THE NATURE OF DAMAGE TO THE NESTS OF THE OSMIA CORNUTA BEE (LATREILLE, 1805) (HYMENOPTERA: MEGACHILIDAE) BY THE KLEPTOPARASITIC FLY CACOXENUS INDAGATOR LOEW, 1858 (DIPTERA: DROSOPHILIDAE)

The results of long-term studies on the parasitism of the Cacoxenus indagator Loew fly in the nests of the Osmia cornuta bee (Latreille) are presented. It was revealed that the fly C. indagator is a characteristic inquilin in the nests of O. cornuta. At the same time, the fact of significant level of infection of this bee nests by the C. indagator fly was established, especially in conditions of artificial breeding. The infection rate of the nests was 56 %, with 13% of nest cells affected. Great maneuverability of the fly was recorded when moving on a solid substrate, female flies can easily move both forward and backward and to the sides (sideways). Parasitism of C. indagator in O. cornuta nests leads to the death of bee larvae, less often to a decrease in the size of the imago. One individual fly usually infects not one, but several bee nests. The seasonal activity of the C. indagator coincides with the nest-building activity of O. cornuta females. The maximum fly activity was recorded between late April and early May, which coincides with the end of the bee’s flight period. The behavior of the fly near the nests allows it to successfully infect the nest cells of the bee, with male cells–located closer to the nest exit–being the most susceptible to infestation. In one nest cell, females of C. indagator lay most often 1 or 3 eggs, with occurrences of more being rare. The number of fly larvae in one nest cell varies from 1 to 14 pieces (on average 2.6). After the end of feeding, C. indagator larvae penetrate by gnawing through the nesting partitions into cells closer to the nest exit, concentrating there or in the nest vestibule. Most of the fly infected cells were located at the exit of the nest (70.7 %), 19.6 % – in the middle and 9.7 % – at the beginning of the nests. A reliable and strong positive correlation was found between the total number of nest cells in infected nests and the number of infected cells in these nests. To prevent infection of O. cornuta nests by the kleptoparasitic fly C. indagator in conditions of artificial bee breeding, it is recommended to open nests and remove fly larvae in the autumn period, as well as to install special traps for C. indagator flies in hives during the period of its search for bee nests.