Biological Control 47 (2008) 216–221
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Biological Control
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Host specificity of Spathius agrili Yang (Hymenoptera: Braconidae), an important parasitoid of the emerald ash borer
Zhong-Qi Yang a,*, Xiao-Yi Wang a, Juli R. Gould b, Hui Wu c a The Key Laboratory of Forest Protection, State Forestry Administration of China, Research Institute of Forest Ecology, Environment and Protection, Chinese Academy of Forestry, Dongxiaofu 2, Haidian District, Beijing 100091, China b United States Department of Agriculture, Animal and Plant Health Inspection Service, Center for Plant Health Science and Technology Laboratory, 1398 West Truck Road, Buzzards Bay, MA 02542, USA c North Greening Center, Changchun, Jilin 130117, China article info abstract
Article history: To investigate the host range of Spathius agrili Yang (Hymenoptera: Braconidae), a total of 18 wood boring Received 11 April 2008 insects either in the genus Agrilus or associated with ash forests were collected, reared, and presented to Accepted 1 August 2008 S. agrili females in no-choice tests. Results showed that S. agrili can parasitize some other insect larvae in Available online 13 August 2008 genus of Agrilus, but attack rates were significantly lower than its natural host, emerald ash borer, Agrilus planipennisi Faimaire (Coleoptera: Buprestidae). In Y-tube olfactometer tests, female S. agrili were only Keywords: attracted to twigs and leaves of EAB infested Fraxinus velutina and F. pennsylvanica, and not to 12 other Spathius agrili potential host plants. Two other plants, Prunus persica (L.) and Ailanthus altissima (Mill.), significantly Emerald ash borer repelled the EAB. Field surveys of 17 wood boring insects, including six species of Agrilus, revealed that Agrilus planipennis Host range none of these species were parasitized by S. agrili. It was indicated that the EAB natural parasitoid S. agrili Specificity has high host specificity. Natural enemy importation Ó 2008 Elsevier Inc. All rights reserved. Biological control
1. Introduction range of the EAB for use in classical biological control (Liu et al., 2003; Yang et al., 2005, 2006; Zhang et al., 2005). The emerald ash borer (EAB), Agrilus planipennis Fairmaire Spathius agrili Yang (Hymenoptera: Braconidae) is an important (Coleoptera: Buprestidae) is native to several countries in north- gregarious idiobiont natural enemy ecto-parasitizing EAB larvae in eastern Asia. This pest feeds on the phloem and cambium of ash Tianjin, China and other locations (Yang et al., 2005). It typically trees (Fraxinus spp.) in its larva stage, constructs overwintering exhibited 3–4 generations per year, overwintering as a full-grown chambers in outer sap wood when it is full grown, then pupates larva in a cocoon inside its host gallery. It’s mean natural parasit- and emerges the following spring (Yu, 1992). EAB are mostly uni- ism rate can over 60% in field (Wang et al., 2006; Yang et al., voltine in Tianjin, northern China. They overwintered as prepupae 2008). This parasitoid is a potential natural enemy for importation in shallow chamber excavated in the outer sapwood by them- to North America for successful biological control of EAB. Studies selves. The average longevity of adults was about 21 days and on the parasitoid biology (Yang et al., 2008), relations of spatial the adulthood lasted through early July. Female adults oviposited pattern between wasp and host (Wang and Yang, 2005), and effects in mid May and eggs hatched on average in 15.74 days. The larval of host size on sex ratios and clutch sizes (Wang et al., 2008a,b) stage lasted about 300 days to complete an entire generation have been conducted in detail. The EAB had four larval instars (Wang, 2005). EAB was discovered in North America in 2002 and (Wang et al., 2005) and the larvae mine under bark of their host has been causing serious damage to American forests (Haack trees, and that the parasitoids locate them might by vibration cues et al., 2002). Because of its cryptic life behavior and the difficulty and drill through the bark to parasitize them (Wang et al., in trapping this insect, it has proven difficult to control and to pre- 2008a,b). The parasitoid is a new species published in 2005, and vent spread throughout the USA. In order to seek a long-term and the EAB larva is just known the only host in natural condition effective control strategy, researchers in China and the USA have (Yang et al., 2005). discovered and screened potential natural enemies from the native Potentially, the introduction of exotic natural enemies or mass release of biological control agents may lead to unwanted non-tar- get effects. Whether or not such effects occur will mainly depend upon the host range of the biological control agent and the pres- * Corresponding author. Fax: +86 10 6288 9502. E-mail address: [email protected] (Z.-Q. Yang). ence of non-target species in the area of release (Lenteren et al.,
1049-9644/$ - see front matter Ó 2008 Elsevier Inc. All rights reserved. doi:10.1016/j.biocontrol.2008.08.001 Z.-Q. Yang et al. / Biological Control 47 (2008) 216–221 217
2005). Although legal requirements for assessing the impact of nat- Thyestilla gebleri Faldermann (Coleoptera: Cerambycidae) from ural enemies on non-target plants have been in place for a long Chingma abulilon (A. theophrasti Medicus); Eucryptorrhynchus chin- time, such testing has recently been required in some countries ensis (Olivier) (Coleoptera: Curculionidae) from Heaven tree (Ailan- for the importation of entomophagous natural enemies (Van Dri- thus altissima (Mill.); and an unidentified Pyralidae from F. esch, 2004). The potential negative impact of released biological velutina). In the USA, Agrilus anxius was collected from European control agents is a key component of the environmental assess- white birch (Betula pendula Roth.) in Amherst, MA, A. bilineata ment. In addition, many scientists believe that host ranges of can- was from White oak (Quercus alba L.) from Freetown, MA, A. rufic- didate natural enemies should be tested prior to introduction olis was from Red raspberry (Rubus idaeus L.) from Morgantown, (Simberloff and Stiling, 1996; Strong and Pemberton, 2000). WV, and EAB larvae were collected from Green ash (Fraxinus penn- Physiological host range tests have to be conducted by deter- sylvanica Marsh.) and White ash (F. americana L.) near Brighton, MI. mining wasp’s acceptance of potential non-target hosts. But this is very difficult to fulfill and the results often overestimated than 2.2. Field investigation that in natural conditions (Rutledge and Wiedenmann, 1999). Usu- ally, parasitic wasps search their host habitats according to smell At present, the wasp S. agrili was known to distribute in Tianjin from host plants (Vinson, 1976). Parasitoids will consequentially and Jilin, China, naturally parasitizing EAB larvae inside ash bark. response to the volatiles emitted from host plants. Thus, examina- But other potential hosts from other places or other plants have tion of a wasp’s habitat preferences could be used as a predictor of not been investigated yet. Besides EAB, other wood boring insect ecological host range (Rutledge and Wiedenmann, 1999). In this species were collected during 2004–2007 in and near ash forests study we evaluate the host range of S. agrili through investigations in Tianjin China. The larvae were reared in the laboratory to deter- in the field and bioassays in laboratory. mine whether these insects had been parasitized by S. agrili. These insects included O. orientalis (Mutuura and Munroe) from X. sibiri- cum Patrin., C. luteellus (Motschulsky) from P. communis (L.), H. ins- 2. Materials and methods ularis Staudinger from F. velutina, T. gebleri (Falderman) from A. theophrasti Medic, Sylepta derogata F. from A. theophrasti Medicus, 2.1. Insects Carposina niponensis Walsingham from Z. jujuba Mill. and an unidentified Pyralidae larva from F. velutina. Some common bup- Spathius agrili was collected from the Guangang Forest Park in restids in the genus Agrilus were also collected in China such as Dagang District, Tianjin Municipality, China. EAB larvae parasitized A. mali from M. pumila in Shaanxi Province, A. lewisiellus from J. re- by S. agrili and parasitoid cocoons were collected from velvet ash, gia in Shaanxi Province, A. zanthoxylumi from Z. bungeanum in Sha- Fraxinus velutina Torr., and reared in the laboratory in both China anxi Province, A. sorocinus from A. julibris in Tianjin, A. auriventris (Insect Culture Laboratory, Guangang Forest Park, Tianjin) and from C. reticulata in Zhejiang Province, L. bellula from P. persica in the United States (USDA-APHIS-PPQ, Center for Plant Health Sci- Beijing, and C. affinis Fabricius from P. tabulaeformis Carr. in Shanxi ence and Technology Laboratory, Buzzards Bay, MA). After emer- Province. No fewer than 50 individuals of each species were col- gence, adult wasps were fed a 20% honey solution (China) or lected. The selection criteria for the host range investigation in- pure honey (USA). clude (1) concealed insect larvae, especially wood borers in the Larvae for use in host specificity testing were collected from the same habitat (ash forest) as EAB lived; (2) other jewel beetle larvae, following host plants in the following locations: Agrilus mali Mat- especially Agrilus species. Certainly, it is impossible to collect all in- sumura from apple (Malus pumila Mill.) in Yijun County of Shanxi sects meet these criteria, we only select some representative Province in August 2005, and from Sievers apple (Malus sieversii insects. (Ledeb.) Roem. in Yili of Xingjiang Uygur Autonomous Region in July and August 2006; Agrilus lewisiellus Kerremans from walnut 2.3. Host specificity testing tree (Juglans regia L.) in Yijun County of Shaanxi Province in August 2005; Agrilus auriventris Saunders from tangerine (Citrus reticulata Host specificity tests were conducted from 2004 to 2007 in Chi- Blanco) in Xiangshan County of Zhejiang Province in October 2005; na and in 2006 in the USA, respectively. Eighteen insect species Agrilus inamoenus Kerremans from tangerine (C. reticulata Blanco) were presented to S. agrili in no-choice tests. Potential host larvae in Chenxi County and Cili County of Hunan Province in August (usually large larvae except H. insularis) were reared in the 2006; Agrilus zanthoxylumi Hou from Chinese pricklyash (Zanthoxy- branches of their natural host plant in the laboratory. Branches lum bungeanum Maxim.) in Fengxian County of Shaanxi Province 1.0–1.5 cm in diameter was cut into sections of 5–10 cm long, October 2006; Chrysobotris affinis Fabricius from Chinese pine (Pi- and then split in half longitudinally. A chamber approximately nus tabulaeformis Carr.) in Yuci and Xinzhou of Shanxi Province 3 cm long was excavated inside one half of the branch through to in September 2005; Lamprodila bellula (Lewis) from peach (Prunus near the bark edge. Test larvae were placed into the chambers then persica (L.)) in Shunyi District of Beijing June 2005, Sphenoptera sp. the two halves of the branches were reunited and bound tightly to- from Round-head wormwood (Artemisia sphaerocephala Krasch.) in gether with rubber bands. Both ends of the branch were waxed to Alashan of Inner Mongolia in July 2007. The following larvae were reduce water loss. The branches containing insects were placed in collected from Guangang Forest Park in Tianjin through May to glass test tubes of 2.8 cm in diameter and 11.5 cm in length, and a October during 2004–2007: A. planipennis from velvet ash (F. velu- pair of newly eclosed Spathius adults with no oviposition experi- tina); Agrilus sorocinus Kurosawus from Silk tree (Albizzia julibrissin ence was then introduced into the test tube and fed with honey. Durass.) (All above insects belong to Buprestidae, Coleoptera); Each treatment included 30 replicates. Insects in the branches Ostrinia orientalis (Mutuura and Munroe) (Lepidoptera: Pyralidae) were examined every 3–5 days to determine if the wasps laid eggs. from Siberia cocklebur (Xanthium sibiricum Patrin.); Chilo luteellus If the larvae died or became pre-pupae, new larvae in fresh sticks Motschulsky (Lepidoptera: Pyralidae) from Common reed (Phrag- were provided. Test larvae were provided continuously until the mites communis (L.) Trin.); Holcocerus insularis Staudinger (Lepido- female parasitoids died. If eggs were laid, the parasitized larvae tera: Cossidae) from velvet ash (F. velutina); Sylepta derogate F. were monitored to determine if S. agrili progeny could develop to (Lepidoptera: Pyralidae) from Chingma abulilon (Abutilon theophr- the adult stage. Insects tested using this method in China include asti Medicus); Carposina nipponensis Walsingham (Lepidop- A. zanthoxylumi, A. mali, A. inamoenus, A. sorocinus, A. lewisiellus, tera:Carposinidae) from Chinese date (Ziziphus jujuba Mill.); Sphenoptera sp., E. chinensis, A. auriventris, A. planipennisi, O. orien- 218 Z.-Q. Yang et al. / Biological Control 47 (2008) 216–221 talis, C. luteellus, H. insularis, S. derogate, C. niponensis, T. gebleri, and separation of means test, was used to compare wasp parasitism an unidentified Pyralidae larva. Insects tested in the USA include A. rates and oviposition on A. mali and EAB larvae, and Fisher’s Exact anxius, A. bilineatus, and A. ruficolis. In all cases, parasitism of EAB Test (PROC FREQ) was used to compare parasitism rates of Spathius larvae was used as a control. on EAB and other species, using the SAS software Version 9.1.3 In a no-choice condition, the wasps may lay eggs on other in- (SAS Institute Inc., 2006). sects which were not their natural hosts. They may choose substi- tute hosts for oviposition for breeding their offspring when they 3. Results can not find the best hosts. So a choice test was conducted compar- ing parasitism by S. agrili on the EAB and A. mali: One ash branch 3.1. Field investigation results containing a single EAB larva and one apple branch containing one A. mali larva were put together in a test tube, and a mated na- Under the natural conditions in China, none of the insect species ive female S. agrili was also introduced and fed with honey. The investigated were parasitized by S. agrili except EAB (A. planipennis) experiment consisted of 30 replicates. After the female parasitoids larvae (Table 1). We found Tetrastichus sp. and Doryctes sp. died, larvae in the branches were checked to determine if the from A. mali in Shaanxi, Atanycolus sp. and Eupelmus sp. from wasps had laid eggs. A. mali in Xinjiang, Tetrastichus sp. from A. lewisiellus in Shaanxi, Tetrastichus sp. and a braconid from A. zanthoxylumi in Shaanxi, 2.4. Response to host plant volatiles in a Y-tube olfactometer Tetrastichus sp. from A. sorocinus in Tianjin, and Spathius sp. (not agrili) from A. auriventris in Zhejiang. In addition, a Sclerodermus Attractiveness of plants to S. agili females was tested in the Lab- sp. from O. orientalis in Tianjin, a Copidosoma sp. from a Pyralidae oratory of Chinese Academy of Forestry from 2005 to 2007. The larva in Tianjin, and a parasitoid of Pteromalidae from Sphenoptera base tube of the Y-tube olfactometer was 18.0 cm in length and sp. in Inner Mongolia were found. No parasitoids were reared from each arm was 23.5 cm long, with an inside diameter of 2.0 cm A. inamoenus collected in Hunan, C. affinis Fabricius in Shanxi, and a 75° angle between two arms. The sample bottles containing L. bellula, T. gebleri, E. chinensis, C. luteellus, H. insularis, S. derogata, plants were 2500 ml, and 250 g of host plant material was used for or C. nipponensis in Tianjin. Another species being considered each test. Airflow was provided by a vacuum pump connected to for release in the USA, Tetrastichus planipennisi Yang (Yang et al., the base tube and controlled with flow meters at 90 ml/min in each 2006), was also not found attacking any larvae other than EAB. arm of the Y-tube. The air was run through a charcoal filter and a humidifier bottle before it went into the chamber with the test 3.2. Host specificity tests material. For each test, one sample bottle was filled with test plant leaves and twigs. Fresh branches and leaves of infested F. velutina The no-choice host specificity tests in the laboratory showed were collected from the Guangang Forest Park in Tianjin, China, that, besides EAB larvae, S. agrili can parasitize larvae of some spe- sealed in plastic bags, stored in a portable cooler at about 10 °C cies in genus Agrilus, such as A. mali, A. zanthoxylumi, A. inamoenus, and brought back to the laboratory of Chinese Academy of Forestry A. anxius, and A. bilineatus, and the progeny can develop success- in Beijing as soon as possible for use in experiments. The immature fully on some Agrilus species. However, percentage parasitism fruits of tangerine (C. reticulata) were collected from Cili County in was significantly lower on non-target Agrilus than on EAB (Tables Hunan Province. Leaves of other plants such as apple (M. pumila 2 and 3). In addition, only male progeny were produced on Mill.), Chinese pricklyash ( Z. bungeanum Max.), walnut ( J. regia A. bilineatus. L.), Silk tree (A. julibrissin Durass.), willow (Salix babylonica L.), pear (Pyrus bretschneideri Rehder), peach (P. persica (L.)), Cottonwood 3.3. Choice tests of parasitism by S. agrili on EAB and A. mali (Populus deltoides Bartr.), Chinese hawthorn (Crataegus pinnatifida Fructus), Japanese spindletree (Euonymus japonica L.), A. altissima In the choice tests, S. agrili attack rates on EAB (33%) and A. mali (Mill.), and Green ash (F. pennsylvanica) were all collected in or (27%) larvae were not significantly different (t = 0.32, P = 0.7514, near the yard of Chinese Academy of Forestry in Beijing. df = 10, 14). However, S. agrili laid significantly more eggs on the One arm of the Y-tub olfactometer contained the test plant, host EAB larvae (8 eggs/host) than on A. mali (2.67 eggs/host) while the other arm contained only air. Newly eclosed, mated, (F = 9.23, P = 0.0229, df = 1, 6). Progeny successfully emerged as and naive female wasps were released individually into the base adults from cocoons on both parasitized EAB and A. mali larvae. of the Y-tube and observed for up to 5 min. A choice was recorded when the wasp crossed the response line (1/3 of the way up of each 3.4. Results of Y-tube olfactometer determinations arm). No response was recorded when the wasp failed to cross the response line after 5 min. Females that did not respond were not Results of the Y-tube olfactometer tests indicate that only included in the statistical analysis. Every treatment included 30 leaves of ash trees (F. pennsylvanica and F. velutina) were attractive replicates (wasps), and each wasp was tested only once. All tests 2 to the female S. agrili (Xc = 9.50, 6.62), while other plants did not were preformed between 8:00–17:00 with the temperature rang- attract the parasitoids. Conversely, the wasps were significantly re- ing from 26 to 28 °C and RH 65–80%. Tubes from the sample bottles pelled by the odor from leaves of P. persica (L.) and A. altissima were switched between arms of the Y-tube after every five runs, (Mill.) (Table 4). and the Y-tube was washed using 95% ethanol after every 10 runs, to minimize confounding influences. During the experiments, the entire Y-tube device was put inside an enclosure made of white 4. Discussion cloth to ensure that light did not attract the wasps to one side or the other. Understanding the mechanisms that result in host specificity may help increase parasitoid safety and predict their efficacy in 2.5. Statistical analysis biological control (Conti et al., 2004). Parasitoid host range may proceed from traits affecting host suitability, or parasitoid foraging 2 behavior (Brodeur and Vet, 1995). There was a genetic basis for For the Y-tube choice experiments a Xc test (one-way) for good- ness-of-fit with one degree of freedom was used to determine sig- host utilization that may limit host-range expansion in parasitoids. nificance. Analyses of variance (PROC GLM), followed by Tukey’s And behavioral evidence suggests mechanisms that could promote Z.-Q. Yang et al. / Biological Control 47 (2008) 216–221 219
Table 1 Parasitoids emerging from Agrilus species collected in China
Agrilus species Order and family Host plant Collection GPS information Number larvae Parasitoids recovered province collected A. mali Coleoptera: Malus pumila Shaanxi 109°040E, 35°260N, 427 Tetrastichus sp. and Doryctes Buprestidae 1394m sp. A. mali Coleoptera: Malus pumila Xinjiang 82°14’E, 43°280N, 502 Atanycolus sp. and Eupelmus Buprestidae 775m sp. A. lewisiellus Coleoptera: Juglans regia Shaanxi 109°040E, 35°260N, 227 Tetrastichus sp. Buprestidae 1394m A. zanthoxylumi Coleoptera: Zanthoxylum Shaanxi 109°040E, 35°260N, 515 Tetrastichus sp. and Buprestidae bungeanum 1394m Paramblynotus sp. A. sorocinus Coleoptera: Albizzia julibrissin Tianjin 38°560N, 117°290E, 4m 176 Tetrastichus sp. Buprestidae A. auriventris Coleoptera: Citrus reticulata Zhejiang 121°520E, 29°280N, 4m 87 Spathius sp. not S. agrili Buprestidae A. inamoenus Coleoptera: Citrus reticulata Hunan 111°080E, 29°260N, 140 No parasitoids Buprestidae 100m Chrysobotris affinis Coleoptera: Pinus tabulaeformis Shanxi 109°040E, 35°260N, >50 No parasitoids Buprestidae 1394m Sphenoptera sp. Coleoptera: Artemisia Inner Mongolia 105°400E, 38°500N, 322 Unidentified Pteromalidae Buprestidae sphaerocephala 1562m Lamprodila bellula Coleoptera: Prunus persica Tianjin 38°560N, 117°290E, 4m 68 No parasitoids Buprestidae Thyestilla gebleri Coleoptera: Abutilon theophrasti Tianjin 38°560N, 117°290E, 4m 665 No parasitoids Cerambycidae Eucryptorrhynchus Coleoptera: Ailanthus altissima Tianjin 38°560N, 117°290E, 4m 73 No parasitoids chinensis Curculionidae Ostrinia orientalis Lepidopera: Xanthium sibiricum Tianjin 38°560N, 117°290E, 4m 81 Sclerodermus sp. Pyralidae Chilo luteellus Lepidopera: Phragmites Tianjin 38°560N, 117°290E, 4m 64 No parasitoids Pyralidae communis Holcocerus insularis Lepidoptera: Fraxinus velutina Tianjin 38°560N, 117°290E, 4m 429 No parasitoids Cossidae Sylepta derogata Lepidopera: Gossypilm Tianjin 38°560N, 117°290E, 4m >50 No parasitoids Pyralidae herbacelm Carposina niponensis Lepidoptera: Zizyphus jujuba Tianjin 38°560N, 117°290E, 4m 57 No parasitoids Carposinidae Pyralidae larva Lepidopera: Fraxinus velutina Tianjin 38°560N, 117°290E, 4m 227 Copidosoma sp. Pyralidae
No S. agrili were reared.
Table 2 No-choice host specificity testing from 2003 to 2005 in China on boring larvae collected in the same ash plantation forest as S. agrili
Species Order and family Host used in testing N Percentage parasitism Outcome Comparison with EAB Agrilus planipennis Coleoptera: Buprestidae Fraxinus velutina 30 33% Adults produced Agrilus auriventris Coleoptera: Buprestidae Citrus reticulata 30 0% No attack P < 0.0001 Ostrinia orientalis Lepidopera: Pyralidae Xanthium sibiricum 30 0% No attack P < 0.0001 Chilo luteellus Lepidoptera: Pyralidae Phragmites communis 30 0% No attack P < 0.0001 Holcocerus insularis Lepidoptera: Cossidae Fraxinus velutina 30 0% No attack P < 0.0001 Sylepta derogata Lepidoptera: Pyralidae Gossypilm herbacelm 30 0% No attack P < 0.0001 Carposina niponensis Lepidoptera: Carposinidae Zizyphus jujuba 30 0% No attack P < 0.0001 Thyestilla gebleri Coleoptera: Cerambycidae Abutilon theophrasti 30 0% No attack P < 0.0001 Pyralid larva Lepidoptera: Pyralidae Fraxinus velutina 30 0% No attack P < 0.0001
Attack rates on all non-target species were significantly lower than for the control (EAB) (Fisher’s Exact Test). specialization through induced host fidelity (Henry et al., 2008). consider the acceptance behavior of the parasitoid before ovipo- Parasitoid attack strategy influenced specialization in parasitoid- sition. Although parasitoid Microctonus aethiopoides Loan at- host interactions within certain host communities, and usually tacked some non-target hosts at lower parasitism rates in no- koinobiont genera utilized fewer host families than idiobionts choice test in laboratory, the natural enemy was finally imported (Althoff, 2003). for release against Sitona lepidus Gyllenhal in New Zealand Research on the natural host ranges of parasitoids is often (Goldson et al., 2005). Parasitic wasps use a broad spectrum of conducted through field investigations combined with laboratory different stimuli for foraging hosts (Wang and Yang, 2008).When experiments and observations. Walsh et al. (2003) studied the parasitoids search for hosts, usually they first find the habitats host range of Centistes gasseni (Hymenoptera: Braconidae) under where the hosts live, i.e., the plants consumed by host insects. natural conditions using field survey and observation in labora- Ecological factors are important determinants of host use in tory, collecting insects in the same family as its natural host in these parasitoids and although phylogenetic history may influ- the same habitat. Morehead and Feenerjr (2000) moved parasit- ence the range of hosts used (Stireman and Singer, 2003). Over oid eggs onto the potential host insect larvae and observed the long distances, parasitoids are often attracted to the habitat offspring fitness compared with those developing on the natural where their hosts may be located based on the volatiles of the host to determine the host range. However, this method did not plants of their preferred hosts consume. The role of semiochem- 220 Z.-Q. Yang et al. / Biological Control 47 (2008) 216–221
Table 3 Host specificity testing in 2006 in China and the United States
Species Host plant used in testing N Percentage parasitism Outcome Comparison with EAB Agrilus planipennis (United States) Fraxinus americana 30 27% Adults produced Agrilus bilineatus Quercus alba 30 7% Adult males only P = 0.0399 Agrilus anxius Betula papyrifera 30 3% No larval survival P = 0.0128 Agrilus ruficollis Rubus idaeus 30 0% No attack P = 0.0023 Agrilus planipennis (China) Fraxinus velutina 23 65% Adults produced Agrilus zanthoxylumi Zanthoxylum bungeanum 31 32% Cocoons produced –but no adults emerged P = 0.0164 Agrilus mali Malus micromalus 30 27% Adults produced P = 0.005 Agrilus inamoenus Citrus reticulata 15 7% Cocoons produced P = 0.0003 Agrilus sorocinus Albizzia julibrissin 15 0% No attack P < 0.0001 Agrilus lewisiellus Juglans regia 26 0% No attack P < 0.0001 Sphenoptera sp. Artemisia sphaerocephala 30 0% No attack P < 0.0001 Eucryptorrhynchus chinensis Ailanthus altissima 5 0% No attack P < 0.0001
All species except Eucryptorrhynchus chinensis (weevil) are buprestid beetles. Attack rates on non-target species were significantly lower than for the control (EAB) (Fisher’s Exact Test).
Table 4 Response of S. agrili to host plant leaf and twig volatiles tested in a Y-tube olfactometer
2 Host species Family Number of wasps choosing treatment Number of wasps choosing control Xc value Green ash, F. pennsylvanica Oleaceae 29 9 10.53* Velvet ash, F. velutina Oleaceae 25 9 7.53* Tangerine tree, Citrus reticulata Rutaceae 12 18 1.20 Apple, Malus pumila Rosaceae 17 14 0.29 Chinese Pricklyash, Zanthoxylum bungeanum Rutaceae 23 15 1.68 Walnut, Juglans regia Juglandaceae 12 19 1.58 Silktree, Albizzia julibrissin Leguminosae 11 19 2.13 Willow, Salix babylonica Salicaceae 23 12 3.46 Pear, Pyrus bretschneideri Rosaceae 15 15 0.00 peach, Prunus persica Rosaceae 9 21 4.80* Cottonwood, Populus deltoidess Salicaceae 16 14 0.13 Chinese Hawthorn, Crataegus pinnatifida Rosaceae 13 17 0.53 Japanese Spindletree, Euonymus japonica Celastraceae 10 20 3.33 Ailanthus altissima Simaroubaceae 8 22 6.53*
2 Notes: Indicates the significant differences at level of a = 0.05, df = 1, X0:05 = 3.84. icals from host plants was important for parasitoids to search cies tested. Research on the ecological relationships between S. hosts (Conti et al., 2004; Tentelier and Fauvergue, 2007). Some agrili and EAB also showed that the emergence date of S. agrili parasitoids spent more time foraging on host damaged plants was highly synchronized with the availability of the preferred than on undamaged plants (Baehrecke et al., 1990). Y-tube olfac- stage for oviposition (late instar larvae) (Wang et al., 2006, tometer studies can show which plants are attractive to female 2008a). By considering the combined results of this research: parasitoids. For example, healthy rice plants attract Cotesia chilo- (a) S. agrili is only attracted by ash leaves, (b) S. agrili oviposits nis, which parasitize Chilo suppressalis (Chen et al., 2002). Rutl- more readily on EAB than on other Agrilus species even when gi- edge and Wiedenmann (1999) determined the responses of ven no other choice, and (c) no S. agrili were reared from collec- three parasitoids to volatiles from host and non-host plants tions of over 3600 wood-boring larvae (2074 of which were using a Y-tube olfactometer. Parasitoids preferentially selected Agrilus), (d) as a newly published species, nothing was previously the host plants, especially volatiles from host plants damaged known about the host range of the parasitoid in its native range by host insects. However, some parasitoids may respond only except of EAB, we conclude that the risk of non-target attack on to the volatiles from damaged plants, and ignore undamaged wood-boring insects in the USA in a classical biological control host plants. For instance, the female endoparasitoid Trybliographa program would be minimal. rapae (Hymenoptera: Eucoilidae) is not attracted by volatiles from undamaged cabbages, but it preferentially selects plants in- Acknowledgments fested by its host, Delia radicum (Diptera: Trypetidae) (Neveu et al., 2002). But in natural conditions, the dead branches may We thank Shu-Jun Wei (College of Agricultural & Bio-Technol- not produce the same volatiles as living plant material and cause ogy, Zhejiang University) for collecting Agrilus auriventris; Ke-Gong similar parasitoid responses (i.e. parasitism/acceptance of certain Kang (Yangling Vocational & Technical College) and Hui Wu and hosts). In addition, some other environmental factors such as Miao-Miao Yang (College of Forestry, Northwest Agriculture & For- barometric pressure, may influence the parasitoid responsiveness estry University) for collecting A. zanthoxylumi. We are indebted to in the laboratory assays (Vet et al., 1983). Host-specificity testing Jian-Xing Zhao and Lan-Fen Qiu, (Research Institute of Forest Ecol- of proposed biocontrol agents is required to provide environ- ogy, Environment and Protection, Chinese Academy of Forestry) for mental safety assurances, but laboratory methods are likely to collecting Chrysobotris affinis Fabricius, and Dr. Wei-Hua Wang be flawed and cannot mimic the reality of nature (Charles and (Shunyi Forestry Bureau, Beijing) for helping to collect Lamprodila Allan, 2002). bellula (Lewis). This work was supported by grants from USDA- Results from our studies show that S. agrili was attracted only APHIS, the International Foundation for Science (D/3689-2, Swe- to ash among the host plants tested and percentage parasitism den), and the National Natural Science Foundation of China of EAB was significantly greater than for any of the other 18 spe- (30671689, 30400343). Z.-Q. Yang et al. / Biological Control 47 (2008) 216–221 221
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