io Circular 107 



and migrations are constantly occurring. Colonies are found on a 

 long list of plants, such as melons, cucumbers, okra, strawberry, 

 purslane, clover, beans, beets, spinach, tomato, hops, pear, hydran- 

 gea, begonia, ground ivy, and morning glory, shepherd's purse, pep- 

 per grass, pigweed, dock, burdock, dandelion, lambsquarters, plan- 

 tain, chick weed, button weed, yarrow and Jimpson weed. 



Under New Jersey conditions it seems that where there are 

 large areas of favorite weed food plants adjacent to fields of melons, 

 a heavy infestation may be quickly produced through migration from 

 the weeds. This may follow a cutting of the weeds or their harden- 

 ing under dry weather or through natural ripening processes. 



Summary of Important Points in Life History 



Plant lice affecting vegetables winter as eggs upon clovers, vetch, 

 weeds and fruit trees. The cabbage aphis and probably the false cab- 

 bage aphis winter also upon the stalks and old leaves of cabbage caul- 

 iflower, etc. 



Hatching occurs in early spring. All lice from spring hatching 

 until fall are females and capable at maturity of bearing living young. 



The first and second and in many cases later generations are 

 produced on fruit trees, clovers, vetch and weeds. Infestation of 

 the vegetable crop takes place by the migration of winged females 

 from the early places of breeding. 



Reproduction on the vegetable crop is rapid, and damage is 

 done before the grower knows that anything is wrong. 



Plant lice are most injurious in the early summer and the early 

 fall because during the high temperatures of midsummer their vigor 

 is impaired and their parasitic enemies destroy them. 



Control of Vegetable Plant-Lice and the Prevention of the Injury 



Which They Do 

 NATURAL CONTROL 



The climate plays a very important part both directly and indi- 

 rectly in combating aphis attacks. Without favorable conditions of 

 weather they do not usually occur. 



Explanation of Figure 7 

 I — Over-wintering egg ; 2 — Just hatched stem mother ; 3 — Matured stem moth- 

 er ; 4 — Winged migrant on way to vegetable field ; 5 — Winged and wing- 

 less lice on various vegetables ; 6 — Winged migrant on way to plants 

 where eggs are to be laid ; 7 — Male and female of the generation which 

 produces the over-wintering egg. These are on the plants where the 

 over-wintering eggs are to be laid 



