Viral Infection Affects Sucrose Responsiveness and Homing Ability of Forager Honey Bees<i>, Apis mellifera</i> L.

<div><p>Honey bee health is mainly affected by <i>Varroa destructor</i>, viruses, <i>Nosema</i> spp., pesticide residues and poor nutrition. Interactions between these proposed factors may be responsible for the colony losses reported worldwide in recent years. In the present study, the effects of a honey bee virus, Israeli acute paralysis virus (IAPV), on the foraging behaviors and homing ability of European honey bees (<i>Apis mellifera</i> L.) were investigated based on proboscis extension response (PER) assays and radio frequency identification (RFID) systems. The pollen forager honey bees originated from colonies that had no detectable level of honey bee viruses and were manually inoculated with IAPV to induce the viral infection. The results showed that IAPV-inoculated honey bees were more responsive to low sucrose solutions compared to that of non-infected foragers. After two days of infection, around 10⁷ copies of IAPV were detected in the heads of these honey bees. The homing ability of IAPV-infected foragers was depressed significantly in comparison to the homing ability of uninfected foragers. The data provided evidence that IAPV infection in the heads may enable the virus to disorder foraging roles of honey bees and to interfere with brain functions that are responsible for learning, navigation, and orientation in the honey bees, thus, making honey bees have a lower response threshold to sucrose and lose their way back to the hive.</p> </div

The RFID system used in homing experiment.

<p>(A) Two RFID readers were placed at the customized tunnel entrance of a nucleus hive with 3 frames. (B) A honey bee with the RFID tag glued to its thorax carrying pollen on its hind legs returns to the hive.</p

Comparisons between IAPV-injected honey bees and PBS-injected honey bees in their responsiveness to sucrose.

<p>Sucrose responsiveness of honey bees injected with IAPV with 1: 500 dilution and PBS-injected honey bees were tested at days 0 (A) and 3 (B) after injection. The number of honeybees tested at day 0 post-injection is 60 for each group; the number of honeybees tested at day 3 for IAPV-injected group is 14 and 29 for the PBS-injected group (*=p<0.05, **=p<0.01); sucrose responsiveness of honey bees injected with IAPV with 1: 200 dilution and PBS-injected honey bees tested at days 0 (C) and 2 (D) after injection. The number of honey bees tested at day 0 post-injection is 60 for each group; the number of honey bees tested at day 2 for IAPV-injected group is 22 and 30 for the PBS-injected group (*=p<0.05, **=p<0.01).</p

The exact number of copies of IAPV in heads of honey bees.

<p>The exact number of copies of IAPV in heads of honey bees collected at day 0, day 1 and day 2 after injections with 1 ul of IAPV (1: 200 dilution) and 1 ul of PBS respectively. Error bars show SD.</p

Analysis of survival rates.

<p>Comparison of survival rates between honey bees injected with IAPV and honey bees of the control groups at 24, 48 hours after injection. The data are expressed as mean ± SD of four independent experiments. </p