## 1 Introduction  
Many _Drosophila_ species are known to oviposit in overripe or damaged fruit. Most species are not considered economic pests of fresh strawberry production since the fruit are harvested prior to becoming sufficiently soft to enable successful oviposition by gravid females. However, strawberries grown for processing are allowed to ripen in the field to facilitate the easy separation of the calyx and core during harvest, thus making those fruit more susceptible to _Drosophila_ infestation [1]. Strawberries infested with drosophilid flies also become prone to secondary infections that impair fruit quality and result in yield loss [2]. When larvae are present at detectable levels in strawberries that arrive at processors, entire shipments can be rejected. Therefore, growers must apply insecticides to reduce populations in their fields when _Drosophila_ populations become sufficiently high to be detectable in harvested fruit. This situation often occurs late in the growing season when harvest intent changes from delivery to the fresh fruit market to processing [1]. The last study to identify _Drosophila_ species present in processing strawberries was performed by [PERSON] and [PERSON] in 1994-1995 [3]. This work revealed that _Drosophila simulans_ Sturtevant was the predominant species present in fruit. In 2008, the invasive _Drosophila suzukii_ (Matsumura), commonly referred to as spotted-wing drosophila (SWD), was discovered in strawberry fields in Santa Cruz County, CA before being detected elsewhere in California and eventually across North America [4, 5]. Unlike other drosophilid flies, this species lays eggs into ripening fruit and therefore poses a unique threat to both fresh and processed berry production. SWD caused substantial yield losses in caneberries, blueberries, and cherries the year following its detection, resulting in growers implementing intensive spray programs aimed at suppressing adult populations to prevent larval fruit infestation. Interestingly, the anticipated impact of this species on fresh strawberry production did not occur in the years following SWD's arrival. We believe that this was due to typical cultural practices such as relatively short harvest intervals and removal of damaged and overripe strawberries in addition to the routine use of insecticides such as spinosad (Entrust and Success, Corteva Inc., Indianapolis IN, USA) and spinerotam (Delegate, Corteva Inc., Indianapolis IN, USA) to control thrips species and light brown apple moth (_Epiphys postvittana_ ([PERSON]), Lepidoptera: Tortricidae), and malathion and pyrethroids targeting other insects especially western starnished plant bug (_Lysgus hesperus_ Knight, Hemiptera: Miridae). These insecticides are also effective in controlling SWD, thus providing incidental SWD suppression when they are applied. Obtaining information on the occurrence of and damage by SWD in California strawberries has become important considering recent grower accounts of drosophilid fly infestations in both fresh and processing fruit. These observations appear to coincide with our findings that some SWD populations have become resistant to spinosad [6; 7], malathion [8], and pyrethroids [9]. These sprays would be ineffective if SWD currently represents the major species infesting fruit, providing support for our hypothesis that use of these insecticides for other insect pests in strawberries had been providing incidental protection against SWD. The objective of this study was thus to determine the current levels of _Drosophila_ infestation in commercial fresh market and processing strawberries, and the extent to which strawberry production contributes to SWD adult populations. The lack of current data regarding the species composition of drosophilid flies in strawberries creates challenges for implementing effective management programs. Therefore, our second objective was to develop new molecular tools for identifying SWD among other _Drosophila_ species.