INI 'I IV- 1 ' 275 



and unaided, almost annihilated the liflh brood of the COttOD worm in 

 Florida, fully ninuly per cent, <!' the e^ <>\ thi- prolific crop en 

 bcin^ infested by the parasite. In [895, in the iity of Washington, 

 more than ninety -e\eii per (enl. of the ca1rrpill;irs of one of our 

 most important shade tree pests \IIcnicroc, nnj)<i, as ju>1 mentioned] 

 \\ere destroyed by parasitic insects, to t he < oinplet e relief if t he < it y the 

 following year. The Hessian lly, that dcstrucl ; ;iy 1o wheat 



crops in the I nited States, is practically unconsidcred by the wheat 

 L^row. . rtain states, for the reason that. when. numbers 



lu^in to l>e injuriously great its parasites increase to such a degree as to 

 prevent appreciable damage. 



"The control of a plant-feeding insect by its insect enemies is an ex- 

 tremely complicated matter, since, as we have already hinted, the 

 parasites of the parasites play an important part. The undue multipli- 

 cation of a vegetable feeder is followed by the undue multiplication of 

 parasites, and their increase is followed by the increase of 

 hyperparasites. Following the very instance of the multiplication of 

 the shade tree caterpillar just mentioned, the writer [Howard] was able 

 to determine this parasitic chain during the next season down to quater- 

 nary parasitism. Beyond this point, true internal parasitism probably 

 did not exist, but even these quaternary parasites were subject to 

 bacterial or fungus disease and to the attacks of predatory insects. 



"The prime cause of the abundance or scarcity of a leaf -feeding 

 species is, therefore, obscure, since it is hindered by an abundance of 

 primary parasites, favored by an abundance of secondary parasites 

 (since these will destroy the primary parasites), hindered again by an 

 abundance of tertiary parasites, and favored again by an abundance of 

 quaternary parasites." 



Entomologists have made many attempts to import and propagate 

 insect enemies of various introduced insect pests, and some of their 

 efforts have been crowned with success, as was notably the case when 

 Novius cardinalis, a lady-bird beetle, was taken from Australia to Cali- 

 fornia to destroy the fluted scale. 



Form of Parasitic Larvae. The peculiar environment of parasitic 

 larvae is responsible for profound changes in their organization. These 

 larva?, in general, are apodous, the body is compact and the head is more 

 or less reduced, sometimes to the merest rudiment. These characters, 

 occurring also in such dipterous larvae as live in a mass of decaying or- 

 ganic matter, and again in those hymenopterous larvae whose food is pro- 

 vided by the mother or by nurses, are to be attributed to the presence 



