2W 



THE AGRICULTURAL NEWS. 



July 28, 1917. 



INSECT NOTES. 



WHITE GRUBS INJURIOUS TO SUGAR- 

 CANE IN PORTO RICO. 



In the last nmiiber of the Agricuhural Ne>cs there wa.s 

 an account of some important investigations which are bei'g 

 carried on by Mr. E. G. Smyth on the five species of May 

 beetles (or hard backs) injurious to sugarcane in Porto Rico 

 Some of the habits of these species were dealt with, and some 

 of the methods of rearing white grubs as used by Mr. Smyth 

 were touched upon. The scientific names of the five species 

 were given, four of them under the genus Phyllophaga 

 (better known as Lachnnsterna), and one under the genus 

 Phy talus. So far as is known at present, none of the Porto 

 Rican species of these beetles occurs in these islands, although 

 closely related species are found in some of the islands. 

 For instance, LacJtnoittrna patruelis occurs in St. Kitts and 

 Dominica, L. patens in St. Vincent and an unknown species 

 •f Lachnosterna is a serious pest to sugar-caue in Antigua. 

 The genus Phytalus is represented by P. smithi in Barbados. 

 The life- history of none of these four species lias been studied, 

 and with the exception of Phytalus xmithi very little is 

 known of their habits. The following details of the life- 

 cycle and habits of I'hyllophaga (Lachnosterna) nandinei as 

 worked out by Mr. Smyth in Porto Rico are in their main 

 features typical of the Other Porto Rican species of Melolon 

 thids, and are of the great interest as giving an idea of what 

 we may expect to find when a more intensive study of our 

 local species comes to be made. 



THE LIFE-CYCLE OF PHYLLOPH.\c,.i (LACHN0STEKN.\) V.\N|iINEI 



Mr. Smyth has found that the life-cycle of this species 

 covers, roughly speaking, one year. The average normal 

 egg-to-adult period covers just ten months, the maximum 

 period being thirteen months, and the minimum period seven 

 months This was calculated from fourteen individuals bred 

 from egg to adult. It was observed that the adult beetle, 

 after issuing from the pupa, may remain underground for 

 a period varying from two weeks to two months. The 

 pre oviposition period, or the time between the emergence 

 above-ground and the beginnirg of egg-laying, was not deter- 

 mined in the laboratory as reared specimens refused to ovi- 

 posit, and it was difficult to ascertain whether specimens 

 caught in the field had just enjerged or rot. But calculating 

 the pre emergence period to average a month and the pre- 

 oviposition period to require about another month this beetle 

 k seen to have a life-cycle 'if virtually one year. Under 

 favourable or adver.se conditions this period may be shortened 

 or lengthened considerably. 



E(.(4. The egg of P. >undinei is o\a\, pearly white, and 

 about j'g-inch long. Iggs are laid among the roots in the 

 soil in >mall globular pits or cavities, the walls of which 

 are cemented or cc mpressed by the ovipositor of the female 

 in such a way that even in dry, sifted soil they remain 

 intact unless subjected to pressure. 



LARVA. These eggs hatch in about two weeks on the 

 average, and the young grubs feed almost entirely upon organic 



matter in the soil until near the first moult, and then begin to 

 attack roots. The average duration of the first instar was 

 found to be thirty-six days, but favouarble or adverse condi- 

 tions tend to shorten or lengthen this period considerably. 

 The duration of the first as well as the other two instars of 

 thL" ground were found to be influenced more by the amount 

 of moisture in the soil, and by the presence or absence of 

 mites, fungus or bacterial diiease than by the amount of 

 food supplied to the grub. 



The average duration of the second instar was found to be 

 forty-seven days, and that of the third instar was 183 days. 

 The length of all the instars was increased by cold and short- 

 ened by warm weather, but the grub never ceases to be active, 

 as is the case in the cold winters further north. The average 

 duration of the whole larval stage was 267 days, the maxi- 

 mum being SoG days and the minimum 179 days This 

 was calculated from fifty larvae of this species reared from 

 egg to pupil stage, and it will be noticed what a great 

 variation there is in the length of the larval stage. 



PRE PDPA. Tovards the end of the third instar the 

 grub begins to get sluggish and stops feeding. The body 

 undergoes certain changes in external appearance, becoming 

 yellow, opaipie and harder to the touch. The actual pre- 

 pupil stage lasts about a week and then the pre-pupa moults. 

 The average duration of the pupal stage, from twenty-two 

 observations, is three weeks. 



AiiuLT. When the adult first issues from the pupa case 

 its body and wing covers are soft, and the latter are white, 

 but in a few hours the beetle becomes a chestnut-brown, 

 and the whole body gradually hardens. As mentioned above, 

 the beetle spends about a month in its pupal cell, until the 

 first heavy rains have so softened the soil that it can dig its 

 way upward to the surface 



FEEDINi; OF AIUJLTS AN1> ATTRACTION TO LIGHT. 



The adult may beetles (or hard backs) do all their feed- 

 ing at night They issue from the ground soon after dark and 

 after a short tlight Listing from fifteen co twenty minutes they 

 begin feeding. They feed on the leaves of plants and trees, 

 and they are described as voracious eaters, sometimes com- 

 pletely stripping simll trees In Porto Rico damage of this 

 nature seems to be caused by general infestations of a severity 

 so far unknown in these islands. The flamboyant and the 

 casuarina are among the favourite food-plants of these beetles 

 and banana and coconut trees are often badly injured by 

 their feeding. 



Observations made by Mr. Smyth show tliat these 

 beetles do not fly long distances but usually hover round the 

 trees near whose bases they hide in their burrows during the 

 day. 



As regards their attraction to light, it was found that 

 'Phyllophaga adults are ordinarily only attracted to light 

 during their flight and before they have .settled on foliage to 

 feed. To have any practical efliciency in attracting these 

 beetles (P. v(mdinei) for destruction a light must be close to 

 the ground, and must be starte.l immediately at dusk, while 

 beetles are flying It need not be lun for over an hour after 

 dark, as time after that is wasted.' 



.MATISi; OVIPOSITION OF FEMALE-S. 



Mating usually takes place between 7 and 8 p.m. Jn 

 the evening, that is, immediately after the cessation of flight. 



Egg-laying takes place underground in the soil near the 

 bases of trees and plants where the young larvae can find 

 the roots. The exact depth has not been determined, but 

 it is probably from 8 to 12 inches, at which depth beetles 

 are usually found in their burrows. 



These notes will be continued in the next issue. 



J.C.H. 



