The leaf beetle Diorhabda elongata Brullé (Coleoptera: Chrysomelidae) has been introduced as a biological control agent for saltcedars, Tamarix spp., an exotic, invasive weedy tree in the western United State. Gas chromatographic (GC) analysis of volatiles collected from feeding male or female beetles, or saltcedar foliage alone, showed two components produced almost exclusively by males. These compounds elicited responses from antennae of male and female beetles in GC-electroantennographic detection (EAD) analyses. The compounds were identified as (2E,4Z)-2,4-heptadienal (1) and (2E,4Z)-2,4-heptadien-1-ol (2) by GC-mass spectrometry (MS), and confirmed with authentic standards. The two compounds were also detected at trace levels from feeding females and foliage controls, but the amounts from feeding males were 8-40 times higher, typically 55-125 ng per day per male. The amounts of 1 and 2 in collections from females did not differ significantly from amounts collected from control foliage. In field trials, 2 as a single component was as attractive as a 1:1 blend of 1 and 2. Compound 1 as a single component was more attractive than controls, but much less attractive than 2 or the blend. Males and females were attracted in about equal numbers, indicating that this is an aggregation pheromone.
It was previously reported that males of the crucifer flea beetle, Phyllotreta cruciferae, feeding on host foliage are attractive to both males and females in the field. Based on this evidence for an aggregation pheromone, volatiles were collected from male and female P. cruciferae feeding on cabbage (Brassica oleracea) and analyzed. For comparison, volatiles were also collected from males and females of three other flea beetle species, Aphthona flava, A. czwalinae, and A. cyparissiae, all feeding on their host, leafy spurge foliage (Euphorbia esula). Six male-specific compounds were isolated from P. cruciferae, and the same compounds plus two additional ones were isolated from males of Aphthona flava, A. czwalinae, and A. cyparissiae. The blends of compounds were relatively consistent within species, but there were characteristic differences between species. Compound structures were studied by mass spectrometry, NMR spectroscopy, UV spectroscopy, polarimetry, chiral and achiral gas chromatography, molecular modeling, and microchemical tests. Three of the compounds were identified as (+)-ar-himachalene; (+)-trans-alpha-himachalene; (+)-y-cadinene. Two others were new enantiomers of himachalene hydrocarbons that were previously identified from the fir trees, Abies alba and Abies nordmanniana. Finally, there were two himachalene alcohols and one norsesquiterpene ketone that is a himachalene analog. Only (+)-ar-himachalene and (+)-y-cadinene are previously known natural products. Electrophysiological activity was demonstrated for five of the compounds. The chemical and electrophysiological patterns are consistent with, but do not prove, a pheromonal function.
The macrocyclic lactone (3Z)-dodecen-12-olide was identified from the emissions of the emerald ash borer, Agrilus planipennis, feeding on ash foliage. The compound was detected from both sexes but was ca. 10 times more abundant from females. It was readily sensed by antennae of both males and females. Identification was confirmed by synthesis. The behavioral effects of the lactone remain unstudied in A. planipennis, but a verified pheromonal function could lead to improved monitoring for this invasive pest. The lactone is part of the pheromone of Cryptolestes pusillus, an unrelated beetle species.
The tamarisk leaf beetle, Diorhabda elongata Brullé deserticola Chen, was collected in northwestern China and has been released in the western United States to control tamarisk (Tamarix spp.). Characteristics of diapause and reproductive development in D. elongata were examined to improve management as a biocontrol agent. Under long days, 16:8 (L:D) h, males began to emit aggregation pheromone within 2-3 d of adult emergence, mating occurred, and females oviposited within 7 d of adult emergence. Under short days, 12:12 (L:D) h, males did not emit pheromone, mating did not occur, and both males and females entered reproductive diapause marked by inconspicuous gonads and hypertrophied fat body. Ovaries of diapausing females lacked vitellogenic oocytes, and the ovarioles were clear and narrow, whereas reproductive females had enlarged ovaries with two to three yellow oocytes per ovariole. Diapausing males had thin, transparent accessory glands and ejaculatory ducts, whereas reproductive males had thick white accessory glands and white opaque ejaculatory ducts. Sensitivity to diapause-inducing photoperiods extended into the adult stage. Reproductive females ceased oviposition, resorbed oocytes, and entered diapause when switched from long to short days. Diapause-destined insects ceased feeding and entered the leaf litter 10-20 d after adult emergence, whereas reproductive insects remained on the plants and fed for at least 30 d. Reproductive insects exhibited dispersal behaviors, such as attempted flights, whereas diapause-destined insects did not show dispersal behaviors. Information gained from these studies will be used to better manage populations in the field and to improve rearing and storage in the laboratory.
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