Modification of Sand Fly Biting Behavior by \u3ci\u3eLeishmania\u3c/i\u3e Leads to Increased Parasite Transmission

To attempt rodent-sand fly-rodent transmission of Leishmania major, laboratory-reared Phlebotomus doboscqi were fed on L. major-infected mice and then refed on uninfected mice 21 days later. Flies which refed either probed 1–2 times and took a full blood meal in less than 10 minutes or probed 3 or more times and took little or no blood during a period of 15 minutes or more. When dissected, 7 of 8 flies which experienced difficulty in obtaining a blood meal had flagellates in their cibaria, an observation supporting the hypothesis that parasites in this part of the alimentary canal modify normal blood feeding behavior. None of the infected females which probed 1–2 times had similar anterior station infections. Infected sand flies transmitted L. major to uninfected mice and a single fly, transferred from 1 mouse to the next while repeatedly attempting to take blood, infected 5 mice. During a year-long survey in Baringo District, Kenya, we collected 9,182 female sand flies. Only 2 of the 278 P. duboscqi captured during this collection were infected with L. major; however, 18 of the 789 small rodents from this area were infected with L. major. Parasite interference with normal blood feeding may explain how a relatively small population of P. duboscqi, only a few of which are infected with L. major, can amplify parasite transmission thereby maintaining a disproportionately large reservoir in local rodents

Infotropism as the underlying principle of perceptual organization

Whether perceptual organization favors the simplest or most likely interpretation of a distal stimulus has long been debated. An unbridgeable gulf has seemed to separate these, the Gestalt and Helmholtzian viewpoints. But in recent decades, the proposal that likelihood and simplicity are two sides of the same coin has been gaining ground, to the extent that their equivalence is now widely assumed. What then arises is a desire to know whether the two principles can be reduced to one. Applying Occam's Razor in this way is particularly desirable given that, as things stand, an account referencing one principle alone cannot be completely satisfactory. The present paper argues that unification of the two principles is possible, and that it can be achieved in terms of an incremental notion of `information seeking' (infotropism). Perceptual processing that is infotropic can be shown to target both simplicity and likelihood. The ability to see perceptual organization as governed by either objective can then be explained in terms of it being an infotropic process. Infotropism can be identified as the principle which underlies, and thus generalizes the principles of likelihood and simplicity