Miriam Kishinevsky

Sugar feeding of parasitoids in an agroecosystem: effects of community composition, habitat and vegetation

Sugar from nectar or from honeydew can prolong parasitoids’ lifespan, enhance their fecundity and foraging ability, and thereby increase their pest suppression efficiency. Sugar sources within crop monocultures are considered to be limiting for parasitoids. Nevertheless, only few studies have measured the sugar feeding of parasitoid assemblages in agricultural areas or in surrounding non‐crop habitats. We used cold anthrone tests to compare the frequency of sugar feeding in parasitoid communities, inside pomegranate orchards and in adjacent natural areas, over two consecutive years. Overall, 40% of the 1610 sampled individuals belonging to 135 species scored positive for sugar. Sugar‐feeding frequency was lower within the orchards than in the neighbouring natural areas. The proportion of sugar‐fed wasps increased with herbaceous vegetation cover, both within and outside the orchards, suggesting that herbs are a sugar‐rich habitat. Parasitoids sampled from trees and from herbs within the orchards had similar frequencies of sugar feeding, despite differences in wasp species composition. Our results probably overestimate sugar‐feeding frequencies in the field because sugar‐fed individuals have higher longevity and hence are more likely to be sampled. We propose a simple model to approximate this over‐sampling bias and apply it to Encarsia inaron (Aphelinidae), one of the most abundant parasitoids in the samples. We conclude that sugar availability potentially limits parasitoid fitness in this agro‐ecosystem. This may be due to the low density of plants in natural areas during the Mediterranean summer, and to herbicide applications within the orchards that further suppress non‐crop herbs.

The Invasive Liriomyza huidobrensis (Diptera: Agromyzidae): Understanding Its Pest Status and Management Globally

Liriomyza huidobrensis (Blanchard) is native to South America but has expanded its range and invaded many regions of the world, primarily on flowers and to a lesser extent on horticultural product shipments. As a result of initial invasion into an area, damage caused is usually significant but not necessarily sustained. Currently, it is an economic pest in selected native and invaded regions of the world. Adults cause damage by puncturing abaxial and adaxial leaf surfaces for feeding and egg laying sites. Larvae mine the leaf parenchyma tissues which can lead to leaves drying and wilting. We have recorded 365 host plant species from 49 families and more than 106 parasitoid species. In a subset of the Argentinian data, we found that parasitoid community composition attacking L. huidobrensis differs significantly in cultivated and uncultivated plants. No such effect was found at the world level, probably due to differences in collection methods in the different references. We review the existing knowledge as a means of setting the context for new and unpublished data. The main objective is to provide an update of widely dispersed and until now unpublished data, evaluate dispersion of the leafminer and management strategies in different regions of the world, and highlight the need to consider the possible effects of climate change on further regional invasions or expansions.

Parasitoid abundance on plants: effects of host abundance, plant species, and plant flowering state

The abundance of parasitoids on plants that harbor their monophagous herbivorous host often correlates with host numbers. However, when hosts are polyphagous, the species-specific characteristics of the plants can affect parasitoid abundance as well. We asked whether parasitoids that attack a polyphagous host aggregate on individual plants with high host densities, and whether plant-related factors (plant species and flowering state) also account for the parasitoids’ abundance on the plants. We sampled Encarsia (Förster) (Hymenoptera: Aphelinidae) parasitoids and their host Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) from three plant species, six times during the summer of 2013. We analyzed the effects of host abundance, plant species, and flowering state on parasitoid abundances. The abundances of three parasitoid species were significantly and positively affected by the abundance of B. tabaci on plants, regardless of plant species. In contrast, the abundance of the fourth species was not affected by host numbers, but rather by plant species identity as well as by flowering state: parasitoid numbers were lower on flowering plants than on non-flowering plants. Although previous field studies have shown correlations between parasitoid and host abundance, our research demonstrates additional, plant-related variables that can influence this relationship when hosts are polyphagous. We also show that although having the same host, different parasitoid species respond differently to host- versus plant-related variables.