Parasitoid Abundance and Community Composition in Desert Vineyards and Their Adjacent Natural Habitats

Parasitoids for biological control in dryland agroecosystems

This review focuses on biological control interactions in arid areas and is motivated by the need to devise sustainable agricultural practices for a warming and drying world. Parasitoids, important natural enemies of crop pests, are diverse and abundant in natural arid habitats. Dryland croplands, which are usually irrigated, are also rich in local parasitoids. Nevertheless, biological control projects in arid croplands mostly involve imported parasitoids (classical biological control) rather than the conservation of native species. Dryland parasitoids experience heat, drought, low relative humidity, sparse vegetation, and low host densities. Heat resistance combines local genetic adaptations, behavioral and physiological flexibility, and microbial symbioses, but how parasitoids cope with other aridity-related challenges is insufficiently understood. How dryland conditions impact host-parasitoid population dynamics also requires further study.

Parasitoids of Lobesia botrana (Lepidoptera: Tortricidae) in the Douro Demarcated Region vineyards and the prospects for enhancing conservation biological control

The more restrictive regulations of pesticides in Europe have led to an increase in conservation biological control (CBC) research. However, little attention has been paid to the main determinants of Lobesia botrana parasitism. The Douro Demarcated Region landscape offers scope for the use of CBC. The study was conducted between 2002 and 2015 aiming at: (i) identifying parasitoids associated with L. botrana and evaluating their impact as biological control agents in each generation of the pest, and (ii) evaluating the effect of both the proportion of ecological infrastructures (EI) near the vineyards, and the impact of management practices (chemical treatments and ground cover) on the parasitism of L. botrana. A total of 3226 larvae/pupae of L. botrana were collected (15% were parasitized and 485 parasitoids emerged). A complex of 16 taxa of parasitoids was identified, the majority belonging to Hymenoptera. The most abundant were Elachertus sp. (Eulophidae), Campoplex capitator Aubert (Ichneumonidae), and Brachymeria tibialis (Walker) (Chalcididae), which represented 62.5, 12.6, and 12.0% of the total assemblage of parasitoids which emerged, respectively. The percentage of parasitism ranged from 0.0 to 61.5% (first generation), from 0.0 to 36.8% (second generation), and from 0.0 to 12.1% (third generation). Importantly, it was found that the parasitism rate was higher in vineyards with ground cover. In addition, EI in the area surrounding the vineyards produced a significant increase in parasitism. These results suggest potential for CBC of L. botrana if EI around vineyards, and ground cover with native perennial plants within vineyards, are encouraged.

Seasonal Variations of Spodoptera frugiperda Host Plant Diversity and Parasitoid Complex in Southern and Central Benin

Fall armyworm (FAW) Spodoptera frugiperda (J.E. Smith, 1797) (Lepidoptera: Noctuidae) was recorded for the first time in 2016 attacking maize fields in central and west Africa. Soon after, several other regions and countries have reported the pest in almost the entire sub-Saharan Africa. In the present study, we assumed that (i) a variety of alternative plant species host FAW, especially during maize off-season, (ii) a wide range of local parasitoids have adapted to FAW and (iii) parasitoid species composition and abundance vary across seasons. During a two-year survey (from June 2018 to January 2020), parasitoids and alternative host plants were identified from maize and vegetable production sites, along streams and lowlands, on garbage dumps and old maize fields in southern and partly in the central part of Benin during both maize growing- and off-season. A total of eleven new host plant species were reported for the first time, including Cymbopogon citratus (de Candolle) Stapf (cultivated lemon grass), Bulbostylis coleotricha (A. Richard) Clarke and Pennisetum macrourum von Trinius (wild). The survey revealed seven parasitoid species belonging to four families, namely Platygastridae, Braconidae, Ichneumonidae, and Tachinidae associated with FAW on maize and alternative host plants. The most abundant parasitoid species across seasons was the egg parasitoid Telenomus remus (Nixon) (Hymenoptera: Platygastridae). These findings demonstrate FAW capability to be active during the maize off-season in the selected agro-ecologies and provide baseline information for classical and augmentative biocontrol efforts.

Effect of Weed Management on the Parasitoid Community in Mediterranean Vineyards

Simple Summary

Parasitoid wasps control insect pests in agricultural crops, but often require additional resources from non-crop plants. Vineyard growers sometimes address this need by planting or sowing pre-selected herbs around the plots or between the vine rows. Here, we explored the simpler strategy of conserving spontaneously growing weeds within Mediterranean vineyards, and trimming them mechanically when they reach large size and interfere with farming activities. We compared this strategy with matched plots, in which resident weeds were sprayed regularly with herbicides, representing the conventional treatment. As predicted, overall parasitoid abundance and the number of parasitoid species were higher in the weed conservation plots. However, the direction and magnitude of the effect differed between the dominant parasitoid species, and populations of some potential pests increased in the weed conservation treatment. Conservation of weeds that grow spontaneously in vineyards is a low-cost practice that offers multiple benefits, such as reduced soil erosion, stabilization of soil temperatures, and diminished exposure of farmers to agrochemicals. Our results show that communities of important biological control agents may gain from this practice as well. Nevertheless, weed conservation within vineyards can only be sustainable if its benefits outweigh the risks of attracting crop pests.

Abstract

Enriching agroecosystems with non-crop vegetation is a popular strategy for conservation biocontrol. In vineyards, the effects of specific seeded or planted cover crops on natural enemies are well-studied, whereas conserving spontaneously developing weeds received less attention. We compared parasitoid communities between matched pairs of vineyard plots in northern Israel, differing in weed management practices: “herbicide”, repeated herbicide applications vs. “ground cover”, maintaining resident weeds and trimming them when needed. Using suction sampling, we assessed the parasitoids’ abundance, richness, and composition during three grape-growing seasons. Ground cover plots had greater parasitoid abundances and cumulative species richness than herbicide-treated plots, possibly because of their higher vegetation cover and richness. Dominant parasitoid species varied in their magnitude and direction of response to weed management. Their responses seem to combine tracking of host distributions with attraction to additional vegetation-provided resources. Parasitoid community composition was mildly yet significantly influenced by weed management, while season, year, and habitat (weeds vs. vine) had stronger effects. Vineyard weeds thus support local biocontrol agents and provide additional previously demonstrated benefits (e.g., soil conservation, lower agrochemical exposure) but might also attract some crop pests. When the benefits outweigh this risk, weed conservation seems a promising step towards more sustainable agricultural management.