The dispersal of certain species of Mallophaga which infest the domestic fowl Callus domesticus.
Abstract
As biting lice (Mallophaga) pass their whole life on the host, they have little opportunity for dispersal, except during direct contact between host individuals. This occurs in wild birds during flocking and the rearing of young, but there are no obvious means by which lice may be transferred from one generation of domestic fowls to the next, since eggs are usually incubated and chicks reared artificially and pullets are kept apart from older birds. Pullets out of doors might be infested from wild birds, but an investigation of pheasants and partridges in a survey area in the north of England showed that they carried none of the species of lice that occurred locally on domestic fowls, of which Menacanthus stramineus (Nitzsch) was the commonest. Lice were found crawling on the hands and clothing of poultry handlers, which suggests that this may be the main method of transmission between flocks managed by the same poultryman, with inter-farm movements of stock probably accounting for wider dissemination. Investigations failed to furnish evidence that lice may be transmitted between primary hosts by agents such as Passerine birds or Hippoboscids or other flies, or that live lice occur off the host near domestic fowls.
Preliminary investigations haying shown that lice that left the host would experience substantial decreases in temperature and increases in light intensity, the survival and behaviour of M. stramineus were investigated to assess the importance of these changes. Adults lived longer at 21 than at 7, 9, 13 or 31°C, but it may be that this is the temperature at which they can survive longest without food. Humidity had no appreciable effect on survival. Cold stupor set in at 7°C. The longer a louse was kept at 5°C, the slower was its response to an increase in temperature or the higher the temperature necessary to induce revival. Maximum revival occurred after exposures of 31/2 hours or less and no revival after 25 hours. It appears unlikely that cold stupor can be a survival mechanism. Hatching of a few eggs from clusters kept for 11 days at 36°C and 85% relative humidity suggested that egg clusters might provide means of dispersal, but no confirmatory evidence was obtained. Adult lice in a temperature gradient of 14-39°C always aggregated in the range 28-36°C, which approximates to the temperature range in the natural environment. Thus, abandonment of the host in the field is unlikely. Observations of linear movement and angle of turn of adult lice off the host showed that their behaviour would prevent effective dispersal when displaced and suggested that they would tend to enter dark niches where further contact with a host would be improbable. Nymphs hatching from eggs that were not attached to a host would probably be subject to the same adversities. Thus, only contact between birds or the interposition of a human agent is likely to facilitate local spread. Transference of lice from infested birds to the skin near the vent of un infested ones indicated that if a single gravid female louse reaches a host, infestation is likely to be established. Fowls in boxes never became infested through the presence of egg clusters on the ceiling or sides of the box, and hardly ever from egg clusters attached to the tibiae, nor did they acquire infestation from heavily infested fowls in adjacent boxes or from heavily infested fowls that had occupied their boxes immediately or 24 or 48 hours before, but they did acquire it from infested fowls in the same box.