By Justin Renkema, Post-Doc, University of Guelph
It was an early morning after a long drive from Guelph to a small fruit farm in Chatham-Kent where my undergraduate student, Caitlyn, and I were conducting a small-plot spray trial to test the effect s of repellents against Drosophila suzukii (Spotted Wing Drosophila), a recent invasive and serious fruit pest. I knew the raspberry patch was heavily infested with D. suzukii so before getting to work, to amuse ourselves at the start of the day, I started gently shaking canes, and we watched the swarms of fruit flies disperse and hover over the fresh fruit. However, as I went to grab a branch low to the ground, I noticed something different about one of the fruit flies sitting on a leaf. It had characteristic white “racing stripes” along its thorax, unlike any other fruit fly I had seen. This was it! This was very likely Zaprionus indianus or African fig fly, another invasive and potential fruit pest that we knew was moving northwards from the southeastern USA. Caitlyn grabbed a vial and we successfully had, on 10 September 2013, what we thought was the first capture of this fly in Ontario and Canada.
Indeed the fly was Z. indianus, as determined by Meredith Miller, a M.Sc. student at the University of Guelph working on taxonomy of Drosophila spp. in Ontario. Through contact with Hannah Fraser at Ontario Ministry of Agriculture Food and Rural Affairs, we learned that their Ontario-wide monitoring program for D. suzukii had also picked up some African fig flies in apple-cider vinegar traps, and a few at an earlier date than our find in Chatham-Kent. Colleagues in Quebec (Jean-Phillipe Légaré and others at MAPAQ) had also found what they believed were Z. indianus. Once all the material was collected and examined by Meredith, we submitted a scientific note documenting our Z. indianus discovery in Canada that was published by the Journal of the Entomological Society of Ontario.
Zaprionus indianus is native to the Afrotropical region. It was found in Brazil in 1998 where it was given its common name because it became a significant pest of figs. In 2005, Z. indianus was discovered in Florida and has since been found successively further north and west in the USA (see a map of its distribution here). It is likely that the North American infestation did not come from the Brazilian population. Zaprionus indianus is the only member of Zaprionus present in Canada, and therefore the reddish-brown head and thorax and particularly the silvery stripes that extend from the antennae to the tip of scutellum can be used as distinguishing features.
Unlike D. suzukii (thankfully!), female Z. indianus do not possess heavily sclerotized and serrated ovipositors and are not currently seen as a serious threat to temperate fruit crops. They have been reared from a number of tropical, tree-ripened fruits in Florida and there is concern in vineyards in the eastern USA, where sometimes they outnumber D. suzukii in traps. It is possible that Z. indianus can use fruit that has been oviposited in by D. suzukii, thus increasing damage and possibly complicating control measures. In Canada, particularly Ontario and Quebec, winter temperatures may preclude establishment of African fig fly, and yearly re-infestation from the south would be necessary for it to show up in future years. At all but one site, we found just 1-4 flies during late summer and early fall per site, so it will be interesting to see what happens to numbers this coming growing season. In tropical and sub-tropical locations much larger populations have been detected the year following first detection.
For the past 1.5 years I have been working as a post-doctoral fellow at the University of Guelph with Rebecca Hallett on D. suzukii. We are developing a push-pull management strategy using volatile plant compounds to repel and attract this pest. With the occurrence of Z. indianus and possible reoccurrence in larger numbers in the future, we may have a unique opportunity to study how two recent invaders using similar resources interact, and also, perhaps, a more significant challenge ahead of us in developing management strategies. If you are interested in this topic or have current or future experiences with Z. indianus, I and co-authors on the scientific note would appreciate hearing from you. You can contact me at firstname.lastname@example.org.
Renkema J.M., Miller M., Fraser H., Légaré J.P. & Hallett R.H. (2013). First records of Zaprionus indianus Gupta (Diptera: Drosophilidae) from commercial fruit fields in Ontario and Quebec, Canada, Journal of the Entomological Society of Ontario, 144 125-130. OPEN ACCESS [PDF]