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Experimental Evidence for Intraspecific Competition in a Lepidopteran Leaf Miner
Author(s) -
Bultman Thomas L.,
Faeth Stanley H.
Publication year - 1986
Publication title -
ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.144
H-Index - 294
eISSN - 1939-9170
pISSN - 0012-9658
DOI - 10.2307/1938588
Subject(s) - gracillariidae , intraspecific competition , biology , lepidoptera genitalia , population density , competition (biology) , larva , leaf miner , ecology , fagaceae , botany , population , demography , sociology
We manipulated field densities of the leaf—mining insect Cameraria sp. nov. (Lepidoptera: Gracillariidae) by caging them on branches of Quercus emoryi in central Arizona to test for intraspecific competition. High density cages (n = 7 replicates) had mean larval densities about 3 times those of low—density cages (n = 3 replicates). Our results demonstrate intraspecific competition in the form of density—dependent larval mortality. While mortality for leaf miners co—occurring on leaves was higher than for those occurring singly on leaves, larval mortality on leaves with multiple mines was just as high in low— as in high—density cages. That is, high mortality in high—density treatments was not related to interactions of larvae co—occurring on leaves. Rather, greater mortality in high density treatments resulted from increased mortality of miners on singly mined leaves in high—density treatments compared to those on singly mined leaves in low—density treatments. We suggest that ovipositing Cameraria compete with one another via interference when searching for leaves of superior quality. Natural field densities of Cameraria were highly variable. We conclude that natural high—density aggregations of Cameraria may result in some intraspecific competition, but, for the most part, Cameraria remains at low levels such that the competitive effect we found would not usually operate. However, intraspecific competition may act as a ceiling that prevents Cameraria aggregation on branches of Emory oak from exceeding the levels we observed in the field. Phytophagous insects that are commonly aggregated may compete to some degree even at relatively low densities, such as those of many leaf miners, if leaf quality (chemical/physical) is variable and leaves superior for insect growth and survival are rare.