# Identification of Blackberry (_Rubus fritticosus_) Volatiles as _Drosophila suzukii_ Attractants
## 1 Introduction  
_Drosophila suzukii_ is an emerging pest species that originated in Southeast Asia, but subsequently invaded large parts of Europe and North America, where it is now causing extensive harm to the fruit growing industry. In Europe, _D. suzukii_ was first recorded in Spain and Italy in 2008 and 2009 [1, 2], after which it quickly spread throughout the rest of western Europe, where it now poses a major threat to the fruit growing industry [3]. Incontrast to endemic _Drosophila_ species, _D. suzukii_ has a serrated ovipositor, which allows it to penetrate the skin of healthy, ripening fruit to lay its eggs. This causes damage due to larval feeding on fruit flesh and increases the susceptibility of the fruit to fungal and bacterial pathogens. The polyphagous nature and broad host range of _D. suzukii_ further mean that it causes extensive damage to a wide variety of soft and thin-skinned fruits, including cherries, blueberries, blackberries, raspberries, grapes, plums and strawberries [2; 4]. The general way by which this pest is managed is via the routine use of broad-spectrum pesticides, which is costly, carries environmental risks, e.g., via carry-over effects on other beneficial insects, and disrupts the integrated pest management of other pests [5]. Other management options, such as exclusion netting [6], the use of repellents [7; 8; 9; 10], sanitation [11; 12] or mass trapping [13; 14; 15; 16; 17; 18], have therefore been considered as more environmentally friendly alternatives. Unfortunately, up till now none of these has proven to be sufficiently effective in practice. Essential for any effective integrated pest management program as well as to limit pesticide use is the availability of reliable monitoring traps. Although insect traps are often based on aggregation or sex pheromones, up till now only short-range contact pheromones have been identified in _Drosophila_[18; 19; 20]. Hence, available fruit fly traps mostly make use of attractive fruit fermentation products, such as wine or apple cider vinegar [18; 21; 22]. Such traditional attractants lack two important aspects of a good lure. Firstly, they generally fail to timely detect the pest species before the infestation develops, which means the lure needs to be highly attractive when population density is low. Secondly, they often display poor selectivity, implying that such lures also attract many non-target species [14; 23]. Recently, significant effort has been put into trying to improve traditional fruit fermentation attractants by adding compounds that improve both their attractiveness as well as their selectivity for _D. suzukii_[18; 21]. Some of the commercial lures now available can detect the presence of _D. suzukii_ up till 21 days before fruit infestation. However, these only work with specific fruit crops and still have a relatively low selectivity [24]. Research has shown that _D. suzukii_ uses host plant volatiles as a cue to find food and oviposition sites [25]. Blackberries, blueberries, raspberries and wine grapes are all very susceptible to egg laying by _D. suzukii_[26; 27], and among these, blackberries (_Rubus fruiticosus_) have been shown to be a preferred host, being the berry which experienced the highest infestation rates [28; 29]. To enable the development of more effective and selective lures for monitoring or mass trapping _D. suzukii_, the volatiles emitted by _R. fruiticosus_ were here identified and quantified using MHS-SPME (multiple headspace Solid Phase Micro Extraction) GC-MS, and the attractivity of the identified compounds to _D. suzukii_ was studied. Although SPME is typically not used as a quantitative extraction technique, multiple consecutive extractions on the same sample (MHS-SPME GC-MS) have recently been shown to be an effective means to semi-quantitatively estimate the total amounts of different volatiles released by fruits, vegetables or other food [30; 31; 32]. All identified and commercially available compounds were subsequently tested for their attractivity to gravid _D.