> I disagree, AS you pointed out the genetics of varroa are odd, essentially clones! That’s why the whole argument falls apart. Fully accepting what Dick said about diluting the gene pool with "partially resistant" genes. In some cases that may be true. In this case since they are clones the case dies. If you use lets call miticide (I should say pesticide) A and it kills 99% we assume that 1 mite is still there and now shes fully resistant genticaly, and breeds...
Hi Charlie,
I don't think this is an accurate picture of varroa genetics. The genetic system of mites actually accelerates their development of resistance.
* * *
The two-spotted spider mite Tetranychus urticae Koch is one of the economically most important pests in
a wide range of outdoor and protected crops worldwide. Its control has been and still is largely based on
the use of insecticides and acaricides. However, due to its short life cycle, abundant progeny and
arrhenotokous reproduction, it is able to develop resistance to these compounds very rapidly. As
a consequence, it has the dubious reputation to be the "most resistant species" in terms of the total
number of pesticides to which populations have become resistant, and its control has become problematic
in many areas worldwide.
Insecticide and acaricide resistance has also been reported in the ectoparasite Sarcoptes scabiei, the
causative organism of scabies, and other economically important Acari, such as the Southern cattle tick
Rhipicephalus microplus, one of the biggest arthropod threats to livestock, and the parasitic mite Varroa
destructor, a major economic burden for beekeepers worldwide.
* * *
Control of T. urticae populations primarily relies on
acaricides and insecticides. This mite can rapidly develop
resistance to acaricides due to its high reproductive potential,
short life cycle and arrhenotokous reproduction (Croft
and Baan 1998). Two spotted spider mites have evolved
resistance to more than 93 pesticides to date and resistance
has been reported from more than 105 areas in the world
* * *
Arrhenotoky seems to confer evolutionary advantages because of the expo- sure in each generation (of the whole genetic complement) to selective forces through the hemizygous males. Advantages of sexual reproduction are main- tained through biparental females by meiotic segregation, crossing-over and fertilization. Genetic recombination can occur in the diploid females, and the new characters are directly exposed to selection in their sons (Havron, 1983 ). Although male haploidy reduces the 'effective' population size and thereby the genetic variation (depending on the sex ratio; Crozier, 1985), it is estimated that the additive genetic variance in arrhenotokous species is 4/3 larger than that of similar but fully diploid species (Harl, 1971). It is expected that the rate of evolution of these species would be accelerated by a factor similar to this ratio. A more complete discussion of the effects of arrhenotokous reproduction on the evolution of pesticide resistance in the Tetranychidae and Phytoseiidae and other groups can be found in Havron (1983), Cranham and Helle (1985), Crozier (1985), and Schulten (1985).
(references available on request)
PLB
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