\2 Landwirtschaftliche und forstliche Biologie. Fischerei. 



This paper is to a large extent a sumniary of various physiological resear- 

 ches on insects, with remarks on their bearing on applied entomology. The first 

 section deals with the "Tropisms", the most interesting of which from the pre- 

 sent point of view is (a) Phototropism. The method of destroying injurious 

 insects by attracting them to artificial light can be traced back as far as 1787: 

 but although trap-lanterns have been developed and improved, very little scien- 

 tific research into the matter has been made. The writer mentions several facts 

 which are known. In the case of a number of species at any rate, the less re- 

 fractive colours of the spectrum (red to green) have been found to exercise by 

 far the strongest attraction (a result agreeing with observations made on fishes). 

 The writer ascertained that among moths attracted to acetylene lamps the Pro- 

 portion of $? increased from Bombycidae upward to Microlepidoptera, and that 

 various groups tended to furnish fixed percentages of $5 among the victims: 

 Bombycidae 4:%, Noctuidae 197o» Geometridae 27^0, Tineina39%. 

 There are also atmospheric conditions, very imperfectly known, which affect the 

 numbers of the sexes flying at night. Phototropism also affects the position of 

 certain insects on plants, etc.: e. g., larvae of Eriocampa adumhrata always try 

 to place themselves so that the rays of light fall vertically on their backs, and 

 hence are found only on the uj)per sides of leaves. (b) Stereotropism: several 

 instances of this "reaction to contact" among insects are given. Many caterpillars 

 when young live huddled together in nests, but later on lead a separate, solitary 

 life: under certain influences their former gregarious liabits can be restored. 

 (c) Rheotropism, one of the most common manifestations of which is the ten- 

 dency of fishes to head against the current. Very little is known of this in con- 

 nection with air-currents, but many insects have a teudency to face the wind 

 (various Diptera, Odonata, Sphingidae). Among Diptera sometimes only t.he c?c? 

 are thus "anemotropous", and the faculty of floating in the air may be closely 

 connected with the possession of holoptic heads by the dS'. (d) Mention is also 

 made of the well-known attractive powers of certain odours. 



The second section deals with "the influence of external and internal factors 

 on the development and life of insects". The destructive effect of hot dry Sum- 

 mers on many insects is referred to. It is sometimes assuraed that the eggs and 

 larvae are dried up, but experiment shows that the heat alone of such summers 

 may be sufficient to destroy them, even when the requisite humidity is present. 

 On the other hand the cold of winter (Avithin normal limits) rather promotes 

 the future well-being of insects: only its occurrence suddenly after mild tempe- 

 ratures, or out of season, proves fatal. In certain species cold (whether ihe cold 

 of winter, or of alpine or polar regions) produces winglessness, especialiy in 

 the ?: this is very noticeable in the Lepidoptera and Diptera of Alpine and Po- 

 lar regions, and in certain Lepidoptera with apterous J? which appear in winter 

 [Cheimaiobia hnnnala, etc.). In some cases artificial refrigeration of pupae pro- 

 duces wingless imagos, but cooling or heating of larvae has no effect on the 

 wings. The effects of humidity are also dealt with, it being mentioned that in 

 a very humid atmosphere certain larvae which normally spin cocoons pupate 

 without so doing. 



Various other points are dealt with in this section, including what the au- 

 thor speaks of as a "Physiology of the Seasons" and the possibilities of lengthe- 

 ning or shortening normal resting periods by artificial means. "The physiological 

 effects of insecticides" are briefly discussed in a third section, and a bibliography 

 is added. H. Scott (Cambridge). 



