The effect of temperature on early Plasmodium falciparum development was examined in Anopheles stephensi. The rates of both ookinete development and bloodmeal digestion were lengthened as temperatures decreased from 27 to 21 degrees C. However, low temperatures (21-27 degrees C) did not significantly influence infection rates or densities of either ookinetes or oocytes. In contrast, high temperatures (30 and 32 degrees C) significantly impacted parasite densities and infection rates by interfering with developmental processes occurring between parasite fertilization and ookinete formation, especially during zygote and early ookinete maturation. This study demonstrates clearly that temperature affects the sporogonic development of P. falciparum in anophelines by altering the kinetics of ookinete maturation. These studies not only confirm the ookinete as the key development stage affecting the probability of vector infectivity, they provide new insights into the epidemiology of P. falciparum infections.
1.We hypothesize that differences in host-handling times among three closely related encyrtid parasitoids ( Metaphycus anneckei Guerrieri & Noyes, Metaphycus hageni Daane & Caltagirone and Metaphycus lounsburyi [Howard]) are influenced by the defences of their host, black scale ( Saissetia oleae [Olivier]). Two forms of host defence were examined: (i) the scale's possession of a hard integument, and (ii) the effect of ants tending S. oleae . 2. Duration of host assessment, host rejection, drilling/oviposition and the presence or absence of host feeding were measured for M. anneckei , M. hageni and M. lounsburyi . Results show that M. anneckei oviposits through the soft ventral integument while M. hageni and M. lounsburyi oviposit through the harder dorsal integument. M. anneckei was never observed to host feed while both M. hageni and M. lounsburyi use hosts for either oviposition or host feeding. The ventral drilling location and absence of non-concurrent host feeding significantly reduced the overall host-handling time of M. anneckei , relative to M . lounsburyi and M . hageni . 3. Oviposition success of M. anneckei and M. hageni in the presence of ants was compared. An observation arena was established with the numbers of Argentine ants, Linepithema humile (Mayr) and S. oleae manipulated on potted oleanders. M. hageni and M. anneckei were placed, individually, onto the observation arena and their interaction with ants and S. oleae recorded. While 55·3% of M. anneckei successfully oviposited, M. hageni was unable to oviposit or host feed in the presence of foraging ants.
4.Field tests were conducted using potted oleander plants, infested with S. oleae , to determine the effect of L. humile on scale density, parasitism levels and parasitoid species composition. Ant-tended plants had significantly more scale, lower scale parasitism and lower levels of host feeding (as indicated by unknown scale mortality levels). There were also significant differences in parasitoid species composition between ant-tended and ant-excluded treatments, with the relative frequency of parasitoid species with faster host-handling times more common in the ant-tended treatment.
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