101 
Part III.] Beeson : Beehole Borer of Teak. 
possibility of other interpretations. Various theories are current with 
regard to the natural, history of the borer and its control and it may be 
profitable to discuss the validity of some of them in the light of the fore¬ 
going data. 
1. The liability of trees to attack. 
Since the borer habitually breeds in living trees it has been generally 
assumed (by analogy with the habits of other borers) that it attacks 
most readily weak, suppressed, moribund and girdled trees. From the 
method of feeding and the construction of the beehole it is now evident 
that vigorous trees are beeholed in preference to weak or decadent 
trees (vide pp. 55 et. seq.) From the stem-analyses in even-aged crops 
it is evident that the average number of beeholes per tree is directly 
proportional to the girth , other factors being equal. [ vide Sample 
Plot Records and Diagram 1] The question now arises : “ Is this rela¬ 
tionship due to the selective action of the female moth during oviposition, 
or to an independent factor such as the area of bark surface exposed per 
girth-unit, or the composition of the crop and the laws of probability 
governing the moth-f- tree combination ?” 
(1) The first explanation cannot be admitted unless we venture into 
the unknown and assume a nicely graded series of chemotropic responses 
stimulated by variations in the growth vigour of the tree. (2) The 
composition of the crop is not the dominant factor since the highest and 
lowest girth-classes include the smallest numbers of trees, hence both 
should show lower incidences of attacks than the middle girth-classes, 
proportional to the probability of concurrence between female moths 
and trees. (3) If we explain the higher frequency of beeholes in higher- 
girth trees as due to the greater area of bark surface (or volume), 
we assume that there is competition between the borers for feeding- 
space. The following example will show the absence of overcrowding 
and consequent lack of competition. In a 21 years old plantation the 
mean number of moths emerging per tree of mean girth 28" is 0-5 
per annum [Mohnyin, 1898]. There are, in a normal crop, 17*0 trees 
per acre at 21 years (Leete,) hence 170 X 0-5=85 moths per acre ; of these 
assume half are females, i.e. 42-5. Without making reductions for 
mortality before oviposition, we have available 42 moths to attack 
170 trees ; as each individual lives only a few days and the moth emer¬ 
gence period extends over 8 to 10 weeks, oviposition is not influenced by 
competition. On the contrary individual trees frequently escape attack 
for several years. For example in a sample plot in a Pyonchaung planta¬ 
tion (1873) the percentage of trees attacked in 1916 = 38 per cent.; in 1918 
= 34 per cent.; and of the whole stand 44 per cent, remained unattacked 
[ 329 ] 
