37S 



THE AGRICULTURAL NEWS. 



November 18, 1916. 



INSECT NOTES, 



METHODS OF CONTROLLING WHITE 



GRUBS IN AMERICA. 



The recDrcls of investigations on the white grub 

 (Lachvosterna spp.) in Wisconsin, abstracted in the 

 Review of Applied Entoviology (Vol. IV, Ser. A, 

 Part 7), are of interest in connexion with the efforts 

 to control this pest in the West Indies, ('ollection of 

 the adults appears to be th(^ most efifective method of 

 control, and the statements regarding the situation of 

 the traps in regard to light, etc, shonld be noted. 



In the experiments carried out in Wisconsin in 19 1 11 5 

 in connexion with Lachnostema, the factors considered 

 were: (1) the determinations of conditions; (2) the crops 

 most seriously damaged with and without rotation; (3) the 

 species present and the habits, lifehi.story, flistiibution and 

 means of control. Lanternlraps were used to collect the beetles. 

 They consi.stcd of the Coleman gasoline arc lantern, from 300 

 to 400 candle power, set into galvanized refrigerator pans, 

 5 inches deep and 24 inches in diameter. The pans were 

 filled about two- thirds full of water and I pint kerosene 

 was poured on this and renewed when necessary. Perforated 

 skimmers were used to remove captured in.sccts. Results 

 were obtained relating to the distribution of species over 

 a comparatively limited area, the optinnjm temperature for 

 flights, and the most favourable location and arrangement 

 of light traps. Seventeen out of the nineteen species known 

 to occur in Wisccmsin were taken in the traps. //. f'tisca 

 was most widely distributed and dominant at Lancaster and 

 Dodgeville. L. ruijoia was dominant at the northeast 

 stations, and L. implicita at Ripon. Males only of 

 L. gi/ibotia and L. niiida were attracted to the lantern, and 

 L. tristis only to a slight degree Several species disappeared 

 at the stations furthest to the north-east, while L. rugosa, 

 L. dtih-ia, and L. graiidu increa.sed in numbers. />. ihihia 

 emerged very early, before May 21 at Dodgeville, and to the 

 extent of 92 per cent, before this date at Baraboo. Flight was 

 found to cease ahnosfe entirely at 62° F. Large pans were 

 found to be desirable; the number of beetles caught in a pan 

 placed by the side of the central pan towards the origin of 

 flight was twice as great as in a |)an placed behind the light. 

 At the La.ioa»ler station flight was always from the north- 

 west towards the .south east. Tr^ps near the margin of woods 

 or close to a fringe of trees were mo.st successful. At Lanaister, 

 more than 440,OUO beetles were taken during the summer, 

 and the maize crop was not noticeably injured. The smallne-ss 

 of the damiige may have been due to the destruction of many 

 beetles by diseases, and the frequent and heavy rains. The 

 cost for fifteen light traps was from Is. to Is. '■kl. a day. The 

 numbers of males caught exceeded the number of females. 

 This is the normal condition, and if, as has been suggested, 

 the beetles are polyandrous, there may be an advantage in 

 catching a larger number f)f males. I""emales of the more 

 common species formed a larger percentage of the catch in 

 the early part of tlie season tlian did males. 



In the biological experiments undertaken to investigate 

 the habits of white grubs, glass cages were used in which earth 

 was placed between two vertical glass plates less than i-iuch 

 apart. The rages were shielded from the light except at the 

 moment of examination. By regulating the distance between 

 the plates larvae of any size could be viewed from at least 

 one side. The results were as follows: ( 1 ) No daily migra- 

 tion was observed; movements and feeding occurred only in 

 warm weather, activity reaching a maximum during the 

 heat of the day; the optimum temperature was between 60' F. 

 and 65° F. (2) The food apparently consisted entirely of 

 the roots of plants. (3) Larvae were reared from May 5 to 

 July IS in soil without apparent food: the soil was then 

 allowed to dry, and on October 22 two larvae were alive and 

 active, starvation methodi for control are therefore 

 useless. (4) Poisoned bran mash was not eaten by the 

 larvae and was thus of no value. (5) Sjdiura arsenite, into 

 which griss roots were dipped before planting, resulted in 

 the death of 222 per cent, of larvae in four days; no injury 

 to the grass was ob^rved. Corrosive sublimate used on one 

 plant caused a mortality of 50 per cent., but the plant died, 

 since the roots were entirely eaten. (6) Kerosene emulsion 

 and Black l^eaf 40, at the ordinary strengths, were useless. 

 (7 1 Creosote acted aw a rep?ll""t. M-irl did not injure the treated 

 plants. In the eontfol pots a mortality of 1.59 per cent., due 

 to bacterial and other disea.scs, was observed. Results in 

 connexion with temperature and nature of food supply seemed 

 most significant. 



THE DEVELOPMENT OF RHODESIA. 



Information of interest to the West Indies is from 

 time to time derived from agricultural activities in 

 Rhodesia, and it \vill perhaps prove instructive to give 

 an accotiut of the general agricultural conditions in 

 that country. These are well described in a paper on 

 the Oevelopment of Riiodesia from a Geographical 

 Stand-point, ajipeiiring in Tlie Geognq^ldcal Joiirmd 

 for October IMKi. 



The stoek-raising, agricultural, and horticultural indus- 

 tries of Kliodesia"have hitherto been mainly confined to 

 regions situated on the plateaux at an altitude of not less 

 than 3,.500 feet. No':hing has as yet been done to di'velop 

 those portions of the territory which, owing to their low 

 elevation, possess a more tropical climate Agricultural 

 development is inirc^ver, for the present for obvious reasons, 

 practically confined to districts which are situated not more 

 than 25 miles from a railway. Stock farmers can, of course, 

 go further afield. ' 



P>oth Northern and Southern Rhodesia are first-rate 

 stock countries, but the extent of th- areas in Northern 

 Rhodesia suited for stock-raising is necessarily limited by the 

 distribution of the tsct.so fiy. F>jiu.i...,it!y the lx4rotse 

 Valley on the upper Zambesi and the Middle Kafue are 

 both free from fly, and are capable of carrying very large 

 herds. In Southern liliodesia the I';sr c.i tie districts for 

 ranching purposes are to be found in .Maiabeleland, which 

 in Lobengulas time was heavily stocked. Mashonaland is 

 also a good cattle country, but owing to its higher rainfall 

 it is generally more suitable for the fattening of stock and 

 dairy! tig than for ranching. 



The chief grain centres of the fcciritory occur in 

 .Southern Rhodesia, in the vicinity of Salisbury, notably 

 on the Owebi Flats, and in the Mazoe Valley, and in the 

 Victoria District. In Nnrllicrn Pdiodesia the best grain 

 districts are to be found in the Kafue neighbourhood. Maize 



