547 



RiEHM (E). Priifung von Pflanzenschutzmitteln im Jahre 1920. 



[An Examination in 1920 of Preparations for protecting Plants.] — 

 Mitt. Biol. Reichsanst. Land- it. Forstw., Berlin, no. 20, July 

 1921, 47 pp. [Received 24th September 1921.] 



This paper summarises the results published in 1920. A similar 

 summary for 1919 has already been noticed [R. A.E., A, ix, 398]. 



BoRNER (C). Insekten-Zeitschliissel. [Diagrams of Insect Develop- 

 ment in Relation to the Calendar.] — Arb. Biol. Reichsanst. Land- 

 11. Forstw., Berlin, x, no. 5, 1921, pp. 395-404. 



Many diagrams and formulae have been invented to portray the 

 development of a given insect and its progeny in relation to the 

 calendar, the " calendar-keys " in Judeich and Nitsche's handbook on 

 Central European forest insects, which apply to species with a simple 

 succession of generations, being the best known. For insects with a 

 variable generation, such as Aphids, the author's circle-diagram 

 keys have been used since 1906. The Judeich-Nitsche system was 

 modified and perfected by Rhumbler [R.A.E., A, viii, 269] so that 

 the keys can be printed in ordinary type with existing typographical 

 characters. 



The improvements described here are based on Rhumbler's system, 

 but avoid his differential treatment between insects with complete 

 and incomplete metamorphosis. They permit the representation of a 

 life-cycle extending over several years, and of one lasting only a part 

 of a year, and can also serve for several successive generations. 



Examples comparing the Judeich-Nitsche, Rhumbler and new 

 systems are given, and the author's circle-diagrams are also shown. 



BoRNER (C), Blunck (H.), Speyer (W.) & Dampf (A.). Beitrage zur 

 Kenntnis vom Massenwechsel (Gradation) schadlicher Insekten. 



[Contributions to the Knowledge of the varying Abundance of 

 injurious Insects.] — Arb. Biol. Reichsanst. Land- ii. Forstw., 

 Berlin, x, no. 5, 1921, pp. 405-466, 12 figs. 



As any organism that is only occasionally injurious may develop 

 into a serious pest under certain conditions, the applied zoologist 

 should not confine his attention exclusively to known pests. A pest 

 becomes more dangerous as its ecological requirements are increasingly 

 met by the environment. Any reversal of this must check its spread, 

 and the practical significance of such cases should be investigated. 



The present investigations included many series of catches aiming 

 at establishing the numerical occurrence of a pest in a given locality. 

 The catch made with thirty wide sweeps of a net was taken as a unit. 

 The number of eggs and larvae was determined by counts at definite 

 intervals, the entire plant being removed carefully in the case of 

 larvae, such as those of Meligethes acneiis, that abandon their food- 

 plant when it withers. 



In 1920 the work was chiefly on Meligethes aenens, F., and on the flea- 

 beetles, Psylliodes chrysocephala, L., Phyllotreta atra, F., P. nigripes, F., 

 P. undidata, Kutsch., and P.vittula, Redt. The weevils, Ccidhorrhynchns 

 assimilis, Payk., C. riibsaameni, Kolbe, C. sulcicollis, Thoms., and 

 C. qiiadridens, Panz., were also subjects of inquiry. The investigations 

 are dealt with in detail, and from the figures obtained in the summer of 

 1920 data of practical value to rape cultivation in Central Europe 



