218 



THE AGRICULTURAL NEWS. 



July U, 1917. 



INSECT NOTES. 



WHITE GRUBS INJURING SUGAR-CANE 

 IN PORTO RIOO 



In the Journal of the Department of Agriculture of 

 Porto Rico, Vol. I, No. 2, Mr. Eugene G. Smyth, Acting 

 Entomologist of the Insular Experiment Station, gives an 

 account of some of the observations that have been made by 

 him during the past four years in studying the life-histories 

 of the species of white grubs injurious to the sugar cane in 

 Porto Eico. Mr. Smyth has during this period studied the life- 

 histories of ten species of white grubs, five belonging to the 

 tribe Melolonthini, and five belonging to the tribe Dynastini, 

 of the family .Scarabaeiclae, to which the white grubs belong. 

 In this paper the five species of Melolonthid.s are dealt with, 

 while the results of the work on the remaining five species 

 of Dyna.stids are promised in a later paper. 



Sugar-cane is grown over large areas in Porto Kico 

 under conditions favourable for the rapid development of 

 these insects, and is grown continuously year after year on the 

 same ground without rotation of crops, so that the control 

 of these pests is a difficult problem. 



The experiments carried out in Porto Rico prior to 

 1913, when the present investigations were begun, consisted 

 mainly in the introduction of poison baits and fumigants 

 into the soil, the use of deterrents on the soil near plants to 

 prevent egg laying, the flooding of the land with water and 

 the destruction of the adult beetles by spraying the leaves 

 with poisons Many of these measures failed to give satis- 

 factory results, and those that .seemed worthy of a further 

 trial have since turned out to be impracticable by reason of 

 the high cost of materials or of application. Mr. Smyth goes on 

 to say that 'it became increasingly apparent that no hope of 

 solution of a problem could come from an application of 

 direct methods of control such as these, but that real benefit 

 to the cane-growing industry could come only through the 

 employment of broadly outlined cultural methods of control, 

 ba.sed upon an accurate knowledge of the insects' life-histories, 

 or perhaps through thf introduction of insect or fungus 

 parasites to prey upon the white grubs ' 



Outside of Europe, until quite recently very little was 

 known about the length of the life-cycle of any of the 

 .species of Melolonthid beetles. In 1912 Mr. d' Emmerez de 

 Charmoy published a report on Phytalus smithi in Mauri- 

 tius, establishing the maximum and minimum number of days 

 required for each of the three stages — egg, larval, and pupal 

 — in the life-cycle of this specie.s, but not determining the 

 length of the separate instars iu the larval stage of the grub. 



In 1916 Mr. J. J. Davis published an article in the 

 Journal of Econonac Entomology, Vol. IX, No. 2, giving 

 the results of .some experiments in rearing Lachnosterna at 

 Lafayette, Indiana. Mr. Davis succeeded in determining the 

 life-cycles of eighteen species of beetles of the genus Lach- 

 nosterna, and found that of the eighteen species, eleven have 

 an invariable life-cycle of three years, one invariably has 

 a life-cycle of two years, three have a life-cycle varying from 

 two to three years, and in the case of two others the life-cycle 

 varies from three to four years. It will be noticed that in 

 a temperature having a cold winter like Indiana, the life- 



cycles of these beetles is never le.ss than two years, and is 

 generally much longer. 



As a result of his studies during the past four years, 

 Mr. Smyth has established the fact that all four Porto Rican 

 species of Lachnosterna as well as the single species of 

 Phytalus have a life-cycle of one year or less, and at the same 

 time he has determined accurately the lengths of the instars 

 of the grub. It may be mentioned that an instar is the 

 period between moults; for instance, the time elapsing between 

 the hatching of the egg and the first moult is the first instar. 

 Mr. Smyth has found that the four species of Lachnos- 

 terna (or Phyllophaga) are all new to Science, as well as the 

 single species of Phytalus. They are being described by him 

 under the names I'hyllojiluiga vandinei, P. portoricensis, 

 P. guanicana, P. citri, and Phytalus insularis. 



CJf these species P. vandinei is the worst pest of sugar- 

 cane in Porto Rico. Some idea of the serious nature of this 

 pest may be gathered from the fact that on one sugar estate 

 4,723,000, and -t, 087, 000 grubs were collected over a period 

 of two years. Allowing 400 beetles to the quart and 300 

 grubs to the quart, these figures represent 369 bushels of 

 beetles and 426 bushels of grubs; the total cost of collection 

 was $6,154'37. In spite of these measures this pest is not 

 being controlled, but continues to increase. This species 

 is fortunately confined to a definite area equivalent to about 

 one-third of the area of the island. 



Mr. .Smyth gives an account of the methods of rearing 

 white grubs, and data on the habits and life-history of 

 Phyllophaga vandinei which are of great interest Most of 

 the work in connexion with white grubs has been done witli 

 this species, so that more is known about it than about any 

 of the other white grubs injurious to sugarcane in Porto 

 Rico. 



METHOriS OF REARING WBITE GRUBS. 



At first there was some difficulty in determining the 

 possible duration of the egg-laying period of adult female 

 beetles, since beetles confined in numbers in a cage or jar 

 with potted plants suflFered a heavy mortality, possibly due 

 to a fungus disease. Later it was found that beetles could 

 live fairly normally in confinement without the necessity of 

 flying or climbing. Beetles were collected after mating, and 

 each female was confined singly in a small battery jar with 

 some finely sifted moistened earth at the bottom and a piece 

 of banana leaf previously dijiped in water. The leaf was 

 put in above the soil and served for food for two or three 

 days. After various experiments in rearing eggs the simplest 

 method was to place the eggs over damp soil in shallow glass 

 petri dishes, care being taken to keep these in a situation of 

 little exposure and of uniform temperature, and to see that 

 the soil be sterile, so as to prevent attacks by mites and 

 nematodes, to which the eggs are very susceptible. 



As soon as the grubs hatched they were placed in small, 

 round tin boxes containing sifted, moistened soil. The grubs 

 were put in small pits made in the soil, as it was found that 

 if placed on the surface they are often unable to penetrate. 

 The young grubs seem to feed almost entirely on the organic 

 matter in the soil until near the first moult. Food was then 

 supplied in the shape of a grain of corn to each box, and 

 a new grain was not put in until the old one had been entirely 

 eaten, germinating roots and all. An excess of food in a box 

 invariably encouraged mites, which attacked the grub some- 

 times killing it, unless they were brushed off in time and 

 fresh earth supplied. The use of these tin boxes was found 

 to be more convenient than larger cages, such as flower pota 

 or battery jars, since the grubs could be more easily exposed 

 to observation without disturbing them too much. Towards 

 the end of the third instar the full-grown grub becomes soft 

 and flabby and lies inert on its back at the bottom of the 



