45 
Part VII] Beeson: Life History of Toon Borer. 
Available data, therefore, point to the fact that it is only in vigorous¬ 
ly growing trees, which produce both succulent leafy shoots and 
fertile fruits, that all five generations of the borer can successively exist. 
3. The Third Generation. 
Larvae of the Third Generation 
1914. In 1911. the field-work carried out during July gave indica¬ 
tions of broods of the pest attacking the growing shoots put out by 
young trees at the break of the rains, but gave no further indication 
beyond the fact that larvae of this generation occur throughout the 
month. 
1915. Field - work .—In June 1915, field-work was commenced at an 
earlier date and extended to the examination of fruits as well as of shoots 
for signs of the existence of the third generation. Fruits collected 
between the 17th and 29th June showed less than 2 per cent, of attack ; 
at this period of the year the majority of the fruits are mature and the 
epidermis has become too suberised to permit of penetration by the 
younger larvae. The appearance of new shoots towards the end of May 
and in June, moreover, provides an alternate supply of soft green plant 
tissue which is evidently more attractive to egg-laden females and more 
suitable for the early development of the first stage larvae. Examina¬ 
tion of new shoots revealed larvae at work as early as the 3rd June. 
First stage larvae were found inside toon shoots on the 8th June ; first 
and second stage larvae were observed on the 18th June ; eggs, first, 
second and third stage larvae were found on the 26th June ; shoots collec¬ 
ted between the 30th June and the 7th July contained larvae of all 
stages, and a few eggs were also seen on the leaves. Shoots collected 
on the 29th July and later contained generally pupae or mature fourth 
stage (bluish-green) larvae. 
It was thus established that larvae of this generation normally occur 
feeding inside the shoots throughout the months of June and July. 
Insectary Work. —Simultaneously with the field-work, experiments 
were carried out in the insectary to determine the absolute length of 
the larval period and of the stages of the life-cycle. 
1. In one of the large outdoor wire-gauze cages of the insectary a 
sapling toon had been planted in the previous year, and on the 
appearance of new shoots breeding experiments were commenced. In 
the absence of eggs, very young first stage larvae obtained from field- 
collections were inoculated each on a separate shoot. The larvae 
began immediately to feed and bore into the soft epidermis. Within 
five minutes of deposit on the plant, the head of the larvae was almost 
.[ 190 ] 
