QUANTITATIVE ASPECTS OF EGG-LAYING BEHAVIOUR CONTRIBUTE TO THE ERUPTIVE SUCCESS OF Cameraria ohridella PARASITING HORSE-CHESTNUTS

The invasive leaf-mining moth, Cameraria ohridella, revealed to be a consistent eruptive species throughout Europe, at the expense of its host, the common horse chest-nut tree Aesculus hippocastanum. Its repeated outbreaks, year after year, are admittedly caused, in part, by the inadequacy of the ambient cortege of natural enemies as an effective mean of control of the dynamics of populations of this pest.
Less attention has been given to other parameters also contributing to the moth’s impact in term of mines density, such as (i) the degree of selectivity of C. ohridella mothers among host-leaves prior to oviposition and (ii) the average clutch-size.
Although these behaviour-related factors might reduce to a lesser extent the density of C. ohridella than the inefficient control of Cameraria by natural enemies, they nevertheless participate to the remarkable originality of C. ohridella, as compared to the bulk of other common but non-eruptive leaf-mining insects. Hereafter, we estimate the respective contributions of these two behaviour-related factors to the level of mining impact, using an appropriate indirect procedure. An unusually low level of mothers’ selectivity and a relatively high clutch-size are highlighted in C. ohridella, by comparison to other common mining moth species on trees. Both parameters are shown to contribute to a 50% increase of the parasite impact on its host.