MANKIND AND THE INSECT 331 



ing upon the scale insect. It was, in fact, the chief 

 " natural enemy ' of the pest. Large numbers of the 

 ladybirds, skilfully packed, were sent across the ocean 

 and liberated in the Californian orchards. The experi- 

 ment was completely successful. The ladybirds settled 

 down in their new home, checked the devastating increase 

 of the scale, and have held the pest in subjection ever 

 since. Small wonder that an extensive system of breed- 

 ing, fostering, and distributing beneficial insects has since 

 been adopted in the United States ! 



But there are some parasites and insects of prey which 

 are harmful to the interests of mankind because they 

 attack species that are useful. If, for example, a little 

 Chalcid wasp lays its eggs in the aphid-feeding grub of a 

 hover-fly, it does the gardener a bad turn. Likewise, 

 when the parasite of a destructive pest becomes the victim 

 of a secondary parasite (a not infrequent occurrence) the 

 pest — not the husbandman — reaps advantage. But this 

 phenomenon of hyperparasitism, as it is called, does not 

 end here ; for some secondary parasites are attacked by 

 tertiary parasites, and there is some reason for thinking 

 that even quaternary parasitism exists among insects. 

 These extraordinary complications may be illustrated by 

 a case which has been investigated by Dr. Howard. The 

 caterpillars of a moth (Hemerocampa hucosiigma), allied 

 to our common " vapourer," defoliate shade trees in the 

 north-eastern United States. These caterpillars are para- 

 sitised by an ichneumon (Pimpla inquisitor) ; but from 

 cocoons spun by the full-fed ichneumon grubs a little 

 Chalcid wasp (Dibrachys bouchecunis) sometimes emerges — 

 showing that the rightful inmate has been done to death 

 by a parasite of the second order. The larva of a second 

 Chalcid (Asecodes albitarsis) is known to feed within the 

 pupa of the first — being, in fact, a parasite of the third 



