Effects of diluents and plasma on honey bee (Apis mellifera L.) drone frozen-thawed semen fertility

- There are no significant effects to adding different plasma and solutions after cryopreservation to increase fertility.
- One possible reason might be because of dilution and or removal of the toxic cryoprotectant immediately following thawing.
- Centrifuge could be used to remove more chemicals; however, this may damage the sperm.

Cryopreservation is an advanced method used to protect germplasm in liquid nitrogen. Honey bees are of special interest to protect because of their pollination activity and critical role in agriculture. There has been important progress in the cryopreservation of honey bee germplasm in recent years, leading to practical recovery of genetic material for breeding purposes following freezing. However, there remains room for improvement and the goal of the present study was to evaluate the effect of different “extenders” added post-thaw on the fertilization rate of cryopreserved honey bee semen. The purpose of adding extender post-thaw was to dilute the cryoprotectant to remove chemicals after centrifugation because of potential adverse effects. The control consisted of frozen-thawed semen without the addition of an extender; treatment groups included the addition of one of the following extenders: glucose solution, fresh ram semen plasma, fresh honey bee semen plasma, extender solution. All of the above treatments and frozen-thawed control were compared to fresh semen. For each group, 15 virgin queens were instrumentally inseminated with the semen-diluent solution and introduced into nucleus colonies to determine the brood patterns of the queens. Percentages of worker brood produced in the fresh semen, frozen-thawed semen control, glucose, fresh ram semen plasma, fresh honey bee semen plasma, and extender solution supplemented groups were 98.±1.1%, 47.0 ± 0.9%, 3.0 ± 0.8%, 0.3 ± 0.1%, 48.1 ± 4.1% and 40.3 ± 2.4%, respectively. Similiarly, spermatozoa numbers in the spermathecae of the same treatment groups were 3.6 × 106, 1.6 × 106, 7.3 × 105, 4.7 × 105, 8.1 × 105, and 4.6 × 105 spermatozoa for the same treatment, respectively. The differences in both worker brood percentage and sperm count in the spermatheca were statistically significant (P < 0.01) among all treatment groups, except the frozen-thawed control group and fresh drone semen plasma group. We found a positive correlation between sperm count in the spermatheca and the percentage of worker brood (r = 0.91). With the exception of fresh honey bee semen plasma, the fertility rate was reduced following the addition of various plasmas and diluents post-freezing.