42 



THE AGRICULTURAL NEWS. 



Febrdaey 8, 1912. 



INSECT NOTES. 



THE MELON OR COTTON AI'HLS 



The University of Nebraska has recently issued a Press 

 Bulletin (No. 34, June 1911) entitled The Control of the 

 Melon Aphis {Aphis ijossyjni, .Glover). The following i.s an 

 abstract of that bulletin, but as this insect is known in the 

 West Indies on account of its attacks on the cotton plant 

 rather than on account of its importance as a pest of melons, 

 these notes are given a heading which indicates that fact. 



The nlelon aphis is the most serious pest of melons and 

 cucumbers in many localities in the United States where 

 the.'^e crop.s are largely grown. It is recorded as badly affect- 

 ing cotton in the Southern States, Mexico, Brazil, South 

 Africa and Australia, and is probably of tropical origin. 



IN.JURY. The loss of crops in Nebraska alone from the 

 melon aphis aggregates thousands of dollars annually. 



This insect possesses sucking mouth part.s, by means of 

 which it punctures the plant tissues and sucks out the sap. 

 It occurs most generally on the under side of the leaves, which 

 assume a wrinkled and distorted appearance. The melon aphis 

 is capable of remarkably rapid reproduction, and the feeding 

 of the enormous numbers of individuals quickly results in the 

 death of the leaves, and eventually of the plants. 



Aphids secrete a sweetish, sticky substance, known as 

 honey-dew, which forms a coating on the under side of the 

 leaves. The cast skins of the insects are held by the honey- 

 dew, and this results in an appearance which is characteristic 

 of the attacks of aphids. In the Wect Indies this honey-dew 

 supports the fungus growth known as black blight. 



LIFE HISTORY. The life-history of the melon aphis is not 

 yet known in all its details. In Nebraska, the first aphids to 

 appear on melons and cucumbers are seen in June; they are 

 winged females, which have probably flown into the fields from 

 weeds on which they have spent the winter. Cool, rainy 

 weather during the spring seems to be especially favouralile to 

 the rapid multiplication of these insects. The over-wintered 

 females give birth to six to twelve young per day for some 

 time. The young grow rapidly, and in about eight days become 

 wingless adults capable of producing another generation of 

 young The adult insect is a soft bodied, sluggish plant 

 louse from -}^- to ji-inch in length: the wing expanse of the 

 winged forms is from i- to |-inch. 



The colour of this insect is variable, the individuals of 

 any colony often range from a uniform pale green through all 

 degrees of mottling to a pale yellow or almost black. 



CONTROL. The melon aphis is attacked by a large 

 number of natural enemies, including internal hymenopterous 

 parasites and several kinds of predaceous insects such as 

 lady bird beetles and their larvae, and the larvae of Syrphus 

 flies and lace-wing Hies. 



Artificial control includes the processes of spraying and 

 fumigating. In spraying, the under surface of the leaves 

 must be reached by the spray fluid. For this purpose, 

 a nozzle extension with a bend near the end to which the 

 Vermorel nozzle i.s attached may be made from a short length 

 of gas pipe. Tlie leaves of melons and cucumbers are tender, 

 and much force must not be used in applying the spray as 

 they may be injAred. 



Kerosene emulsion and other strong, oily washes are 

 not recommended for use on these plants, since they often 

 injure the leaves A mixture of soap and tobacco is prepared 

 by dissolving 1| ft>. of soap in 2 quarts of water and adding an 

 equal amount of strong tobacco decoction. This is diluted at 

 the rate of 1 part to 4 parts of water. A commercial product 

 of tobacco known as Black Leaf Extract is very useful for 

 this purpose. It is diluted at the rate of 1 part to 50 of 

 water, and at this strength is effective against the aphis, and 

 does not injure the tender leaves 



Fumigation with carbon bisulphide is useful in dealing 

 with a limited number of plants. A tight tub, bucket, box 

 etc. inverted over the plants makes a satisfactory fumigating 

 chamber in which carbon bisulphide at the rate of 1 teaspoon- 

 ful per cubic foot of enclosed space may be evaporated. 

 This treatment will kill the aphis and not injure the plants. 

 For use on a large scale, cages or tents are recommended. 

 These are 4x6 feet in area and about 8 inches to 1 foot in 

 height, made of light wooden frames covered with cloth 

 which may be oiled to render it more impervious, although 

 good results are obtained even when the oiling is omitted. 

 The enclosed, plants are fumigated for fifteen minutes, by 

 means of a commercial tobacco fumigant such as ' To-bak-ine ' 

 ' Nico-fume '. 



Clean culture is strongly recommended as a means of 

 reducing the numbers of thi,s pest. All old vines should be 

 collected and burned as soon as the crop is harvested, and all 

 weeds in the fields and vicinity should also be destroyed, 

 since the.se harbour the aphis during winter. 



THE NATURE OF THE LIGHT EMITTED 

 BY FIRE-FLIES. 



The nature of the light emitted by fire-flies has been the 

 subject of speculation for many years, and it has generally 

 been described as phosphorescent. An article in Nature for 

 November 23, 1911, from which the following notes are ab- 

 stracted, gives results of experiments in testing the light given 

 by fire flies, by means of photographic plates. 



The investigators who carried out the experiments, state 

 that they observed the beautiful green fluorescence of the light 

 emitted by an insect of the genus Luciola, of the family 

 Malacodermidae, and were led to enquire whether the light 

 was of the nature of the X-rays produced in the Crookes tube. 



An enquiry was instituted to see how this light affected 

 photographic plates, especially when media of several sorts 

 were interposed between the plates and the source of light. The 

 media tried were wood, dark-brown leather, fie.sh (nuutm) and 

 black paper. After several trials, it was found that iliu plates 

 were affected. after exposure for two hours through flesh and 

 black paper, and three hours through le.ither and wood. 



The trials showed further that, as far as its effect on 

 photographic plates is concerned, insect light is similar in 

 intensity to lamplight, but it also has the important charac- 

 teristic that this intensity is not varied, even when objects 

 opaque to ordinary light are interposed between the insect 

 and the plate. This light is intercepted by glass, in which 

 respect also it ditters from ordinary light. 



It is concluded that the light of the fire-tty experimented 

 with is not phosphorescent. It may, on the other hand, be 

 premature to conclude that the light rays emitted by the 

 insect are the same as X-rays, but it may safely be asserted 

 that they are similar to the X rays and the ultra violet light, 

 in that they render certain opaque media transparent, and 

 are intercepted by glass. 



