10 



THE AGKICULTURAL NEWS. 



January 7, 1911. 



INSECT NOTES. 



TO INCREASE THE NUMBERS OF THE 

 BLACK SCALE PARASITE. 



From suitable materia], the parasites continue to emerge for 

 more than a week, and this period is sometimes much longer. 

 Many parasites are checked in their efficiency by the 

 action of secondary parasites, that is, parasites on the para- 

 site; but up to the present time, no parasite of Zalophothrix 

 mirnm has been recorded. 



The black scale (Saissetia nigra) is well controlled in 

 certain of the West Indian islands by the parasite Zaloph- 

 othrix mirum, Craw., while in other islands the control exer- 

 cised by this beneficial insect appears to be much less effective, 

 especially in connexion with the occurrence of the black 

 scale as a pest of cotton. (See Ai/rim/ttiral N'ews, Vols. VII, 

 p. 170, and IX, p. 170.) 



In localities where the parasite is not sufficiently abund- 

 ant to check the increase of the scale in cotton fields, it may 

 be possible for a certain amount of assistance to be given with 

 a view to remedying this condition of affairs. 



The parasite occurs most abundantly on the black scale: 

 but it is also a parasite of the two related scales, Saissetia 

 oleae and .S'. hemixphaerica. 



It is recommended that the following suggestions might 

 be adopted in making a trial of producing the black scale 

 parasite in increased numbers. 



The black scale appears to make its best development 

 on Sea Island cotton and Hibiscus. Plants of one 

 or both of these should be chosen, and repeated 

 introductions of black scale should be made 

 until the branches are well covered. For this 

 purpose, there should be an abundance of young 

 scales crawling on the introduced material, which 

 should be carefully tied to the branches of the 

 plants to be infested, so that the young may 

 easil}' leave the cut twigs and settle on the living 

 ones. 



It may happen that ants occur on the plants, 

 and prevent the establishment of the .scales. In 

 such a case, care should taken that the plants being 

 infe.sted do not come into contact with any other 

 plants, and that the branches do not touch the 

 ground. Ants can be prevented from climbing the 

 stems by wrapping the latter with strips of cloth 

 soaked in corrosive sublimate solution (1 in 1,000), 

 or by the use, in the same way, of any sticky sub- 

 stance over which the ants are unable to travel. 



It would be well, also, when introducing the 

 scales, not to introduce the parasite. In order to 

 guard against this, the old, fully grown scales on the 

 branches which are to be cut and transferred should 

 be removed, two or three days before the transfer 

 is made. This may be done with the blade of 

 a pocket knife, and will result in liberating any 

 eggs and young scales, which may be under the 

 parent scales, and will remove the jiarasites. 



When the scales are well established and there Flies. (Natural size.) epidermis, one 

 are many fully grown ones to be .seen, the parasites 

 should be introduced. The introduction of the parasites among 

 an abundance of the host in.sect should result in a rapid 

 development of vigorous individuals which might be used 

 for distribution to other localities. 



The foregoing suggestions are for trials where no well- 

 infested plants are available for the purpose, and where it is 

 jircsumed also, that the parasite occurs naturally in the island, 

 th'iugh perhaps not well distributed. 



It .should be an easy matter to introduce the parasite 

 from one island to another, by merely enclosing well-parasit- 

 ized, scale-infested twigs, cut in convenient lengths and packed 

 in a cardboard box in .such a way as to prevent shaking about. 



Fig. 1. Manoo Leaf 

 Attackeo i)y Cecip 



A OECIDOMYIID ON MANGO LEAVES. 



In a former number of the A;/riculUiral Neivs (see Vol. 

 VIII, p. 250), mention was made of a cecidomyiid tly, the 

 larva of whicli was found under the bark of the twigs of the 

 mango {Maixjifera indica), in Barbados. Grafted mangoes 

 seemed to be the most often attacked, the twigs infected 

 with the maggot dying back from the tips; and as these are 

 attacked and killed one after another, it often happens that 

 young trees are killed outright. 



The mango twig maggot is the larva of a small fly, to 

 which the name Agynapta inatigiferae, Felt, has been 

 given. It is related to the tlower-bud maggot of cotton 

 {Coiitarinia gos:<ypii. Felt), and to the red maggot of cotton 

 {Porricondyla gossypii, Coq.). 



A letter received recently by the Imperial 

 Commissioner of Agriculture from Mrs. W. H. 

 Patterson, forwarding specimens of mango leaves 

 from St. Vincent, records the occurrence of 

 a cecidomyiid larva attacking the mango in 

 a difi'erent manner. The specimens of leaves 

 show numerous small holes or spots, which 

 give the impression of being the effect of 

 a disease such as that caused by a species 

 of the shot-hole fungus. 



There seems to be no fungus present, how- 

 ever, and Mrs. Patterson states: 'the young leaves, 

 shortly after bursting from the bud, are found 

 to have semi-transparent patches, which reveal 

 the presence of a cecid larva.' 



The accompanying figure (Fig. 1) is a draw- 

 ing, natural size, of a small leaf from the speci- 

 mens received at the Head Office. 



The examination of the dried leaves leads 

 to the conclusion that the insect lives in the 

 soft tissue of the leaf, between the upper and 

 the lower epidermis, and it seems likely that 

 the eggs may be deposited in the bud before 

 it opens. The spots on the leaf are seen to be 

 nearly circular in outline, about /„■ to J-inch 

 (2'5 mm. to 3 mm.) in diameter, bordered with 

 a dark-brown or blackish ring, the central por- 

 tion being somewhat transparent. This central 

 area appears to be composed of the two layers of 

 of which is at first entire, the 

 other being broken, probalily showing where 

 the larva of the adult made its way out. When the leaves 

 are thoroughly dried, the transparent area is often traversed 

 by a narrow slit, which results from the shrinking of that 

 layer of epidermis which at first remained intact. Eventually, 

 all the central tissue of spots may fall awaj', and leave 

 a circular hole. 



It will be of interest to learn whether the maggot causing 

 the death of twigs of the mango in Barbados is the same as 

 that causing the shot holes in the leaves of the mango in 

 St. Vincent. 'I'he observations here recorded may be useful 

 in leading tn the discovery of other ways in which these 

 minute insects injure West Indian plants. 



