| Adult bees serve as intermediate hosts when little or
no brood is available and as a means of transport. The females attach to
the adult bee between the abdominal segments or between body regions
(head-thorax-abdomen), making them difficult to detect. These are also
places from which they can easily feed on the bees' hemolymph. The adult
bee suffers not only the loss of blood but may be subjected to microbial
invasion, leading to a reduced life expectancy
The most severe parasitism occurs on the older larvae and pupae, drone
brood being preferred to worker brood. The degree of damage depends on the
number of mites parasitizing each bee larva. One or two mites will cause a
decrease in vitality of the emerging bee. Higher numbers of Varroa
per cell result in malformations like shortened abdomens, misshapen wings,
deformed legs or even in the death of the pupa.
The adult female Varroa enter the brood cells shortly before
capping and must feed on larval hemolymph before they can lay eggs. Each
mite lays 2-6 eggs at approximately 30-hour intervals. The first egg
usually develops into a male and the later ones into females. The
development proceeds from egg to six-legged larvae, to eight-legged
protonymphs, to deutonymphs, to sexually mature adult mites in 6 to 10
days. They mate in the capped cells with the males dying soon afterward.
All immature mites will die after the emerging bee opens the cell, while
the young adult female mites and the mature (gravid) females move on to
passing bees. The mite enters another brood cell in 3 to more than 150
days depending on the season and availability of brood.