50 



THE CABBAGE PLANT-LOUSE. 



(Aphis brassicce L.) 



This insect was quite troublesome this season from about the 1st of 

 August to 1st of September. After the latter date they could only be 

 found in scattering colonies. During the worst period of attack they 

 were so plentiful as to nearly ruin many plants. 



I mention them more for the purpose of speaking of the insects which 

 preyed upon them than anything else. 



Of these the larvae of the Syrphus flies (two species were reared) were 

 the most persistent and literally swept the lice off by thousands. It 

 was very interesting to watch these blind maggots in their work of de- 

 struction. There were also present the larv» of Lady-birds and Lace- 

 winged flies. These, however, did not do anything like the execution 

 of the first-named insects. I uoticed where lice were very numerous 

 that a large per cent, became winged, while on other portions of the field 

 it seemed that a much larger per cent, were apterous. 



CABBAGE WOKXS. 



(Plus i a brassicce and Pieris rapce.) 



August 3 a few larvae of brassicce were noticed in a patch of a 

 couple of acres of Cabbage where rapce were already quite abundant and 

 doing considerable injury. They were so few that it was hardly thought 

 possible they could do much harm the present year. On this date the 

 rapce as above stated were already numerous and doing much harm. 

 A series of experiments was at once begun looking towards their de- 

 struction. However, many of this brood pupated, and from the 10th to 

 the loth of August I never saw the rapce butterfly so abundant as they 

 were over the cabbage beds in the University garden. These deposited 

 their eggs in great abundance, and after several days disappeared. 

 Among the first brood of worms (rapce) I had noticed a few larvae af- 

 fected by Apanteles glomeratus, and also several pupae which had been 

 stung by Pteromalus puparum. These did not appear to be abundant, 

 but probably many were not noticed. As this second brood of rapce 

 developed it was hardly possible to find a larva? not affected by one of 

 these parasites. A. glomeratus was most abundant, as it stings the 

 young larva?, but should one be so fortunate as to escape this insect, P. 

 puparum was sure to find it. I noticed that the last named always 

 stings the larva just before it makes the last molt or immediately after 

 the pupa is formed. So well did these parasites do their work, that 

 after the large brood of butterflies previously mentioned not an adult 

 was seen except that now and then a straggling individual would sail 

 over the field. In all of my experiments in boxes, during which I con- 



