laboratory trials supported these results: Vicia faba L. (Fabaceae) was the preferred host in the laboratory as well as in the field, performance of L. huidobrensis being also best on this host, with highest survival rates and shortest development time. The actively feeding larval stage showed the largest plant‐related effects. Higher overall parasitism rates were found on plants from which smaller leafminers were reared, reinforcing the preference–performance linkage. On the other hand, the main parasitoid Phaedrotoma scabriventris Nixon (Hymenoptera: Braconidae) reached larger body size, and caused higher mortality rates on crops where the leafminer was larger. Changes in abundance of particular parasitoid species could thus modify overall parasitism trends.

Dominant predators mediate the impact of habitat size on trophic structure in bromeliad invertebrate communities

Local habitat size has been shown to influence colonization and extinction processes of species in patchy environments. However, species differ in body size, mobility, and trophic level, and may not respond in the same way to habitat size. Thus far, we have a limited understanding of how habitat size influences the structure of multitrophic communities and to what extent the effects may be generalizable over a broad geographic range. Here, we used water-filled bromeliads of different sizes as a natural model system to examine the effects of habitat size on the trophic structure of their inhabiting invertebrate communities. We collected composition and biomass data from 651 bromeliad communities from eight sites across Central and South America differing in environmental conditions, species pools, and the presence of large-bodied odonate predators. We found that trophic structure in the communities changed dramatically with changes in habitat (bromeliad) size. Detritivore : resource ratios showed a consistent negative relationship with habitat size across sites. In contrast, changes in predator: detritivore (prey) ratios depended on the presence of odonates as dominant predators in the regional pool. At sites without odonates, predator: detritivore biomass ratios decreased with increasing habitat size. At sites with odonates, we found odonates to be more frequently present in large than in small bromeliads, and predator: detritivore biomass ratios increased with increasing habitat size to the point where some trophic pyramids became inverted. Our results show that the distribution of biomass amongst food-web levels depends strongly on habitat size, largely irrespective of geographic differences in environmental conditions or detritivore species compositions. However, the presence of large-bodied predators in the regional species pool may fundamentally alter this relationship between habitat size and trophic structure. We conclude that taking into account the response and multitrophic effects of dominant, mobile species may be critical when predicting changes in community structure along a habitat-size gradient.

Plant patch structure modifies parasitoid assemblage richness of a specialist herbivore

1. The spatial structure of plant patches has been shown to affect host–parasitoid interactions, but its influence on parasitoid diversity remains largely ignored. Here we tested the prediction that parasitoid species richness of the specialist leafminer Liriomyza commelinae increases in larger and less isolated patches of its host plant Commelina erecta. We also explored whether parasitoid abundance and body size affected the occurrence of parasitoid species in local assemblages.

Differential effects of experience on feeding and ovipositing preferences of a polyphagous leafminer.

Host preferences of phytophagous insects, although generally showing a strong hereditary component, can be modified by experience. Here we aim to elucidate the relative roles of larval and adult experience on host plant selection by Liriomyza huidobrensis (Blanchard) (Diptera: Agromyzidae), a widely distributed pest on ornamentals and vegetables. Laboratory and field experiments evaluating feeding and oviposition preferences of L. huidobrensis females with larval, adult, or larva plus adult experience on either Vicia faba L. (Fabaceae) or Beta vulgaris var. cicla L. (Chenopodiaceae) were performed. Also, we measured offspring performance of L. huidobrensis on both host plant species. Our results show that L. huidobrensis females strongly preferred V. faba over B. vulgaris var. cicla for feeding and egg laying. Only larval and adult experience acting in concert modified feeding behaviour, whereas oviposition preferences remained unaltered regardless of female previous experience. Offspring performance was higher on the preferred host (V. faba), indicating a preference–performance linkage for this leafminer. Experience on B. vulgaris var. cicla could not overcome oviposition preferences, which appear driven by fitness benefits for offspring.

Induced resistance against leafminer eggs by extrusion in young potato plants

Abstract Egg extrusion patterns were investigated as an inducible defensive mechanism in potato plants against the leafminer Liriomyza huidobrensis (Blanchard) (Diptera: Agromyzidae). Increased multiplication rates in leaf cells surrounding an egg of L. huidobrensis leads to its exposure through the leaf cuticle, which might increase the risk of mortality. Extrusion rates were evaluated in laboratory tests, in relation to plant and leaf age in Solanum tuberosum L. var. Spunta. Stratified field sampling was also carried out in order to assess leafminer distribution on new and old leaves. Extrusion was higher in young plants, being restricted in older ones to new, still expanding leaves. Plant reaction was independent of egg density. In the field, damage was concentrated in older foliage, in line with the extrusion results. The relevance of egg extrusion for pest management is discussed.

Leafminer egg distribution at decreasing leaf availability levels: do females avoid intraspecific competition?

Female oviposition choices are expected to maximize offspring fitness. Leafminers often lay their eggs in an aggregated fashion, leading to exploitative or interference competition among larvae. However, few studies have explored whether egg distribution patterns vary with leaf availability and whether these changes are an attempt to reduce competition effects on offspring fitness. Here, we evaluated the egg distribution patterns of the specialist leafminer Liriomyza commelinae Frost (Diptera: Agromyzidae) for decreasing levels of leaf availability of their host plant Commelina erecta L. (Commelinaceae). Competition effects on insect performance were evaluated at various leaf larval densities in the laboratory and egg distribution was investigated for a wide range of leaf availability levels, both in the laboratory and in the field. Liriomyza commelinae performance indicated that larvae competed for resources (exploitative competition), with a negative impact on survival and adult size at emergence when four or more larvae shared a leaf. The distribution of the immature stages of the leafminer was aggregated in both the laboratory and in the field. As this pattern did not change with leaf availability, increasing levels of larval competition occurred when available leaves were scarce. Moreover, the proportion of total individuals subjected to the strongest competition level (six or more larvae per leaf) increased exponentially at the lower levels of leaf availability. Competition was found to be irrelevant as a selective force in shaping L. commelinae oviposition decisions, as egg distribution was aggregated and did not vary with leaf availability, leading to relatively strong levels of competition. The egg distribution patterns observed in L. commelinae may have resulted from trade‐offs between competition and factors such as enemy‐free space and leaf quality.