170 



THE AGRICULTURAL NEWS. 



May 30, 1908 



INSECT NOTES. 



Red Spider on Sweet Potatos. 



Ill :l letter to the Imperial L'oir.iuissioner of Ao;ri- 

 culture, Dr. Watts. C.M.G., writer that 8 acres of 

 sweet potatos on an estate in Antigua were seriously 

 attaeked by what seetnod to be reil spidc.T, and speci- 

 mens of potato leav^■s with the pest on them were 

 forwarded for examination. 



Dr. Watts states that he leani.s that .sm-li an attack is 

 very unusual in Antigua ami ini|uin's wliftliLT it is known in 

 other places. 



()n examination of the material received at the Head 

 Office, it has been found that the surmise as to the nature of 

 the pest is a correct one. Red spider is present in large 

 numbers on the leaves and stems. 



This is not a rare occurrence in other places, the attacks 

 being always much worse in very dry weather than during 

 the rainy .season. The following account of the red spider 

 (TKlrdni/cltus telarlim) of the sweet potato is taken from the 

 pamphlet, published by the Imperial i)e|)artment of Agricul- 

 ture in 1906, entitled 'Lectures to Sugar Planters' : — 



' The red spider is not an insect but a near ally of the 

 true spider.s, and its minute size renders it ditticidt of ob.serva- 

 tion. 



'Sweet potatos attacked by this pest are easily recognized. 

 'I'he leaves curl up, turn yellow antl drop otf. The vines 

 wither and the plants do not form large tubers. The red 

 spider may be found in enormous nundiers on the leaves of 

 the.se plants, and it will spread from one spot, slowly e.xtend- 

 ing over a whole field. There are two simple remedies for 

 this pest — spraying with kero.sene emulsion, und dusting 

 with lime and sulphur.' 



The spraying could be done with any of the jiortable 

 sjM'ayers, such as the 'Success' knapsack or the ' Autospray,' 

 and the dusting ^\itli lime and sulphur, in etpial parts, would 

 be done in the same way as the dusting to control the leaf 

 blister ndtc of cotton. 



Severe outbieaks of red spicier on sweet potatos have 

 occui-re<l in ISarbados dnriiig the past few years, and the 

 prompt a|iplication of snl|)hur anil lime lias resulted in 

 marked im[irovcMnent of the condition of the potato vines. 



The Parasite of the Black Scale. 



The parasite of the black scale of euttoii {Leraii i uin 

 nUjrum) which has been mentioned in recent numbers 

 of the Ai/riridturul Ncivs (Hee Vol. VI, pp. 1.54 and 

 814) is proving; to be verj' useful in <-heeking the 

 attack of the beale insect on cotton in Barbados. 

 Diiiinsi the past year on .several estates it has been 

 noticed that the black scale has seemed to afi'w't the 

 cotton less than formerly, although it has been present 

 in large numbers. In such eases it has been found 

 that many of the scales have been parasitized. 



The parasite has proved to be a very interesting insect. 

 It has been studied, through the kimlncs.s of I )i-. I,. ( ). 



Howard, Chief of the Bureau of Entomology, I'nited States- 

 Department of Agriculture, by Mr. Crawford, one of the 

 assistants ;U the f'nrcau of Entomology, who has found that 

 it is of a new genus and new species. He has given it the 

 name Zitlaphotliri.r iiilniiii. Dr. Howard, writing to the 

 Imiierial L'omini.ssioner of Agriculture, states that from its 

 structure and relationship.s, it would be exi)ectcd to be parasi- 

 tic on the eggs of other insects, perhaps the eggs of the cock- 

 roach, and it is very interesting to find it a parasite of 

 a scale insect. 



The relation of insect host and in.sect parasite is always 

 of interest. It "is not ])o.ssible to tell how far attacks of the 

 scale insect will be controlled by the activities of the parasite, 

 but the more favourable the conditions for the rapid increase 

 of the scale in.sect or host, the more favourable will they be 

 for the development of the parasite, and the greater will lie 

 the proportion of the host destroyed by the i)arasite. 



Another factor comes in, at times, in the form of .second 

 ary parasites. These are not to be regarded as beneficial insects, 

 though they are ]iarasitic in their habits. They attack the 

 beneficial jjarasites anil tend to reduce their numbers. It will 

 be seen how complex this subject i.s, and how these nnnute 

 in.sects help to maintain the balance of nature. 



Tp to the present time no secondary parasites of the 

 black scale have been ff)und, so that it is hoped that the parasite 

 Zalojihothrix minim will increase with sufficient rapidity to 

 reduce the black scale to inconsiderable numbers. 



A Cocoa-nut Palm Blight at Lagos. 



The Imperial Commissioner of Agriculture has 

 recently received from the Lender-Secretary of State 

 for the Colonies a rejiort by Mr. H. N. Thompson, 

 Conservator of Forests for Lagos, dealing with the 

 occurrence of a scale insect on cocoa-nut palms in the 

 Badagry district of that colony. 



It is reported that the presence of the pest on the trees 

 is indicated by the yellow and brown colours assumed bv the 

 leaves as a result of the feeding of enormous ntanbers of the 

 scale insects, which are to be found on the under surface of 

 the leaf and on the fruit. Piadly infected trees lose all their 

 leaves except the apical shoot and one or two of the youngest 

 leaves, the oldest leaves on the tree being the first attacked. 

 The growth of the tree is often seriously cheekeil, and thi- 

 fruit falls otf while small and immatuie. 



The attack is at its worst in the wet sea.son, while the 

 dry days and bright sun of August seem to have an effect in 

 lessening the .severity of the attack. 



Other trees 1 adly attacked by this scale in.sect in I.,agos 

 are the papaw, banana, sweet .sop, cashew nut, and mango. 

 Yams are also badly attacked ; ro.ses an- affected to :i slight 

 extent, and in one instance mdy the oil palm Ls recorded 

 as being attacked. 



The reconunendations for preventing the s]ireiicl of the 

 di.sea.se and for reducing the severity of the attack include 

 the burning of all infected parts of the cocoa-nut ])alm, and 

 other trees and plants attacked by the .same .scale in.sect, and 

 the preventing of thi' imjiortation fif unhusked cocoa-nuts 

 from diseased areas unless they have been sterilized by being 

 thrown into a tire for half a nunute or .so. 



The scale insect of the eoe.ia nut in the \\'i\s| jiulies 

 is Ax/iitli<il>ix iii!itnirt<))\ and though it may not be the .same 

 as that in I^agos, yet in its manner of attacking the leaf and 

 fruit it is viMV sinnlar to it. 



