J Rennie 135 



As regards the influence of the weather in affecting numbers it has 

 been already noted that the newly hatched larvae are very susceptible 

 to drought and that the mortality in laboratory reared larvae which 

 are not kept moist is high. There is a fairly general popular impression 

 that severe winter with plenty of frost kills the larvae, but our experi- 

 ence so far does not bear this out. Larvae were left in the open exposed 

 upon stones during a night of severe frost, and were found alive the 

 following morning. The apparent beneficial result following frosts 

 seems to be due to the improved tilth favouring a more rapid primary 

 growth of the crop in spring. The environmental factors are the subject 

 of continued investigation. Unfortunately, owing to the presence of the 

 larvae on cultivated land, the food supply is adequate. Food is not 

 ordinarily scarce, and as already indicated a high percentage of larvae 

 kept in captivity complete their development upon ordinary turf in 

 the soil. 



The question of natural enemies is dealt with in a succeeding paper. 



Tipula attacks on Oats. 



Conditions unfavourable to the oat crop may render it suscep- 

 tible, and Tipula, even when the numbers are not excessive, may 

 work havoc. Apart from the question of manuring and general 

 farm practice which are not considered here, the weather in spring 

 has been found to be a significant factor. These observations have 

 been carried on during a period of seven years; along with these 

 the experience of over 130 farmers on a wide area has been collated 

 and there is a universal testimony to the fact that a cold late spring 

 in which the primary growth of the plant is delayed constitutes one 

 of the most certain conditions for crop failure due to Tipula attack. 

 It is during the early days of growth from the time of sowing until the 

 adventitious root system is established that Tipula attack results in 

 the destruction of the individual plant. After this period the plant 

 may be regarded as out of danger; it may be weakened but probably 

 it will not be killed outright by subsequent attack. Any cause there- 

 fore tending to extend the period of germination or immediately 

 subsequent growth increases the liability of the crop to loss from 

 Tipula attack. In this area the time between sowing and brairding 

 for oats in an average season is 10 to 14 days. In a series of seven 

 cases which came vmder observation in one season in which failure of 

 parts of the oat crop, attributed to Tipula attack, took place, this 



