Abstract
Heavy reliance on pesticide inputs to maintain crop yields has been an important aspect of agricultural intensification. Insecticide use has had detrimental impacts on pollinators and natural pest control agents, contributing to a decline in associated ecosystem services, and has also led to resistance development in pest populations. Throughout Europe, in oilseed rape (Brassica napus L.) crops, prophylactic use of insecticides against pollen beetles (Meligethes aeneus F. also known as Brassicogethes aeneus) has led to such issues, and there is an urgent need to develop more sustainable pest management practices for the crop. Although advice is available to oilseed rape growers regarding control thresholds, it may not be adhered to due to the expense of pollen beetle monitoring relative to the inexpensive cost of pyrethroid insecticides. Thus, the key to reducing prophylactic insecticide applications may lie with improved, less labour intensive methods of pollen beetle monitoring. For these to be realized, a better understanding is needed of the effects of agri-landscape features and meteorological conditions on pollen beetle immigration into the crop. In this study, based on data from four years of pollen beetle monitoring on a total of 41 field sites, we model the effects of meteorological (wind speed and direction, rainfall and accumulated temperature) and landscape (areas of woodland, residential gardens, the current and previous seasons’ oilseed rape crops, and lengths of hedgerows and treelines) variables on directional sticky trap catches, at both the single trap and field scales. Meteorological variables, particularly accumulated temperature and wind speed were more important than landscape variables in predicting the abundance of pollen beetles immigrating into OSR fields. Sticky traps that were facing downwind caught more beetles than those that were facing across-wind or upwind; this is the first study to show at a landscape-scale, direct evidence for use of upwind anemotaxis by pollen beetles at the point of entry during immigration into the crop. At the field scale, the area of oilseed rape grown in the previous season was found to be positively related to trap catch, but no relationships with other landscape variables were found. Optimally-placed monitoring traps could complement existing decision support systems to reduce pollen beetle monitoring effort and encourage use of insecticides only when control thresholds are breached, thus enhancing the sustainability of oilseed rape production. Knowledge of the area of oilseed rape crops grown during the previous season in the surrounding landscape could contribute to risk assessment of potential pest pressure for individual OSR crops.
Highlights
The heavy reliance on pesticide inputs associated with postWW2 agricultural intensification, along with habitat loss and aM.P
Throughout Europe, pollen beetles (Meligethes aeneus F.; known as Brassicogethes aeneus) are a major pest of oilseed rape (OSR) (Brassica napus L.) (Williams, 2010), a crop that has seen significant production increases over recent years, mostly due to rising demand for biofuel use (Eurostat, 2016b)
The modelling procedure identified the presence of a field site on the Rothamsted estate, wind speed, accumulated temperature, a deviation of 2–4 octants between downwind direction and trap direction, and the area of OSR crops in the previous year within the 3 octants facing the trap as important explanatory terms for trap counts (Table 2)
Summary
The heavy reliance on pesticide inputs associated with postWW2 agricultural intensification, along with habitat loss and a. Pollen beetles in winter OSR are frequently the target of spring insecticide treatments, usually pyrethroids (Williams, 2010; Garthwaite et al, 2011), many of which are applied as prophylactic ‘insurance’ sprays (Thieme et al, 2010) This overuse has damaging effects on beneficial insects (Mänd et al, 2010; Hanson et al, 2015) and has led to increasingly widespread pyrethroid resistance, threatening to limit the arsenal of products remaining active against the pest (Thieme et al, 2010; Zimmer and Nauen 2011; Nauen et al, 2012; Heimbach and Mueller, 2013). We hypothesize that (i) temperature, rainfall and wind speed will affect trap catches by determining when conditions are optimal for beetle immigration into the crop, (ii) since the beetles may be expected to fly towards the crop using upwind anemotaxis, wind direction will affect the direction from which they enter, and (iii) that landscape features will interact with wind direction to affect trap catches by influencing beetle abundance at source
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