This is the business end of a Western Cherry Fruit Fly, Rhagoletis indifferens.
Or perhaps I should say the "anti-business end", since one of these things can easily cost a commercial orchardist tens of thousands of dollars.
It's the ovipositor. Fairly easy to see how the egg gets inside the cherry!
See http://www.ncw.wsu.edu/treefruit/cffartcl_000.htm for extensive discussion of this insect. In brief,
Here's what the whole fly looks like.Even though they are rarely found in commercial orchards, cherry fruit fly is considered the primary insect pest of sweet cherries in the region. Quarantine agreements between the region and other states or countries result in a zero tolerance for cherry fruit fly larvae in packed fruit. Washington State Department of Agriculture inspectors are stationed at each cherry packing facility during the harvest season to check fruit for infestation as it comes to the packinghouse, prior to acceptance, and again after packing. Fruit may be inspected again prior to entering California. Fruit is rarely found to be infested. However, single larvae are found during inspections of over 100,000 tons of fruit produced in Washington State's 35,000 acres (14,000 hectares) of sweet cherries from one to ten times per season. When a larva is found, the entire load of infested fruit is rejected, and all other fruit from that grower is intensively inspected for signs of cherry fruit fly. It is quite rare that subsequent inspections of the "infested" fruit result in discovery of other larvae.
They're kind of randy little critters. Most of the individuals I see are males, apparently holding court waiting for a female to show up. If I pull several males into an aspirator, then pull in a female, it's typically only seconds before mating begins.
These are from a residential area, by the way, miles away from any commercial orchards. And these particular flies are doomed anyway, soon to be victims of residue from periodic sprayings that protect these trees from re-infestation so I can get a decent crop.
Technical: Canon 300D. Image #1 (ovipositor) is with Nikon CF N Plan Achro 10X NA 0.30 objective on 150 mm extension, 81 frames stacked at 0.0002" with CombineZP "Pyramid Maximum Contrast", cropped to about 50% of frame width. Image #2 (full fly) is with Olympus 38 mm bellows lens at f/4, 116 frames stacked at 0.002" with TuFuse Pro after registering with CombineZP, cropped to about 70% of frame width. (I tried doing this whole problem in CZP, but it crashed with no diagnostic.) Both #1 and #2 are with dual fiber halogen, using two layers of thin bubble-wrap for diffusion. Image #3 (mating pair) is with Sigma 105 mm and electronic flash, through wall of plastic vial, cropped to about 40% of field width.
Edit: to correct typo.