Oviposition scars from a female spotted wing drosophila, Drosophila suzukii (Matsumura), on a cherry fruit. Photograph by Martin Hauser, California Department of Food and Agriculture
Farmers won't sell these cherries in the market. The fruit flies that caused this laid their eggs inside the ripening cherries and their larvae caused this visible damage by feed on the fruit inside. The larger larvae cut breathing holes through the skin of the cherry. Pretty soon these cherries collapse around the larvae's feeding site and the cherry rots from mold that got inside through these holes.
We never had this type of damage before. Why is it happening now?
In August 2008 this damage was first seen in the U.S. and it was found out to be caused by a new (non-native invasive) fruit fly from Japan, Drosophila Suzuki (Matsamura). It infests un-ripened cherries, and it spread from California to Michigan in 2010.
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| Adult female spotted wing drosophila, Drosophila suzukii (Matsumura). Photograph by Martin Hauser, California Department of Food and Agriculture |
These females have a saw-like (serrated) ovipositor that they use to penetrate the un-ripe cherries to lay their eggs. (Kanzawa 1939, Walsh et al 2011)
An extremely detailed view of this egg depositor is from a scanning electron microscope. It shows how well equipped this fruit fly is to puncture the fruit it chooses.
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SEM of an ovipositor of an adult female spotted wing drosophila, Drosophilia suzukii (Matsumura), lateral view. Photograph by Martin Hauser, California Department of Food and Agriculture
They grow from egg to being able to lay eggs (ie.total life cycle) usually in one to two weeks, just like most other species of Drosophila. Their entire life is three to nine weeks. Just one female can lay 60 eggs in a day, one at a time, and 200-600 in her lifetime. They choose not just cherries, but also strawberries, mulberries, pears, currants, blackberries, figs, tomatoes, and apples. Farmers monitor for these flies before their fruits are ripening and before these flies begin laying their eggs. They collect them in bucket style traps, or quart containers using a mixture of yeast, sugar, water, fruit puree, or distilled apple cider or distilled wine. A drop of dish detergent in this mixture holds the flies in the water. These traps work best when put out in cool, shady areas in the growing field.
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| Simple funnel trap baited with vinegar to trap adult Drosophila. Photograph by Whitney Cranshaw, Colorado State University, Bugwood.org |
Some Drosphila show that they have develolped a cross-resistance to a toxin they've never been exposed to. This poses a warning for growers to use this type of trapping to prevent futile pesticide applications. At Michigan Technological University, Assistant Professor Thomas Werner published 3 articles in 2015 about Drosophila, how their genetics give insight into human cancer-causing genes. More about their research
The fruit flies that come in with your bananas do not like to eat mushrooms. But some fruit flies (Drosophila melanogaster) from Asia can survive the deadliest of all mushroom toxins that are more than thirty time more toxic than cyanide. These flies developed their resistance at least fifty years ago without ever having eaten these toxic mushrooms, but possibly being exposed to an insecticide that gave them a cross-resistance to the mushroom toxin. These fruit flies have maintained this resistance for at least 1,200 generations in those fifty years. Dr. Werner's undergraduate students' lab work counted over 10,000 fruit fly eggs and measured the thoraxes of thousand of adults over a 4 year period. They found that the egg laying capacity of these flies had doubled. This is the fruit flies response to the resiting the insecticide exposure. This is one of the mechanisms in individual fruit flies, that results in a newly developed population resistance. This particular fruit fly strain prefers eating rotten fruit, not valuable crops. But, a closely related Drosophila species could easily develop this same resistance, and it infects growing fruit.
Humans share the same genes with fruit flies that enable pesticide resistance and cross-resistance, as part of the 75% of human genes we share with them. As it is, their genes have been activated while ours have been turned off. this "up-down regulation" actually controls their resistance genes to be several hundred times more active than the pesticide resistance flies.One of these master control genes is essential for both fruit fly embryos as well as human embryos. In fruit flies this same gene controls black wing spot formation. In humans it starts cancer growth (acts as an oncogene) when it is misregulated. consequently these fruit flies make a good experimental model for better understanding cancer-causing genes.
Thomas Werner's lab at Michigan Tech is exploring the commonalities between poison mushrooms, pesticide resistance and human proto-oncogenes by studying fruit flies.
References:
Allison Mills, Michigan Tech News, July 1, 2015 Fruit Fly Genetics Reveal Pesticide Reistance and Insight Into Cancer
Rajinder Mann and Lukasz Stelinski, University of Florida, May 2011. Reviewed: February 2017 Publication Number EENY-492 http://entnemdept.ufl.edu/creatures/
Kanzawa T. 1939. Studies on Drosophila suzukii Mats. Kofu. Review of Applied Entomology 29: 622
Walsh DB, Bolda MP, Goodhue RE, Dreves AJ, Lee J, Bruck DJ, Walton VM, O'Neal SD, Frank G Z. 2011. Drosophila suzukii (Diptera: Drosophilidae): Invasive pest of ripening soft fruit expanding its geographic range and damage potential. Integrated Pest Management 106: 289-295
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