Hierarchical structure in kairomone preference of the predatory mite Amblyseius potentillae: dietary component indispensable for diapause induction affects prey location behaviour

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Abstract
The phytoseiid predator Amblyseius potentillae (Garman) responded to volatile kairomones emitted from leaves infested by the two‐spotted spider mite ( Tetranychus urticae Koch), the apple rust mite ( Aculus schlechtendali (Nalepa)) or the thrips Frankliniella pallida (Uzel), only when the predators had been reared on a carotenoid‐free diet. In contrast A.potentillae responded to the European red spider mite ( Panonychus ulmi (Koch)) both when the predators had been reared on a carotenoid‐containing and a carotenoid‐free diet. Carotenoid‐deficient predators did not respond to odour emitted from a host plant that was infested by larvae of the fruit‐tree leaf roller ( Adoxophyes orana (F.v.R)), a carotenoid‐containing phytophage, that cannot be preyed upon by A.potentillae. Carotenoids are indispensable for diapause induction in A.potentillae. Hence, carotenoid‐deficient predators can increase their fitness by feeding from a carotenoid source. This may explain the response of carotenoid‐deficient predators to the kairomones of the two‐spotted spider mite, F.pallida and the apple rust mite (all containing ingestible carotenoids). As the fruit‐tree leaf roller cannot serve as prey and thus as a carotenoid source, it makes sense that the predators lacking carotenoids do not respond to the kairomone of this phytophagous insect. Two‐choice experiments in a Y‐tube olfactometer showed that the kairomone preference of A.potentillae has a hierarchical structure: the kairomone of the European red spider mite is the most preferred one, followed by that of apple rust mite, whereas the kairomone of the two‐spotted spider mite is the least preferred of these three.

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