Fly parasitoid Megaselia opacicornis uses defensive secretions of the leaf beetle Chrysomela lapponica to locate its host

Abstract

Larvae of the leaf beetle Chrysomela lapponica derive a defensive secretion from salicyl glucosides found in the host plant Salix borealis. This secretion protects beetle larvae from some natural enemies, but does not appear to repel parasitoids. We tested the hypothesis that the fly parasitoid Megaselia opacicornis (Diptera, Phoridae) uses the larval defensive secretion of Ch. lapponica in its search for prey. In the field, nearly 30 times more M. opacicornis individuals were caught on leaves coated with sticky resin next to a source of secretion than on control leaves. In the laboratory, M. opacicornis females laid six times more eggs next to a cotton ball soaked in secretion than next to one soaked in water. Fly females also lay more eggs on prey rich in larval secretion than on secretion-poor prey. In the field, removal of defensive secretion from beetle prepupae resulted in a 7.5-fold reduction of oviposition by fly females. Parasitoids were nearly twice as likely to lay eggs on prepupae, rich in secretion, as on pupae, which contain little secretion. Fly offspring reared from beetle prepupae reached a 21% larger body mass than those reared from pupae. Finally, M. opacicornis females avoided host prepupae already parasitized by the tachinid fly Cleonice nitidiuscula, which possess little secretion. These experiments indicate that host plant-derived defensive secretions are used by this parasitoid for host location. Adaptation of parasitoids to use defensive secretions of hosts may selectively favor an increase in diet breadth in specialist herbivores.

Does ant predation favour leaf beetle specialization on toxic host plants?

“…Host plant-derived salicylaldehyde appeared not to be effective against some generalist predators, such as predatory bugs (Rank et al, 1998) or wasps (Pasteels & Gregoire, 1984;Sears et al, 2001), but has been proven to attract specialist predators and parasitoids (Rank, Smiley & K€ opf, 1996;Gross et al, 2004;Zvereva & Rank, 2004;von Fragstein et al, 2013). Consistently, meta-analysis showed non-significant overall effectiveness of salicylaldehyde-containing secretions across several prey and enemy species (Zvereva & Kozlov, 2016).…”

The role of competitors for Chrysomela lapponica, a north Eurasian willow pest, in pioneering a new host plant

“…Three main possible selection factors have been investigated so far: (1) the inXuence of abiotic factors like irradiation and temperature (Gross et al 2004c), (2) bottom-up eVects which inXuence the performance of the beetles directly, like the diVerent host plants (Gross et al 2004a;Zvereva and Rank 2003), or indirect bottom up eVects inXuencing the larval defensive abilities (Gross et al 2002;Pasteels et al 1983;Schulz et al 1997), and (3) top down eVects by predators, parasitoids and entomopathogens (Gross et al 2004b;Zvereva and Rank 2004). Further, crossing experiments were conducted, showing reproductive isolation between the birch and willow-specialised populations of C. lapponica (Fatouros et al 2006).…”

Do exotic generalist predators alter host plant preference of a native willow beetle?

“…Chrysomela knabi may choose a suboptimal host plant because the larvae grown on S. eriocephala would be less attractive to natural enemies that specialize on larvae grown on S. sericea. As previously stated, natural enemies have been noted to exploit larval defence as signals to locate their prey ( Köpf et al , 1998;Rank et al , 1998;Zvereva & Rank, 2004 ). Avoidance of intraspecific competition may also favour oviposition on suboptimal plants ( Craig et al , 1990 ).…”

“…Zvereva and Rank (2004) found that the fly parasitoid Megaselia opacicornis uses the larval defensive secretions of the leaf beetle Chrysomela lapponica as a host finding cue. Thus, C. lapponica experience higher mortality by M. opacicornis when they have a greater concentration of defensive secretions.…”