464 



of egg-laying appears to depend on the degree of succulency and 

 tenderness of growth, rather than on the variety or species of the plant. 

 Injury to cabbage crops in the vicinity of Geneva is restricted to the 

 spring months. In New York it is the custom to leave the cabbage 

 stumps in the ground during the winter ; consequently the new growth 

 proves very suitable for egg-laying, with the result that the stumps 

 become thoroughly infested. The normal duration of the larval stage 

 is about three weeks, but in the absence of food and moisture may be 

 considerably reduced. Pupation takes place in the soil close to the 

 host plant, 90 per cent, of pupae of the first brood, found in June, 

 lying within 3 inches of the injured plant and in the first 3 inches of 

 soil. A small number of larvae pupate in infested aerial parts of the 

 host. The duration of the pupal stage under warm conditions varies 

 from 12 to 18 days ; in the hibernating generation it is from five to 

 eight months and the larvae migrate from the plant to a distance of 

 4 or 5 inches. 



Emergence of adults in spring extends over a considerable period ; 

 in 1911 this lasted from 9th May until 14th June. Under experi- 

 mental conditions, emergence was able to take place from a 

 depth of 12 inches. Adults kept in captivity fed readily on banana, 

 sugar and water, and on blossoms of S. officinale, Daucus carota, etc., 

 living for a period of two to four weeks, and in one case for nine weeks. 

 No eggs were deposited in captivity. Eggs are probably deposited 

 in from three to five days after emergence, and are laid either singly or 

 in masses. In the latitude of Geneva three broods usually occur 

 annually and in favourable seasons a partial fourth brood may be 

 produced, while in other years only two broods appear. Observations 

 extending over several years indicate that the winter is passed in the 

 puparium and not in the adult stage, as previous investigators have 

 suggested. 



In addition to hot, dry weather the most important natural enemies 

 in this region are Staphylinids belonging to the genus Aleochara, the 

 Cynipid parasite, Pseudoeucoila gillettei, and a mite, Tromhidium sp. 

 The commonest Staphylinid is A. bipustulata, L. ; in addition, 

 Philonthus nigritulus and Homalota sordida have occasionally been 

 reared from puparia. The following species have been taken near 

 infested plants : — Tachyporus jocosus, Aleochara sp., near aihata, 

 Oxytelus nitidulus and Staphylinus badipes. Parasitisation by P. gillettei 

 amounted to 4| per cent, during August and September 1909. In 

 Minnesota, a parasitisation of 36*6 per cent, has been recorded. 

 Tromhidium sericeum occurs in large numbers during the oviposition 

 period of 0. brassicae and is responsible for the destruction of a con- 

 siderable percentage of eggs. Three species of ants appeared to be 

 predaceous on the eggs, young larvae and adults ; these were Stenamma 

 breviccyrne, Mayr, Formica fusca, L. var. subsericea, Say, and Solenopsis 

 molesta, Say. Lasius niger, L. var. americanus, Emery, and the Carabid, 

 Clivina impressifrons, were obser\^ed in the earth near infested plants. 

 Adults were attacked by an Anthomyid, Caenosia flavifrons, Stein, by 

 a fungus (Empusa), and possibly also by a red mite. 



Experiments for the control of the cabbage maggot included attempts 

 to destroy the adults by the use of poisoned bait. Flies in captivity 

 died in less than two hours after feeding on a sweetened solution of a 

 soluble arsenic compound. A spray consisting of 21b. molasses, 



