Glandular trichomes on perennial alfalfa affect host-selection behavior of Empoasca fabae

Selected behavior of Empoasca fabae (Harris) (Homoptera: Cicadellidae) was examined to elucidate resistance of commercially-available glandular-haired alfalfa to this key forage pest. The overall objective was to assess the effects of the glandular trichomes on the behavior of nymphs and adults. Studies of host-plant acceptance by E. fabae nymphs found first and third instars to show a higher degree of change in settling location on the glandular-haired FGplh13 alfalfa than on the nonglandular P5373 alfalfa. Nymphs also cleaned their tarsi more frequently when in contact with the glandular trichomes on FGplh13 alfalfa, and in addition a larger number of nymphs jumped/fell off the surface of FGplh13 alfalfa. The glandular trichomes on FGplh13 also impeded nymphal mobility more effectively than the nonglandular trichomes on P5373. No choice, time-course analysis of adult host-plant acceptance behavior found that adults settled less frequently on FGplh13 alfalfa with the glandular trichomes intact, than on either FGplh13 with the glandular trichomes removed, or P5373 alfalfa with the nonglandular trichomes intact or removed. Free choice, time-course analysis of adult host-preference behavior determined that at each observation, stems of the nonglandular P5373 alfalfa were preferred over FGplh13 alfalfa. Similarly, at each observation, stems of FGplh13 alfalfa with the glandular trichomes removed were preferred over FGplh13 with the glandular trichomes intact. These data provide additional evidence for the localization of a resistance factor in the glandular trichomes of FGplh13 alfalfa. An antixenotic resistance mechanism also appears to be present, which may function, in part, through a tactile avenue.     

Influence of Xylella fastidiosa infection of citrus on host selection by leafhopper vectors

Infection of plants by pathogens can influence their attractiveness and suitability to insect vectors and other herbivores. Here we examined the effects of Citrus sinensis (L.) Osbeck (Rutaceae) infection by the bacterium Xylella fastidiosa, which causes citrus variegated chlorosis (CVC), on the feeding preferences of two sharpshooter vectors, Dilobopterus costalimai Young and Oncometopia facialis (Signoret) (Homoptera: Cicadellidae). Experiments were performed inside observation chambers, in which a healthy plant and an infected one (with or without CVC symptoms) were supplied to a group of 40 sharpshooters. The number of insects that selected each treatment was recorded at several time intervals in 48 h. In another experiment, the ingestion rate on healthy and infected (symptomatic or not) plants was evaluated by measuring the liquid excretion of sharpshooters that were confined on branches of each plant for 72 h. Both sharpshooter species preferred healthy plants to those with CVC symptoms. However, O. facialis did not discriminate between healthy citrus and symptomless infected plants. Feeding by D. costalimai was markedly reduced when confined on CVC‐symptomatic plants, but not on asymptomatic infected ones. The ingestion rate by O. facialis was not affected by the presence of CVC symptoms. The results suggest that citrus trees with early (asymptomatic) infections by X. fastidiosa may be more effective as inoculum sources for CVC spread by insect vectors than those with advanced symptoms.     

Behavioral evidence that the precibarial sensilla of leafhoppers are chemosensory and function in host discrimination

Leafhoppers (Homoptera: Cicadellidae) possess epi-and hypopharyngeal chemosensilla within the head. In this paper, we describe the behaviors of leafhoppers (Graphocephala atropunctata Signoret) which have had two of the four main nerves to these sensilla cut. Insects with severed nerves (treated) and control insects (both sham-operated and normal) were offered a choice of two small mustard leaves infused with either distilled water or a 5% sucrose solution. The control insects showed a preference for the 5% sucrose leaf, whereas the treated leafhoppers did not; they distributed themselves on both leaves with similar frequency. Thus, severing the nerves of only half of the precibarial chemosensilla (epipharyngeal organ) resulted in major changes in leafhopper feeding behavior. This evidence supports the hypothesis that the precibarial chemosensilla mediate gustatory discrimination of chemical compounds within the plant.

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Résumé Les cicadelles (Homoptera) possèdent dans la tête des sensilles gustatives sur l'épi et l'hypopharynx. Cette note décrit le comportement de Graphocephala atropunctata Signoret dont deux des quatre principaux nerfs de ces sensilles ont été coupés. Le choix entre des petites feuilles de moutarde infusées, soit dans de l'eau distillée, soit dans une solution de sucrose à 5%, a été proposé à ces insectes et à deux catégories de témoins, les uns intacts, les autres ayant subi une opération à blanc. Les témoins ont montré une préférence pour les feuilles traitées au sucrose, mais pas les cicadelles aux nerfs sectionnés. Les insectes sectionnés ont perforé les deux types de feuilles avec les mêmes fréquences. Ainsi la section de la moitié seulement des nerfs des sensilles gustatives précibariales (organe épipharyngien) a induit un changement fondamental du comportement alimentaire des cicadelles. Cette expérience appuie l'hypothèse selon laquelle les sensilles précibariales fournissent la discrimination gustative des composés chimiques de la plante.

     

Glandular Trichomes on Alfalfa Impede Searching Behavior of the Potato Leafhopper Parasitoid

New cultivars of alfalfa, Medicago sativa L., have been released with glandular trichomes for resistance to potato leafhopper, Empoasca fabae (Harris). Yet, the impact of the glandular trichomes on the primary natural enemy of the leafhopper, Anagrus nigriventris Girault, is unknown. We compared the host searching behavior of the egg parasitoid on four alfalfa clones varying in trichome characters. Female wasps were videotaped on Ranger, a susceptible clone with relatively sparse trichomes, B14, a resistant clone with dense but nonglandular trichomes, and FG12 and FG18, two resistant clones with glandular trichomes. Although the number of leafhopper eggs per stem exposed to wasps did not significantly differ among the four clones, the frequency of foraging and total foraging time were less on the two clones with glandular trichomes than on the two clones with nonglandular trichomes. In addition, an analysis of covariance demonstrated that, although the number of ovipositional probes increased with egg density on a stem, the number of probes on stems with glandular trichomes was significantly less than that on stems without glandular trichomes. The allocation of time by wasps among drumming, probing, and grooming behaviors was similar among the clones. Wasps tended to fly off of clones with glandular trichomes more often than off of clones with nonglandular trichomes. This study suggests that cultivars with glandular trichomes may interfere with host searching by A. nigriventris.     

Life-table study of Anagrus atomus, an egg parasitoid of the green leafhopper Empoasca decipiens, at four different temperatures

The objective of our study was to assess thepotential of the egg parasitoid Anagrusatomus L. (Hymenoptera: Mymaridae) for controlof the greenhouse leafhopper Empoascadecipiens Paoli (Homoptera: Cicadellidae). Theegg-adult development time, survivorship andreproduction of A. atomus were evaluatedat four constant temperatures (16, 20, 24 and28°C). Developmental time ranged from33.6 days at 16°C to 13.3 days at 28°C. Based on a linear regression ofdevelopment rate on temperature the lowerthreshold was estimated at 8.39°C. Anagrus atomus required 263.2 degree-days tocomplete its development from egg to adult. Theegg-adult survival rate and the sex ratio weresignificantly lower at 28°C than at theother three temperatures tested. The intrinsicrate of increase (r _m) variedsignificantly between all four temperatures.The potential of A. atomus to attackdifferent host ages was additionallyinvestigated. Host eggs were parasitizedthroughout their development but rate ofparasitism was reduced in host eggs older thansix days. The number of eggs parasitized waspositively density dependent but the rate ofparasitism decreased with increasing hostdensity. A maximum rate of parasitism of 62.5%was recorded. The potential impact of the eggparasitoid on the population dynamics of E. decipiens is discussed.     

First record of the grape leafhopper Erythroneura vulnerata Fitch (Hom., Cicadellidae) in Europe

Abstract:  The leafhopper Erythroneura vulnerata Fitch is native to North America, where it infests wild and cultivated grapes. In July 2004, E. vulnerata was recorded for the first time on Vitis vinifera L. (cv. Cabernet Sauvignon) in north-eastern Italy (Veneto region). This record is assumed to be the first in Europe. Preliminary observations on the pest distribution, seasonal abundance and the extent of symptoms in north-eastern Italy are reported.     

Two new species of the genus Abrus Dai & Zhang, 2002 (Hemiptera,Cicadellidae, Deltocephalinae) from China

Two new species of leafhoppers: Abrus damingshanensissp. n. (from Guangxi) and A. expansivussp. n. (from Guizhou) are described and illustrated from China. A map showing the geographic distribution of the two new species is given. Taxonomic notes on species of the genus Abrus is also provided.     

Isolation and characterization of polymorphic microsatellite loci in the green leafhopper Empoasca vitis Goethe (Homoptera)

Eight dinucleotide microsatellite loci were isolated and characterized within the green leafhopper Empoasca vitis (Goethe) using an enrichment cloning procedure. Primers were tested on 171 individuals collected in the southwest of France from the vine plants. The identified loci were polymorphic, with allelic diversity ranging from two to 18 alleles per locus. Observed heterozygosities were from 0.021 to 0.760. These microsatellite markers should prove to be a useful tool for estimating the population genetic structure, host-plant specialization and migration capacity of this insect.     

中国扁叶蝉属二新种(同翅目,叶蝉科)

记述扁叶蝉属2新种,黄斑扁叶蝉Penthimia fulviguttata sp.nov和茂兰扁叶蝉Penthimia maolanensis sp.nov,模式标本保存在贵州大学昆虫研究所。     

福建武夷山条大叶蝉属一新种(同翅目:大叶蝉科)

本文记述条大叶蝉属１新种：指突条大叶蝉Ａｔｋｉｎｓｏｎｉｅｌｌａ ｄａｃｔｙｌｉａ Ｙａｎｇ ｅｔ Ｌｉ,ｓｐ．ｎｏｖ．。文中详细描记了新种的外部形态牲和雄虫外生殖器构造,并附主要特征图。     

中国坦小叶蝉属研究(同翅目:叶蝉科:小叶蝉亚科)

记述坦小叶蝉属9新种,中国1新纪录种和1新组合,确认了1新异名,编制了中国坦小叶蝉属种检索表。模式标本均保存于西北农林科技大学昆虫博物馆。     

捷克Moravian博物馆馆藏巨索杆蝉属两种的再描记（同翅目：叶蝉科：杆叶蝉亚科）

作为杆叶蝉亚科分类订正研究的一部分,本文依据捷克Moravian博物馆收藏的Karasekia 属的模式标本和定名标本及英国自然博物馆（BM）馆藏定名标本对该属20世纪初记述的该属2个已知种作了再描记、绘出了形态特征图,并补充了属征。所有研究标本均归还原所属博物馆保藏。巨索杆蝉属Karasekia Melichar Karasekia Melichar, 1912c117. 模式种 巨索杆蝉Karasekialata (Melichar)。 分布 非洲。 1．巨索杆蝉Karasekia lata (Melichar) （图1）Wolfella lata Melichar,1905a299. Karasekia lata (Melichar), Melichar,1912c118. 分布Tanganyika, 非洲。 观察标本 1♀ (正模,无腹部和前胸背板), Amani,1904-Ⅲ-23, L. Melichar 采;1♂, Maherangulu, 东非;标本均借自 Moravian Museum,Brno。 2．冠齿巨索杆蝉Karasekia pugionata Melichar (图2) Karasekia pugionataMelichar, 1912c118. 分布Tanganyika, 肯尼亚,非洲。 观察标本 2♀♀(全模标本,MM),Maherangulu,东非,L.Melichar 采。 1♂( ?, 无腹部末端), 1♀（BM,1961-343）,肯尼亚Emali Range, Sultan Hamud, (1493 m～1798 m), P. E. S.和 E. M. Whalley采;2♀♀（BM,1961-343）,肯尼亚Wandanyi(1524 m),P. E. S. 和E. M. Whalley采;W. Knight鉴定。