Temperature Stresses on the Mosquito Phase of Plasmodium relictum

Culex tarsalis infected with Plasmodium relictum, strain 1P1-1, were exposed to temperatures above or below 27 C, which is close to the optimum for the development of the mosquito phase of the parasite's life cycle. At 18 C it requires about twice as long for P. relictum to produce salivary gland sporozoites as at 27 C. At the latter temperature the sporozoites are infective when they first appear in the salivary glands; in mosquitoes maintained at 18 C the sporozoites do not acquire infectivity until 5 days or more following their initial appearance in the salivary glands. Mosquitoes remain infective at least 2 months at 18 C. At 31 C sporozoites appear in the salivary glands in about half the period required at 27 C, but again are not infective at the time of their appearance. Infectivity appears a few days later. Exposure of the mosquitoes to 31 C for 10 days renders them noninfective in subsequent bitings for at least 29 days. At 35 C the earliest stages in the mosquito are most easily injured; intermediate stages can withstand this temperature for 3 to 4 days, while the sporozoites retain their infectivity for as long as 13 days at 35 C. The sporozoites are already partly adapted for existence at higher temperatures before they are transferred to the avian host. There is ample evidence that human malarial parasites will complete their development in suitable mosquito vectors within a temperature range of about 16 to 30 C (Boyd, 1949, Table 68). Similar data for other plasmodia have been comparatively few. Sergent (1919) found that the temperature for development of Plasmodium relictum in Culex pipiens was from 20 to 30 C. Using the same parasite and vector, Goritzkaya (1934) observed that the development of the parasite ceased if the mosquitoes were placed at 37 C or at 5 to 15 C immediately after biting. Huff (1932) infected various species of mosquitoes with P. relictum, P. elongatum, and P. rouxi at temperatures varying from 21 to 25 C. Rosen and Reeves (1954) infected C. tarsalis and other mosquitoes with P. relictum at daytime temperatures ranging from 20 to 37 C, the temperature being 30 C for most of the day. Huff (1940) stated that P. lophurae did not develop in Aedes aegypti at temperatures lower than 28 C; this was confirmed later by Trager Received for publication 13 July 1964. * This investigation was supported by Research Grant AI-00087, Institute of Allergy and Infectious Diseases, Public Health Service, and by Research Grant 254, Zoology, University of California. (1942), who kept stock and experimental mosquitoes at a temperature of 30 to 32 C. In the same paper Huff also reported that P. cathemerium, strain M, did not develop in C. pipiens at 22 C unless it had been kept for 18 hr at 28 C following the infective blood meal. Shute and Maryon (1952) found that sporozoites of P. relictum developed in C. molestus in 8 days at 25 C but that sporozoites of P. gallinaceum in A. aegypti did not appear until the mosquitoes had been 10 days at this temperature. At 25.6 ? 1 C, Hunninen (1953) found sporozoites of P. relictum in 6 to 8 days in the salivary glands of C. pipiens and Anopheles quadrimaculatus, and in 9 to 13 days in the salivary glands of A. albimanus. We have reported previously the effect of a temperature of 4 C on P. relictum in C. tarsalis (Chao and Ball, 1962). In the present work higher temperatures up to 35 C were selected for study with the aim of comparing the capacity of P. relictum to develop at temperatures above and below the optimum for the mosquito phase. One question we sought to answer is whether those stages which will be transferred to a very different temperature at the time of entering a new type of host already have a greater ability to live at the new temperature than have the stages not so destined.