Abstract
The feeding habits of adult Brachycera are understudied and may provide important context for understanding invasive pest biology, as with the polyphagous small fruit pest Drosophila suzukii. We developed molecular methods to study adult D. suzukii gut content in order to understand its feeding habits. We designed and verified two primer pairs specific for either blueberries or blackberries and used a qPCR melt curve analysis to determine whether we can detect the presence or absence of berry feeding by adult flies. In a laboratory assay, the blueberry fly meal DNA can be detected for longer periods than the blackberry meal DNA. Generally, female gut contents are less variable than male gut contents. We also tested recently emerged flies that were not fed as adults but developed as larvae in either blueberries or blackberries. Some adult flies from each fruit had detectable fruit DNA in their gut, which could be due to pupal meconium feeding after emergence. Next, we aimed to test the primers in the field to develop techniques to track fruit feeding by D. suzukii in its natural field environment. First, to identify the most appropriate collection method, we determined how long we could detect fruit DNA, using previously developed primers within D. suzukii gut preserved in four types of trap fluid in the laboratory. The likelihood of detecting blackberry DNA differed by day, trap fluid, and between sexes. For the blueberry primer, the possibility of detecting blueberry DNA differed by trap fluid only. Based on those results, we used RV antifreeze with a Scentry SWD lure in field trials at two research station locations, one containing blackberries and one with blueberries. We established transects away from each fruit planting and collected up to 120 total flies at each point along transects. There were no significant differences in the number of flies containing berry DNA among collection points along the transect in both locations. These results suggest that adult flies move between crop and non-crop habitats and may not be highly dependent on fruit food resources.
Highlights
Food resource use by adult, non-animal feeding higher flies (Brachycera) has been understudied because it is often considered secondary to adult oviposition in and larval damage of crops (Clarke et al, 2011; Walsh et al, 2011)
No blackberry DNA was present in a total of 30 newly emerged adults who fed on blackberry as larvae
We found that 25 out of 30 pupal cases from larvae which fed on blackberries were positive for blackberry DNA and 30 out of 30 pupal cases were positive from larvae that fed on blueberries
Summary
Food resource use by adult, non-animal feeding higher flies (Brachycera) has been understudied because it is often considered secondary to adult oviposition in and larval damage of crops (Clarke et al, 2011; Walsh et al, 2011). While blood-feeding flies in the family Muscidae have prestomal teeth that cause the characteristic “bite” felt when they puncture skin, most Brachycera have “lapping” mouthparts (Elzinga and Broce, 1986; Yeates and Wiegmann, 1999). The “lapping” mouthparts evolved 100 million years before flowering plants and limited flies to liquid resources, such as extrafloral nectaries, hemipteran honeydew, flower nectar, decaying materials, fecal matter, yeast, fungi, and other similar substrates (Elzinga and Broce, 1986; Yeates and Wiegmann, 1999). Drosophilidae in particular may be capable of making minute scratches to soft materials to release fluids for feeding but “particulates released would have to be very narrow to pass through the very narrow pseudotracheae found in this family” (Elzinga and Broce, 1986)
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