102 
Indian Forest Records. 
[Vol. VIII. 
during the period 1916-18. Again 22 trees in a plot [Yanaungmyin, 
1895] remained unattacked for 6 years out of 10, and in another plot 
[Mohnyin, 1898] 21 trees remained unattacked 7 years out of 10. The 
greater available bark-space on higher girth trees is therefore not the 
decisive factor. (4) It is suggested that the frequent occurrence of high 
numbers of beeholes in the higher girthed trees of an evenaged crop 
is the result of a relatively higher percentage of survivals to the pupal 
stage in such trees. The liability to attack is not greater,—in any case 
the number of eggs laid on a particular tree by a particular moth is a 
matter of pure chance, as the Sample Plot Records show—but the liability 
of larvae to successful development is proportional to the richer food- 
supply. Vigorous trees provide the most certain food-supply and 
produce the healthiest borers and the largest beeholes. An examination 
of the analysis data shows that there is a tendency for beeholes of maximum 
size to occur in rapidly grown crops, and that in slow-grown crops beeholes 
are smaller and accompanied by a higher proportion of failed larval 
galleries. 
2. The annual incidence and rate of increase of the borer. 
The annual incidence curves given in Diagram 2 show that (in pure 
evenaged stands) the borer usually appears early in the life of the 
plantation and may appear as early as the 2nd year after foundation, 
vide also Plate IV. The current annual incidence, thereafter, fluctuates 
considerably but the mean annual incidence increases steadily although 
relatively slowly ( vide also p. 56). The most important fact arising 
from the data is the recognition of a very low rate of increase 
and frequent natural reductions in the mean annual incidence. It sug¬ 
gests that a possible method of control in plantations lies in the forced 
growth of teak, i.e . in the production of a high girth-increment in indi¬ 
vidual trees, so that the wood-increment outstrips the borer-increment. 
The writer has compared the annual incidence curves with all the known 
measureable factors, viz. (1) total annual rainfall, (2) mean annual temper¬ 
ature, (3) occurrence of thmnings, and (4) of fires, (5) incidence of wood¬ 
peckers, and with none of these is there constant agreement of effect. 
(1) and (2) Effect of Rainfall and Temperature. The data yield 
negative results, possibly because the meteorological stations are at 
considerable distances from the sample plots. 
(3) Effect of Thinnings. —After a thinning the incidence curves 
behave irregularly, but there are indications that thinnings can be 
carried out so as to reduce the incidence of the borer. 
(4) Effect of Fires. —The use of fire as a means of controlling the beehole 
borer has frequently been advocated. Mr. W. N. Grieve was the first 
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