Biological Control 24 (2002) 167–175 www.academicpress.com
A description of the commercial rearing and distribution of Microctonus hyperodae (Hymenoptera: Braconidae) for biological control of Listronotus bonariensis (Kuschel) (Coleoptera: Curculionidae) M.R. McNeill,a,* S.L. Goldson,a J.R. Proffitt,a C.B. Phillips,a and P.J. Addisonb a
AgResearch, Canterbury Agriculture and Science Centre, P.O. Box 60, Lincoln, New Zealand b AgResearch, Ruakura Research Centre, Private Bag 3123, Hamilton, New Zealand Received 25 May 2001; accepted 30 December 2001
Abstract A classical biological control program against Listronotus bonariensis (Kuschel) (Coleoptera: Curculionidae) in New Zealand commenced in 1989 with the importation of the braconid endoparasitoid Microctonus hyperodae Loan. In 1991, approximately 99,000 parasitized weevils were released at eight sites in the North and South Islands. Parasitoid establishment occurred at all sites and rates of parasitism suggested that the biological control agent would be successful. Research, which indicated that M. hyperodae dispersed at about 1.5–3.0 km yr1 , made multiple releases worthwhile. From 1993 to 1998 releases were made on a commercial basis. This approach, in part, was driven by a government requirement that, where possible, science should operate on a commercial/ cost recovery basis. Clients included individual farmers and territorial authorities. The creation and development of a successful commercial program to sell the parasitoid are reviewed along with discussion of results and problems encountered. At the conclusion of the program about 613,000 parasitized weevils had been sold and released at 112 locations within New Zealand. Ó 2002 Elsevier Science (USA). All rights reserved. Keywords: Microctonus hyperodae; Listronotus bonariensis; Argentine stem weevil; Commercial biological control; Marketing of biological control; Pastoral agriculture
1. Introduction Argentine stem weevil, Listronotus bonariensis (Kuschel) (Coleoptera: Curculionidae), is recognized as one of New Zealand’s most damaging pests of pasture (Prestidge et al., 1991). Accidentally introduced at the beginning of the 20th century (Marshall, 1937), and exclusive of the natural enemies found in its native South America (Lloyd, 1966), L. bonariensis rapidly became a pervasive pest of several economically important graminaceous species including ryegrass (Lolium spp.), wheat and sweet corn (Barker, 1989; Goldson, 1982; Morrison, 1938). Adult feeding is characterized by windowing of the leaves (Barker et al., 1981), but it is larval mining of the stem that causes the most significant *
Corresponding author. Fax: +643-983-3946. E-mail address:
[email protected] (M.R. McNeill).
yield losses in pasture (Barker et al., 1989; Hunt, 1990). In general, insecticide applications have been ineffective because the larval stage is protected inside the stem and because the mobile adults can rapidly re-infest pasture (Pottinger et al., 1984). In addition, the economic returns from treating pasture with insecticides are marginal. For this reason, management of L. bonariensis in perennial ryegrass has been based on a mutualistic association between ryegrass and the endophytic fungus Neotyphodium lolii (Latch, Christensen, and Samuels) Glenn, Bacon, and Hanlin (Ball et al., 1995). While peramine produced by the endophyte inhibits insect feeding and oviposition (Prestidge and Ball, 1993), other toxins produced by the endophyte can cause animal health problems (Fletcher, 1993; Fletcher and Easton, 1997). The animal health problems led to successful research to develop endophytes that conferred resistance to L. bonariensis but were not toxic to stock (Fletcher
1049-9644/02/$ - see front matter Ó 2002 Elsevier Science (USA). All rights reserved. PII: S 1 0 4 9 - 9 6 4 4 ( 0 2 ) 0 0 0 1 8 - X
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and Easton, 1997; Fletcher, 1999). However, biological control was perceived as highly complementary to plant resistance within an IPM system (Goldson et al., 1990). Natural enemy complexes are associated with all L. bonariensis life stages in South America (Lloyd, 1966). The adult parasitoid Microctonus hyperodae Loan (Hymenoptera: Braconidae, Euphorinae) was identified as being relatively host specific (Loan and Lloyd, 1974). This aspect was important in addressing one of the concerns about the impact of biological control agents on non-target species in New Zealand (Howarth, 1983; Longworth, 1987; Roberts, 1986). A visit to South America in 1988 confirmed M. hyperodae as the most suitable candidate for further evaluation (Goldson et al., 1990) and during 1989–1990 the parasitoid was collected from Concepci on, La Serena (Chile), P^ orto Alegre (Brazil), Colonia (Uruguay), Ascasubi, General Roca and Bariloche (Argentina) (Table 1). This collection was supplemented by parasitoids founded on one female collected from Mendoza (Argentina) (Goldson et al., 1993a). Each of these geographic populations was reared separately as individual lines of parthenogenetic parasitoids. A laboratory culture comprising 247 parasitoid ‘lines’ (founded on individual females) from the eight populations was established in quarantine (Goldson et al., 1990). Host-range testing indicated that M. hyperodae was oligophagous (Goldson et al., 1992a) and following consultation with interest groups, permission for release was gained from the New Zealand Ministry of Agriculture and Fisheries in 1991. A mass-rearing program commenced immediately and about 99,000 parasitized weevils were released during winter 1991 at eight New Zealand locations (Goldson et al., 1993a). The parasitoid established readily at six of the eight experimental release sites, with levels of parasitism between 0.2% and 5.3% after one year (Goldson et al., 1993a). This was followed by a rapid build-up in parasitism at the majority of sites, with parasitism levels of 60–80% measured in the winter of 1994 (Goldson et al., 1994). Preliminary research which indicated that M. hyperodae dispersed at only 1.5–3.0 km yr1 meant that it would have taken many years for its benefits to be Table 1 South American collection sites of M. hyperodae (Hymenoptera: Braconidae) Country
Region
Latitude, longitude
Brazil Argentina
P^ orto Alegre Rio Negro—General Roca Hilario Ascasubi San Carlos de Bariloche Mendoza Colonia La Serena Concepci on
28.00S, 39.00S, 39.23S, 41.11S, 32.48S, 34.29S, 29.54S, 36.50S,
Uruguay Chile
51.10W 67.35W 62.37W 71.23W 68.52W 57.48W 71.18W 73.03W
realized throughout the country. The Government had earlier indicated that science organizations, where possible, were to operate on a cost-recovery basis. One of the consequences of this policy was that the Government was not prepared to fund the parasitoid’s mass rearing and distribution. This marked a significant departure from previous government-funded broad-acre parasitoid releases (e.g., Stufkens et al., 1987). Because no suitable commercial biological control producers were available with whom a licensing contract could be negotiated, AgResearch researchers were in the position of having to undertake the commercial production, marketing and distribution of the parasitoid. In 1993, Watties Frozen Foods (now Heinz Watties) approached AgResearch about releasing the parasitoid in the East Coast region of the North Island to assist in the organic production of sweet corn. Accordingly, in August 1993, 15,000 parasitized weevils were released at three sites in the sweet corn producing region of the East Coast. This marked the start of the commercial program, which continued until 1998. This paper describes the development of the commercial program against L. bonariensis and highlights the role concurrent research played in the marketing and selling of the parasitoid. Research on the bionomics of L. bonariensis in Canterbury and the establishment and phenology of the parasitoid M. hyperodae have been detailed in other contributions (Goldson et al., 1998a,b). The impact of the parasitoid on L. bonariensis will be explored through life table analysis (Goldson et al., unpublished data). 1.1. Research Government-funded research was used to understand the biology of L. bonariensis and M. hyperodae and the impact of the parasitoid on the weevil. The work also sought to contribute to the development of biological control theory. Field sampling at the 1991 release sites at Ruakura (central North Island) and Lincoln (central South Island) showed a very rapid build-up of the parasitoid (Goldson et al., 1994). These early results indicated that the pest potential of the L. bonariensis populations in the parasitoid release areas would be substantially reduced. This was consistent with modeling, which predicted that parasitism would result in a 50% decline in peak weevil abundance within 4–5 yr of release (Barlow, 1993). Further laboratory and field researches investigated the effects of photoperiod and host condition on parasitoid diapause (Goldson and McNeill, 1992; Goldson et al., 1993b), the effect of parasitoid exposure on L. bonariensis survival (Goldson et al., 1993c), parasitoid host discrimination (McNeill et al., 1996), parasitoid fecundity and longevity (Goldson et al., 1995), parasitoid searching efficiency (Barlow et al., 1993) and susceptibility of M. hyperodae to selected insecticides and
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herbicides (P.J. Addison, unpublished data). DNA molecular techniques were used to identify the presumed South American origin of New Zealand L. bonariensis (Lenny-Williams et al., 1994) and morphometric techniques were used to define the geographic populations of M. hyperodae established in New Zealand (Phillips et al., 1997). This fundamental research on L. bonariensis and M. hyperodae was useful to the success of the commercial program because it provided key information on the biology of the parasitoid and its likely impact on L. bonariensis. This was essential when dealing with potential clients.
2. Key components of the commercial program 2.1. Selling and marketing strategies The commercial program adopted a ‘selling’ approach in part to raise farmer interest. This was necessary to overcome the incomplete understanding that most growers had of the pest status of L. bonariensis. For example, a telephone survey conducted in 1994 of dairy farmers in Waikato and mixed-cropping farmers in Canterbury indicated that only 12% and 7%, respectively, considered L. bonariensis to be their worst pasture pest. At the same time, 61% and 47%, respectively, of these groups had sown high-endophyte ryegrass in the previous two years, ostensibly to control insect pests or to improve pasture persistence. Also, 91% and 89% of respondents, respectively, were unaware that a biological control agent had been released against L. bonariensis. A marketing plan and organizational structure were developed in response to the business opportunity. Two research staff were re-positioned into the part-time roles of project leader and production manager, with support from a business manager who had marketing responsibilities. The titles of project leader and production manager were useful in publicity and advertising and provided clients with a clear organizational structure. 2.2. Publicity From the outset, one of the key considerations was to promote the parasitoid to potential purchasers. To this end, a 10-min introductory video, ‘‘Getting Even,’’ described the pest problem and the biological control program. Endorsements from farm and industry leaders were used to promote the benefits of biological control. Advertising in rural newspapers was used to publicize the commercial program, supported by articles in regional newspapers describing the research program and the commercial releases. As part of the sales process, generally one to three meetings were held with potential
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clients to discuss the biological control program. Researchers involved in the program were able to answer many of the fundamental questions relating to weevil and parasitoid life cycles, population dynamics, economic impact of L. bonariensis, and the likely effects of the biological control agent. Graphic presentation of the build-up in parasitism and associated impact on L. bonariensis (Fig. 1) was also very important in conveying the message. Ongoing support to farmers who purchased the parasitoid was provided by the extension publication ‘‘pestNEWS.’’ This kept participants informed of developments in the biological control program, as well as other pest issues considered to be of interest to the purchasers. In two major North Island contracts, farmers on whose properties releases had been made were provided with signs, which advertised the release and provided a brief description of the site management. This concept was well supported by the farmers with over 90% displaying the signs on gates or fences. 2.3. The economics of biological control of L. bonariensis Farmers will favorably consider technologies that will increase efficiencies, production, and profitability (Morris et al., 1995). Therefore, the primary concern of farmers related to the economic benefit of biological control. In general, attempts at measuring the impact of L. bonariensis were based on comparative studies between insecticide-treated and untreated ryegrass pasture conducted in the North Island. Frequent applications of systemic insecticide (e.g., carbofuran, oxamyl) were shown to produce a mean annual increase of 20% in perennial ryegrass pasture (Kain et al., 1977). Barker et al. (1984) reported a 17% increase in the yield of Lolium perenne L. (Grasslands Nui) ryegrass over the spring–autumn period, while increases of 6–17% were recorded on the central Volcanic Plateau region (Prestidge et al., 1984). This information was used to provide a conservative estimate of the cost of L. bonariensis to sheep and dairy farms on a yearly basis for a ‘typical’ northern North Island dairy farm (Table 2). An independent cost/benefit analysis was undertaken in 1996 to provide a more precise indication of the likely benefits of biological control. Using the assumption that parasitism would lead to a 50% reduction of L. bonariensis impact (Barlow, 1993), two outcomes were postulated as a result of biological control. These were that: (a) the only impact of the project would be to reduce infestation of existing pastures, leading to a 4.2% increase in productivity from those pastures; and (b) biological control of L. bonariensis would permit the adoption of new pasture species such as non-endophytic ryegrass cultivars, previously susceptible to the weevil. The improved quality of these pastures would lead to a 10% increase in animal productivity.
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Fig. 1. Listronotus bonariensis adults m2 measured at Lincoln, Canterbury, between December 1990 and June 1997 and the percent parasitism by M. hyperodae from 1991 onwards.
Once the one-off cost (NZ$15,000) of the parasitoid purchase was removed, the predicted economic benefits from a 4.2% productivity increase were increased net returns of NZ$78 ha1 and NZ$11 ha1 for dairy and sheep producers, respectively. Where biological control led to a 10% increase in animal productivity, returns increased to NZ$155 ha1 and NZ$19 ha1 for dairy and sheep producers, respectively. These returns were calculated using 1996 costs and primary product values. 2.4. Rearing facility Two rearing laboratories (about 25 m2 each) were built, where temperature and photoperiod could be controlled. One laboratory housed the parasitoid cultures, while the second was used for mass rearing. A controlled-environment glasshouse, adjacent to the insect-rearing laboratories, was used for growing the ryegrass required to feed the weevils. For cool storage, weevils were held either in an insectary or in a purposebuilt cooler maintained at 4 °C with a 12:12 (L:D) h photoperiod. Table 2 Estimated yearly costs (NZ$) of L. bonariensis larval damage on sheep and dairy farms (s.u. = stock units) Assumptions
200 ha sheep farm 100 ha dairy farm (NZ$35.80/s.u.) (NZ$67.50/s.u.)
Reduced production potential (10% pasture loss/year) Pasture renewal costs (10% renewal/year) Total losses/year
$4330
$11,090
$5610
$2450
$9940
$13,540
2.5. Mass-rearing protocol All rearings were conducted at 22–24 °C with a 12:12 (L:D) h photoperiod. With the exception of the Brazilian ecotype, M. hyperodae enters diapause when the photoperiod is less than about 13.3:11.7 (L:D) h (day length of about 12.3:11.7 (L:D) h) (Goldson et al., 1993b). Maintaining a photoperiod of 12:12 (L:D) h ensured that M. hyperodae did not advance beyond the larval first instar stage. In addition, to ensure that parasitoids derived from the Brazilian ecotype did not develop during storage, all parasitoid-exposed weevils were maintained at 6 °C. Mass-rearing cycles were generally completed in six weeks, this being the maximum period that parasitized weevils could be stored without significant mortality (Goldson et al., 1992b).
3. Insect cultures and parasitoid rearing 3.1. Adult M. hyperodae At the commencement of the commercial program, 55 ‘lines’ were available for commercial release. This represented ca. 22% of the 247 ‘lines’ originally established in quarantine and used in the initial releases (Goldson et al., 1993a). The logistics of maintaining all 247 lines had been found to be prohibitive and some had to be terminated. To maintain a supply of parasitoids for mass rearing, batches of 150 weevils were exposed to six parasitoids for 5 d in clear polycarbonate cages ð220 mm 130 mm 75 mm depth). Parasitoids were supplied from the culture collection. Each batch was then transferred to a parasitoid-rearing cage consisting
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of upper and lower chambers. The floor of the upper chamber consisted of fine mesh (64 squares 10 mm2 ) through which prepupae fell into the lower chamber which was lined with sheets of paper toweling. Parasitoids pupated under the paper and, after emergence was complete, cocoons were removed and were placed in a petri dish. A dental roll moistened with water prevented desiccation of the developing pupae. Parasitoid development rate could be controlled to suit the demands of mass rearing by manipulating temperature within a controlled-environment chamber. 3.2. Adult L. bonariensis Up to 60,000 parasitized weevils could be produced in one mass-rearing cycle. Although, L. bonariensis can be reared from egg to adult in culture (Power and Singh, 1974), this was not practical for the commercial program so adults were collected from pasture at night. A collecting bin that was dragged behind a vehicle was used to collect weevils when the grass was dry. Up to 50,000 weevils could be collected in 2 h of sweeping. However, low temperatures and wet pasture made it impossible to collect weevils by sweeping during midwinter (June–July). At this time, heated pads powered by a portable generator were used to attract the insects out of the grass onto the pads (Goldson and Proffitt, 1991). After collection, weevils were stored for up to 12 weeks either in the insectary or at 6 °C and 12:12 (L:D) h. Storage does not affect the weevils’ ability to support parasitoid development (Goldson and Proffitt, 1990). There were no disease problems in the cultures. However, adventitious parasitism by Microctonus aethiopoides Loan (Hymenoptera: Braconidae) (Goldson and Proffitt, 1991) required that collected weevils be purged of M. aethiopoides prior to use in the rearing of M. hyperodae. Differences between M. aethiopoides and M. hyperodae in development rate and appearance of the cocoon (McNeill et al., 1993) were used to selectively remove any M. aethiopoides that had been inadvertently introduced into the mass-rearing cycle. 3.3. Mass parasitism of weevils The method for mass parasitism of L. bonariensis by M. hyperodae was based on the method described by Goldson et al. (1993a), except that weevils were exposed to parasitoids for 8 d using a parasitoid:weevil ratio of 1:30. This exposure period was sufficient for parasitoids to lay the majority of their eggs (Goldson et al., 1995). As each geographic population comprised varying numbers of individual females (5–10), lines with only five females were bred more intensively than those with 10 lines (e.g., 5 lines: 6 parasitoids/180 weevils; 10 lines: 3 parasitoids/90 weevils). Because M. hyperodae is the-
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lytocous, the absence of males simplified maintenance of the cultures and bulking up of lines for each mass rearing. In the commercial program, the number of insects per cage ranged from 60 weevils with two parasitoids to 1400 weevils with 46 parasitoids. Weevil numbers were estimated by weighing using the following relationship: Weevil number ¼ 9:8 þ 491 ðweevil weight ðgÞÞ ðR2 ¼ 95:7; df ¼ 66; 1; P < 0:001Þ: During the exposure period, weevils were supplied with 3–4 bouquets of glasshouse grown L. multiflorum L. (Grasslands Tama) ryegrass, supplemented with an insect general-purpose diet (Clare et al., 1987). At the end of the exposure period (8 d), parasitoids were removed, the weevils were transferred to 220 mm 130 mm 75 mm deep transparent cages, and were supplied with two bouquets of ryegrass. These were placed either in the insectary or in a controlled-environment room maintained at 6 °C and 12:12 (L:D) h. Coinciding with the removal of parasitoids, a subsample of about 20 weevils was taken for dissection to determine the level of parasitism. As with the experimental releases of M. hyperodae, each South American geographic population was released in approximately equal numbers. At the completion of each rearing, numbers of each of the seven principal geographic populations (Table 1) were adjusted (based on dissection results) by removing weevils with a known level of parasitism from a selected parasitoid line. In practice, the balance was allowed to vary by a maximum of 14% of the mean number of parasitized weevils per ecotype. This was based on the maximum variation permitted in the original research releases (Goldson et al., 1993a). The geographic populations were combined, mixed, and then divided equally among release sites. Parasitoids derived from the individual female collected from Mendoza were used to supplement each release. Insects were then couriered by air to AgResearch staff for release. With one exception, all rearings and releases were conducted in winter. This synchronized the parasitized weevils with the L. bonariensis field population and had proved successful in the initial research releases (Goldson et al., 1993a). Microctonus hyperodae and L. bonariensis diapause in winter (Goldson and Emberson, 1980; Goldson et al., 1993b), thus winter releases allowed immature M. hyperodae to resume development in spring with the cessation of diapause. Overall, parasitism rates in the 22 rearings conducted between 1993 and 1998 averaged 74%. At its conclusion, the program had used approximately 33,000 parasitoids and 990,000 weevils. For historical record, information about each rearing, including its release and establishment, was recorded on an electronic database.
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4. Release and recovery of M: hyperodae 4.1. Release strategy Ten thousand parasitoids were selected as a minimum number for a release and comprised ca. 1400 parasitoids from each of the principal seven geographic populations. This large number was chosen for three reasons. Firstly, previous experimental releases, where an average of 13,400 parasitized weevils were released per site, had shown successful establishment (Goldson et al., 1993a). Secondly, analyses of previous biological control introductions have demonstrated the benefit of large releases (Clausen, 1978; Hopper and Roush, 1993). Finally, from a commercial perspective, large releases minimized the risk of failure and therefore the necessity for re-releases. Research at Lincoln had indicated that the parasitoid’s dispersal rate was biased downwind from the direction of the prevailing wind (Goldson et al., 1999). Therefore, releases were made on sites windward of the contributing farmers’ properties, provided they met the release requirements. 4.2. Cost of release The price of a release of 10,000 parasitized weevils was NZ$15,000 plus 12.5% goods and service taxes. This price was based on rearing and production costs, which included seasonal start-up costs, low production volume, and a labor-intensive rearing process plus profit margin. The New Zealand market is also very small so individual production runs were small, with the consequence that the cost per parasitoid was high. Since NZ$15,000 was likely to be prohibitive to individual farmers, the parasitoid was predominately marketed to farmer groups represented by irrigation schemes and dairy companies. Given a rate of spread of 1.5 km yr1 , it was expected that the parasitoid would cover 1000 ha in about 4–5 yr, thereby reducing the total cost over a five-year period to NZ$15.00 ha1 . 4.3. Guarantee of establishment To maximize the probability of establishment and build-up of the parasitoid, AgResearch required that the purchaser met the following criteria: the release paddock was no smaller than 1 ha, pasture was to be 2- to 4-yrold, preferably sown in low endophyte ryegrass, to remain in pasture and to be grazed between 3 and 15 cm in height, not to be heavily mob stocked (>300 stock units h1 d1 ), and that the release and adjacent paddocks were not to be treated with insecticides for at least 18 months after release. Some of these requirements were relaxed as appropriate. For example, pasture containing grasses favor-
able to L. bonariensis (e.g., cocksfoot Dactylis glomerata L.; Poa annua L.) were found to be suitable for parasitoid establishment, even if high-endophyte ryegrass was present. In practice, these requirements relied on the good faith of the purchasers, as no verification system was established to ensure compliance. An essential component of the contract was the guarantee by AgResearch of parasitoid establishment. If no parasitized weevils were detected two years after release and the purchaser had adhered to the post-release management conditions, another release was made free of charge. Once establishment or otherwise was determined a report was sent to the client(s). AgResearch did not guarantee that the parasitoid would be singularly successful in suppressing L. bonariensis, but rather that it would form a significant component of an integrated pest management program which included attention to soil moisture, fertility, and grazing management. 4.4. Parasitoid establishment Attempts to confirm M. hyperodae establishment were normally made in winter of the following year of a release. Depending on climate, this would have allowed 2–3 parasitoid generations to occur (Barlow et al., 1994), so that parasitism could reach detectable levels. The sampling was undertaken by AgResearch staff and involved collecting adult weevils using a commercial leaf blower-vacuum (e.g., Homelite HB180V) with a catching net fitted to the inlet. Weevils were sorted from the litter, were counted, and were then either held in the laboratory to rear M. hyperodae to the adult stage or were dissected under a binocular microscope. Numbers collected at any one site varied widely (20–1000). The parasitoid was considered to have established if a single parasitoid emerged, although in general, more than one parasitoid was recovered at each site. Based on the research releases (Goldson et al., 1993a) and other studies (e.g., Goldson et al., 1999), once M. hyperodae established at a site, there was generally a subsequent buildup in parasitism. With a few exceptions (see below) this assumption was confirmed where contracts with clients required monitoring of sites for 2–3 yr after a release. Climate was important to the establishment of M. hyperodae and subsequent levels of parasitism. In general, parasitism levels increased more rapidly in the warmer North Island regions than the cooler South Island, this finding being consistent with the phenology of the parasitoid (Barlow et al., 1994). In the North Island, parasitism after one year averaged 13% (range 0.3– 60.6%). In Canterbury, where all South Island releases occurred, parasitism averaged 1.2% (range 0.1–5.0%) after one year. Microctonus hyperodae successfully established at all North Island release sites. However, in Canterbury the
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parasitoid failed to establish at three sites, which necessitated re-release. Supplementary releases were made at a further four sites in Canterbury, because levels of parasitism in the original sites had failed to increase above 1% two years after releases were made. The rereleases were at no extra cost to the farmers. These subsequent releases established successfully and levels of parasitism were found to increase in the two years following re-release.
5. Outcome of commercial program The commercial program was financially profitable and achieved widespread distribution of the parasitoid in the North Island, where 79% of the releases occurred (Fig. 2). Significantly, sales were made to a pastoral industry that previously had little direct association with biological control. Investment in the parasitoid was most pronounced in the more profitable dairy industry, particularly in the North Island; about 77% of releases occurred on dairy farms. Purchase of the parasitoid in the South Island was restricted to the province of Can-
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terbury (Fig. 2). Sheep farming is the predominate pastoral industry in the South Island and the inability to achieve more widespread uptake of the parasitoid may have been due to the fact that the commercial program was operating at a time where economic conditions for the sheep industry were poor (Statistics New Zealand, 1998). Overall, the major impediments to selling M. hyperodae were the cost of release, ambiguity associated with perceived benefits, an inability to guarantee complete control of L. bonariensis, and problems in forming unified farmer groups. There were inevitable problems in the formation of farmer groups prepared to purchase the parasitoid. A farmer who was unwilling to contribute to a release, but was geographically located in the center of a potential group, was a major disincentive to final purchase by the other members who were reluctant to ‘give away’ the benefits of a biological control that they had purchased. Including re-releases, the parasitoid was released at 112 sites between 1993 and 1998, with an average (range) of 5649 (4363–7476) parasitoids released at each site. While most sales were to farmer groups and dairy boards, two North Island regional councils were involved in substantial purchases of parasitoids. Three farmers made individual purchases of the parasitoid. All purchasers have continued to receive the publication ‘‘pestNEWS,’’ which has proven to be a valuable means of disseminating information on issues such as new pests and diseases. 5.1. Analyzing the success of biological control
Fig. 2. Map indicating the research (1991) and commercial release sites (1993–1998) for M. hyperodae in New Zealand.
Work is in progress to quantify the parasitoid’s impact and test the prediction of a >50% reduction in damage in Canterbury (Barlow et al., unpublished data.). There are clear anecdotal indications that M. hyperodae has reduced the damage potential of L. bonariensis. Research at Lincoln has shown a reduction in the size of the L. bonariensis first summer generation egg and larval peaks (Goldson et al., 1998a). There has also been a decline in L. bonariensis populations in Waikato, which has substantially reduced both the level of larval feeding in endophyte-free-ryegrass stands and the rate of increase in endophyte levels (Van Vught and Thom, 1998). Prior to parasitoid establishment, high L. bonariensis larval densities resulted in the selective removal of endophyte-free tillers and a rapid reversion to high-endophyte ryegrass pasture (Barker and Addison, 1993). In conclusion, the commercial production and release of M. hyperodae arose from the requirement that government-funded research was not be invested in the distribution of the parasitoid. However, the comparative success of the program is largely due to research that was able to elucidate key aspects of the L. bonariensis–
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M. hyperodae relationship. The results were then used to support the marketing of the parasitoid. This was complemented by an economic analysis of biological control that indicated a positive financial benefit to farmers. The involvement of research staff in the mass rearing, promotion, release, and recovery of the parasitoid was also significant to this success. A new pastoral pest, clover root weevil (Sitona lepidus) (Coleoptera: Curculionidae) (Barratt et al., 1996), is the target of a classical biological control program (Phillips et al., 2000). If, and when, a suitable biological control agent is selected for introduction, the release and distribution strategy will require careful consideration. The commercial program described above is a suitable model for duplication but its implementation will depend on both the inherent features of the parasitoid–host relationship (particularly rate of dispersal) and government philosophy.
Acknowledgments The authors gratefully acknowledge Nigel Barlow for his contribution to the scientific understanding of the M. hyperodae–L. bonariensis interaction and editorial comment. We also thank Alison Popay for her valuable comments on an earlier draft of the manuscript. Technical support for the commercial program came from C. Galbraith, G. Caird, A. Rose, E. Rose, M. Thorpe, A. McCaw, D. Roberts, R. Cane, G. Hirst, and H.R. Macnab. S. Kelly ensured a plentiful supply of parasitoids for the commercial program. M. Garnham, R. van Toor, and F. Pauwels provided assistance in marketing of the parasitoid.
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