330 



THE AGKICULTURAL NEWS, 



October 20, 1917. 



INSECT NOTES. 



SUGAR-CANE WHITE GRUBS IN 



PORTO RICO. 



It may be remembered that in recent numbers of 

 the Agricultural News an account was given of some white 

 grubs injuiious to sugarcane in Porto Rico, as studied by 

 Mr. Eugene G. Smyth of the Insular Experiment Station. 

 In the issue of July li mention was made of five species of 

 hard-back beetles (the larvae of which are white grubs), 

 and it was noted that four of these belonged to the genus 

 Phyllophat:a (or Lachnosterna) and one to the genus Phytalus. 

 Some of the methods of rearing white grub« were also given. 

 Under the date of July 28 appeared a summary of the life- 

 cycle and habits of the most important of these species, viz. 

 the sugarcane white grub (thyllophaga vavdinei). In the 

 issue of August 1 1 the natural enemies of these white grubs 

 in Porto Rico were reviewed. The results of the above 

 investigations were published in the Journal of the 

 Department of Agriculture of Porto Rico, Vol. I, No. 2, and 

 the details of the habits and life-cycles of the four remaining 

 species have recently appeared in Vol. I, No. 3 of the same 

 journal. The life-histories of these four species are very 

 similar to that of P. vajidinei given on July 28, so that it is 

 unnecessary to refer to them in detail. The notes on the 

 feeding habits of these species are of interest, however, and 

 are referred to below under each species. 



The common white grub (F. pnrtoricensif) has a much 

 wider distribution in Porto Rico than P. mindiriei, occupying 

 at present approximately the eastern two-thirds of the i.sland. 

 It is not, however, very prominent as a pest of sugar-cane, 

 but has been found to be particularly injurious in the grub 

 stage to coffee groves and pine-apple plantations. The 

 damage to coSee groves is due to the fact that coffee is grown 

 under certain forest shade trees, to the leaves of which the 

 beetles are very partial. Mr. Smyth states that after 

 feeding, the beetles descend to the coffee trees beneath 

 the larger shade trees, burrow down into the soil in great 

 numbers at their bases, and there deposit their eggs 

 'The beetles do not feed upon the coffee foliage, but that 

 fact does not, however, prevent the larvae from attacking the 

 coffee roots.' As in the case of P. vandiuei, the adults of this 

 species, P. portoncensis, are sometimes very destructive to the 

 foliage of banana, casuarina, and flamboyant; they also feed 

 on the leaves of many other trees and plants, including Indian 

 almond, coco-nut, breadfruit, bamboo, avocado, cacao, and 

 mango. 



There is one strange characteristic which has been noticed 

 in connexion with the feeding habits of this species, namely, 

 that large numbers of the a<lults are often found in the soil 

 at the bases of trees and weeds upon which they do not feed, 

 such as coffee or young citrus trees, while they are seldom 

 found »t the bases of certain trees to the foliage of which 

 they are very partial, such as banana and coco-nut trees. 

 This habit 'is explained by the fact that the beetles before 

 retiring to the soil for the day after feeding, take flight and 



alight upon small trees or weeds, or upon any upright 

 object affording them a good fool purchase, down which they 

 crawl to the soil and enter it. Their holes are thus often 

 found around the bases of posts and dead weeds. Banana 

 trees are too smooth to offer good foot purchase, hence ihey 

 are not settled upon; and coco-nut palms are provided with a 

 heavy abutment of closely interwoven rooi.s at the base that 

 prevent the beetles from reaching the ground from them.' 



. The south coast white grub (P. guarticana) is so called 

 from its occurrence in the Guanica District of the south- 

 west coast of Porto Rico, and so far it seems to be confined 

 to that locality. It is not of much importance as a sugar- 

 cane pest in comparison with P. vandinei, which aUo occurs 

 in the same district. Collections of beetles made from 

 March to June 1911 in cane fields showed that P. gaanicana 

 adults amounted to less than 1 per cent, of the total, the 

 remainder being adults of /'. vandinei. Outside of cane- 

 helds however, this species is just as abundant as 

 P. vandinei in the spring, and it was observed that this 

 species feeds mainly upon trees and planti not frequented 

 by the larger species, P. vatidinei; for instance, the adults of 

 P. guani'-ana are found abundant on leaves of Lantana 

 raiiiani, the black sage {Cordia cyiindi osi-achy i), and the 

 ucar tree (Bucida huceras) — known in Antigua as White wood, 

 and in Barbados as White Cedar — which are all upland species 

 growing along fences or scattered through pasture land. 

 They also feed on tiie leaves of flamb lyant, casuarina, 

 tamarind, and guava, among others. It is thought thic the 

 grub of tliis species may be a sod-frequenter, preferring dry 

 upland soils, and that it has not yet got into the cane fields 

 to any extent 



The citrus white grub (P. citri) gets its name from the 

 fact that, although it has a large variety of food-plants, 

 it is primarily a pest of citrus trees. The beetles feed on 

 the leaves of grape fruit and orange among other food-plants, 

 and the grubs injure the citrus roots, the damage being 

 more evident in the case of young trees than of old. This 

 seems to be the most widely distributed species of Phyl- 

 lophaga in Porto Rico. The citrus groves in the north and 

 west of the island suffer considerable damage from this pest, 

 and even such measures as spraying or hand collecting 

 appear to give only temporary relief. This species attacks 

 a large variety of trees and plants, and must be considered 

 an important general crop pest. 



The little brown may-beetle {Phytalus insularis) is by 

 far the smallest of the five Porto Rican species of Melo- 

 lonthids. It is probably generally distributed over the 

 western two-thirds of the island, but is not of much 

 importance as a cane pest. Its life-cycle is similar to those 

 of Phyllopha^a, and occupies just about a year. Its range 

 of food- plants seems to be rather small as compared with the 

 other species, since the beetles are only recorded as 

 feeding on pigweed {Amarantfius spp.). Para grass (Panicum 

 harbinode), and Lantana involucrata, to any great extent. 



N-VTUR.\L ENEMIES. 



The insect and fungus enemies of the above four species 

 of white grubs, so far as they have been observed, are identical 

 with those given for P vundtnei in the Agricultural Neiaior 

 August 11, 1917. The predaceous wire worm (Pyroplurrus 

 luminosas) is the most important enemy of the grubs of 

 P. pwtoricensis and P. citri, but has not been observed in 

 relation to P. guanicana or P. insularis. The parasitic 

 Tachinid fly (Crypiomeigenia aurifacies) is u.seful against th« 

 adults of P. portoricensis, and it is thought that it may 

 attack P. citri Another Tachinid is known to be a useful 

 parasite of P. vandinei. but the other hosts of this fly have 

 not as yet been exactly determined. 



