Consequences for a specialist insect and its parasitoid of the response of Allium porrum to conspecific herbivore attack

Abstract

Abstract. Recent studies on the leek Allium porrum L. demonstrate that a sharp increase in the release of volatile and nonvolatile sulphur compounds occurs in response to attack by the specialist phytophage, the leek moth Acrolepiopsis assectella (Zeller). The consequences of that response on the developmental capacity and behaviour of the leek moth and on the host‐searching behaviour of the parasitoid hymenoptera Diadromus pulchellus Wesmael have been studied. No immediate adverse effect on larval development is seen, but the duration of male development is significantly longer. In addition, an almost 20% decrease is observed in the number of oocytes produced by adult females that developed on attack‐damaged leek plants. Leek moths do not avoid damaged plants systematically. On attacked plants, larvae tend to consume more and females to lay more eggs, although the latter tendency disappears after intensive attack. Concerning host‐searching by D. pulchellus, the data indicate that females make use of the induced leek response. Parasitoids are attracted more strongly to attacked plants than to undamaged plants and mechanically damaged plants. The results of this study in a tritrophic system involving a biannual plant suggest a complex defence system combining direct and indirect mechanisms. Sulphur compounds may act by reducing second‐generation pests, thereby preventing the specialist insect population from exploding at the expense of the leek.

Identification of a Widespread Monomolecular Odor Differentially Attractive to Several Delia Radicum Ground-dwelling Predators in the Field

“…capitata), the phytophagous lepidoptera Plutella xylostella, its specialist parasitoid wasp Cotesia plutellae, and a generalist predator, the lacewing Chrysoperla carnea (Neuroptera) (Reddy et al 2002). The second involves leek (Allium porum), the phytophagous specialist microlepidoptera Acrolepiopsis assectella, and its parasitoid wasp Diadromus pulchellus (Dugravot and Thibout 2006). In the first study, Reddy et al (2002) found DMDS in the frass of P. xylostella that was attractive to C. plutellae and C. carnea in a Y-tube olfactometer setup.…”

“…In the first study, Reddy et al (2002) found DMDS in the frass of P. xylostella that was attractive to C. plutellae and C. carnea in a Y-tube olfactometer setup. In the second, the parasitoid wasp D. pulchellus was attracted by a blend of odors coming from attacked leeks (that emit thiosulfinates) and odors of A. assectella larval frass (Dugravot et al 2005;Dugravot and Thibout 2006), the latter material being known to emit a high concentration of DMDS (Auger et al 1989a). Although DMDS appears to be present in interactions that involve sulfur-containing plants and their associate herbivorous species, little is known about its importance as a cue at the third trophic level (i.e., predators and parasitoids).…”

Indirect defence via tritrophic interactions

“…, 2000; De Moraes et al. , 2001; Kessler & Baldwin, 2001; Dugravot & Thibout, 2006). Less welcome for the plant is the attractive effect of cotton EFN on herbivorous moths (Beach et al.…”

Insect Odorscapes: From Plant Volatiles to Natural Olfactory Scenes

“…Attacked leek plants are not avoided by the moth but females of Diadromus pulchellus an endoparasitoid wasp of young moth chrysalids, are more strongly attracted to damaged leek. In addition, the frass of A. assectella larvae contains dimethyl disulfide, dipropyl disulfide, and methyl-propyl disulfide that attract the wasps (Dugravot and Thibout, 2006). In poplars ( Populus nigra ) attacked by Lymantria dispar caterpillars, a clear increase of nitrogenous and aromatic compounds has been observed in the volatile emissions (McCormick et al, 2014).…”