PARTICULAR EVOLUTIONARY PHENOMENA IN ONTOGENESIS OF VARROA by dfgh4bnmu

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									    LUCRĂRI ŞTIINłIFICE MEDICINĂ VETERINARĂ VOL. XLII (1), 2009, TIMIŞOARA

PARTICULAR EVOLUTIONARY PHENOMENA IN ONTOGENESIS
            OF VARROA DESTRUCTOR MITE
                              1                    1                   1
                  A. BALINT , I. COSOROABĂ , GH. DĂRĂBUŞ ,
                                    1             2
                           MS. ILIE , D.N. MĂNDIłĂ
                       1
                      Faculty of Veterinary Medicine Timisoara
                Calea Aradului No. 119, 300645, Timisoara, Romania
                 2
                  Faculty of Zootechny and Biotechnology Timisoara
                         E-mail: balintadrian26@yahoo.com

                                        Summary

         The Varroa destructor mite ontogenesis has an embryonic and a post-embryonic
development. The post-embryonic development in both sexes has four evaluative stages
that present particularities regarding the development evolution and the mobility and
immobility of the protonymph and deutonymph. From the biological cycle there are removed
pre-larval and tritonymph stages in order to reduce the development of the mite. The larval
calyptostatic inhibition is the regression phenomenon when the mite larvae is immobile, does
not feed and shows morphological changes. During its evolution, to the most Gamasida
larva, the fourth pair of legs disappeared, excepting the Phalangiacarus brosseti
(Opiliocaridae) larva where, there is present in a rudimentary form.
         Key words: Varroa destructor, ontogenesis, calyptostatic inhibition, stages.

        The externally parasitic mite, Varroa destructor (Andeson and Trueman
2000) is the primary concerns for beekeepers (1). Varroa destructor is a highly
destructive pest, responsible for reduced honey and brood production and for
higher bee mortality in winter and considerable colony mortality (13). Therefore
varoosis represent the principal concern of the beekeepers about bee
pathology.The original host of the mite is the Asian honey bee, Apis cerana, and as
the mite enters Apis mellifera populations worldwide, beekeepers experience
substantial colony loss and damage (6, 15, 17).
        Varroa destructor is a relatively large ectoparasite that develops and
reproduces in the cell of a developing bee. Adult female enter the cell just before it
is capped, lay eggs and puncture the larval skin to feed on its hemolymph. The
mite and its offspring usually do not kill the bee, they emerge with it to undergo a
phoretic period on adult bees before they enter in another cell to reproduce (7).
        In colonies of A. cerana, reproduction occurs almost exclusively on drone
brood (2, 15, 17, 18). In colonies of A. mellifera, mites reproduce on both worker
and drone brood, but not on queen brood (3, 8, 10). The reproductive success of a
mite on A. mellifera is positively correlated with the duration of its host’s capped
stage, which is longest for drones (16 days), intermediate for workers (12 days),
and shortest for queens (8 days). Mite levels tend to be higher in drone brood than
worker brood (4).

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    LUCRĂRI ŞTIINłIFICE MEDICINĂ VETERINARĂ VOL. XLII (1), 2009, TIMIŞOARA

          During ontogenesis are produced biological processes in which organisms
are developed and pass in rapid and evidently morphological changes. These
changes are named metamorphoses (“meta” = changes, “morfe” = form), which in
case of Varroa are more evidently at larva in inhibition (19).
          Investigations into the ontogenesis of a parasite are important for
developing or improving methods of control. (16).
          Stages and phases of ontogenesis
          The period of ontogenesis can be estimated in days: it is 7, 1 – 8, 3 days
for the female and 4, 9 – 6, 0 days for the male. These values are the lowest
reported so far in the literature on Varroa. The first egg in both worker and drone
cells is laid about 60 h after sealing and that mite producing an egg about every 30
h. In common with the other Mesostigmata, Varroa has only one ovary which
contains germs cells in different stages of development. In Mesostigmata, a
maturing oocyte inhibits the development of all the others.
          The ontogenesis of the Varroa mite can be structured in: embryonic
development, post-embryonic development and adult. The post-embryonic
development has four stages: the larva, the protonymph with a mobile phase and
an immobile phase the deutonymph with the same two phase and adult. Though,
the male hatched second, reaches the adult stage about 20 h earlier than the
female. Development of the male in its first mobile stage is faster than in the female
development so that is reaches the immobile phase somewhat earlier than the
female. The temporary synchronization in the development of the first two
individuals from every normal brood of Varroa, namely, the first female and the
single male, can be said to start with the onset of the first immobile phase, when
the male again grows more rapidly than the female. The second mobile phase is of
the same duration for both sexes, but the female increases in size proportionately
more than the male. The vigorous growth of the female brood may be one of the
main reasons that the host loses weight (5, 12).
          The average number of mature female offspring produced is about one in a
worker cell and 2.2 in a drone cell, when mite mortality and infertility are taken into
account (12).
          Eliminating of prelarva and tritonymph stages
          The mite post-embryonic development takes place gradualy, that are
separated from each other by moulting and accompanied by changes, which
belong to vital stages of the ontogeny. There are six stages: prelarva, larva,
protonimph, deutonimph, tritonimph and adult. This concept of stages can be
applied to Anactinotrichida, within which Varroa is classified. Within this grup during
the course of its evolution the prelarva and the tritonimph have disappeared. In
most cases, the final stages are: larva, protonimph, deutonimph and adult (Fig. 1).
          Protonymph is the first stage that appears after larval stage and presents
four pairs of legs. By eliminating some evolutionary stages it might be interpreted
as one of the strategies by who the Varroa mite was able to develop and has as an
effect the reduction of the development from the egg stage to the adult stage.

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        By reducing the development period, Varroa has an advantage on the time
race, and its reproduction represents a continuous fight. So, after eight days a
Varroa layed egg in a caped worker cell, it dosen’t have any chance to become an
adult.




Fig.1. Post-embryonic development of Varroa destructor with disappearance of the
        prelarva and tritonymph stages (after Fernandez N. and Coineau Y)

         The reported information with regard to the first step in the growth process
of Varroa is confusing and almost always contradictory. This is due the fact that
during this period of development, which includes the final step of the embryonic
phase and the beginning of the post-embryonic phase, are produce two particular
evolutionary phenomena (9, 11).
         The larval calyptostatic inhibition
         The stages present themselves in most cases as active , normally formed
organisms, but, in other cases, is find the presence of a greatly-mutilated organism,
due to the curious regressive phenomena called calyptostase (kalyptos =
covered; stasis = standing). (9)
          In this form it does not move or feed. Its appendages look like gloved
fingers without any protuberances the chelicerae are reduce to non-functional
stumps.
         The calyptostatic inhibition presents all degree, even the complete
disappearance of its appendages and it looks like a second egg. When the
calyptostase occurs at the beginning of the development process, it can be
attempted to observe the stumps of the legs. Among the different mite groups the
calyptostase can appear at different developmental stages, excluding adult. The
Varroa destructor larva is a calyptostase, the equivalent of a chrysalis. It does not
feed, is immobile and in fact is unable to hatch, thus remain within the membrane
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of the egg. Its appendage are recognizable but have lost all traces of segmentation.
It has tree pairs of legs (9, 14). This concept is applicable to other arthropod groups
and the bee chrysalis, the pupa, may be considered a calyptostase (9).
         Disappearace of the embryonic fourth pair of legs
         The primitive larva has four pair of legs as suggested by the minute leg of
the larva of a primitive mite, Phalangiacarus brosseti (Opiliocaridae). While the
mite’s larva usually has three pairs of legs, this primitive mite has retained the
fourth pairs of legs in vestigial form like stumps. During its evolution this fourth pair
has disappeared in the larva but its “memory” still exists in the course of its
embryonic development. They appear at the moment that the outline of the
appendages is established. This rudiment of the fourth pair of legs has a temporary
regression that leads to its absence in the larva, which represents the first stage of
the post-embryonic development of the Gamasida. They appear again in the next
stages when it becomes an active protonymph with four pairs of legs. We can
conclude that the larval stage of the ancestral mites had four functional pairs of
legs (9).

                                     References

    1. Anderson, D.L., Trueman, J.W.H., Varroa jacobsoni (Acari: Varroidae) is
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10. Finley, J., Camazine, S., Frazier, M., The epidemic of honey bee colony
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19. *** http://www. ro.wikipedia.org/wiki/metamorphosis




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