Sophonia orientalis
(two-spotted leafhopper)

S. orientalis proved to be highly invasive on the Hawaiian Islands, although its populations decreased eventually, probably because of the impact of several natural enemies (Alyokhin et al., 2001). Nevertheless, it still remains a significant problem. Outside of Hawaii, a resident, breeding population of S. orientalis was found in Los Angeles County in California, USA (Garrison, 1996). However, its density remains fairly low and this species has not (yet?) become invasive in continental USA. Similarly, S. orientalis was collected in 1999 in Tahiti (Polhemus, 2001), but there were no reports on its invasiveness on that island. There are no records of it being invasive in its native regions.

S. orientalis is native to, and widely distributed in, South and South-East Asia. Following inadvertent introductions, it is currently present on all major Hawaiian Islands, on Tahiti (French Polynesia) and in southern California, USA, and has recently been recorded on Madeira and the Canary Islands.

The small size and concealed nature of S. orientalis eggs make their detection on imported plant material very difficult. The risk of introduction is therefore fairly high.

S. orientalis has been recorded from a wide variety of habitats (Fukada, 1996). Nevertheless, in a survey by Alyokhin et al. (2001), the leafhoppers appeared to have a preference for wetter, closed habitats rather than drier, open ones. Wild plants had a higher leafhopper infestation than cultivated plants. More eggs were found on the foliage from closed natural habitats than from open natural habitats. There was no difference in egg density between dry and mesic open natural habitats, but wet closed habitats harboured more eggs than mesic closed habitats. The type of mesic closed habitat also appeared to be an important factor, with habitats that had a shrub understorey harbouring more leafhopper eggs than habitats that had a fern understorey. The presence of preferred host plants may increase leafhopper density compared to otherwise very similar habitats (Lenz and Taylor, 2001).

S. orientalis is extremely polyphagous. Its nymphs develop on over 300 species of host plants in 83 families (Fukada, 1996). However, not all these hosts are equally preferred by the leafhoppers. For example, in a survey by Alyokhin et al. (2001), egg density varied from 227.83 ± 82.22 eggs per m² on the most preferred host, Hawaiian tree fern (Cibotium chamissoi) to 2.93 ± 1.10 on the least preferred host, grapefruit (Citrus paradisi). Similarly, Lenz and Taylor (2001) captured significantly more leafhoppers on the nitrogen-fixing Myrica faya [Morella faya] that had glabrous foliage compared to the non-nitrogen-fixing 'ohi'a lehua tree (Metrosideros polymorpha) that had hirsute foliage. On the Hawaiian Islands, where most work has been carried out, the impact of the leafhoppers on some host species has received more attention than on other species because of their economic, ecological or conservation significance. This might create a potentially misleading impression that those species are most affected by S. orientalis. In fact, little is known about the host preference of this insect.

Physiology and Phenology

All the information on this subject was obtained on the Hawaiian Islands, North America. Therefore, it is possible that the leafhopper phenology will be different in the areas with more pronounced seasonal changes. Under conditions typical to the Hawaiian winter (18.0-23.5ºC and 81.3-97.7% RH), it took S. orientalis between 3 and 4 months to complete a single generation (Duan and Messing, 2000). Because of the long oviposition and egg-hatching periods (approximately 10 and 4 weeks, respectively), it is likely that S. orientalis has overlapping generations (Duan and Messing, 2000). The adult leafhoppers were captured by yellow sticky cards throughout the year in a number of habitats on the islands of Kauai and Hawaii. However, their densities were usually highest during the summer months (Lenz and Taylor, 2001; Yang et al., 2002).

Reproductive Biology

S. orientalis is similar to many other cicadellid leafhoppers in that it reproduces sexually and is oviparous. In the laboratory at 23 ± 1.5ºC, adult S. orientalis did not mate until 7-9 days after eclosion. The proportion of mating pairs increased from 10 to 100% as age increased from 9 to 15 days. A complete mating process in S. orientalis consisted of mounting, back-to-back copulation, and postmating rest phases, which lasted for a mean ± SE period of 0.7 ± 0.04, 64.7 ± 1.20 and 3.5 ± 0.39 minutes, respectively (Duan and Messing, 2000). A single female produces approximately 30-35 eggs throughout her life span (Duan and Messing, 2000). Females insert their eggs on the underside (abaxial surface) of the foliage, usually at the juncture of the midrib and lamina, sometimes directly in the midrib and often near the intersection of the midrib and a cross-vein (Culliney, 1998; Yang et al., 2000). The eggs are usually located in the pith of the midrib with their long axis aligned with the axis of the vein. They may be positioned either with the operculum protruding slightly from the oviposition scar, or entirely concealed just below the scar surface (Culliney, 1998). On plants with thicker leaves, some of the eggs may be deposited away from the midrib (Yang et al., 2000). A variation in egg position relative to the basal, middle and apical third of the leaf also exists, but usually the middle third of the leaf is the most common oviposition site (Yang et al., 2000). When the adults were caged onto individual shoots of host plants [Cordyline terminalis (ti) and Psidium guajava (guava)] growing outdoors at 18.0-23.5ºC and 81.3-97.7% RH, they did not lay eggs until the second week after emergence. The oviposition period lasted 8-9 weeks, and the weekly oviposition rate peaked 4-5 weeks after emergence (9.8 ± 2.9 eggs per female on ti and 8.1 ± 0.9 eggs per female on guava). There was no significant difference in the total number of eggs laid per female on guava versus ti plants. Under outdoor ambient conditions, the eggs of S. rufofascia did not begin to hatch until 4 weeks after oviposition, and the peak rate of hatch occurred 6 weeks after oviposition. The newly hatched nymphs took a mean of 56.9 ± 2.8 days to complete development to the adult stage on guava and 47.2 ± 1.7 days on ti plants (Duan and Messing, 2000).

Environmental Requirements

S. orientalis is widely distributed in areas with a warm climate, ranging from Pakistan to California, USA. In Hawaii it has been collected from the sea level up to 1460 m (Fukada, 1996). It is not known to occur in areas with colder climates. Therefore, it appears that this species can survive under a variety of environmental conditions, as long as it does not get too cold. However, its exact environmental tolerances and preferences are unknown.

Associations

Jones et al. (1998) demonstrated that S. orientalis did not vector phytoplasmas in guava plantations in Hawaii. It is also not known to form any other interspecific associations.

A series of surveys conducted in Hawaii (Yang et al., 2000, 2002; Alyokhin et al., 2001; Johnson et al., 2001) revealed a fairly robust complex of generalist egg parasitoids (Hymenoptera: Mymaridae). In the survey by Alyokhin et al. (2001), approximately 40% of S. orientalis eggs, averaged over all host species and locations surveyed, were parasitized by Chaetomymar sophoniae, Schizophragma bicolor and Polynema sp. The percentage of parasitism varied widely among different plant species and habitats. Ch. sophoniae was the most abundant and widely distributed species, but the parasitoid guild varied depending on plant and habitat. Ch. sophoniae is a new species described by Huber (2003). It was previously called Chaetomymar sp. nr. bagichi (Alyokhin et al., 2001) or Chaetomymar sp. (Johnson et al., 2001). It is a new, adventive species in Hawaii that probably arrived from Asia together with S. orientalis. S. bicolor is native to North America and was first collected in Hawaii in 1963 (Huber, 1987; Beardsley and Huber, 2000). Polynema sp. is native to Hawaii, where it is known to attack the eggs of a number of native leafhopper species (Beardsley and Huber, 2000). Therefore, the parasitism of two-spotted leafhopper eggs represents a host range expansion for both S. bicolor and Polynema sp. (Johnson et al., 2001).

Both the nymphs and adults can be easily detected by visual inspections of the plant foliage. The adult populations have also been successfully monitored using yellow sticky aphid/whitefly cards (Lenz and Taylor, 2001; Yang et al., 2002). Oviposition scars may be visible to the naked eye on some, but not all, host plants (Culliney, 1998). Yang et al. (2000) developed a more reliable method for detecting S. orientalis eggs using backlighting of excised leaves by a fibreoptic microscope light source. Also, excised foliage containing S. orientalis eggs can be successfully incubated in plastic bags in the laboratory until nymphal emergence (Alyokhin et al., 2001).

The symptoms of damage caused by S. orientalis are fairly general (hopperburn) and are very similar to those caused by other leafhopper species.

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Phytosanitary Measures

Quarantine inspections may help to prevent S. orientalis introductions into new areas.

Host-Plant Resistance

Foliar pubescence appears to make plants significantly less suitable as S. orientalis hosts (Fukada, 1996; Jones et al., 2000; Lenz and Taylor, 2001).

Biological Control

A complex of two inadvertently introduced (Chaetomymar sophoniae and Schizophragma bicolor) and one or more native (Polynema sp.) egg parasitoids parasitized approximately 40% of S. orientalis eggs in Hawaii, North America. Percent parasitism increased dramatically between 1995 and 2000, and was accompanied by a substantial reduction in leafhopper densities (Yang et al., 2000, 2002; Alyokhin et al., 2001; Johnson et al., 2001). Since its first appearance in Hawaii, Ch. sophoniae rapidly expanded its range and began to dominate the parasitoid complex attacking S. orientalis. It is not known if the parasitoids were solely responsible for the observed suppression of S. orientalis, but it is likely that their contribution was substantial. Unfortunately, all the species have a fairly wide host range. Therefore, their possible future introductions into new areas for S. orientalis control should be carefully weighed against possible non-target effects on native leafhopper species.

Chemical Control

Chemical control appears to be highly efficient in controlling S. orientalis, with substantial reductions in both leafhopper populations and damage observed following the applications of a rotenone-azadiractin tank mix (Jones et al., 1998), orthene (Lenz, 2000) and imidacloprid (Follett et al., 2000).

IPM Programmes

No IPM programmes have been developed to specifically target S. orientalis.