Patterns in the abundance and distribution of ichneumonid parasitoids within and across habitat patches

Abstract

1. Knowing how species are distributed across a landscape can considerably aid the management of populations and species richness. Insect parasitoids constitute a large fraction of terrestrial biodiversity and help regulate other insect populations, but their ecology is poorly known at a landscape scale. 2. Using Malaise traps distributed first extensively and then intensively across woodland patches in an agricultural landscape, we tested whether four ichneumonid subfamilies display (i) a positive relationship between abundance and occupancy, (ii) a positive relationship between abundance in the extensive sample and abundance in the intensive sample, and (iii) aggregation across traps. 3. A positive relationship between abundance and occupancy was found across species in both samples, and was relatively strong. Abundance in the extensive samples was positively correlated with abundance in the intensive samples. On average, species were aggregated in both samples, although aggregation was not necessary for a positive abundance–occupancy relationship. 4. These results suggest that ichneumonid species can largely be classified on a continuum from widespread and locally abundant to localised and locally scarce. The former species allow the potential for pervasive natural control of host populations. The latter species, which constitute a substantial majority of the species list, will be vulnerable to extinction through both stochastic forces and widespread adverse forces such as climate change and habitat modification. However, the assessment of species’ status is likely to be facilitated by the positive abundance–occupancy relationship. 5. Species inventories for ichneumonids will be taxing because of the need to sample both intensively and extensively to detect rare species, which constitute the majority of species. However, it is possible to generalise species abundances across spatial scales and years, facilitating monitoring.

Field margins: a comparison of establishment methods and effects on hymenopteran parasitoid communities

“…Hymenopteran parasitoids (hereafter referred to as parasitoids) are extremely species rich, comprising one of the most diverse groups of arthropods (Gauld & Bolton, ; LaSalle & Gauld, ; Quicke, ). They play important ecological and economic roles in natural and managed ecosystems, including acting as natural enemies (LaSalle, ; Bianchi & Wackers, ; Fraser et al ., ). Parasitoid wasps occupy high trophic levels and feed on a diverse range of plant and invertebrate hosts (LaSalle, ).…”

Larger wildflower plantings increase natural enemy density, diversity, and biological control of sentinel prey, without increasing herbivore density

“…While a positive response from insect natural enemies to the size of host patch size has been documented previously (Bach, 1988b;Olson & Andow, 2008), there is little information on the response of natural enemies or herbivorous insects as a function of wildflower patch size. Beneficial insects respond positively to the addition of flowering resources in farmland, but different insect taxa respond to these manipulations in varying ways (Fraser et al, 2008;Osborne et al, 2008;Tscharntke et al, 2008), and may also respond to habitat at different scales. Meyer et al (2007) and Olson and Andow (2008) found that larger grassland habitat areas resulted in greater insect abundance and diversity.…”

The potential of parasitoid Hymenoptera as bioindicators of arthropod diversity in agricultural grasslands

“…Parasitoid Hymenoptera comprise one of the most diverse groups of arthropods (Gauld & Bolton 1988;Quicke 1997), are an important functional component of agricultural ecosystems (Altieri, Cure & Garcia 1993;Marino & Landis 2000), and are known to be sensitive to habitat fragmentation and environmental changes (Kruess & Tscharntke 1994;Siemann 1998;Lewis & Whitfield 1999;Komonen et al 2000;Fraser, Dytham & Mayhew 2008;Maeto et al 2009). An initial survey of 10 agricultural grassland sites in the southeast of Ireland gave an indication that parasitoid Hymenoptera, identified to family level, have potential as bioindicators of other terrestrial arthropods (Anderson et al 2005; Table S1, Supporting Information).…”