Hi Mohamed,

I guess the most logical explanations are based on what we know of the behaviour of Tetranychus, and that would be (a) overwintering or near-overwintering individuals, as we know that's what at least females do, or (b) huge infestations on the leaves, which lead to numerous wandering individuals that might end up in a bird's nest. As dispersal is by wind or walking for spider mites, it wouldn't surprise me to find some roaming the trunks of trees. But failing those explanations, that just leaves unfounded but interesting speculation. One possibility would be over-summering, which isn't well documented, but in hot climates would not be a surprising behaviour to discover; another is nocturnal behaviour, which I think isn't shown for spider mites but I suspect that's because few have looked (there's a nice paper showing nocturnal behaviour in phytoseiids, http://onlinelibrary.wiley.com/doi/10.1034/j.1600-0706.2003.12572.x/full). Perhaps spider mites are unlikely to be nocturnal as they would have to give up feeding for a significant part of each day, thus slowing their development... but if phytoseiids do it, why not the spider mites?

Less likely is that it's a bark-feeding Tetranychus: their distant tuckerellid ancestors might do this, but I know of no Tetranychini - or even Tetranychidae for that matter - that do this.

All the best, Owen.

Thank you Owen for help and remarkable explanations.

Regards......Mohamed

Dear Mohamed, did you collect more specimens from the tree? did you ID the species. checking were are on the tree will help also to understand the different possibilities. Dispersal is a good reason, accidental, large population on the tree... regards Ron

Generally, in my area (Assiut province), citrus trees are infested with the citrus brown mite, Eutetranychus orientalis; however, some Tetranychus specimens (near urticae) can be encountered at low populations comparing to E. orientalis. Thank you Ron for stopping by......Cheers.....Mohamed