45« 



Journal of Agricultural Research 



Vol. XV, No. 8 



The parasitism of unnatural hosts has been investigated by others. 

 Of Americans, the work of Mr. P. H. Timberlake is of unusual interest. 



He succeeded in inducing Limnerium validum 

 Cresson, which is a natural parasite of the 

 fall webworm {Hyphantria cunea Drury), to 

 oviposit in caterpillars of the brown-tail moth 

 (Euproctis chrysorrhoca Linnaeus), the gipsy 

 Fig. 36.— Gaiesus siivestrii: Egg, i day moth (Porthctria dispar Liunacus) , and the 

 o . Lengt 0.36 mm. rusty vaporer moth (Notolophus aniiquus 



Linnaeus). In all the larvae of L. validum failed to develop. Timber- 

 lake (7) states that the larvae 



fail to survive the protective reactions of the host, which are visibly manifested by 

 an accumulation of active blood cells or amoebocytes around the larvae, the cast 

 eggshells, and even the eggs themselves. The amoebocytes presumably attack the 

 living eggs and larvae, or at least ultimately efface the latter entirely. 



RELATION OF THE INTRODUCED PUPAL PARASITES TO THE ESTAB- 

 LISHED LARVAL PARASITES OF THE FRUIT FLY 



GALESUS SILVESTRII 



In addition to the larval parasites brought into Hawaii to control the 

 Mediterranean fruit fly, a proctotrupid, Gaiesus siivestrii Kieffer, was 

 introduced by Silvestri in May, 191 3. This is a 

 pupal parasite. Though readily breeding in fruit- 

 fly puparia in confinement, it has never been 

 established in the open. 



Experiments with this species in the laboratory 

 have shown definitely that it may act either as a 

 primary or a secondary parasite, and that its 

 tendencies are suspiciously more those of a sec- 

 ondary than of a primary parasite. Fruit-fly 

 puparia containing developing larvae of any of 

 the opiine parasites above described or of Tetra- 

 stichus giffardianus, when exposed to attack by 

 G. siivestrii, may produce adults of G. siivestrii. 

 Extensive experiments with combinations of G. 

 siivestrii and the larval parasites of the fruit fly 

 have proved beyond doubt that a female of G. 

 siivestrii will never place her egg loosely in a fruit- 

 fly puparium if that puparium contams already 

 the developing larv^a of some other parasite. In 

 such cases she invariably feels about with her 

 ovipositor until she locates the parasitic larva, 

 into which she oviposits. This egg may hatch 

 and ultimately a normal adult of G. siivestrii may 

 emerge from the fully developed parasitic larva and bite its way out. 

 of the puparium. 



Fig. 37. — Gaiesus siivestrii: 

 Newly hatched larva. 

 Length i mm. 



