410 



TciE AGKicLiLTUKAL NEWS, 



December 16, lS>It 



INSECT NOTES. 



PESTS OF SUGAR-CANE IN BRITISH 

 GUIANA. 



In the present and succeeding number ("if the Ai/ricultunil 

 A'eus it is proposed to give a review of the last two reports 

 by Mr. H. W. B. Moore, Entomologist for a number of 

 estates in British Guiana. These two reports cover the years 

 U»14 and 191-"). The report for 1912 was reviewed in the 

 Agricultural Neir:i for August 1 6 and 30,1913 (Vol. XII, 

 pp. 266 and 282), while that for 1913 was taken up in the 

 number for July 18,1914 (Vol. XIII, p. 234). 



The reports for 1914 and 1915 are concerned entirely 

 with the insect pests of the sugarcane, and are not only of 

 great interest as showing what can be done in the way of 

 control by efficient organization and co-operation, but are of 

 considerable value as records of the diffeient pesls with their 

 parasites, predators and other natural enemies. 



It is intended in the present article to confine attention 

 to the small black hard back, which has only recently come 

 into prominence as a pest in British Guiana 



THE SMALL BL.\CK IHED Ii.\( K {DifscineUni bidenhiHis). 



In 1914an outbrenk of the small black hard back on young 

 canes after the heavy rains brought this insect into imme- 

 diate prominence on all the estates but five of them suffered 

 heavily. The adults, which do all the damage, attacked the 

 young shoots in such numbers that all these were killed oft' 

 as they sprouted, and in many ca.ses the beetles bored in and 

 destroyed everything from which fresh shoots could grow. 

 E.xperiments were undertaken in the worst infested fields to 

 dertemine the amount of infestation, and the.se experiments 

 showed that the small black hard back alone was responsible 

 for about 7.") percent, of the dead hearts, while the smaller 

 moth borers accounted for the remaining 25 per cent. This 

 infestation continued on all the estates until well into 

 August while in December there was another outbreak, but 

 the damage was only slight, perhaps because the rains were 

 not heavy. 



Two attacks occurred in 191-"), the first in January at 

 two estates over .small areas, severe on one estate and .slight 

 on the other. The .second attack la.sted from about April to 

 the end of July and was felt on several estates, although 

 .slightly in most cases. t)n the three estates most .severely 

 infested a grand total of over 210,000 grubs was collected 

 These numbers, however, arc very small compared with the 

 severity of the infestation, but show that the beetles are not 

 very easilj' collected or trapped, and that very likely one 

 beetle was responsible for more than one dead heart. 



Mr. Moore in his 1914 re[)ort gives some interesting 

 details of the life-history and habits of this beotle. The 

 milk-white, nearly globular eggs are laid singly and loosely 

 in the earth about the cane stools at a depth of about 1 to 5 

 inches below the surface, and several may be deposited at 

 a stool. Kggs collected on June 23, and probably laid 

 some days before, were hatching on the 29th and SOtli. 



The newly hatched larva is while, with red mandibles 

 and short reddish hair, while the adult larva is dirty white 

 with the posterior end dark brown to almost black, due to the 

 accumulated excrementitious matter within. The segments 

 are wrinkled and clothed with short reddish hair, while the 

 head is yellow. The pupa is formed in an earthern cell. 



Mr Moore considers that under favourable cocditions the 

 larval period would be about two months, but this period 

 may be considerably lengthened by bad feeding or by dry 

 weather 



The pupal period is probably about a month, so that 

 ucder suitable condiiions the time from egg-laying to adult 

 can be a little over three months. This wa- shown by the 

 fact that laivae hatching about the middle of July emerged 

 as adults on October 12. (The eggs in this case must 

 have been laid early in July.) These beetles kept alive 

 without food for a month, and under natural conditions 

 would have remained underground until the end-year wet 

 .season. It would appear, therefore, that eggs deposited at 

 the mid-year rainy season develop into adults in time to 

 enierte at the end-year rainy season: also that eggs laid at 

 the end-year wet .season develop into active beetles by the 

 time of the mid year rains. 



The larvae live in the earth about the cane .stools, 

 feeding almost entirely on soil containing decayed vegetable 

 matter. Thus they do not appear to be harmful, but must 

 be destroyed before they can develop into destructive adults. 



The beetles are active at night, but hide in the daytime 

 in the earth about the stools, or in a hole they make at the 

 base of the young shoots. 



It is stated in the 1914 report that two things are 

 essential for the growth and development of the small black 

 hard back, namely, (1) an abundant and long-continued 

 supply of moisture, and (2) decaying vegetable matter. 

 Eggs left without moisture soon shrivel up, while young 

 larvae deprived of moistened vegetable food ijuickly perish", 

 and older larvae may survive for months with practically no 

 growth at all. But where the larvae find the cane stools 

 decayed or in a poor condition, and the moisture conditions 

 .suitable, they are almost certain to cause serious damage 

 to the crop. The larvae of the large moth borer {Castnia 

 liens) is primarily the cause of the bad state of the cane 

 stools, but poor or unsuitable soil and bad weather are also 

 resiponsible. 



Following on the decaying of the stools come a number 

 of scavengers, which besides the grub of the small black 

 hard back include weevil borer larvae, stool moth larvae 

 (Acrolof)h(s .■iacc/iari), root scale (Aspi'iiotus sacc/tari), wood 

 ants, millipede earthworms, wood lice, and small molluscs. 

 The best proteciion against the attack of the small black 

 hard back lies in a healthy, vigorous condition of the cane 

 stools. To induce this healthy condition Mr. Moore recom- 

 mends control of stool eating insects, such as Castnia, and 

 more frequent replanting, since ratoons suflFer most from the 

 pest. Also digging out of dead stools is an important 

 measure of control, since in this way not only can the grubs 

 be collected in large numbers, but the forked up stools soon 

 dry on exposure to wind and sun, so that numbers of eggs 

 are deprived of the necessary moisture, and both eggs and 

 grubs are exposed to their predaceous enemies. 



Furthermore, replants should not be made on lands 

 previously occupied by such grasses as arrow grass (Anal/ie7-twi 

 Income), or razor-grass, the shoots of which are attacked by 

 the hard back in the same way as are thnse of the suttar-cane. 



Trip-lights were suggested at first, but it was not con- 

 sidered that these would be a success, as the adult beetles 

 are rarely found at lights in houses. The use of trap-lights 

 was thoroughly tried out in 1915, but proved a failure. 



The experiment of sending boys to hunt for the beetles 

 at night witli lanterns (as was done in Mauritius with PUytalus 

 siiiilhi) was tried in 1915, but abandoned as giving poor 

 results. 



It is further recommended that a portion of the mid-year 

 grinding* be drawn up to February or early March, and the 

 remaining portion left over to late Juno or July. In the 

 former case (February and March being usually dry) the 

 canes would be all too high for seriotis attack by the beetle* 



