MAN IN A WORLD OF INSECTS — DE LONG 429 



A ladybird beetle, Coccinella calif ornica^ according to Clausen, re- 

 quires 475 aphids at the rate of 25 a day for development and, after 

 transforming into an adult beetle, eats 34 per day during its remaining 

 life. Perhaps the greediest coccinellid species recorded is Chilocoris 

 similis, which Nakayama has found consumes on an average 1,563 

 aphids per individual during its lifetime. In the case of the aphis 

 lion, Chrysopa calif ornica, a larva may consume 141 aphids during its 

 larval development. The syrphid fly larvae have equally voracious 

 appetites. Two species reported by Curran, Allograpta ohliqua and 

 Syrphus americanus, consumed 265 and 474 aphids, respectively, 

 durmg their larval development. 



The ground beetles, one of the largest families of Coleoptera, often 

 attack larger insects. Their importance lies in the fact that here is 

 a predacious group which covers the surface of the earth, continuously 

 patrolling it and devouring untold numbers of insects, particularly 

 caterpillars whose life cycle is such that they must drop to the ground 

 as full-grown larvae and penetrate its surface twice, once to pupate 

 and again to emerge. This offers the opportunity to our carabid 

 patrolmen to see that few pass or repass without being apprehended. 

 Considering the large numbers of prey that are destroyed by a single 

 individual during the course of its life, we are forced to admit that 

 predatory insects play a primary role in checking the increase of 

 destructive forms and are thus of great value to man. 



Insect parasites. — Insect parasitism is extremely diverse and may 

 in some mstances verge on predatism, scavengerism, and commensal- 

 ism. In addition to this there is a wide range of parasitic behavior 

 among the truly parasitic species. This is probably due to the fact 

 that parasitism has arisen independently in various groups of insects 

 although certain parallel developments have occurred among these 

 different types. 



One group of parasitic insects is known as ectoparasites and these 

 are predominantly blood-sucking species such as mosquitoes, black 

 flies, horse flies, blood-sucking lice, bed bugs, other Hemiptera, etc., 

 which attack vertebrate animals. With few exceptions these are not 

 beneficial to man. 



The entomophagous parasites are usually forms that feed inside the 

 bodies of their insect hosts and either destroy them or render them 

 sterile so that they are not able to reproduce. These parasites occur 

 in several orders, and one insect order, the Strepsiptera, is composed 

 entirely of parasitic species. These develop internally as parasites of 

 bees, wasps, and certain Homoptera. 



By far the greatest number of parasites are Hymenoptera, and 

 probably half or more of the known species of this group are parasitic 

 on other insects. Certain minute forms like Tricliogratnma will para- 

 sitize insect eggs, and an individual parasite can develop to maturity 



