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ABSTRACT. The zoogeographical distribution of 42 cicadellid subfamilies and their assigned tribes and genera is compiled with distributional maps and proposed dispersaI pathways of genera that are shared interzoogeographicaJJy. Possible origin of the subfamiJies and tribes is proposed in an ancestral context from which the more modem extant groups evolved whereas origin of genera is in a more modem contex!. Notwithstanding their complex biogeography, the distributional data ofthe higher groups indicate that ali ofthe cosmopolitan and near cosmopolitan subfamilies arose during early Cretaceous or possibly the late Jurassic period (140-116 m.y.a.) when continental drift was in its early stages. Nearly ali of the New World and some Old World subfamilies are considered of more recent origin (Iate Cretaceous-Tet1iary). Ninety percent of the known genera (2,126) are endemic to their respective zoogeographical region and subregion, thus indicating relatively high host specificity and low rate of dispersaI. The majority (76%) ofknown extant genera are pantropical in origin, suggesting early or possible Gondwanaland origin of their ancestors. Dispersai pathways of genera shared by more than one zoogeographical region were generally south to north (Neotropical/Nearctic, Oriental/Palaearctic) or west to east (Palaearctic/Nearctic, Oriental/ Australian), from regions of high diversity to regions of low diversity and from warmer c1imates to coo ler c1imates. The most di verse and richest leafhopper fauna are present in the Neotropical and Ethiopian regions although taxai aflinities between them are poores!. The most depauperate fauna are in the Nearctic region and in Australia, reflecting the impact of isolating and ecological factors on distribution and radiation. Ecological barriers were more evident between the Ethiopian and Oriental fauna than between any other zoogeographical combination. Taxai aflinities appeared to be correlated with close continental proximities. Vicariance (physical) was the principal event that appeared to explain the distribution ofmany subfamilies and tribes whereas dispersai accounted for distribution ofthe majority ofinterzoogeographical genera.

Germacrene A, the elusive biogenetic "parent" of many sesquiterpenes, has been isolated from the spotted alfalfa aphid and identified as a new intrageneric aphid alarm pheromone.

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The probing behavior of four biotypes of the spotted alfalfa aphid, Therioaphis maculata (Buckton), feeding on resistant and susceptible alfalfa clones (genotypes) was investigated. Salivation, X‐pattern, and ingestion waveforms, and probing sequences were similar among four biotypes probing the substrate of a susceptible clone. On one resistant clone (‘Moapa’ C‐905) probing sequences produced by biotypes A and C were similar but abnormal; stylet penetration of the phloem sieve element and ingestion were lacking or greatly suppressed. On another resistant clone (Moapa C‐908) probing sequences produced by biotype A were normal whereas those produced by biotype C were abnormal; stylet penetration of phloem sieve elements and ingestion were completely lacking. The salivation probe was successfully completed by both biotypes on the resistant clones; salivation time was significantly longer on the resistant clone than on the susceptible clone. The data suggest that the mechanism of resistance is based on a chemical interaction between the plant and aphid, and that the system is related to the phytoalexin theory of host‐plant resistance and to the phenol‐phenolase reactions of plants and sap‐sucking insects. Zusammenfassung PROBEVERHALTEN VON BIOTYPEN DER LUZERNEZIERLAUS AN RESISTENTEN UND ANFÄLLIGEN LUZERNEKLONEN Untersucht wurde das Probeverhalten von vier Biotypen der Luzernezierlaus (Therioaphis maculata (Buckton)) an resistenten und anfälligen Luzerneklonen (Genotypen) mit Hilfe der McLean‐schen elektronischen Messung. Dabei wurden die drei Wellenformen (1) für Speichelfluss, (2) für das Eindringen in ein Siebelement (= X‐pattern) und (3) für die Nahrungsaufnahme graphoanalytisch aufgenommen und analysiert. Auf anfälligen Klonen war das Probeverhalten, gemessen an Form und Abfolge von (1)–(3) bei allen Biotypen gleichartig. Dagegen waren auf einem resistenten Klon („Moapa” C‐905) die Probestiche der A‐ und C‐Biotypen zwar ähnlich aber anormal: Stechborstenpenetration in das Siebelement und Nahrungsaufnahme daraus waren stark gehemmt bzw. fehlten. Bei einem anderen resistenten Klon („Moapa” C‐908) waren die Probestiche des A‐Biotypus normal, während die des C‐Biotypus anormal waren; beim letzteren unterblieben Stechborstenpenetration in das Siebelement und Nahrungsaufnahme vollständig. Bei beiden Biotypen lief die Speichelflussphase auf resistenten Klonen erfolgreich ab; die Dauer des Speichelflusses war dabei auf resistenten Klonen bedeutend länger als auf anfälligen. Die Daten weisen darauf hin, dass der Resistenzmechanismus auf einer chemischen Interaktion zwischen Wirtspflanze und Blattlaus beruht und dass dieser Mechanismus in Zusammenhang gebracht werden kann mit der Phytoalexintheorie über die Resistenz der Wirtspflanze und mit den Phenol‐Phenolasereaktionen zwischen Pflanzen und saftsaugenden Insekten.

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Six alfalfa (Medicago sativa L.) cultivars, ‘DuPuits,’ ‘Ladak,’ ‘Lahontan,’ ‘Ranger,’ ‘Uinta,’ and ‘Vernal’ were selected for low and high saponin concentration and tested at various locations for seven agronomic traits and resistance to six diseases, five insects, and two nematodes. Although the selection for saponin concentration was effective, none of the agronomic traits (yield, foliage color, frost damage, lodging, digestibility, fraction I protein, and soluble protein) was consistently affected by the selection. High saponin concentration retarded the in vitro growth of southern blight (Sclerotium rolfsii Sacc.) but had very little effect on any of the other disease organisms studied: anthracnose (Colletrotrichum trifolii Bain); bacterial wilt (Corynebacterium insidiosum (Mc‐Cull.) H. L. Jens.); common leafspot (Pseudopeziza medicaginis (Lib.) Sacc.); downy mildew (Peronospora trifoliorum deBary); and phytophthora root rot (Phytoph‐thora megasperma Drechs.). High saponin concentration was also correlated with resistance to pea aphids (Acyr‐thosiphon pisum (Harris)) but had no appreciable effect on chalcids (Bruchophagus roddi (Gussakovsky)), clover root curculio (Sitona hispidulus (F.)), spotted alfalfa aphid (Therioaphis maculata (Buckton)), alfalfa weevil (Hypera postica (Gyllenhal)), northern root‐knot nematode (Meloildogyne hapla Chitwood), or stem nematode (Ditylenchus dipsaci (Kühn) Filip.). Significant correlations among the pest resistance traits suggest the possibility of linkages or pleiotropic factors.