144 



THE EEPOET OF THE 



No. 36 



Control by Predacious Larvae. 



In addition to establishing the appetite record of the adult beetles, both Cara- 

 bid and Staphilinid, an attempt was made to mature carabid larvas. Carabid beetle 

 eggs may frequently be seen on the soil surface, and at different times some of these 

 Avere taken from the field, at other times some eggs were deposited in the tubes in 

 the laboratory. Poor success seemed to attend the hatching of these eggs, and in 

 fact many disappointments were encountered in bringing the larvae to maturity. 

 Without detailing all these troubles I will relate some of the facts obtained. The 

 eggs and larvs of these beetles were handled in the same way as the adults, in 

 vials, etc. 



Table C — Carabid Larvae Appetite Recced. 



Summary. 



Even from these records it is impossible to state with accuracy the actual appe- 

 tite record of any predacious beetle or its larva. The limitation in the manner in 

 which the work was done does not allow us to form any definite conclusion. 



We are justified in stating, however, that despite the artificial methods em- 

 ployed, these predacious beetles present an immense aid in the control of the 

 maggots. Their voracious appetites in confinement and from the fact that they did 

 not hesitate to attack the food offered clearly proves some marked similar action in 

 nature. Further than this, on many occasions, both Carabid and Staphilinid 

 beetles, and the larva3, at any rate of the former, may often be found embedded in 

 the roots of plants in close association with maggots, and have been observed actu- 

 ally at work devouring maggots. The actual amount of food they dispose of in a 

 day or throughout their life is the point of which we cannot be too sure from the 

 records obtained. We might, however, be perfectly justified in assuming that five 

 eggs or five young maggots a day would represent a normal appetite. We have also 

 seen that a beetle will live with food for four months (120 days). On the above 

 ratio it will destroy about 600 eggs or young maggots. This in itself would just 

 about equal the number of eggs deposited by a fly on a single plant in a season, 

 under conditions we have mentioned. Possibly this may be a little high, but never- 

 theless, we cannot avoid the fact that the percentage of usefulness of these little 

 bottles is exceptional, and of unquestionable value. 



