SD07: Do deep diving larvae exploit enemy free space? Spotted wing drosophila larval depth in berries and parasitism by the natural enemy Ganaspis kimorum

Drosophila suzukii, also known as the spotted-wing drosophila (SWD), is an economically significant agricultural pest from Southeast Asia that was first detected in the mainland U.S. in 2008.  SWD’s heavily sclerotized and saw-like ovipositor allows it to lay eggs in ripening, undamaged fruit such as cane berries, blueberries, cherries, and strawberries. The invasive range of SWD lacks effective natural enemies and its only approved biocontrol agent in the U.S. is Ganaspis kimorum, (Gk), a small figitid larval parasitoid. The large size of cultivated fruits can lead to enemy-free space available to burrowing larvae that feed at depths that the wasps can’t reach. Gk’s ovipositor is only 1 mm long which is shorter than SWD’s ability to dive in media and berries.  Parasitsm rates of Gk on SWD in blueberries are highest in 1-day old larvae and 3-day old larvae.  1-day old larvae were mostly first instars and 3-day old larvae were roughly evenly split between 1st and 2nd instars.  In blueberries, the average depth of 1st and 2nd instars was not significantly different and so depth does not appear to explain the higher parasitism rates on early instar larvae.