Spatial and temporal diversity in hyperparasitoid communities of Cotesia glomerata on garlic mustard, Alliaria petiolata

Abstract

1. Interactions between two trophic levels can be very intimate, often making species dependent on each other, something that increases with specialisation. Some specialised multivoltine herbivores may depend on multiple plant species for their survival over the course of a growing season, especially if their food plants are short-lived and grow at different times. Later generations may exploit different plant species from those exploited by previous generations.2. Multivoltine parasitoids as well as their natural enemies must also find their hosts on different food plants in different habitats across the season. Secondary hyperparasitoid communities have been studied on cocoons of the primary parasitoid, Cotesia glomerata (Hymenoptera: Braconidae), on black mustard (Brassica nigra) -a major food plant of its host, the large cabbage white (Pieris brassicae) -which grows in mid-summer.3. Here, hyperparasitoid communities on C. glomerata pupal clusters were studied on an early-season host, garlic mustard, Alliaria petiolata, over 'time' (one season, April-July) in six closely located 'populations' (c. 2 km apart), and within two different 'areas' at greater separation (c. 100 km apart). At the plant level, spatial effects of pupal 'location' (canopy or bottom) on the plant were tested.4. Although large-scale separation (area) did not influence hyperparasitism, sampling time and small-scale separation (population) affected hyperparasitism levels and composition of hyperparasitoid communities. Location on the plant strongly increased proportions of winged species in the canopy and proportions of wingless species in bottom-located pupae.5. These results show that hyperparasitism varies considerably at the local level, but that differences in hyperparasitoid communities do not increase with spatial distance.

Honeydew composition and its effect on life‐history parameters of hyperparasitoids

“…By contrast, G. agilis is wingless and can cover a smaller area per unit of time compared with A. nens. Wingless Gelis species appear to prefer searching for hosts on or close to the ground instead of in the canopy of forbs (Harvey et al, 2014;Heinen & Harvey, 2019). Honeydew excreted by aphids not only accumulates on leaf surfaces of the food plant, but also falls to the ground (Moller & Tilley, 1989).…”

Variation in parasitoid attraction to herbivore-infested plants and alternative host plant cover mediate tritrophic interactions at the landscape scale

“…In contrast, Pieris spp. and C. glomerata prefer open landscapes with low tree cover where wild Brassicaceae cover is often higher (Heinen and Harvey 2019). Brassicaceae cover was highest in arable land, in particular cabbage fields, which suggests that (organic) arable land can support P. brassicae and P. rapae populations.…”

“…Brassicaceae cover in forests was rather low in our study area and consisted mostly of the species Allaria petiolata. While the main hosts of C. glomerata, P. brassicae and P. rapae, can oviposit on and feed from this plant species (Heinen et al 2016), it may not be their preferred host plant in natural conditions because of their occurrence in shaded habitats (Heinen and Harvey 2019). In contrast, Pieris spp.…”

Exploiting chemical ecology to manage hyperparasitoids in biological control of arthropod pests

“…In a study on C. glomerata cocoons attached to leaves at the bottom of the plant or in the canopy, it was shown that wingless species such as Gelis proximus were predominant in the vegetation close to the ground whereas winged species such as Acrolyta nens were more abundant in the canopy. This demonstrates that community composition of hyperparasitoids can greatly vary even at small spatial scales . Temporal changes in hyperparasitoid communities were recorded in a monthly survey of aphid hyperparasitoids in organic sweet pepper greenhouses, where Dendrocerus aphidum was more abundant before summer and Asaphes vulgaris became more abundant in late summer (Table S1).…”