INTERFERENCE AT SEVERAL TEMPORAL AND SPATIAL SCALES BETWEEN 2 CHESTNUT INSECTS

Detection of interspecific competition between insects is often sensit ive to scaling. We give an example of scale-dependent interference bet ween the weevil Curculio elephas and the moth Cydia splendana, which b oth have larvae that develop in the fruits of chestnut Castanea sativa . Measures at three scales were considered: chestnut, husk (with one t o three fertile fruits) and tree. Data come from observations in the f ield over 14 years, complemented by experiments done directly in trees . Data on individual chestnut fruits revealed a marked statistical int erference between the two insects. Experiments demonstrated that prese nce of a moth larva in a fruit usually inhibits weevil egg-laying. Con versely, weevil presence does not strongly modify moth larval behavior . Cases of double infestation often correspond to fruits first attacke d by the weevil. With measures on husks, interference between the two insects was observed only in some trees; its intensity was always weak er than in the chestnuts themselves. At the scale of entire trees, rat es of infestation by each insect are not correlated. Interference in c hestnut fruits is interpreted by assuming that the weevil female eithe r sensitive to a repellent molecule originating from a moth larval or its frass, or can detect moth larval sounds. Mechanisms governing infe station rates from data per tree are discussed in relation to those fo und at fruit scale and to plant-insect interactions. The need to estim ate available resources both from quantitative and qualitative points of view is emphasized.