Local weed communities vs. landscape composition as drivers of aphid alightment in crops

Pathways of aphid-vectored nonpersistent virus infection within crop systems are difficult to disentangle. The viruses are transmissible by many species, and because they can be vectored with shallow, non-feeding probes of the stylet, may be vectored to host and non-host plants alike. These reasons, coupled with aphid propensity for long- and short-range movements, make it exceedingly difficult to identify aphids responsible for targeted management. However, trends among many aphid species have surfaced involving alightment in response to local vegetation patterns, such as an attraction to high contrast between plant and background, or to landscape features such as open fields versus wooded areas. Such features may be useful indicators of a crop’s attraction to aphid vectors, but the spatial scale that most strongly drives aphid alightment is not clear. To examine the relationship between aphid vector alightment and local- or landscape-scale features, alighting alates were collected with pan traps in 15 commercial pumpkin fields across Indiana in 2010 and 2011 and identified to species. Concurrently, measurements of local-scale weed cover within fields and larger landscape-scale GIS-based analyses of National Land Cover data in a 6 km² radius surrounding each field were conducted. The six numerically dominant aphid species were similar in 2010 and 2011, including Aphis gossypii (a colonizer of cucurbits) and five non-colonizing species (most importantly, the cowpea aphid, Aphis craccivora). Notably, aphid alightment was negatively correlated with within-field weed coverage, suggesting local vegetation patterns are important in predicting vector alightment behavior with probable secondary effects on virus transmission.