SUPERPABASITI8M 325 



caterpillars already infested with Tachinid larvse, both types of 

 parasites succumb in every case, with but one exception. Pierce 

 found with weevil parasites that survival was rare when more 

 than two species of parasites were involved. 



Superparasitism. Superparasitism is but a phase of multi- 

 parasitism in which two or more parasites pertaining to the same 

 species occur in the same individual host. In many cases it is a 

 normal and regular occurrence, and results in no fatal effects 

 upon the parasite individuals involved. It is especially prevalent, 

 for example, among Braconids and Chalcids, as records of rearings 

 of these parasites testify. In the polyembryonic Chalcids super- 

 parasitism is obligatory, and as many as nearly 3,000 individuals 

 of a single species have been reared from one individual Plusia 

 larva. In other cases its occurrence is irregular, and is the 

 result either of errors of instinct or of pressure of competition 

 induced by scarcity of suitable hosts. In such instances fatal 

 consequences commonly supervene. Thus H. S. Smith (1912) 

 records finding up to five planidia ^ of the Chalcid Perilampus 

 in a single individual host, but in no instance out of many hundreds 

 has more than one adult Perilampus emerged. It appears that 

 the individual most advanced in its development gains the 

 ascendancy by starving out its confreres, either through devouring 

 the host, or by rendering it unsuitable as a source of food. 

 E. W. Wheeler (1923) states that from one to eight larvae of 

 the Braconid Aphidius phorodontis may occur within the same 

 individual aphid host, but never more than one attains maturity. 

 This same fact has been noted by Spencer and other observers 

 of Aphidiine parasites. Timberlake (1912) has induced super- 

 parasitism under obligatory experimental conditions. In one 

 experiment five females of the Ichneumon Limnerium validum 

 were placed in consort with ten caterpillars of the brown-tail 

 moth. All the hosts were heavily attacked, and succumbed before 

 the parasitic larvae had grown to any appreciable extent, as the 

 result of the parasitisation. 



In many cases it is noteworthy that the female parasites are 

 guided by their own instincts so as to avoid hosts which they 

 ^ For definition, see p. 333. 



