Suction sampling of grassland invertebrates using the G-vac: Quantifying and avoiding peripheral suction effects

Suction sampling with modified garden leaf-blowers (G-vacs) is a widely used method for research on invertebrates in agricultural and grassland habitats. Approaches vary from sweeping the collecting nozzle across the surface of the vegetation within a known area, applying the nozzle firmly to the ground to delimit a sample area equal to nozzle crosssection, or applying the nozzle repeatedly within a larger open-ended cylinder placed on the ground. These approaches vary in potential for the inadvertent capture of specimens from outside of the sample area as a result of air being drawn into the nozzle from adjacent vegetation. This has never been studied adequately and is defined here for the first time as the Peripheral Suction Effect (PSE). Invertebrate species are likely to differ in susceptibility to PSE and so both sample size and composition could be impacted. This study compares two series of samples of Auchenorrhyncha taken using the same G-vac suction sampler (nozzle area, 0.01 m(2)) from areas enclosed and unenclosed by an openended cylindrical enclosure (area 0.17 m(2)) intended to prevent PSE. The unenclosed samples contained greater numbers of leafhoppers including Arthaldeus pascuellus, Javesella pellucida and immature Deltocephalinae. Numbers of immature Delphacinae did not differ between enclosed and unenclosed samples. The species composition of the two series of samples was similar, but the proportional representation of immature Delphacinae in unenclosed samples was diluted by the inflated numbers of other taxa that were drawn from the surrounding area. Peripheral suction effects are taxa-specific and therefore have the potential to bias measures of invertebrate community composition. Use of an open-ended cylinder to delimit the sample area is recommended as a simple, inexpensive and effective method of avoiding problems associated with PSE when using a G-vac. The potential for PSE with other models of suction samplers is discussed and questions for further research are identified.