258 ENTOMOLOGY 



"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 multiplication of 

 a vegetable feeder is followed by the undue multiplication of parasites, 

 and their increase is followed by the increase of hyperparasites. Fol- 

 lowing the very instance of the multiplication of the shade-tree cater- 

 pillar just mentioned, the writer [Howard] was able to determine this 

 parasitic chain during the next season down to quaternary 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 

 Nomus 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 

 larvae, 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 

 of a plentiful supply of food, obtainable with little or no exertion, and 

 indicate, not primitive simplicity of organization, but a high degree of 

 specialization, as we have said before. The embryonic development of 

 parasitic larvae is frequently highly anomalous, as appears in the chapter 

 on development. 



Maternal Provision. Excepting several families of Hymenoptera 

 and the Termitidae, few insects make any special provision for the wel- 

 fare of the young beyond laying the eggs in some appropriate situation. 

 Many insects, as walking-sticks (Phasmidae) and some butterflies (Argyn- 

 nis) simply drop their eggs to the ground, leaving the young to shift for 

 themselves. Most insects, however, instinctively lay their eggs in 



