THK WAI'KK-CKESS LEAF-F.KKTLK. 19 



adults attack the cuticle of the stem after feeding on the leaves, as 

 has been noticed in the case of armo7xwia?. E. A. Fitch has ob- 

 served the partiality of the latter for water cress and other crueif- 

 ers which grow in watery places and mentions the destruction of an 

 entire crop of horseradish. 



Kaltenbach " records, according to (jrN'llenhall and his own obser- 

 vations, Veronica beccahunga, Cardamine amara., and Cochlearia 

 (innoracia or horsei'adish as food plants, and states that the larva 

 undergoes metamorphosis in the earth, the pupa state lasting four- 

 teen days. Cornelius '' is cited as having observed two generations, 

 the si)ring generation being found in ^Nfay and June and the second in 

 Sei^t ember. Thonuis II. Hart records the water starwort of England 

 {Callitricha renia) as another host plant. T. R. Billups,*^ an ento- 

 mologist as well as truck grower, mentioning this species as Phadon 

 het>d((\ states that it is " one of the greatest insect pests the mai-ket 

 gardeners around London have to contend with." Our American 

 species undoubtedly hibernate as adults and ai)pear in early ■spring- 

 under boards and similai- shelter. 



METHODS OF CONTROL. 



How to succe.ssfully control this insect under ordinary conditions 

 is quite a problem. Paris green Avas tried by our correspondent, 

 mixed with flour and sprinkled over the plants when the dew was on, 

 and this reduced the numbers of the insect somewhat. Owing to the 

 moist condition of the plants, howevei-. the flour formed a paste 

 which stuck like glue, and it was therefore abandoned. Applied in 

 water it rolled otf the plants. AVe were not infojined if this appli- 

 cation was made with a spraying machine. If the [)lants were 

 sprayed lightly with a flne spray, it might answer, or, better, Paris 

 green diy Avith (mly 20 parts of flour, or plaster or air-slaked lime. 

 An arsenical should not be used within about a week of the time of 

 cutting the cress for market. In the case of Paris green there is 

 practical!}^ no danger of poisoning even if it were used later, as the 

 washing which is given the cress will carry away all perceptible 

 traces of the poison. 



If conditions should be such that the pond or stream in which 

 water cress infested b}^ this species is growing could be completely 

 o\ HTllowed, it would cause the insects to rise to the surface, and in the 

 ca.se of running water would wash tiiem downstream. Flooding 

 alone jniglit not entirely solve the problem, as these beetles are able to 

 survive considerable immersion. 



AVhen the cress is grown in sufficiently large bodies of water ex- 



1 Pfliinzenfeiiule. p. 2(!; '< Slett. Kiit. Zeif.. 1,S(«. p. 12^; '■ Tbe KntonioIoRist. 

 Vol. XIV. 1881, p. 2.36. 



