Linton Winder

The within-field spatial and temporal distribution of arthropods in winter wheat

The within-field spatial distribution of some common farmland arthropods from the Carabidae, Araneae and Collembola was assessed using two-dimensional grids of pitfall traps distributed across whole winter wheat fields. In the first year, the extent to which arthropod capture was influenced by location within the field and sampling intensity was examined using a nested grid design (1.5 m, 7.5 m and 30 m spacings). In the second year, distributions within two different-sized winter wheat fields were compared. Spatial pattern and association between arthropods and weed cover were analysed using SADIE and trend surfaces were used to visualize distributions. Many of these arthropod groups exhibited aggregated distributions within the fields in clusters larger than 30 m across, demonstrating that the numbers captured will vary depending on the location of sampling within a field. Amara species, Bembidion lampros Herbst, Carabidae and Lycosidae were predominantly found within 60 m of the field edge. Nebria brevicollis Fabricius and Pterostichus madidus Illiger were found within the field in patches of one and two hectares, respectively. Linyphiidae were relatively homogeneously distributed across the fields. There was some evidence of clustering by Collembola. The spermophagous Carabidae and Lycosidae were positively associated with the degree of weed cover. SADIE analytical techniques were useful for identifying the importance and location of patches with greater and less than average numbers, although a minimum of 36 sample points is recommended.

The spatial and temporal distribution of the grain aphid Sitobion avenae in winter wheat

The spatial and temporal distribution of the grain aphid Sitobion avenae F. (Homoptera: Aphididae) was studied within a field of winter wheat during the summer of 1996. Sampling was done using four nested grids comprising 133 locations. Analysis by Taylors power law gave results typical for insect populations. Analysis by SADIE (Spatial Analysis by Distance Indices) showed spatial pattern due to edge effects and sampling scale, and positive but mild spatial association, although spatial patterns were ephemeral. Reasons for these findings and the implications for integrated crop management are discussed.

The spatial pattern of soil-dwelling termites in primary and logged forest in Sabah, Malaysia

Abstract 1. Primary and logged lowland dipterocarp forest sites were sampled for subterranean termites using soil pits located on a grid system in order to detect any patchiness in their distribution.

The spatial dynamics of crop and ground active predatory arthropods and their aphid prey in winter wheat

The distribution of aphid predators within arable fields has been previously examined using pitfall traps. With this technique predominantly larger invertebrate species are captured, especially Carabidae, but the technique provides no estimate of density unless mark-recapture is used. However, many other numerically important aphid predators occur in arable fields and relatively little is known about their distribution patterns nor whether they exhibit a density-dependent response to patches of cereal aphids. Identification of the most effective predators can allow management practices to be developed accordingly. In this study, the distribution of cereal aphids and their predators was examined by suction sampling within a field of winter wheat in Devon, UK, along with visual estimates of weed patchiness. Sampling was conducted on four occasions in 1999 across a grid of 128 sample locations. The distribution of 11 predatory taxa from the Carabidae, Staphylinidae and Linyphiidae was examined. Additionally, the total number of aphid predators and a predation index were used in these analyses. Carabid adults and larvae, along with staphylinid larvae showed the strongest aggregation into patches and the most temporal stability in their distribution. Other taxa had more ephemeral distributions as did the cereal aphids. The distribution of carabid larvae was disassociated from the distribution of cereal aphids for the first two sampling occasions indicating biocontrol was occurring. Other predatory groups showed both association and disassociation. Carabid larvae, Bathyphantes and total numbers of Linyphiidae showed a strong correlation with weed cover for two of the sample dates. Cereal aphids were disassociated from weed cover on three sampling occasions.

The use of barrier‐connected pitfall trapping for sampling predatory beetles and spiders

The efficiency of barrier‐connected pitfall trapping was compared to conventional single traps or arrays. For ground‐active beetles, the use of a pitfall system incorporating a wetting agent with five traps arranged in a cross formation connected by plastic barriers was more efficient than a single dry trap by at least an order of magnitude and at least twice as efficient as five traps without connecting barriers. It is argued that the efficiency of pitfall trapping may be improved markedly by using barrier‐connected traps, particularly for some carabid and staphylinid beetles and lycosid spiders. Capture of linyphiids was not improved by the use of barriers and was dependent only on the use of wetting agent and number of traps used.

Monoclonal antibodies reveal changes in predator efficiency with prey spatial pattern

Spatially explicit predator–prey interactions can alter the predatory potential of natural enemies augmented through conservation biological control. To test hypotheses regarding such interactions and predatory efficiency, we used a combination of molecular techniques and mark–release–recapture to study the foraging behaviour of a generalist carabid predator, Poecilus cupreus, in response to spatial patterns of its cereal aphid prey (Metapolophium dirhodum and Sitobion avenae). Beetle and aphid numbers were measured across two grids of sampling locations, within which aphid spatial pattern had been manipulated to generate patchy and more homogenous distributions. Aphid consumption was measured by enzyme‐linked immunosorbent assays (ELISA) of beetle gut contents, using an aphid‐specific monoclonal antibody. Movement and distribution patterns suggest that P. cupreus does not aggregate at, nor instigate prey‐taxis within, aphid patches. However, more than two‐thirds of the 2169 P. cupreus tested by ELISA had consumed aphids and the proportion of beetles containing aphid proteins was positively related to aphid density. Against expectation, the proportion of predators feeding on aphids was greatest where prey were homogenously distributed, and this was attributed to the loss of partial refuges for prey in aphid patches. The functional value of this type of uniform foraging strategy is ideally suited to early colonization of the crop habitat, when aphid numbers are low, before populations build up and form strong spatial patterns.

The role of large-scale spatially explicit and small-scale localized processes on the population dynamics of cereal aphids

A field-scale study of the spatially explicit interaction between the carabid Poecilus cupreus Linnaeus, and two common aphid species (Sitobion avenae (Fabricius) and Metopolophium dirhodum (Walker)) in winter wheat was conducted. All three species showed considerable spatial pattern at the field scale. Activity-density of P. cupreus was an order of magnitude higher in the central part of the field compared to its periphery. Where P. cupreus activity-density was highest, S. avenae and M. dirhodum population peaks were delayed. Additionally, in the case of M. dirhodum, lower maximum counts were evident where P. cupreus activity-density was highest. An analysis of the movement of individual P. cupreus using release-recapture indicated that those beetles within the centre of the field exhibited reduced displacement, which may have caused the generation or maintenance of spatial pattern. Crop density was also measured throughout the field. Although crop density had no large-scale spatial pattern, its variability at the small-scale was consistent with an influence on aphid population dynamics. This study demonstrates empirically that both large-scale spatially explicit and small-scale localized processes influenced aphid population dynamics simultaneously.

The effect of the small Indian mongoose (Urva auropunctatus), island quality and habitat on the distribution of native and endemic birds on small islands within Fiji.

This study investigated the effect of the presence of introduced mongoose, environmental quality and habitat on the distribution of native and endemic birds on 16 small islands within Fiji. In total, 9055 birds representing 45 species were observed within four key habitats (forest, villages, crop land and coastal vegetation) on the 16 islands, half of which had mongoose present. Previous studies attribute bird declines and extirpation anecdotally to the mongoose. The presence of mongoose, environmental quality and habitat type had a measurable influence on observed extant native and endemic bird communities. We conclude that three ground birds; Gallirallus phillipensis, Anas supericiliosa and Porphyrio porhyrio were negatively influenced by the presence of mongoose and that Ptilinopus perousii, Phigys solitarius, Chrysoenas victor, Ducula latrans, Clytorhyrchus vitiensis, Pachycephala pectoralis, Prospeia tabunesis, and Foulehaio carunculata were particularly dependent on good quality forest habitat. Conservation priorities in relation to protecting Fijis endemic birds from the effect of mongoose are discussed and preventative measures suggested.

The spatial distribution of canopy-resident and ground-resident cereal aphids (Sitobion avenae and Metopolophium dirhodum) in winter wheat

We investigated, within two cereal fields in Southern England, the within-canopy spatial distribution of the aphids Sitobion avenae and Metopolophium dirhodum in relation to crop yield and plant nitrogen. We extended the study to investigate the spatial distribution of aphids that fell to, or returned from, the ground in order to estimate availability of the within-canopy aphid population to ground-active predators. We revealed that crop canopy aphid spatial pattern was associated with nitrogen or yield. Differences were evident between species: S. avenae was generally negatively associated with yield or plant nitrogen, whilst M. dirhodum exhibited positive association. For both aphid species, we observed strong spatial pattern for aphids falling to the ground and conclude that this could, in part, mediate the effectiveness of ground-active predators as pest control agents.

A method for rapidly mass laser-marking individually coded ground beetles (Coleoptera: Carabidae) in the field

Abstract.  1. A laser‐marking technique is described that may be used to rapidly mass‐mark and individually code insects in the field. In this study, ground beetles were marked but the method is applicable to a wide range of organisms with a hard exoskeleton or shell.