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DEFOLIATING INSECT IMMUNE DEFENSE INTERACTS WITH INDUCED PLANT DEFENSE DURING A POPULATION OUTBREAK
Author(s) -
Kapari Lauri,
Haukioja Erkki,
Rantala Markus J.,
Ruuhola Teija
Publication year - 2006
Publication title -
ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.144
H-Index - 294
eISSN - 1939-9170
pISSN - 0012-9658
DOI - 10.1890/05-0362
Subject(s) - biology , larva , population , immunocompetence , insect , outbreak , pupa , mountain pine beetle , ecology , population density , susceptible individual , immune system , zoology , immunology , virology , demography , sociology
During population outbreaks, top‐down and bottom‐up factors are unable to control defoliator numbers. To our knowledge, details of biotic interactions leading to increased population density have not been studied during real population outbreaks. We experimentally assessed the strength of plant defenses and of insect immunocompetence, assumed to contribute to active insect resistance against parasitoids and pathogens, in the geometrid Epirrita autumnata during a steep increase in population density. We demonstrated rapid (same‐season) induced resistance in the foliage of its host, mountain birch. The response was systemic, spreading throughout the tree, and retarded larval growth rate by ∼10%. On the other hand, no direct delayed carry‐over effects were found in the next season in larval growth rate, mortality, or pupal mass. Larval damage to a tree during the previous year, however, significantly (by ∼13%) accelerated the advance of the immune response (measured as melanization of an implant inserted into the pupal hemocoel). The encapsulation rate correlated positively with larval mortality in trees in which larvae had been introduced the previous year, but not in control trees. Both of these observations suggest that induced plant defense was associated with an increased insect immunocompetence during the population increase.