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Plant Phenotype and Interspecific Competition between Insects Determine Sawfly Performance and Density
Author(s) -
Mopper Susan,
Whitham Thomas G.,
Price Peter W.
Publication year - 1990
Publication title -
ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.144
H-Index - 294
eISSN - 1939-9170
pISSN - 0012-9658
DOI - 10.2307/1938627
Subject(s) - sawfly , biology , fecundity , interspecific competition , competition (biology) , herbivore , population , ecology , botany , hymenoptera , demography , sociology
Host plants not only influence herbivore performance, they can also mediate interactions between herbivores. We conducted a 5—yr field study to test the effects of pinyon pine (Pinus edulis) phenotype and competitive interactions on the colonization success, mortality, fecundity, and sex ratios of a foliage—feeding sawfly, Neodiprion edulicolis. Our experiments revealed four major patterns. (1) Sawfly survival was significantly higher on susceptible trees than on resistant trees. (2) In contrast, sawfly fecundity was significantly lower on susceptible trees than on resistant trees. (3) Interactions with a stem moth, Dioryctria albovitella, caused significantly reduced sawfly fecundity on susceptible trees. (4) Sawfly mortality, rather than sawfly fecundity, was the dominant factor influencing population growth rates: after four generations, sawflies transferred to resistant trees. A model developed with performance information from our field experiments accurately described patterns of population increase in the field: sawflies rapidly attain high densities on susceptible tress, and accumulate slowly on resistant trees. Trees displaying a susceptible phenotype are therefore better hosts than resistant phenotypes, despite the negative competitive interactions that occur between sawflies and moths on heavily infested susceptible trees.