VARROA-SPECIFIC HYGIENIC BEHAVIOUR AND POPULATION ABUNDANCE OF Varroa destructor IN COLONIES OF Apis mellifera scutellate IN KARURA FOREST, KENYA

Abstract

The ectoparasitic mite Varroa destructor is one of the parasiteglobally reported affecting honeybee healthand causing high colony losses.Of notable importance is the associationof the mite with viruses and their transmission to honeybees which causesgreatharm to bees. Kenyan beekeepers have reportedthat bee populationshave been ondecline in recent years and therefore the need for research to establish whether Varroa destructoris negativelyaffectinghoneybee survival and development.The objectives of thisstudy were to evaluate Varroa-specific hygienic behaviourof Apis mellifera scutellata,assess population abundanceof V. destructorand determine the effects of V. destructoron local honeybeeA.m.scutellata.The study was conducted at International Centre of Insect Physiology and Ecology (icipe)research apiaries located in Karura forest, Nairobi County. Thirty colonies were randomly selectedandmonitored from April to November 2016. Data collection on Varroa-specific hygienic behaviour was done fromten colonies and the response of A. m. scutellatato mite introduction were evaluated at intervals of 72 hoursfor a period of three months. The pre-pupae worker brood cells were uncapped and 10, 8 and 5 adult female phoretic mites were introduced repeatedly per colony andbrood cells recapped. Assessing population abundance and the effects of V. destructor on colony size and productivity of Apis mellifera scutellatawere done ontwenty colonies. For each experimental colony, infestation of V. destructoron adult bees wasmeasured twice a month using sugar shake method. Mite infestation in worker brood cells wasassessed fortnightly by uncapping 200 purple eyed pupae and adult mites found were counted and recorded. Quantifying the amount of brood, adult bees and colony stores (pollen, nectarandhoney) wasdone once every month.The data on Varroa-specific hygienic behaviour of Apis mellifera scutellata, population abundanceof V. destructorand effects of V. destructoron Apismellifera scutellatawere analyzed using Generalized Linear Mixed Model and the means separated using Tukey’s HSD at P value = 0.05 (5% significance level).The mean percentage of untouched brood cellswas significantly high in controlexperiments(80%, n=579) compared to manipulated brood cells in which mites had been introduced (12.5%, n=110)(P=<0.001).There were significant differencesbetween thedifferent densities of mites introducedand percentage response ofApis mellifera scutellatain untouched brood cells (UBC, P = <0.001) and where mites were removedand brood cells recapped (MRBR, P = <0.001).The population abundance of V.destructorvaried withinthe monthsof study and wasgenerally characterized bylow mite infestation levels.The mites collected within the first four months of study (April, May, June and July) were significantly lower than those collected within the last four months (August, September, October and November) (P = <0.001). Colony stores also varied throughout the study periodwith the month of July recording the lowest mean numbers of nectar(38.8 ± 12.5 cm2), pollen(33.8 ± 8.8cm2)and honey(45 ± 10.5 cm2). Thenumber of adult bee population was positively correlated with overall V. destructorpopulation with significant difference(P=0.0014).The amount of honey was positively correlated with overall V. destructorpopulation with significant difference (P=0.03).In spite of the presence of the parasitic V. destructorin bee colonies, all the colonies appeared healthy. Therefore, control measures should be put in place by the government in order to curb any increase ininfestation levels of V. destructorandmaintain the apparent healthy status of honeybees inKenya.