Indirect cues in selecting a hunting site in a sit‐and‐wait predator

Sit‐and‐wait predators use relatively simple rules for their decisions to choose and leave a patch, such as using the direct presence of prey to select a hunting site. However, the direct presence of prey can only be used when there is a highly visited patch in the proximity of the predator. Therefore, it is plausible that sit‐and‐wait predators also exploit indirect cues of prey presence and, consequently, use associative learning to select a hunting site. The present study tests for the role of associative learning in a sit‐and‐wait predator species for which the ecology is well understood: Misumena vatia Clerck crab spiders. An ecologically relevant scenario is used by selecting flower colour as the conditioned stimulus and prey presence as the unconditioned stimulus. The results provide no evidence that M. vatia crab spiders use the association between flower colour and food presence for selecting a hunting site. After a training phase of being exposed to a colourful artificial flower highly visited by bees, spiders select a hunting site independently of its colour during the testing phase. Investigations of similar scope and ecological relevance are required with other sit‐and‐wait predators to identify the conditions promoting the use of associative learning for foraging site selection when animals face an unpredictable food supply.     

Parasitoid vibrations as potential releasing stimulus of evasive behaviour in a leafminer

Abstract. The aim of this study was to characterize the vibratory signals produced by the parasitoid Sympiesis sericeicornis Nees (Hymenoptera: Eulophidae) while foraging on apple leaves infested by one of its hosts, the spotted tentiform leafminer Phyllonorycter malella (Ger.) (Lepidoptera: Gracillariidae).This leafminer changes its behaviour as a function of the parasitoid's behaviour to escape parasitization.We propose that the leafminer uses vibrations triggered by the parasitoid to detect the presence of its enemy.We measured vibrations produced by a foraging parasitoid on a mine with a laser vibrometer.By recording concurrently the behaviour of the parasitoid on video, vibrations could be assigned to particular behaviours.Subsequently, vibrations were characterized by their dominant frequencies and intensities.The behaviours Landing and Take-off both produced strong impact-like vibrations characterized by an initial irregular phase during which frequencies up to 25 kHz occurred followed by a slow decaying regular phase.Vibrations elicited by Moving, Standing and Probing showed no clear temporal pattern.During Probing , dominant frequencies of up to 5.6 kHz were observed frequently at intensities well above the background noise (>10 dB).During Moving and Standing , vibrations were more scarce and of lower frequencies and intensities.Due to their impact-like nature, vibrations produced by Landing and Take-off are probably not specific to the parasitoid.Vibrations produced by Moving and Standing are difficult to detect and not reliable because of their non-specificity.Therefore, only Probing provides a reliable and detectable source of information for the host.The vibrations elicited during Probing could account for the evasive behaviour that is observed in this and other leafminers.