282 



THE AGRICULTURAL NEWS. 



September 4, 1909. 



INSECT NOTES. 



THE SWEET POTATO WEEVIL. 



Reference to the weevil {Cryj)ti>rlii/i)r/>us hoJutae) 

 which attacks the sweet potato in the field have 

 frequently been made in 

 the Ac/rlcidturcU N^ews 

 and the other publica- 

 tions of the Imperial 

 Department of Aj^ri- 

 culture. This small 

 insect, which is known 

 in Barbados as the 

 Scarabee, and in the 

 Leeward Islands as the 

 Jacobs, is shown four 

 times the natural size 

 at Figf. 26 : the larva, 

 which is a small white 

 grub, is represented, also 

 magnified four times, at 

 Fig. 27 ; and Fig. 2.S 

 shows the pupa, enlarged 

 to the same extent. 



Fi. 



2(i. 



■M. 



Vu:. ■2G. 

 Si'AKABEE {(JryptorhyiichHS hatatae). 



L.VKVA (CUL'I;) OF THE Sc\K.\BEE. 



Fk:. l'S. Piu'a (('IIUY; 



^.^^ 



Vu:. 29. 



The attacks of this 

 pest liave been very se- 

 vere, in Barbados, for the 

 past four or five years, 

 according to the state- 

 ments of e.xperienced 

 planters the most severe 

 they have ever known. 

 Barbados Las had several 

 years of short rainfall, and 

 the extreme severity of 

 the scarabee attacks is 

 .said to be due to this, in 

 large part at least. 



The life cycle of the 

 weevil occupies about 

 thirty days, as follows : 

 from tlie laying of the egg to the time of hatching, five days ; 

 the larval jseriod of twenty days, during which the damage to 

 the potato is caused, and during which also practically all 

 the feeding and growing is done by the insect ; and the 

 pupal stage of five days, during which the weevil transforms 

 from the grub to the adult, winged insect. Tender favour- 

 able conditions, the i)rocess of egg-laying jirobably begins 

 very shortly after the emergence of the adults, but it 

 is likely that the adults are capable of surviving long 

 jjcrioils of time when the conditions are not favourable, and 

 then laying their eggs. 



The usual practice in ]5arbados is to plant potatoes in 

 rotation with cane, cotton or other crops, so that the 

 first attack is by Ijeetles which conic from outside of the 

 field. The eggs arc laid in the first instance in the swollen 

 part of the stem near the base, or in jiotatos which are 

 exposed. The resulting brood of insects spreads throughout 

 the field, jienetratcs deeper into the infested potatos, an<l 

 attacks others which may be completely covered by the soil. 

 One may often find potatos in the field, csiicciidly when the 

 crops have been allowed to remain for some time in the ground 

 after becoming ripe, which show two or thrc(^ distinct attacks 



in this way. 



Very dry weather favours the growth and develop- 

 ment of the scarabee in two ways at least : the dry soil allows 

 air to penetrate more freely to the potatos, and it also 

 allows the adult insect to prosecute the search for the deeply 

 buried potatos more easily. 



The practice of keeji- 

 ing potatos in the ground 

 after they are ripe for 

 digging is very favour- 

 able for the development 

 of the scarabee, and it 

 is likely that if, for two 

 or three seasons, all pota- 

 tos could be dug as soon 

 as they are ready, the 

 numl>ers of the pest 

 ^\■ould be greatly reduced. 



Several experiments 

 have been carried out in 

 Barbados during the past 

 year with the object of 

 devising measures of con- 

 trol for the scarabee, but 

 no very definite results 

 were obtained. In two 

 instances there were no 

 attacks in the field in 

 which the experimental 

 plots were laid out, in 

 two others the owners or 

 managers dug the potatos 

 as soon as scarabee ap- 

 peared, and in the re- 

 mainder the plots were 

 all attacked — the control 

 plot and the treated plot 

 alike. These experiments 

 indicate, however, that 

 the practice of growing 

 slips, for planting, in 

 a nuiserj' instead of 

 taking them from the 

 ordinary field is worthy 

 can easily be established 

 by planting ' pickings 

 may be collected after 



Fic. 28. 

 \Lis) OF Scarabee. 



Fio. -I'J. 

 Sweet Fotato' Attacked by Scarabee. 



of adoption. Such a nursery 



away from the potato fields, 



(small bits of roots), which 



a crop of potatos has been harvested. This practice gives 



strong plants, and there is no chance of transporting the 



pest to the newly-planted field with the slips if care is 



taken that the nursery is not infested. Except at times 



when the scarabee is very abundant, the jjotatos are not 



attacked until fairly well grown, and the plants in a nursery 



would not bo ke|)t long enough to attract the weevils in any 



numbers. 



The attack of the scarabee results in the complete loss of 

 every potato in which the grubs of the weevil have lived. 

 Not only do they destroy all the tissues surrounding their 

 tunnels, but they impart such a disagreeable taste and odour 

 to the remainder, even when it appears quite sound, that no 

 use can be made i)f it, all estate animals refusing to eat such 

 portions. The appearance of an attacked potato is shown in 



The scarabee is cjuitc different from the sweet potato 

 weevil which is a iiest in Jamaica and the Southern pait of 

 the United States. This insect is Cylas formicarius. 



