Defensive role ofAllium sulfur compounds for leek mothAcrolepiopsis assectella Z. (Lepidoptera) against generalist predators

It has been shown previously that sulfur volatiles produced byAllium plants affect the behavior of their specialist phytophages and of their specialist entomophages. The action of these compounds in protecting the leek mothAcrolepiopsis assectella against generalist entomophages was studied in comparison to the proposed original defensive role of these compounds against generalist herbivorous insects. Two ants species,Formica selysi andF. fusca, were used as generalist predators. Six behavioral criteria of the predatory behavior of the ants were studied in presence of the last-instar caterpillars (C₅). C₅ reared on artificial diets with or without leek components were tested, as well as C₅ soaked in frass of leek-reared caterpillars or disulfide solutions. In addition, the response of the ants to pure chemicals found in leek was studied using honey solutions with or without sulfur compounds. The sulfur allelochemicals ofAllium plants have a negative action on predatory ants. Interestingly, the nonvolatile precursors of sulfur volatiles ofAllium plants seem to have a protective role for their phytophagous insects against generalist entomophages.     

Dietary effects of phytoecdysones in the leek-moth,Acrolepiopsis assectella Zell. (Lepidoptera: Acrolepiidae)

Incorporation of certain phytoecdysones (ecdysterone, polypodine B, and ponasterone A) into a semisynthetic artificial diet induces pathophysiological effects in larvae of the leek-moth (Acrolepiopsis assectella Zell., Acrolepiidae). The effects include lethality of the newly hatched, first-instar larvae; special ecdysial failures associated with the appearance of larvae with two head capsules; and developmental anomalies during metamorphosis. The effective range of dietary ecdysteroid, as evaluated by larval mortality, varies from 25 to 250 ppm. The EC₅₀ value is 100 ppm for polypodine B and 130 ppm for ecdysterone. The dietary effects of the phytoecdysones are similar to the previously observed effects caused by the dried flowers, but not leaves, of the leek plant. However, the active compound of the leek flowers is a saponin.     

Nature and role of sexual pheromones emitted by males ofAcrolepiopsis assectella (LEP.)

Seven compounds that do not exist in the extracts from legs of males have been isolated in the hair-pencil extracts of maleAcrolepiopsis assectella. By combining techniques of GC-MS and GC-FT-IR, six of these compounds have been identified. They are sixn-alkanes: hexadecane (C₁₆), heptadecane (C₁₇), octadecane (C₁₈), nonadecane (C₁₉), eicosane (C₂₀), and heneicosane (C₂₁). Twelven-alkanes of the homologous series, from the C₁₄–C₂₅ compounds were presented to virgin females, mated females, and males. At the end of the scotophase, four of then-alkanes (C₁₆, C₁₇, C₁₉, C₂₁) present in the hair-pencil extract induced the virgin females to adopt the acceptance posture after having induced the virgin females to remain stationary. The two othern-alkanes (C₁₈ and C₂₀) present in the extract have less effect on the females similar to then-alkanes not present in the males. The blends tested do not seem to indicate any synergy between the most active compounds. The threen-alkanes with an odd number of carbons and the C₁₆ compound would thus be the principle components of the male pheromone ofA. assectella. As well as their role of female aphrodisiac, they tend to make males and fertilized females flee.     

Origin of kairomones in the leek moth (Acrolepiopsis assectella,Lep.) frass

Feeding leek moths on an artificial diet has shown that dimethyl and dipropyl disulfides and methyl-propyl disulfide found in frass arise from sulfur compounds specific toAllium. The addition of either propyl or methyl disulfide or their precursors to the diet leads to appearance of the three disulfides in the frass. This implies the transformation of theS-propyl moiety toS-methyl and vice versa by an as yet unknown mechanism.