122 



THE AGRICULTURAL NEWS. 



Ai'KiL 17, 1909. 



INSECT NOTES. 



Natural Enemies of Scale Insects. 



Insects may be beneficial in several different ways : 

 as producing valuable products; as natural enemies of 

 other insects which are pests attacUiii^' crops, domestic 

 animals, household materials, or even man himself; or 

 l.hey may merely be scavengers and be beneficial on 

 account of their habit of feeding on decaying organic 

 matter. 



In these notes, however, it is intended to discuss 

 only one of these groups of beneficial insects, viz., natural 

 enemies of other insects, especially of scales. 



Readers of the Aiji iciiltural i\VM^s■ may have noted 

 in the 'Department News' that the Entomologist on 

 the staff of this Department had been on a visit to 

 Montserrat in eoniio.xion with an e.vU'iided study of 

 scale insects and their natural enemies. 



The natural enemies of scale insects arc- of two kind.s : 

 parasitic and prcdaceous ; Ijoth of these are to he 

 found in tl)e West Indies. Among the predaceous insects 

 which attack scales are the lady-ljirds, and the laee-wing Hy. 

 Tliere arc many kinds of lady-hinJs in the \Vcst Indies. Two 

 or three which are large enough to be ca.sily seen are well 

 known, but these are not, perhaps, more useful than certain 

 others which arc very small in size, and very jilain and 

 inconspicuous in their colouring. Tlicy are not generally 

 known, and the planter does not often realize how much 

 good is continually being done by these small creatures. 



The parasitic insects are even more important than those 

 which are prcdaceous in nature, and while it is very likely 

 that there are many species which' live at the e.\|)en.se of the 

 .scale insects, very little is actually known of the parasites 

 which attack scale insects in the West Indies. 



It is probable tiiat all, or nearly all, nf the 120 species of 

 scale insects known to occur in the Lesser Antilles are 

 attacked by par;,sitcs to a greater or loss extent, and thus 

 soi»ewhat kept in check. 



There arc recorded from the island of St. Vincent alone as 

 many as eighty-six species of parasitic llymcnopteni, of which 

 many nie probably parasites on scale in.^ects, and many others 

 also rtic probably parasites on other parasites. The latter kind 

 are known as ' .sccondaiy parasite*.' an<l it will readily be 

 >een that, although paia.'^itic inhabit, llicy (Miinut be counted 

 as beneficial insects. 



Swile insects which arc abundantly attacked by parasites 

 cjin easily be distinguished. foi- many of them will be sicn to 

 have a little round hole in the buck. Tliis hole is the aperture 

 through which the adult parasite 1ms escaped, having spent the 

 larval portion ot its existence and tin' pupal stage under the 

 protective scale of the host in.sect. The fee(hng of the 

 para.site larva cause.'< the death of the insect on wliicji it feeds, 

 and so well is the relationship ail.justed between the iiarasite 

 ami its In^t. that the food material lasts the parasite larva 

 until it is full grown. If the food material were exhausted 

 lu'toie the larval growth of the parasite Wius completed, the 

 jiara.si.te would natufiilly die. 



There can be no (foubt that in all the islands of the 

 Lesser Antilles, the nafeiral enemies of scale insects are always 

 abundantly and actively,', engaged in doing their part toward 

 maintaining the equilibrium, otherwise the scale insects 

 would multiply in perhaps one year, or iit the most in two 

 year.s, to a point where their numbers would be so great that 

 none of the plants on which thev feed would be able to live. 



Scale insects become unusually abundant when for one 

 reason or another they increase greatly beyond the numbers 

 of their parasites and r>ther natural enemies. On the other 

 hand, when for any reason the natural enemies become 

 unusually abundant, scale insects are less numerous and the 

 effect of their attacks on plants are not so easily to be seen. 

 One of the first indicaiions of the presence of certain .species 

 of scale insects is tile appearance on the leaves of the 

 unsightly soot fungus c'ommonlv known throughout the West 

 Indies as ' Black might.' 



It is rather ren)gi)-kal)Ie that the habits of parasitic 

 bisects are generally associated with certain definite struc- 

 tures, and that closely related insects have similar habits. 

 For instance, certain groups of parasitic Hymenoptera are 

 known to be egg parasites, 'i'he specialist, on examining an 

 insect of one of these groups for the first time, would be able 

 to say that it probably was an egg parasite, because of its 

 relationship as evidenced liy its structure. An exception to 

 this, however, was recently found in the parasite of the Black 

 Scale which attacks cotton. This parasite was sent from 

 this Department to theJPureau of Entomology at Wa.shington 

 for identitication, where it was named /Cnlopliotln-i.r inirum. 

 Dr. Howard, Chief of the Bureau, wrote to the Conunissioner 

 of Agiiculture to enqfiiire whether thei'e might be any 

 mistake in the I'ccords, because, as he said, it ought from its 

 affinities to Ijo an egg 'parasite, and not a parasite of scale 

 insects. Specimens of the scale in.sect containing ]iarasites 

 were .sent on to \Vashington, however, ■v\hich [>ro\ed that 

 this insect was an o.^cfception to the general rule, and 

 was really a parasite of the scale. 



:♦•■ .. 



In the editorial of the present number of the A<in.- 

 ciiltiiral Xi'irx, mention is made of the work that is being 

 done hy the United States Department of Agriculture, in 

 importing from Kurope.^nd establishing in Eastern Jla.ssachii- 

 setts certain beneficial insects. Jfuch has been done in other 

 States and in other jjar.ts of the world in this lin". Insect 

 pests transported from the countries in which they are native, 

 are often transported at the same time away from their 

 natural enemies, so tli'at it frecpiently happens that many 

 pests are much more trdublesomc in new localities thm they 

 were in their native lanth 



The lin|ijrial Department of Agiiculture hopes to get 

 a considerable amount ,of knowledge of the natural enemies 

 of the .scale insects of ithe Lesser .Antilles, with the object 

 finally of endeavouring to utilize these parasites in the control 

 of scale insects. It may be addetl that in addition to parasitic 

 insects, there are certaii) fungi which aj-e parasitic on scale 

 insects. In Florida, aud peihaps in other places, much ha-s 

 already been accomplished in the control of scale insects and 

 white flies {Alr;/r<)drx)h\ means of parasitic fungi. It is hoped 

 that all readers of the A;/rifu/tiiiii/ Xnrs in tlie.West Indies^ 

 will take an interest in this work, and will forward specimens 

 whenever they notice anything of interest, which .seems to 

 them likely to be in any way connected with this study of 

 natural enemies Any.,, such specimens may be .sent to the 

 local Agricultural Officer, who will forward them to the Head 

 Office of the Department. 



