578 



unfolding leaves of some grasses. When attacked by a dozen or more 

 individuals at one time, the leaves become badly mutilated in a few 

 hours and soon acquire a rusty appearance. The injury often becomes 

 serious by preventing the new shoot from developing. The heads are 

 first attacked when in blossom, the pollen being eaten and the stamens 

 and pistils badly damaged, so that destruction of embryo seeds occurs. 

 As soon as the grains begin to form, the thrips attack the husk, and 

 later the tender integument of the newly forming grain, remaining on 

 the wheat head until it becomes dry. Both adults and larvae have 

 been foimd hibernating beneath the sheaths of the following grasses : 

 Andropogon scoparius, A. furcatus, Poa pratensis, Agropyron smithii 

 and Tripsacimi dacfyloides. None of the stages of this pest have been 

 fomid hibernating in Panicutn crus-gaUi or Syntherisma sanguinalis, 

 which become quite dead and dry after the first frost. Triplileps 

 insidiosus, Say, and the larvae of (Jhrysopo. ocuJata, F., are among the 

 more important enemies of P. cognatus. No Cocinellids or birds have 

 been observed feeding on them and no parasites have been reared. 

 No really practical remedy can be suggested for the control of this 

 pest. Where possible, the burning off of all grasses will destroy large 

 numbers. Early ploughing appears to be useful, and fields ploughed 

 in June and harrowed in July, were less attacked ; they contained 

 practically no self-sown wheat. These measures give less opportunity 

 for the thrips to increase in numbers sufficient to damage the crop. 



Parker (J. K.). Influence of Soil Moisture upon the Rate of Increase 

 in Sugar-Beet Root-Louse Colonies. — Jl. Agric. Research, Wash- 

 ington, D.C., iv, no. 3, Jane 1915, pp. 241-250. 



Outside fields of the sugar-beet {Beta vulgaris), the subterranean 

 form of the sugar-beet root-louse, Petriphigus betae, Doane, is most 

 commonly found upon lamb's -quarters {Chenopodium album, L.) 

 growing in dry situations ; in damp situations it is rarely heavily 

 infested. In the beet fields it has often been noticed that the Aphids 

 are most abundant and that injury first appears where the soil is driest. 

 A striking illustration of this was observed in a large sugar-beet field 

 which was cut diagonally by a depression in which the ground remained 

 moist without irrigation during the entire summer. In October, beets 

 were growing well in the moist soil and no Aphids could be found upon 

 them, while in the drier soil, around the borders of the depression, 

 every plant was heavily infested. From a large amount of data, it 

 seems safe to assume that soil moisture is a very important factor in 

 controlling the rate of increase in colonies of this pest. During the 

 first year's experiments irrigation greatly reduced the numbers, and 

 it is hoped that a system of irrigation may be arrived at which will 

 reduce injury by P. betae to a negligible amount without interfering 

 with the approved cultural methods. The principal immediate 

 source of infestation of sugar-beets is the presence of the cotton woods, 

 Popidiis balsatnifera, L., and P. angiistifolia, James, upon which the 

 Aphid develops galls in the spring. During the latter part of June 

 and early July, some of the numerous migrants fly from the galls to 

 the sugar-beets, where they deposit living young, which descend to 

 the roots and start new colonies. It has been found very difficult to 

 induce the progeny of migrants to colonise upon sugar-beets in soil 



