Once sporozoites enter the salivary glands they remain until the female mosquito dies. i am not aware of any evidence, in the literature, to the contrary. Unpublished - i have seen mosquitoes in an insectary loose PF sporozoites when temperature spiked one night. Despite experiments, we could not replicate it. The question you have is interesting and worth investigating.

Hi John,

Thanks for your answer - actually I've just run a series of experiments on temp and Pf, so that's why I was asking. There's some odd stuff I've observed, and there's several mechanisms for it that could be reasonable explanations.

Successful sporozoite invasion of the salivary gland is an essential step for the completion of the Plasmodium cycle in the mosquito. As is apparent from this review, our understanding of this complex, multistep invasion process is rather superficial. Since disruption of any of these many steps is likely to abrogate parasite cycle in the mosquito, further investigation of these processes should prove to be rewarding and should receive high priority. Answers to some of these questions may lead to new means to interfere with parasite transmission.

more so read futher on it:

Sterling CR, Aikawa M, Vanderberg JP. The passage of Plasmodium berghei sporozoites through the salivary glands of Anopheles stephensi: an electron microscope study. J Parasitol. 1973;59:593–605. [PubMed]

I am glad that Dr Beier answered this question because I used his protocol, optimized at the MRTC, Mali, for my csp ELISA.

However, I am not sure I understand what is addressed in Lillian's question.

After the 1st infective blood meal, are we searching for live sporozoites in the salivary gland (ie like dissecting the gland and looking for sporozoite using a stain under the microscope in the case of experimental infestation) or are we searching, using tools and techniques like ELISA, for antigenic determinants of PF, evidence of a prior infection or the potential to have infected earlier through subsequent feeding? 

I may be wrong here but let me just share with you my thoughts and some observations I personally made at the field during mosquito collections.

From parasites biology, for survival purposes, the parasite moves to the point of exit (salivary glands) in a stage infective (sporozoites) to the next host (vertebrate) and induces feeding behaviour in its vectors to enable it continue its development. Once the sporozoite matures, it exits into a vertebrate host and continues its developmental process. Eco-physiologists will call it SURVIVAL STRATEGIES.

I think there is no time of dormancy, reduced activity or waiting as in storage in the salivary glands by sporozoites. This is where the biology of parasite and the biology of vector synchronize into a non consenting agreement to insure parasites survival. 

From the insect biology standpoint, I have never asked myself if there is a limit in the salivary glands for sporozoite load but I believe nature regulates things such that there is no overcrowding of sporozoites in salivary glands. There must be a regulatory mechanism to slow parasite development or enhance exit of sporozoites from the salivary glands. Hence this induced feeding strategy for exit  to the vertebrate host that regulates the gonotrophic cycle in insects.

In case there is no specific host, the insect feeds on any alternative host to free the gland pouch, the space that is needed for the next maturing sporozoites. This is the basis for host substitution as a vector-borne disease control method that has proven effective among rural dwellers in Yoruba land where housing patterns are the" face-me- I- face- you" type with corridors where domestic animals (companion and livestock) pass the night. By this process, anthropophilic vectors gradually develop a zoophilic behaviour. This was also observed among the fulani herdsmen who spend the night covered amid their herds, insects end up exhibiting animal and human blood meal sources.

Finally, I think that if an insect bites once and picks up gametocytes that all develop into sporozoites which exit into the vertebrate host, no live sporozoite will be left if there is no intake of a new batch of gametocytes to develop into fresh sporozoites.

so Clearance of live sporozoites in the case of a single infection is possible but this is impossible in the case of recurrent infections (like in endemic areas) although evidence of infection/ infectivity is once after the first infection via the everlasting presence of antigenic determinants.

I hope I did not confuse you the more Lillian