|
|
|
|
Evaluating IPM Tactics for Varroa Destructor to Delay Onset of Treatment Threshold J. P. Parkman, J. A. Skinner and M. D. Studer Department of Entomology & Plant Pathology., University of Tennessee, Knoxville Because populations of Varroa Destructor have exhibited resistance to fluvalinate and coumaphos in recent years, we are conducting a cooperative study in three southeastern states (Georgia, South Carolina and Tennessee) to evaluate alternative Varroa management tactics which may delay the need for or alleviate mite treatments. First-year results from Tennessee are presented. Tactics evaluated include using honey bee stock expressing the Suppression of Mite Reproduction (SMR) trait (Harbo & Harris, 1999 J. Econ. Entomol. 92: 261-265); using screened, open bottom boards (Pettis & Shimanuki, 1999 Am. Bee J. 139: 471-473); and isolation of apiaries (Safoskie et al., 1990 Apidologie 27: 245-260). In spring 2002, 40 new colonies were established in each state using 1-kg packages, consisting of adults from established colonies, and new queens: either Italian production queens or instrumentally inseminated, SMR queens. Management tactics were randomly assigned to colonies so that there were 5 replications of each combination of tactics: 1) SMR queen or non-resistant queen, 2) open bottom board (OBB) or solid bottom board, and 3) isolated or non-isolated apiary. Isolated apiaries were located at least 2 km from known apiaries; non-isolated apiaries were located adjacent to Varroa-infested colonies. Mite abundance, estimated using bottom board sticky trap collections of natural mite fall (Parkman et al. 2002 Bee Culture. 130 (4): 30-31, 33) , was determined at three-week intervals. Colony strength estimates of bee, brood and stores abundance (Skinner et al., 2001 J. Apic. Res. 40 (3-4): 81-89) were made at six-week intervals. Colonies exceeding established Varroa treatment thresholds (Delaplane & Hood, 1999 Apidologie 30: 383-395) were treated with ApiLife VAR or 65% formic acid gel. In Tennessee, establishment proved difficult for colonies with SMR queens and/or OBBs. Twenty-three colonies with SMR queens, OBBs or a combination of both had to be re-established, some more than once. Several SMR queens were observed as failing (suboptimal oviposition). Also OBBs did not appear to be conducive to establishing small packages. By September (125 d post-establishment), however, a sufficient number of colonies had been established for an adequate amount of time to allow for data analysis. Varroa abundance differed among the treatment combinations; there were greater than 40 times more Varroa in non-isolated colonies with non-resistant queens and closed bottom boards than in isolated colonies with SMR queens and OBBs. The differences in Varroa abundance among the treatment combinations could be accounted for, in magnitude, by genetics > apiary location > bottom board type. Because of differences in establishment date, colony strength was not used to compare treatment effects. By 105 d post-establishment, 4 colonies required treatment. None had the treatment combination of SMR queen + isolation + OBB. Colonies in South Carolina, however, did not experience establishment problems. (They were begun earlier, were fed soon after establishment and held in a deep hive body. Tennessee colonies were initially held in one Illinois, or medium-sized, hive body.) Establishment success in Georgia was better than that occurring in Tennessee, but not as good as that in South Carolina. Mite suppression in Georgia and South Carolina was variable and not as substantial as that occurring in Tennessee. Results suggest that Varroa populations can be suppressed with non-chemical management tactics. Caution should be taken, however, when establishing small packages over open bottom boards.
|
|