Blossom midges - Contarinia agrimoniae Felt

Midges in the genus Contarinia attack hosts in a wide range of hosts - for example, some species attack conifers, and some feed in sorghum.  Two species in the genus have been infesting bramble fruits.  The Virginia Crop Profile for Brambles gives the following text: "Since the 1980's, numerous instances of inadequate fruit-set or poor drupelet development have been observed in blackberry cultivars in Virginia (13). However, the reason for these observations was not initially understood. Further observation revealed gall midge larvae in unopened flower buds and partially opened blossoms. Gall midge larvae presence can also cause the pistils and stamens of infested buds and blossoms to show varying degrees of necrosis. Injury caused by these pests seems greater in buds that contain more numerous larvae, although, additional work will be necessary in Virginia to more fully understand and hence control outbreaks of the gall midge."  There are currently no monitoring methods established, nor control measures known.

Stiles and Semtner (1999) reported the following as symptoms indicating midge infestation: (1) very small areas of rusty-brown discoloration on petals of "balloon-stage" flower buds, (2) blackened, wet appearance of pistils and stamens throughout, or in sectors of, newly dissected balloon-stage buds, (3) after anthesis (flower opening), moisture evaporates from affected areas so that dry, blackened, dead-looking, undeveloped pistils occur in large or small sectors of individual flowers; larvae are seldom detected in open flowers, (4) tight to white-tip buds are wider or bulkier than normal with calyces (sepals) that seem slightly off-color but healthy; enclosed petals may be partially or entirely brown or dead looking, (5) in extreme cases, petals may die without unfolding and dissection shows both male and female organs in such buds to be badly affected; close inspection reveals numerous midge larvae.

References:
Stiles, H. D., and P. J. Semtner. 1995. Midges may injure drupelets and reduce fruit-set in blackberries. (abstract) HortScience 30:430.

Stiles, H. D., and P. J. Semtner. 1996. Gall midges, Contarinia agrimoniae Felt and  Dasinuera spp. (Diptera: Cecidomyiidae), associated with blackberry flower injuries and nubbins. (abstract) HortScience 31:743.

Stiles, H. D. and P. J. Semtner. 1999. Drupelet Failure in Blackberry (#4) in The Bramble of the NABGA. http://www.hort.cornell.edu/grower/nabga/newsletters/news1199.html#Drupelet

Stiles, H. D., P. J. Semtner, and T. D. Reed. 1996. Discovery of Contarinia agrimoniae (Diptera: Cecidomyiidae) larvae in damaged blackberry (Rubus subgenus Eubatus spp.) flower buds. J. Entomol. Sci. 31:138-141.