A comparison of the hygienic response of Africanized and European (Apis mellifera carnica) honey bees to Varroa-infested brood in tropical Brazil

Abstract

In order to examine the significance of hygienic behavior for the tolerance to varroosis of Africanized honey bees, they were compared with non-tolerant Carniolans in tropical Brazil. Capped worker brood cells were artificially infested with living Varroa mites, and inspected some days later. Uncapping, disappearance of the introduced mite and removal of the pupa were recorded in a total of manipulated 3,096 cells during three summer seasons. The hygienic response varied between Africanized and Carniolan colonies, but this difference was significant only in one year, during which Africanized honey bees removed a significantly greater proportion of Varroa mites than European honey bees. A high proportion of the mites disappeared from artificially infested brood cells without damage to the pupae. The opening of the cell and the removal of the bee brood are independent traits of a graded response by adult workers towards mite-infested brood cells. We found a higher between-colony variation in the reaction towards Varroa-infested brood of Africanized honey bees compared to Carniolans. The overall similar response of the two bee types indicates that hygienic behavior is not a key factor in the tolerance to varroosis of Africanized bees in Brazil.<br>Com o intuito de examinar o significado do comportamento higiênico na tolerância à varroose de abelhas africanizadas, elas foram comparadas com as não tolerantes Cárnicas no Brasil tropical. Células de cria de operárias operculadas foram artificialmente infestadas com ácaros Varroa vivos e inspecionadas alguns dias depois. Desoperculação, desaparecimento dos ácaros introduzidos e remoção da pupa foram anotados em um total de 3096 células manipuladas durante três verões. A resposta higiênica variou entre as colônias africanizadas e de Cárnicas, mas esta diferença foi significante apenas em um ano, durante o qual as abelhas africanizadas removeram uma proporção significantemente maior de ácaros Varroa que as abelhas européias. Uma grande porporção de ácaros desapareceram das células das crias artificialmente infestadas, sem danos às pupas. A abertura da célula e remoção das crias das abelhas são características independentes de uma resposta graduada por parte de operárias adultas com relação a células de crias infestadas por ácaros. Nós encontramos uma variação maior entre colônias na reação de abelhas africanizadas à cria infestada por Varroa, quando comparadas a abelhas Cárnicas. A resposta geralmente similar dos dois tipos de abelhas indica que o comportamento higiênico não é um fator importante na tolerância à varroose de abelhas africanizadas no Brasil

Scent or movement of Varroa destructor mites does not elicit hygienic behaviour by Africanized and Carniolan honey bees

“…From approximately one third of brood cells infested with dead or extracted mites, the mite disappeared, but only 10% of the infested pupae was removed by the bees. This was also confirmed by similar experiments with live mites (Aumeier et al, 2001). In the case of live mites, some of them may have actively escaped from uncapped brood cells (Bär and Rosenkranz, 1992;Boecking, 1994).…”

“…Bees responded to dead mites to the same degree as live mites (brood cells artificially infested with one live mite were responded to in 24.2% to 44.1% by Africanized bees and 30% to 37.5% by Carniolan bees (Aumeier et al, 2001). This clearly indicates that movement and other activities of the mite within the sealed brood cell was not a crucial trigger to elicit hygienic behaviour in our experiments.…”

“…All colonies were infested with mites of local Brazilian origin (Anderson, 2000;Anderson and Trueman, 2000;Aumeier et al, 2001). However, for artificial brood cell infestation we also used freeze-killed mites imported from Germany.…”

“…For artificial infestation we only used phoretic mites, representing the natural invading mites, and cells containing an early prepupa to prevent the larva from spinning a cocoon around the introduced subjects. As the maximal response towards artificially infested brood cells was evident within three days of treatment (Aumeier et al, 2001), all tests were evaluated after this time period.…”

“…The classical studies of hygienic behaviour by Rothenbuhler (1964) demonstrated a genetic basis to the variation among colonies in their removal of American 1999; Aumeier et al, 2001). According to recent publications, hygienic reactions towards Varroa destructor in capped brood cells contributes to a colony's tolerance of these mites, although overall tolerance is evidently a multifactorial trait (Boecking and Spivak, 1999;Rosenkranz, 1999;Rosenkranz et al, 1997).…”