Uptake of plant-derived specific alkaloids allows males of a butterfly to copulate

Pyrrolizidine alkaloids are synthesized and accumulated in flower of Myosotis scorpioides

Pyrrolizidine alkaloids (PAs) are specialized metabolites that are produced by various plant families that act as defense compounds against herbivores. On the other hand, certain lepidopteran insects uptake and utilize these PAs as defense compounds against their predators and as precursors of their sex pheromones. Adult males of Parantica sita, a danaine butterfly, convert PAs into their sex pheromones. In early summer, P. sita swarms over the flowers of Myosotis scorpioides, which belongs to the family Boraginaceae. M. scorpioides produces PAs, but the organs in which PAs are produced and whether P. sita utilizes PAs in M. scorpioides are largely unknown. In the present study, we clarified that M. scorpioides accumulates retronecine-core PAs in N-oxide form in all organs, including flowers. We also identified two M. scorpioides genes encoding homospermidine synthase (HSS), a key enzyme in the PA biosynthetic pathway, and clarified that these genes are expressed in all organs where PAs accumulate. Phylogenetic analysis suggested that these two HSS genes were originated from gene duplication of deoxyhypusine synthase gene like other HSS genes in PA-producing plants. These results suggest that PAs are synthesized and accumulated in the flower of M. scorpioides and provide a possibility for a PA-mediated interaction between P. sita and M. scorpioides.

Odor Perception in the Cotton Bollworm, Helicoverpa armigera, Exposed to Juglans regia, a Marginal Host Plant

The cotton bollworm, Helicoverpa armigera, is one of the most destructive agricultural pests in the world, infesting cotton, maize, soybean, and many other crops. In recent years, H. armigera has been observed damaging walnuts, Juglans regia, in Xinjiang China. Here we examine the chemical perception by H. armigera of the marginal host J. regia. In Y-tube olfactometer tests, we found H. armigera females and males both showed significant behavioral responses to odors from walnut branches. Furthermore, nine electrophysiologically active volatiles (α-pinene, β-pinene, myrcene, limonene, eucalyptol, ocimene, β-caryophyllene, (E)-β-farnesene, and germacrene D) were identified from walnuts with gas chromatography coupled with electroantennography (GC-EAD) and gas chromatography-mass spectrometry (GC-MS). Among these volatiles, β-pinene and eucalyptol were released in relatively higher amounts. In electroantennogram (EAG) dose-dependent trials, all compounds evoked responses in H. armigera adults when tested at high concentrations, with germacrene D evoking the greatest response. In wind tunnel tests, H. armigera females preferred eight of the electrophysiologically active volatile dilutions compared with clean air, while males showed preference for only five compounds. As such we describe the chemical recognition of H. armigera for walnut, a marginal host. This study contributes to understanding the interaction between polyphagous pests and their host plants.

Attraction of Brown Marmorated Stink Bugs, Halyomorpha halys, to Blooming Sunflower Semiochemicals

The polyphagous invasive brown marmorated stink bug, Halyomorpha halys, reportedly discriminates among phenological stages of host plants. To determine whether olfaction is involved in host plant stage discrimination, we selected (dwarf) sunflower, Helianthus annuus, as a model host plant species. When adult females of a still-air laboratory experiment were offered a choice of four potted sunflowers at distinct phenological stages (vegetative, pre-bloom, bloom, seeding), most females settled onto blooming plants but oviposited evenly on plants of all four stages. In moving-air two-choice olfactometer experiments, we then tested each plant stage versus filtered air and versus one another, for attraction of H. halys females. Blooming sunflowers performed best overall, but no one plant stage was most attractive in all experiments. Capturing and analyzing (by GC-MS) the headspace odorants of each plant stage revealed a marked increase of odorant abundance (e.g., monoterpenes) as plants transitioned from pre-bloom to bloom. Analyzing the headspace odorant blend of blooming sunflower by gas chromatographic-electroantennographic detection (GC-EAD) revealed 13 odorants that consistently elicited responses from female H. halys antennae. An 11-component synthetic blend of these odorants attracted H. halys females in laboratory olfactometer experiments. Furthermore, in field settings, the synthetic blend enhanced the attractiveness of synthetic H. halys pheromone as a trap lure, particularly in spring (April to mid-June). A simpler yet fully effective sunflower semiochemical blend could be developed and coupled with synthetic H. halys aggregation pheromones to improve monitoring efforts or could improve the efficacy of modified attract-and-kill control tactics for H. halys.