Defence effectiveness of easy bleeding sawfly larvae towards invertebrate and avian predators

Abstract

Easy bleeding is a phenomenon discovered in some tenthredinid insects which possess a particularly low mechanical resistance of the integument, leading under mechanical stress to haemolymph exudation. It has a defensive effect against ants and wasps through harmful plant compounds which are sequestered in the haemolymph. Here we describe etho-ecological and some chemical aspects of the defence of easy bleeders and specify the range of predators to which easy bleeding might be effective. Beside a high haemolymph deterrence associated with low integument resistance across sawfly species, we also detected toxicity of the haemolymph of some species to workers of the ant Myrmica rubra. The behaviour of easy bleeders is to move slowly and, once disturbed, to become motionless, thereby probably impeding the tendency of a predator to attack. This behaviour had no beneficial effect for easy bleeders when attacked by the predatory bug Podisus maculiventris. Bugs could successfully and without harm prey on sawfly larvae without evoking easy bleeding. For the easy bleeder Athalia rosae, host plants with different secondary metabolite profiles, and, consequently, changes in haemolymph chemistry only slightly affected the feeding behaviour of the bugs. To test the effectiveness of easy bleeding towards a vertebrate predator, easy bleeders were offered to birds, Sturnus vulgaris. The body colouration of the sawfly larvae was of prime importance in determining the predator's response when testing birds in a group. It is likely that easy bleeding is a defence strategy directed primarily towards foraging insects with biting-chewing mandibles and that it is much less active towards predatory insects with piercing-sucking mandibles as well as birds. The involvement of chemical and/or physical cues in the strategy is discussed with respect to these types of predators.Key words. Tenthredinidae -easy bleeding in sawfly larvae -anti-predator defence strategy -defensive behaviourintegument -haemolymph deterrence and toxicityMyrmica rubra -Podisus maculiventris -Sturnus vulgaris

Dynamic state-dependent modelling predicts optimal usage patterns of responsive defences

“…to the expected Y max ). Smaller responses are seen as the expected predation increases from (Y max = 0.1, circles) to intermediate (Y max = 0.2, squares; Y max = 0.3, triangles), to high (Y max = 0.4, diamonds), but the responses to the later attacks are similar that accords with the survival per predation attempt observed in regurgitation and easy bleeding in response to natural predators [70% (Peterson et al 1987); 85% (Gentry and Dyer 2002); 73% (Vlieger et al 2004); 75% (Boevé and Müller 2005)]. …”

“…Regurgitation is widespread in the larvae of the lepidoptera and symphyta (Bowers 1993;Grant 2006), and involves the production of digested fluids and often parts of the gustatory system that are aversive to predators because of secondary compounds, which are often stored in specialised gut diverticula (Whitman et al 1990). Easy and reflex bleeding involve the externalising of haemolymph, which typically contains high levels of noxious compounds Müller et al 2001), often supplemented by gland secretions (Whitman et al 1990) that are aversive to predators (Peck 2000;Vlieger et al 2004;Boevé and Müller 2005). Easy bleeding has been heavily studied in the larvae of several sawfly species (Boevé and Schaffner 2003;Müller and Brakefield 2003;Vlieger et al 2004).…”

Anti-predator defence mechanisms in sawfly larvae of Arge (Hymenoptera, Argidae)

“…Starlings avoid preying on A. pagana larvae (Boevé and Müller, 2005). Full-grown larvae of this species were also tested on three young, naïve blackbirds, Turdus merula.…”

“…Full-grown larvae of A. pagana Panzer are brightly coloured and gregarious. Boevé and Müller (2005) tested Arge sp. (later identified as A. pagana) on starlings, Sturnus vulgaris, which avoided feeding on a majority of the larvae.…”

Sequestration of Glucosinolates and Iridoid Glucosides in Sawfly Species of the Genus Athalia and Their Role in Defense Against Ants

“…Thereby hemolymph is presented rapidly upon attack of biting predators through the easily disrupted integument of the larvae. Several potential predators are deterred by the hemolymph, whereas the sawfly larvae survive the attack (Boevé and Müller 2005).…”