This is an interesting question - we certainly see yellow engorged female R microplus in many cases. We also know that many ticks ingest huge numbers of leukocytes when they feed (see pic - green cells are neutrophils - courtesy Constantin Constantinoiu). We have never looked at the yellow ticks specifically, but I guess they have a higher proportion of leukocytes. Regards, Nick

This is an interesting question - we certainly see yellow engorged female R microplus in many cases. We also know that many ticks ingest huge numbers of leukocytes when they feed (see pic - green cells are neutrophils - courtesy Constantin Constantinoiu). We have never looked at the yellow ticks specifically, but I guess they have a higher proportion of leukocytes. Regards, Nick

Dear Dr. Jonsson,

Thank you for the help. We face these ''yellow'' ticks when we work with artificial membrane feeding system where there is no immune reaction and also no dynamic blood flow. We have observed that even closely attached ticks engorge red or yellow in vitro especially the immature stages of Hylomma and Rhipicephalus. I myself believe that these ticks have only taken up serum devoid of cells especially for those stages of ticks with mouse short parts (Hyalomma and Rhipicephalus larvae and nymphae and Boophilus (Rhipicephalus) adults as you said). The feeding pool that is formed by these ticks is filled with serum and the cells can not pass the tissue to reach the pool. Do you have any suggestions for testing the basis of this phenomenon (provided your hypothesis is true and that some ticks only engorge themselves with WBC and some with total blood)?

Regards,

Shahin

Dear Shahin, Some of my colleagues used to call these "serum ticks." I think you are probably right with your theory. I'll give it some thought. Cheers, Nick

Dear Shahin, the idea on serum in the feedng pool is interesting, still WBC can be present even in such "depleted" pool. The dark colour of the fed ticks is coming from the RBC as I know.

You can try to do artificial feeding with only serum or a mix of blood and serum 1:1 - one of my colleagues tried to feed I. ricinus ticks with serum and they survived (of course they did not like it :). If you will have more yellow tick, then the serum can be the answer.

May be these ticks differ in intestine microbiome. Varied bacteria, fungi, protozoa product varied enzimes, that lead to varied metabolisms of haemoglobin, lipids etc.

That is hypothesis only :).

Dear Nicholas, Jan and Oleg,

Thank you all for the comments. Lets wait for other ideas...

Dear Shahin, I captured some engorged yellow rhipicephalus (boophilus) annulatus on cattle from one farm in mazandaran province, Iran that after oviposition in controled insectary (28 C, 87% RH), all of eggs and  larvae hatched were white yellowish colour eggs and larvae instead brown colour. In same farm and same time I captured dark green engoeged of Rh (boophilus) annulatus but oviposited brown eggs and hatched brown larvae.   I think this is an inherited trait and they are new strains of this species that proven by molecular assays??? what is your idea?

Sorry for the delayed participation. The term 'serum tick' was first used for unusually light or colorless engorged specimens by Arthur (see Sonenshine, Biology of Ticks, Vol. 1, 1991, p. 183). The description of the phenomenon can be found in the book of Balashov (1972). Best regards.