EVALUATING DIFFERENT RELEASE STRATEGIES FOR THE CONTROL OF AMERICAN COCKROACHES USING THE EGG PARASITOID, APROSTOCETUS HAGENO WII

Abstract:
The ability of Aprostocetus (Tetrastichus) hagenowii (Ratzeburg) to find oothecae in plumbing chases infested with American cockroaches was evaluated using different release strategies for six weeks. This pilot study used forty-three plumbing chases. Chases were assigned one of four treatments (release strategy) which were: (1) weekly releases of 300 female A. hagenowii using parasitized oothecae, (2) bi-weekly releases of 300 female A. hagenowii using parasitized oothecae, (3) weekly releases of 50 female A. hagenowii using free-living adults and (4) no releases which served as controls. Sentinel oothecae (laboratory-reared oothecae placed in 2 x 3 an fibreglass-window screen bags) were placed in plumbing chases to monitor parasitoid releases. Sentinel bags were placed at five locations in release chases and at three locations in non-release chases. Sentinel locations (I, 2, 3,4 and 5) were 4,0.5, 4, 5 and 16 m from the release point, respectively. Locations 1, 2 and 3 were on the floor of the plumbing chase; locations 4 and 5 were 1 m above the floor. Sentinel locations in non- release chases corresponded to locations 1, 3 and 5 in release chases. The overall parasitism levels of sentinel oothecae placed in plumbing chases were 30.6, 18.2,20.6 and 0% for Treatments 1, 2, 3 and 4, respectively. Weekly releases of A. hagenowii using parasitized oothecae produced parasitism levels ranging from 23 to 39% throughout the six week study period. Releases of live females resulted in parasitism levels ranging from 13 to 35%. Bi-weekly releases of A. hagenowii showed the highest variation in parasitism levels. During weeks 2, 4 and 6 when releases were made, parasitism levels were 2, 40 and 44%, respectively. During weeks 1, 3 and 5 when no releases were made, parasitism levels were 0, 17 and 6%, respectively. Mean wasp emergence was highest for Treatment 3 averaging 60 wasps per parasitized oothecae followed by Treatment 2 (55 wasps) and Treatment 1 (53 wasps). A. hagenowii was capable of finding and parasitizing sentinel oothecae at all locations within the plumbing chase. Average parasitism levels for sentinel oothecae at locations 1,2, 3,4 and 5 were 21,29,24, 35 and 9%, respectively. These results indicate that the potential exists for using A. hagenowii to control American cockroaches.