December, '22] duruz: peach twig-borer control 399 



Referring to these tables, it will be observed that liquid lime-sulphur 

 ("Rex") has given an average control of 88 per cent, 86.6 perc ent and 

 83.2 per cent at the three different stages. The addition of arsenate 

 of lead increased the efficiency of lime-sulphur, in the full bloom 

 spray. The arsenicals also were highly efficient in controlling this 

 insect, especially when spraying was done during the blooming period; 

 when applied earlier the rains washed them off before the caterpillars 

 emerged. Nicotine sulphate has given a higher average control than 

 any other spray tested. It is most effective during full bloom, however. 



Life History Experiments 



Evidences of a Second Generation. As has been previously 

 stated, there have been conflicting theories regarding the life history 

 of the peach twig-borer. Evidence is here presented to prove the ex- 

 istence of a distinct second generation, rather than one irregular brood. 



The writer has followed closely the activities of the insect at Davis and 

 these observations agree closely with those of Clarke made in Placer 

 County in 1902. In order to prove that these observations were not 

 those of only a few chance individuals, careful counts were made on each 

 of 562 almond seedlings. The infested shoots were counted first between 

 April 1 and 21, in comparing the effectiveness of the spray treatments 

 already discussed. A second count was made between June 10 and 13. 



Considering only the unsprayed check trees (ninnbering 304), there 

 was an average of five larvae per tree at the first count. After April 21, 

 there was no indication of an irregular infestation; all the larvae had 

 pupated and there were no "stragglers." On June 8th large nimibers of 

 larvae were again noticed attacking the twigs on these trees. The 

 second count was then made over the entire orchard, and a tremendous 

 increase in number of larvae was found. There was an average of 12.5 

 larvae per tree at this time, showing an increase of 150 per cent in 

 approximately one month. What is more significant is the fact that 

 the sprayed trees, some of which showed no infestation in the first 

 count, had the same average ntimber per tree as the unsprayed trees.. 

 The increase in ntunber and spread of the attack is attributed to egg 

 laying and the flight of the moths. This is conclusive proof 

 of the existence of a definite second generation. (The writer believes 

 from his general observations that there is a third distinct generation 

 also, but has not had opportunity to collect positive data.) 



Conclusions 

 The results of two years investigation are not conclusive enough to 

 warrant definite recommendations. Some very good "leads" have been 



