MARCH,
1959]
CONTROL OF LICE
7
and the lice population developed on these goats more or less normally long before that on the
goats treated with other insecticides. In none of the goats treated with insecticides in both
these trials was any symptom of ill effect of insecticidal treatment observed. Goats which
were badly infested with lice in the beginning showed improvement in their condition some
time after treatments with insecticides.
DISCUSSION
Certain apparent inconsistencies in the results obtained at different occasions with the
same insecticide require discussion.
In Table I, it has been seen that buffalo calves treated with 0.1 per cent lindane re-
mained free from lice longer (four weeks) than those treated with 0.5 per cent DDT (one week)
though it is well known that the residual effect of DDT is longer than that of lindane. The
longer effective period of lindane in this case is believed to be due to its lethal action on the
eggs of the buffalo louse present on the body of the calves at the time of treatment. As can
be seen from the literature cited, some investigators [Wells and Barrett, 1946; Furman,
1947] reported that BHC and not DDT killed eggs of lice. The month of January, when
these treatments were applied, was the time when the eggs of this species of lice are found
in large numbers on the body of the infested buffaloes.
No information regarding the population fluctuation, breeding season, bionomics under
the conditions obtaining here, etc., of any of the species of lice included in this study were
known to us at the time of the trials. However, some of this information about goat lice
L. stenopsis and D. caprae have since been obtained by us. It is quite likely that the picture in
these respects of all the different species of sucking lice affecting livestock here will be more or less
similar to that of L. stenopsis, the sucking louse of goats. If so, there is not much difficulty in
explaining the results of the trials given here.
In the case of trials with cattle
louse L. vituli, the treatments were applied at a time (April and June) when the population
of the lice was lowest and it was probably not the breeding time of the insect. As such there
was no ovicidal action of the insecticides involved in the trials and all the insecticides acted
only on a few motile lice present on the body of the treated animals. Again, if the activity
of this species of sucking lice is like that of L. stenopsis (February to March is the period of its
greatest activity) and had the treatments been applied either immediately before or during this
period, the effective periods would have been found to be much shorter than what was found
in these trials.
Of the trials against goat lice L. stenopsis and D. caprae, in the case of the first application
of treatments which were made in April, no ovicidal action was involved and the
treatments were applied at a time when the population of both the species of lice was
lowest—the beginning of April to the end of July being the period when the population of both
the species of lice are found to be the lowest in the year. This might be the reason why the
effective periods with all the insecticidal treatments were very long. One of the two peak
periods of the population of the biting louse D. caprae is January and the population of this
species of lice starts developing for this peak from late November. Therefore, in the treatments
of the second trial which were applied in mid-November, the effective periods were compara-
tively shorter than those in the case of the first trial. Besides, the different physical conditions
of different seasons affect the residual properties of the insecticides differently.
SUMMARY
A series of semi-field trials to see the efficacy of a number of modern insecticides in
controlling the buffalo louse Haematopinus tuberculatus, cattle louse Linognathus vituli and goat
lice L. stenopsis and Damalinia caprae were conducted at the Indian Veterinary Research Insti-
tute, Izatnagar, in 1956.
All the insecticides were applied as wash in such a way that the body of the treated animals
was thoroughly wet with the fluid and all the insecticides used, except malathion (on emulsi-
fiable liquid), were in wettable powder forms.