Plant diseases caused by, or associated with, phytoplasmas occur in hundreds of commercial and native plants, causing minor to extensive damage. Insect vectors, primarily leafhoppers, planthoppers, and psyllids, have been identified for relatively few phytoplasma diseases, limiting the capacity of managers to make informed decisions to protect crops and endangered indigenous plants. In the past two decades our knowledge of insect vector-phytoplasma interactions has increased dramatically, allowing researchers to make more accurate predictions about the nature and epidemiology of phytoplasma diseases. These better-characterized systems also may provide clues to the identity of insect vectors of other phytoplasma-associated diseases. We review the literature addressing the ecology of insect vectors, phytoplasma-insect ecological and molecular interactions, vector movement and dispersal, and possible management strategies with an emphasis on research from the past 20 years.

Insect vectors of phytoplasmas

Vibrational communication is widespread in insect social and ecological interactions. Of the insect species that communicate using sound, water surface ripples, or substrate vibrations, we estimate that 92% use substrate vibrations alone or with other forms of mechanical signaling. Vibrational signals differ dramatically from airborne insect sounds, often having low frequencies, pure tones, and combinations of contrasting acoustic elements. Plants are the most widely used substrate for transmitting vibrational signals. Plant species can vary in their signal transmission properties, and thus host plant use may influence signal divergence. Vibrational communication occurs in a complex environment containing noise from wind and rain, the signals of multiple individuals and species, and vibration-sensitive predators and parasitoids. We anticipate that many new examples and functions of vibrational communication will be discovered, and that study of this modality will continue to provide important insights into insect social behavior, ecology, and evolution.

https://www.jstor.org/stable/10.1641/0006-3568(2005)055[0323:TBEOIV]2.0.CO;2

The Behavioral Ecology of Insect Vibrational Communication

Climate change can occur over evolutionary and ecological time scales as a result of natural and anthropogenic causes. Considerable attention has been focused in recent years on the biological cons...

Implications of climate change for parasitism of animals in the aquatic environment

▪ Abstract The evolution of reproductive isolation is perhaps the most significant stage in the process of species formation, and the study of reproductive barriers currently dominates investigations of speciation. The discovery that conspecific sperm and pollen precedence play an important role in the reproductive isolation of some closely related animals and plants is one of the real surprises to emerge from this field in recent years. This review begins with a brief history of the study of reproductive isolation with the aim of understanding why conspecific sperm and pollen precedence were generally overlooked in early work on reproductive barriers. It then examines: case studies, the prevalence of conspecific sperm and pollen precedence, the isolating potential of this class of reproductive barriers, the mechanisms that account for the operation of these barriers, and potential explanations for the rapid divergence of populations in traits related to fertilization. Conspecific sperm and pollen precede...

Conspecific Sperm and Pollen Precedence and Speciation

The use of terrestrial and aquatic invertebrates as a management tool for monitoring change in ecosystems is reviewed and critically evaluated. Their suitability and value for assessing a range of environmental problems from pollution impacts, through habitat evaluation for conservation to the long-term degradation and recovery of ecosystems, is critically discussed. Guidelines are provided for the choice of appropriate bioindicators. Examples of the use of a broad spectrum of invertebrates to assess a variety of environmental problems are summarized. The particular potential of invertebrates for monitoring montane ecosystems is highlighted.

Terrestrial and Aquatic Invertebrates as Bioindicators for Environmental Monitoring, with Particular Reference to Mountain Ecosystems

Recovery of Burrowing Mayflies (Ephemeroptera: Ephemeridae: Hexagenia) in Western Lake Erie

Leafhopper populations were sampled with sweep nets in grain cover and vegetable crops during 1988 and 1989. Populations in vegetable crops consisted primarily of aster leafhopper, Macrosteles quadrilineatus Forbes, except for potato crops in which Empoasca spp. were common. Adult aster leafhoppers were caught several weeks before nymphs in each year. Peak catches of aster leafhopper adults and nymphs occurred in both June and July. Data were consistent with the hypothesis that aster leafhoppers migrate to Ohio vegetable-growing areas in late May and June. Air trajectory analysis indicated three possible source areas of M. quadrilineatus migrating into Ohio vegetable-production areas: Arkansas, Louisiana, Texas, and Oklahoma; western Ohio, Indiana, and Illinois; and a corridor extending from Ohio to the Dakotas. Bioassays for aster yellows during 1989 and 1990 indicated that the leafhopper populations present during those years contained very few inoculative individuals. Growers should base treatment decisions on monitoring for inoculative aster leafhoppers.

Species composition, phenology, and possible origins of leafhoppers (Cicadellidae) in Ohio vegetable crops.

Few leafhopper species are known to be ant-attended. Evidence is presented that unequivocally demonstrates that Dalbulus quinquenotatusis a myrmecophile. In a greenhouse study, the behavior of D. quinquenotatusand four Dalbulusspecies not associated with ants was observed in the absence and presence of the pavement ant, Tetramorium caespitum. D. quinquenotatusis readily contacted by tending ants and responds to stroking on the abdomen from ants' antennae by excreting and holding honeydew droplets until droplets are removed by ants. Nonattended Dalbulusspecies avoid contact with ants by walking,jumping, or flying away when approached. D. quinquenotatusexcretes three to six times the volume of honeydew as do two nonattended species, D. maidisand D. gelbus.Droplets of D. quinquenotatusare about 23% larger in diameter and excreted two to four times more frequently than for the other species. D. quinquenotatustakes about 0.15 s to form honeydew droplets on the anal tube, then holds the droplet an average of 0.28 s before expelling it when ants are absent. In the presence of ants, D. quinquenotatusholds the droplet an average of 1.31 s, which gives ants time to harvest the droplet. Nonattended species, however, immediately expel droplets from the anal tube after droplet formation. This ant-leafhopper mutualism apparently has evolved due to the ability of D. quinquenotatusto have extensive physical contact with ants and excrete large amounts of honeydew. D. chiapensis,a possible descendent of D. quinquenotatus,may secondarily have lost its mutualistic relationship with ants.

Influence of ants (Hymenoptera: Formicidae) on honeydew excretion and escape behaviors in a myrmecophile,dalbulus quinquenotatus (Homoptera: Cicadellidae), and its congeners

Males and females of Prokelisia marginata (Van Duzee) and Prokelisia dolusWilson communicate through substrate-transmitted vibrations. The acoustic signals (attraction and courtship calls) of these planthoppers are effective in mate location, attraction, and mate choice. Attraction calls are structurally distinct for both species and differ in pulse type, pulse repetition rate, and pulse duration. Using playback of prerecorded calls, individuals discriminated between conspecific and heterospecific signals. Depending on the sex and species, response calls were produced three to eight times more frequently to conspecifics than to heterospecifics. However, acoustic signals alone did not explain reproductive isolation and hybridization failure in these two congeners. Some heterospecific pairs called, courted, and attempted to join genitalia, but no connections were successful and no progeny were produced. Thus, acoustic behavior is not a guaranteed premating isolating mechanism in no-choice situations. Other courtship behaviors and possibly morphological differences in genitalia also contributed to their isolation. Females displayed a variety of rejection behaviors to conspecific and heterospecific males, suggesting that sexual selection (female choice), in addition to species recognition, may be an important force in the evolution of the acoustic signals of planthoppers. Although signal structure was not dependent on wing form (planthoppers exhibit wing dimorphism), the age when females first began to call was related to wing form. Brachypterous (flightless) females of both species began calling early in adult life (day 2), whereas macropterous (migratory) females began calling later in adult life (day 6). This pattern is consistent with the oogenesis-flight syndrome, in which reproductive maturity is delayed until after migration occurs.

Susan E. Heady

Papers

Recovery of Burrowing Mayflies (Ephemeroptera: Ephemeridae: Hexagenia) in Western Lake Erie

Species composition, phenology, and possible origins of leafhoppers (Cicadellidae) in Ohio vegetable crops.

Influence of ants (Hymenoptera: Formicidae) on honeydew excretion and escape behaviors in a myrmecophile,dalbulus quinquenotatus (Homoptera: Cicadellidae), and its congeners

Reproductive isolation in Prokelisia planthoppers (Homoptera : Delphacidae) : acoustic differentiation and hybridization failure