Native saltbush (Rhagodia spp.; Chenopodiaceae) as a potential reservoir for agromyzid leafminer parasitoids on horticultural farms

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Australian Journal of Entomology (2010) 49, 82–90

Native saltbush (Rhagodia spp.; Chenopodiaceae) as a potential reservoir for agromyzid leafminer parasitoids on horticultural farms aen_725

82..90

Glenys Wood,1* Gitta Siekmann,1 Claire Stephens,1 Helen DeGraaf,1 John La Salle2 and Richard Glatz1 1

South Australian Research and Development Institute (SARDI), Sustainable Systems – Entomology, Waite Research Precinct Plant Research Centre, 2b Hartley Grove, Urrbrae, SA 5064, Australia. 2 CSIRO Entomology, GPO Box 1700, Canberra, ACT 2601, Australia.

Abstract

Australia has to date been spared the introduction of highly polyphagous invasive pest agromyzid leafminers; however, their arrival and spread should be considered imminent. To develop a pre-emptive control strategy to deal with exotic leafminer outbreaks the first step is to identify Australian leafmining flies, their plant hosts and their parasitoids to gain an understanding of their population dynamics. Native vegetation may be providing resources for beneficial parasitic wasps plus access to alternative hosts and refuge from disturbance. Here, two Australian endemic saltbushes (Rhagodia candolleana and R. parabolica, Caryophyllales: Chenopodiaceae) have been investigated for their potential to act as reservoirs for endemic agromyzid hosts and their key parasitoids. Mined leaves of the two Rhagodia species were sampled on two commercial horticultural properties in the Virginia horticulture area on the Northern Adelaide Plains between September 2007 and April 2008. Leaf mines on both Rhagodia species were caused by an endemic leafminer species, putatively Phytoliriomyza praecellens Spencer (Diptera: Agromyzidae). Ten species of parasitoids (all Hymenoptera) emerged from R. candolleana mines and seven different species from R. parabolica mines, mainly from the family Eulophidae and with some Pteromalidae and Braconidae. Trigonogastrella Girault sp. (Pteromalidae), Zagrammosoma latilineatum Ubaidillah and Hemiptarsenus varicornis Girault (both Eulophidae) were the most abundant species on R. candolleana, whereas two Opius Wesmael spp. (Braconidae) were the most abundant species on R. parabolica. Findings from this survey suggest an opportunity to plant purpose-designed refuges that could play a role in conservation biological control as part of an Integrated Pest Management strategy developed prior to incursion of pest leafminers such as Liriomyza species.

Key words

biological control, Liriomyza, revegetation.

I NTRODUCTIO N Conservation biological control, the establishment and maintenance of suitable on-farm and/or adjacent habitat, has been widely investigated as a strategy to enhance the survival of natural enemies (such as parasitic Hymenoptera) and thus improve biological control of pest species (Landis et al. 2000; Gurr et al. 2004; Zehnder et al. 2007). Non-crop vegetation may provide parasitic wasps with access to alternative hosts, adult food sources such as nectar, and refuge from disturbance such as insecticide sprays and crop harvesting (Schellhorn et al. 2000; Tscharntke 2000). Since the 1980s, three highly polyphagous agromyzid leafminers, Liriomyza huidobrensis Blanchard, L. sativae Blanchard and L. trifolii Burgess, have become cosmopolitan in distribution (Spencer 1973; Waterhouse & Norris 1987; Murphy & LaSalle 1999; Dempewolf 2004). Some of these invasive leafminers are now present in China, Vietnam, the

*[email protected] © 2010 South Australian Research and Development Institute Journal compilation © 2010 Australian Entomological Society

Philippines and Indonesia (Rauf et al. 2000; Andersen et al. 2002; He et al. 2002; Scheffer et al. 2006) and the impact of their introduction to Australia should be considered seriously by the Australian horticultural and floricultural industries. These leafminers are increasingly difficult to manage with insecticides (Keil & Parrella 1990; Murphy & LaSalle 1999; Salvo & Valladares 2007). Potentially vulnerable Australian crops include potatoes, celery, tomato, onion, brassicas, and ornamentals such as chrysanthemum and gerbera. Leafminer damage results mainly from larval feeding, which causes aesthetic damage, reduces yield, and at high larval densities, can destroy plants. Agromyzid leafminers are typically attacked as eggs, larvae or pupae by numerous parasitoid wasps in as many as five hymenopteran families (Spencer 1973; Murphy & LaSalle 1999). This species-rich parasitoid complex will be of great importance in controlling invasive agromyzid leafminers (Murphy & LaSalle 1999). So far, Australia has been spared the introduction of highly polyphagous pest leafminers, with the agromyzid bean fly Ophiomyia phaseoli Tryon currently the only species with pest status (Spencer 1973). The first step doi:10.1111/j.1440-6055.2009.00725.x

Native saltbush and leafminer parasitoids in developing pre-emptive control strategies to deal with exotic leafminer outbreaks is to identify Australian leafmining flies (e.g. Malipatil & Ridland 2008), their plant hosts and their parasitoids, to gain an understanding of their population dynamics (Bjorksten et al. 2005). Here we investigate Australian endemic saltbushes for their potential to act as reservoirs for key agromyzid leafminer parasitoids and their endemic agromyzid hosts. Major parasitoid species in previous surveys of Liriomyza brassicae Riley in South Australia were Hemiptarsenus varicornis Girault and a Zagrammosoma sp. (Hymenoptera: Eulophidae) (Lardner 1991). Targeted parasitoid surveys between 2003 and 2006 of native vegetation, including Rhagodia species, in the horticultural area in the Northern Adelaide Plains again found the leafminer parasitoid H. varicornis to be a frequently occurring parasitoid species (Stephens et al. 2006). This species has been reported as one of the dominant species in other studies of agromyzid–parasitoid associations (Shepard et al. 1998; Bjorksten et al. 2005; Lambkin et al. 2008). It has been used as a biological control agent of Liriomyza flies in greenhouses in Japan and Spain (Noyes 2002, 2003). Inspection of native revegetation on horticulture production properties in this area revealed leaf mines on Rhagodia candolleana and R. parabolica (Caryophyllales: Chenopodiaceae) that were potential sources for leafminers and their parasitoids. Rhagodia candolleana (seaberry saltbush) and R. parabolica (fragrant saltbush) are dioecious woody shrubs with small clustered flowers. All Rhagodia species are endemic to Australia (Black 1986). Rhagodia spp. tend to be long-lived perennial saltbushes that were chosen as likely candidates to replace short-lived annual exotic weeds near crops that are known to harbour vegetable pests (Taverner & Wood 2006). These shrubs effectively suppress weeds and can potentially provide a perennial refuge for generalist and specialist natural enemies. Intense horticultural areas tend to have minimal diversity and therefore, inclusion of enough endemic plants

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can potentially impart an ‘ecosystem service’ to Integrated Pest Management (IPM) programs. To this end, we surveyed the two endemic saltbush species for leaf mines over an 8-month period, at two vegetable production sites in the Virginia horticulture area on the Northern Adelaide Plains. We compare parasitic wasp abundances and species diversity between saltbush species over spring, summer and autumn. Based on the biology of the dominant species recorded we discuss the implications for conservation biocontrol to deal with future pest leafminer species.

MAT ERIAL AN D MET H ODS Study area and plant species Leafminer and parasitoid abundance and diversity were surveyed in the Virginia horticulture area, Northern Adelaide Plains, South Australia. Sampling of mined leaves of the two Rhagodia species was conducted fortnightly in spring and monthly in summer and autumn between September 2007 and April 2008. Sampling was conducted on two commercial horticultural properties, 5 km apart, that produce greenhouse tomatoes, cucumbers or capsicums (Site 1: 34o38′58.86S, 138o33′20.13E and Site 2: 34o39′55.33S, 138o34′54.92E) (Fig. 1). The mean maximum summer temperatures in the summer months ranged from 28°C to 30°C and in winter from 15°C to 16°C. The area has a winter-dominated rainfall pattern, with a mean annual rainfall of 428 mm (Bureau of Meteorology 2008). All Rhagodia plants occurred within 5 m of greenhouses. At Site 1 (Fig. 1a), the area covered by the two species was 14 ¥ 9 m and at Site 2, 10 ¥ 5 m (Fig. 1b). Rhagodia plants at Site 1 were planted in 2003 through weed-mat, into soil previously used for growing potatoes. Plants at Site 1 were larger than at Site 2 as they were a year older and experienced better

(a) Fig. 1. Schematic layout of revegetation including Rhagodia candolleana (Rc) and R. parabolica (Rp) and at two different agricultural sites: (a) Site 1 and (b) Site 2, on the Northern Adelaide Plains in 2007–2008. Rhagodia at Site 1 were surrounded by other chenopods Enchylaena tomentosa (Et), Atriplex semibaccata (As), Maireana brevifolia (Mb), as well as the grass Themeda triandra (Tt) and prostrate Kunzea pomifera: Myrtaceae (Kp). Rhagodia at Site 2 were surrounded by E. tomentosa (Et) and bare earth. Revegetation areas (rectangle) were covered by various native vegetation except where indicated ‘bare’; only the plant species surrounding Rhagodia spp. are shown in detail.

Site 1 greenhouse area

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Total native revegetation area: 21 m x 77 m

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growth conditions (weeds were excluded by the weed-mat and soil moisture better retained). At Site 2, Rhagodia seedlings were planted in 2004 into bare earth degraded by long-term soil compaction and herbicide use. Rhagodia shrubs at Site 1 were adjacent to native plants and grasses and Site 2 was adjacent to bare earth. No other sites that might have been more similar in growing conditions were available for this study.

fore, it was not known if multiple parasitoids emerged from individual mines (multiparasitism). In addition, the number of mines that were empty (post emergence) was not recorded at the time of collection. Leaf mines were dissected after emergence to estimate numbers of dead agromyzid larvae. All leafminer pupae and empty pupal cases were found inside leafmines. We estimated parasitism rate using the following formula:

Parasitism estimated (%) = Parasitoids emerged ( Parasitoidsemerged + Leafmineremerged + Immaturesdead ) × 100

Survey Single-species stands of plants were searched for mined leaves for 20 min per species. Rhagodia candolleana has succulent, shiny-green, lancet-shaped leaves, 1–3 cm long and 4–12 mm wide with the widest part of the leaf towards the base. They usually carry a single blotch mine which occupies 60–80% of the leaf area. The mine is situated on the upper side of the leaf. Rhagodia parabolica has slightly larger, triangular-shaped leaves, which are covered by granular wax particles and measuring approximately 2 cm at their widest point and 3 cm long. A single R. parabolica leaf can carry one to three blotch mines that are irregular in shape and extend to both sides of the leaf. Leaves were collected directly into food storage containers (15 ¥ 15 ¥ 5 cm) modified with silk windows (6 ¥ 1 cm), and chilled for transport to the laboratory. Containers with leaves were sealed with a layer of clingwrap and plastic fitted lid, and held under natural light at 22oC in the laboratory until parasitoids and adult leafminers had emerged. Containers were inspected fortnightly and emerged flies and parasitoids collected into 80% ethanol for subsequent identification. Leafminer flies were identified using a key to Australian agromyzidae (Spencer 1977) with advice provided through the Australian National Insect Collection (ANIC). Parasitoids were identified by John La Salle (ANIC). Voucher specimens of leafminers and parasitoids are preserved in alcohol and held at SARDI Entomology Waite Research Precinct in Adelaide. We did not dissect the leaf mines before emergence to avoid damaging pupating insects and affecting emergence. There-

RES U LT S Leaf mines on both Rhagodia species were caused by Phytoliriomyza sp. (Agromyzidae), most likely a species native to Australia (Spencer 1977). The majority (if not all) of emerged flies were most likely Phytoliriomyza praecellens Spencer and a small fraction could be the related species P. mollis Spencer (C Manchester pers. comm. 2008). The number of leaf mines per sampling date and emergent insects was up to 10 times higher on R. candolleana than on R. parabolica with differences most pronounced in spring and early summer (Figs 2,3). Species diversity was similar, but relative abundances of parasitoid species differed between plants (Table 1). Ten species of parasitoids emerged from R. candolleana mines and seven species from R. parabolica mines, mainly from the family Eulophidae and with some Pteromalidae and Braconidae (Table 1). Both Rhagodia species shared the same suite of parasitoids, but each plant supported different abundances of wasp species. Trigonogastrella sp. (Pteromalidae), and Zagrammosoma latilineatum and H. varicornis (Eulophidae), were the most abundant species on R.

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Fig. 2. Total number of leaf mines recorded for each sample date from Rhagodia candolleana (Rc) and R. parabolica (Rp) in a 20 min sampling period (per date), at two different locations in the Virginia horticultural area. n.a., not analysable. Total number of leaf mines overall: Rc Site 1: 1772, Rc Site 2: 1555, Rp Site 1: 246 and Rp Site 2: 55.

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Fig. 3. Total number of agromyzid and parasitoid emergences from leaf mines collected from two Rhagodia species (Rc, R. candolleana (black lines), Rp, R. parabolica (grey lines)) from August 2007 to April 2008, at two agricultural sites: (a) Site 1 and (b) Site 2.

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candolleana, whereas two Opius spp. (Braconidae) were the most abundant species on R. parabolica. Rhagodia candolleana supported the highest numbers of agromyzids and their parasitoids, in spring (October– November), at both locations (Fig. 3). At Site 1, the relationship of parasitoids to hosts on R. candolleana were temporally synchronised (a peak in host numbers was followed by a peak in parasitoid numbers); however, this was not the case at Site 2 in the summer months. On R. parabolica at Site 1, agromyzid abundance did not show distinct peaks; however, parasitoids peaked in September and April. At Site 2, very few agromyzids were found on R. parabolica with a slight peak in December, and almost no parasitoids emerged (Fig. 3). Early in the sampling period (spring), all three major parasitoid species Trigonogastrella sp., Z. latilineatum and H. varicornis were present, with parasitoid numbers peaking in November (Fig. 4). During this peak Z. latilineatum was about five times more abundant at Site 1 than at Site 2. In contrast, H. varicornis was about twice as abundant at Site 2 as at Site 1. A second, somewhat flatter and wider peak for Z. latilineatum numbers was found over the summer period at both sites.

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On R. candolleana the estimated percentage parasitism was the highest in October/November 2007 at the time of the highest parasitoid density (Fig. 5). At Site 1, an estimated 70% of leafminers were parasitised in October and at Site 2, about 55% of leafminers were parasitised in November. Agromyzid and parasitoid numbers on R. parabolica were too low to calculate percentage parasitism. Throughout summer, a high proportion of leafminer stages were dead within mines at the time of collection, presumably due to rising summer temperatures and abnormally hot and dry conditions during early March 2008 (mean daily maximum temperature = 31.1°C with 15 days >35°C (opposed to a historical mean of 26.9°C), Bureau of Meteorology 2008). It is also possible that a considerable proportion of these dead leafminers reflected high levels of host feeding.

DIS CUS S ION Two endemic Rhagodia species from revegetated areas adjacent to greenhouse crops on the Northern Adelaide Plains were © 2010 South Australian Research and Development Institute Journal compilation © 2010 Australian Entomological Society

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Table 1 Larval/pupal parasitoids collected from agromyzid leaf mines on two native saltbush species in the Virginia horticultural area, from August 2007 to April 2008 Parasitoid family Rhagodia candolleana Pteromalidae Eulophidae Eulophidae Pteromalidae Eulophidae Eulophidae Eulophidae Eulophidae Braconidae Braconidae Rhagodia parabolica Braconidae Braconidae Pteromalidae Pteromalidae Eulophidae Eulophidae Eulophidae

Parasitoid species

Site 1

Site 2

Total

Trigonogastrella sp. Zagrammosoma latilineatum Hemiptarsenus varicornis Callitula sp. Aprostocetus sp. (1) Aprostocetus sp. (2) Cirrospilus sp. Aprostocetus sp. (3) Opius sp. (1) Opius sp. (2) Total

159 169 54 48 35 32 19 18 0 0 534

175 56 79 30 18 16 13 4 15 7 413

334 225 133 78 53 48 32 22 15 7 947

Opius sp. (1) Opius sp. (2) Trigonogastrella sp. Callitula sp. Zagrammosoma latilineatum Aprostocetus sp. (2) Hemiptarsenus varicornis Total

35 33 15 13 8 8 2 114

1 1 0 0 0 0 0 2

36 34 15 13 8 8 2 116

the only indigenous plants observed to consistently display agromyzid leaf mines in high numbers (G Wood unpubl. data 2008). An endemic agromyzid leafminer species, putatively P. praecellens (Diptera: Agromyzidae), was found pupating in and emerging from leaf mines. This species was shown to support up to 10 species of hymenopteran parasitoids. As this native leafminer species is present at the study sites throughout the year, including winter (G Siekmann unpubl. data 2008), these results suggest an opportunity to manipulate endemic saltbush refuges supporting endemic hosts of leafminer parasitoids aimed at controlling invasive Liriomyza leafminer pests. Within this unique endemic plant genus, plant species appeared to exercise a strong influence on the abundance of the leafminer Phytoliriomyza sp. The agromyzid leafminer was very abundant on the saltbush R. candolleana and only occurred sporadically on R. parabolica as were the associated parasitoids. Leaf morphology differed markedly between the two Rhagodia species, which may have influenced host acceptance, oviposition and/or larval mortality of the leafminers. Not only fewer parasitoid species were found on R. parabolica but also species composition in terms of relative abundance was different. Whereas pteromalid and eulophid parasitoids were the most abundant on R. candolleana, braconid parasitoids were the most abundant on R. parabolica. Our study sites differed in plant diversity, Rhagodia biomass and plant quality; however, the leafminer host occurred in similar abundances at both sites suggesting a degree of robustness to varying site conditions. Also the dominant parasitoid species Trigonogastrella sp. and H. varicornis were found in similar numbers at both sites indicating their potential as biocontrol agents. In contrast, the remaining dominant parasitoid species Z. latilineatum was about three times © 2010 South Australian Research and Development Institute Journal compilation © 2010 Australian Entomological Society

more abundant at Site 1 suggesting that this parasitoid species might not appear as readily in random Rhagodia plantings. Zagrammosoma latilineatum was the only species that was found in high numbers in late summer and early autumn. This trend was observed at both sites, with the other abundant wasps showing peaks in the spring period only. This could imply that this particular parasitoid species might be better adapted to hot and dry conditions. Further research with laboratory temperature experiments could be worthwhile as yearround persistence in moderate to high numbers is a desirable feature for biocontrol parasitoids. Most of the parasitoid genera found on R. candolleana, i.e. Hemiptarsenus, Zagrammosoma, Aprostocetus, Cirrospilus (Eulophidae), Trigonogastrella, Callitula (Pteromalidae) and Opius (Braconidae), contain species that have been found on other agromyzid leafminers and plant hosts in Australia and South-East Asia (La Salle 1989; Lardner 1991; Shepard et al. 1998; Belokobylskij et al. 2004; Bjorksten et al. 2005; Lambkin et al. 2008). The parasitoid population hosted by the putative P. praecellens was dominated by two regionally endemic (Australia and South-East Asia) wasps, Trigonogastrella sp. and Z. latilineatum, which together accounted for more than 50% of the total number of parasitoids. Parasitoids in this study that are known to attack pest Liriomyza spp. are Opius spp. (Oatman 1960; Genung & Janes 1975; Lardner 1991; Schuster et al. 1991; Bordat et al. 1995b; Belokobylskij et al. 2004; Xu et al. 2007) and H. varicornis (Lardner 1991; Bordat et al. 1995b; Shepard et al. 1998; Giang & Ueno 2007) and fairly recently Z. latilineatum (Ubaidillah et al. 2000). The genus Trigonogastrella is known only from Australia, where there are two described species (Boucek 1988; Noyes 2002, 2003). These species are ectoparasitic idiobionts of Brachycera, especially (or perhaps exclusively) Agromyzidae,

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Trigonogastrella sp. Zagrammosoma latilineatum Hemiptarsenus varicornis

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mining in leaves or other parts of herbaceous plants (Boucek 1988; Noyes 2002, 2003). The related Trigonogastrella parasitica Girault is often found attacking the leafminer Chromatomyia syngenesiae Hardy on sow thistle Sonchus oleraceus (Bjorksten et al. 2005; Lambkin et al. 2008), but has also been recorded on a range of other agromyzid leafminers (Noyes 2003). The second most frequently recorded parasitoid was Z. latilineatum. The genus Zagrammosoma has about 15 species, being mainly found in the Americas (Reina & La Salle 2006), although there are a few species from Africa, Europe and Australasia (Noyes 2002, 2003). These species are mainly parasitoids of lepidopteran leafminers, although a few are known to attack agromyzids. As with the Trigonogastrella species recorded in the current study, Z. latilineatum is known only from South-East Asia and Australia (Noyes 2002, 2003; Reina & La Salle 2006). Until now Z. latilineatum has never been observed to occur in population densities high enough to expect good levels of biological control (Bjorksten et al. 2005; Reina & La Salle 2006). However, Lardner (1991) found a

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Zagrammosoma sp., which might be the same species, to be one of the major parasitoids of L. brassicae in the Adelaide region. Zagrammosoma latilineatum is also a solitary, idiobiont ectoparasitoid that probably prefers late-instar host larvae (Ubaidillah et al. 2000). The eulophid H. varicornis, often reported as a dominant species in other studies of agromyzid-parasitoid associations (Shepard et al. 1998; Bjorksten et al. 2005; Lambkin et al. 2008), ranked third in overall abundance in this study. This cosmopolitan parasitoid is an Old World species, known from the Middle East: Afrotropical, Oriental and Australasian regions (Reina & La Salle 2006). It has been used as a biological control agent of Liriomyza flies in greenhouses in Japan and Spain (Noyes 2002, 2003). Intriguingly, the relative abundances of the two braconids (Opius spp.) were markedly different between the two Rhagodia species. Opius spp. were clearly more abundant on R. parabolica. These parasitoid species were completely absent from R. candolleana at Site 1 and found only in low numbers at Site 2. As all previously discussed parasitoid species are © 2010 South Australian Research and Development Institute Journal compilation © 2010 Australian Entomological Society

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ectoparasitic, the endoparasitic behaviour of Opius spp. might be better supported by R. parabolica. Therefore, R. parabolica should also be seriously considered as a parasitoid refuge plant as Opius spp. have been reported to be important biocontrol agents of the pest Liriomyza spp. (Oatman 1960; Genung & Janes 1975; Schuster et al. 1991; Bordat et al. 1995a; Xu et al. 2007). Opius is a large genus, and species are widely distributed on all continents, with over 550 species described (Fisher et al. 2005). Opius attack Diptera, mainly leaf-mining Agromyzidae and fruit-infesting Tephritidae; they oviposit in egg or larval stages and emerge from host puparia (Wharton et al. 1990). The association of parasitoids of cosmopolitan vegetable leafminer flies with endemic saltbushes may have important implications for Australian horticulture as L. huidobrensis, L. sativae and L. trifolii have been classified as ‘Emerging Plant Pests’ by Plant Health Australia (2007). Findings from this survey suggest an opportunity to plant purpose-designed refuges that could perform a conservation biological control

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Fig. 5. Proportion of live agromyzids (black), dead immature agromyzids (grey) and live parasitoids (white) on Rhagodia candolleana at two agricultural sites: (a) Site 1 and (b) Site 2, in the Virginia horticultural area. Numbers above bars indicate total number of leaf mines collected at each date.

role in developing an IPM strategy prior to incursion of pest Liriomyza species. Our data suggest that in southern Australia, the saltbushes, R. candolleana and R. parabolica, can support benign endemic agromyzid fly hosts that will provide a range of leafminer parasitoids, some of which (particularly H. varicornis) are expected to parasitise Liriomyza species. There are a range of studies to show that Liriomyza species are attacked by a multitude of parasitoids (Murphy 1984; Minkenberg & van Lenteren 1986; Johnson & Hara 1987; LaSalle & Parrella 1991; Shepard et al. 1998; Murphy & LaSalle 1999; Rauf et al. 2000), some of which may be shared with other hosts. Most leafminer parasitoids attack multiple leafminer species in both natural and agricultural ecosystems (Hawkins et al. 1992; Salvo & Valladares 1998; Lewis et al. 2002), so attracting and maintaining these wasps in areas vulnerable to pest Liriomyza infestations could provide an ecosystem service to control leafminer pests. To optimise potential levels of control, we suggest that further research should examine the factors regulating native

Native saltbush and leafminer parasitoids agromyzid fly and parasitoid populations and the ability of naturally occurring parasitoids to parasitise harmful Liriomyza species on crop plants.

ACKNOWLE DG E ME NT S We thank the vegetable growers who hosted our on-farm trials. Christine Lambkin (QM, Qld) and Chris Manchester (ANIC) helped with the identification of the agromyzid flies. This work was undertaken through grants awarded to the South Australian Research and Development Institute with funding bodies including Horticulture Australia Ltd. (Project VG06014), Virginia Horticulture Centre, City of Playford and the Rural Industries Research & Development Corporation (project SAR59A).

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