Varroa destructor resistance of honey bees in Hawaii, USA, with different genetic proportions of Varroa Sensitive Hygiene (VSH)

Abstract

Apis mellifera, Varroa destructor, honey bees, genetic resistance, integrated pest management, bee breeding Journal of Apicultural Research 51(3): 288-290 (2012) © IBRA 2012 DOI 10.3896/IBRA.1.51.3.13 The Big Island of Hawaii, USA, supports an important honey bee (Apis mellifera) queen rearing industry that supplies queens worldwide. This industry now is threatened by Varroa destructor, as the mite was detected on the Big Island in 2008. Mite parasitism is now high in queen production operations because of the extended brood rearing season in the tropics, the deliberate production of large numbers of drones in many colonies, and invasion of mites from dying feral colonies. Mites can currently be managed with acaricides, and beekeepers typically treat colonies at two to four month intervals (compared to at six to twelve month intervals on the USA mainland). Acaricides may be problematic for queen producers, however, because they can interfere with queen rearing and sperm production (e.g., Haarman et al., 2002, Rinderer et al., 1999). An alternative management strategy might employ bees bred for mite resistance. Bees with Varroa Sensitive Hygiene (VSH) offer good resistance to V. destructor (Harbo and Harris, 2009). This trait could be used for breeding in Hawaii through importations of semen, as queens cannot be imported into the state. We sought to determine what proportion of VSH genetics can confer useful honey bee resistance to V. destructor in queen production operations in Hawaii. In July 2010, a cooperating queen breeder established 30 colonies (without sealed brood) that were assigned to three treatment groups. Groups were created so that initial mite density was equal for the groups (0.10-0.11 ± s.d. 0.09-0.12 mites per 100 adult bees). Instrumentally inseminated queens were added to each colony. The queens were created so that their workers had either 0%, 50% or 75% of the genetics for VSH. Genetic groups were as follows: 0% VSH = commercial Hawaiian X commercial Hawaiian; 50% VSH = commercial Hawaiian X VSH; and 75% VSH = 50% VSH X VSH. Mated queens were produced from five colonies of the operation. VSH semen was from drones from Glenn Apiaries and our USDA laboratory. Previously inseminated queens (commercial Hawaiian X VSH) produced hybrid daughter queens that were inseminated to make the 75% VSH group. We initiated testing with two other queen producers, but their colonies became unusable; in one case there was inadvertent treatment with acaricide, and in the other case colonies became unviable because of small size, poor nutrition and high mite populations (which increased from July to September from 1.1 to 14.7 mites per 100 bees). Beginning in September when experimental populations of workers were fully established, the colonies were sampled every two months to monitor the density of mites and to measure the population of brood. Mite densities were measured by sampling ca. 300 adult bees from the broodnest, shaking the sample in 70% ethanol to wash off phoretic mites, and counting bees and mites. Brood populations were measured by using a grid to estimate the area of sealed brood on each side of each comb to the nearest 1/6 of the side, and summing these counts to get the number of comb equivalents covered with brood. Colonies were managed initially without treatment against V. destructor; later, individual colonies that reached a density of 10 mites per 100 bees were treated with fluvalinate (Apistan