Journal of Chemical Ecology

The sex attractants for many Lepidoptera are long-chain, monounsaturated acetate esters, alcohols, and aldehydes. In vivo metabolic studies and enzyme analysis in vitro have provided evidence that the aldehyde pheromone of the eastern spruce budworm is synthesized de novo via an acetate ester precursor. Interconversion of the functional groups (ester, alcohol, aldehyde) can explain differences in the pheromone blends used by closely related species.

We examined how variability in phenolic metabolism of four closely related Tribulus taxa might affect palatability to Schistocerca gregaria. Plants were collected in the Mauritanian breeding areas of the locust. Eighteen flavonoids (caffeoyl derivatives, quercetin glycosides, including rutin, and kaempferol glycosides) were detected with high-performance liquid chromatography in leaf extracts. Principal component analysis (PCA) differentiated relative abundance of flavonoids of Tribulus terrestris from T. longipetalus, T. ochroleucus, and T. bimucronatus. Flavonoid content of T. terrestris leaves varied between northern and southern Mauritanian sites. Dual choice tests with plants whose flavonoid profiles had been determined previously were analyzed by multiple regression. The data suggest that the desert locust prefers T. terrestris plants rich in quercetin glycosides.

The responses of male western spruce budworm moths,Choristoneura occidentalis Freeman, to a range of concentrations of the major sex pheromone, 92∶8 (E/Z)-11-tetradecenal (Ald), in polyvinyl chloride lures, were observed using the electroantennogram technique, a flight tunnel, and field-trapping bioassays. The responses to virgin female moths were also observed in the flight tunnel and field bioassays. The moths were from three strains: a nondiapausing laboratory colony; field-collected wild budworm; and laboratory-wild crosses. The mean peak amplitude of antennal response and the time required for the electroantennogram signal to return to the baseline after stimulation (lag) increased with Ald concentration in both laboratory and wild moths. However, at Ald concentrations of 0.005% and greater, the lag period of the wild male's antennae was significantly shorter than that of the laboratory male's. The mean number of moths caught in the field in delta sticky traps increased with Ald concentration, but the number of moths caught per trap was not significantly different between concentrations of 0.005 % and 0.5 %. The threshold concentration required to elicit upwind flight in the flight tunnel was between 0.0005 and 0.005% Ald; peak response occurred to 0.05 % Ald but was not significantly different from that to 0.005 % or 0.5% Ald. Moths from all three populations significantly reduced their net upwind groundspeed as they approached the pheromone lure. When pheromone concentration was increased, the net upwind groundspeed of laboratory and lab-wild moths, but not wild moths, was significantly reduced between 2 m and 1 m downwind from the pheromone lure. The three populations of moths differed significantly in the percentage of wing-fanning and copulatory attempts, and in the net upwind groundspeed of flight from 2 m to 1 m downwind from the lure.

In this study we investigated the effect of methyl jasmonate (MeJA) application on pyrrolizidine alkaloid (PA) concentration and composition of two closely related Jacobaea species. In addition, we examined whether MeJA application affected herbivory of the polyphagous leaf feeding herbivore Spodoptera exigua. A range of concentrations of MeJA was added to the medium of Jacobaea vulgaris and J. aquatica tissue culture plants grown under axenic conditions. PA concentrations were measured in roots and shoots using LC-MS/MS. In neither species MeJA application did affect the total PA concentration at the whole plant level. In J. vulgaris the total PA concentration decreased in roots but increased in shoots. In J. aquatica a similar non-significant trend was observed. In both Jacobaea species MeJA application induced a strong shift from senecionine- to erucifoline-like PAs, while the jacobine- and otosenine-like PAs remained largely unaffected. The results show that MeJA application does not necessarily elicits de novo synthesis, but rather leads to PA conversion combined with reallocation of certain PAs from roots to shoots. S. exigua preferred feeding on control leaves of J. aquatica over MeJA treated leaves, while for J. vulgaris both the control and MeJA treated leaves were hardly eaten. This suggests that the MeJA-induced increase of erucifoline-like PAs can play a role in resistance of J. aquatica to S. exigua. In J. vulgaris resistance to S. exigua may already be high due to the presence of jacobine-like PAs or other resistance factors.

Heterocrossa rubophaga, the raspberry bud moth, is a pest of commercial Rubus berry crops and wild Rubus species. Its pheromone was initially identified as a single component, (7Z)-nonadecen-11-one. Here we report further investigation of this carposinid pheromone including volatile collection, gland extraction, mass spectrometry, microchemical analysis, electrophysiology and field testing. The alkene (7Z)-tricosene was identified from female gland extracts and the synthetic compound gave antennal responses from the male moth. Field testing of (7Z)-tricosene showed that it was unattractive alone but in combination with (7Z)-nonadecen-11-one it more than doubled male moth trap catch for all doses tested compared to that of (7Z)-nonadecen-11-one alone. We recommend a blend of 300 µg of (7Z)-nonadecen-11-one and 300 µg of (7Z)-tricosene as an improved monitoring tool for raspberry bud moth for use by berry growers. This is the second report of the Z-alkene as a pheromone component in the Carposinidae family among the three carposisnid pheromones identified to date.

Although within-plant variation in the nutrient and allelochemical composition of phloem sap has been invoked to explain patterns of host use by phloem-feeding insects, little is known about within-plant variation in phloem chemistry. Here I describe a new technique in which I use the green peach aphid,Myzus persicae Sulz., to investigate within-plant variation in the concentrations of chemicals in the phloem sap of black mustard,Brassica nigra (L.) Koch (Cruciferae). Relationships between the concentrations of chemicals in aphid diets and honeydew were established using honeydew from aphids fed on artificial diets with known concentrations of amino acids, sucrose, and sinigrin. These relationships were applied to honeydew from aphids fed on different aged leaves of black mustard to estimate the concentrations of the chemicals in phloem sap. Sinigrin concentration was estimated to be high (>10 mM) in phloem sap in young leaves, calling into question the prevailing opinion that phloem sap contains only low concentrations of allelochemicals. High concentrations may function as defenses against sap-feeding herbivores. Within-plant variation in phloem sap composition was high: (1) young leaves had high concentrations of nutrients (216 mM amino acids, 26% sugar) and sinigrin (>10 mM); (2) mature and presenescent leaves had lower concentrations of nutrients (77–83 mM amino acids, 19–20% sugar) and low concentrations of sinigrin (1–2 mM); and (3) senescing leaves had high concentrations of nutrients (199 mM amino acids, 25% sugar) and low concentrations of sinigrin (3 mM).