Monitored releases of Rhinoncomimus latipes (Coleoptera: Curculionidae), a biological control agent of mile-a-minute weed (Persicaria perfoliata), 2004–2008

Mile-a-minute weed, Persicaria perfoliata (L.) H. Gross, is an invasive annual vine of Asian origin that has developed extensive monocultures, especially in disturbed open areas in the Mid-Atlantic region of the United States. A host-specific Asian weevil, Rhinoncomimus latipes Korotyaev, was approved for release in North America in 2004, and weevils have been reared at the New Jersey Department of Agriculture Beneficial Insect Laboratory since then. By the end of 2007 more than 53,000 weevils had been reared and released, mostly in New Jersey, but also in Delaware, Maryland, Pennsylvania, and West Virginia. The beetles established at 63 out of 65 sites (96.9%) where they were released between 2004 and 2007, with successful releases consisting of as few as 200 weevils. Weevils were recorded at 30 additional non-release sites in New Jersey, where they had dispersed at an average rate of 4.3 km/year. Standardized monitoring of fixed quadrats was conducted in paired release and control sites at eight locations. Significant differences in mile-a-minute weed populations in the presence and absence of weevils were found at three locations, with reduction in spring densities to 25% or less of what they had been at the start within 2–3 years at release sites, while weed densities at control sites were largely unchanged. Mile-a-minute weed populations at a fourth site were similarly reduced at the release site, but without control data for comparison due to rapid colonization of the paired control site. At the other four locations, all on islands, mile-a-minute weed populations were reduced at both release and control sites without large weevil populations developing, apparently due to environmental conditions such as late frost and extreme drought.     

Establishment and dispersal of the biological control weevil Rhinoncomimus latipes on mile-a-minute weed, Persicaria perfoliata

Mile-a-minute weed, Persicaria perfoliata (L.) H. Gross (Polygonaceae), is an annual vine from Asia that has invaded the eastern US where it can form dense monocultures and outcompete other vegetation in a variety of habitats. The host-specific Asian weevil Rhinoncomimus latipes Korotyaev (Coleoptera: Curculionidae) was first released in the US in 2004 as part of a classical biological control program. The weevil was intensively monitored in three release arrays over 4 years, and field cages at each site were used to determine the number of generations produced. The weevil established at all three sites and produced three to four generations before entering a reproductive diapause in late summer. Weevils dispersed at an average rate of 1.5–2.9 m wk⁻¹ through the 50 m diameter arrays, which had fairly contiguous mile-a-minute cover. Weevils dispersing in the broader, more variable landscape located both large monocultures and small isolated patches of mile-a-minute 600–760 m from the release within 14 months. Weevil density ranged from fewer than 10 to nearly 200 weevils m⁻² mile-a-minute weed. Mile-a-minute cover decreased at the site with the highest weevil density. The production of P. perfoliata seed clusters decreased with increasing weevil populations at two sites, and seedling production declined over time at two sites by 75% and 87%. The ability of the weevil to establish, produce multiple generations per season, disperse to new patches, and likelihood of having an impact on plants in the field suggests that R. latipes has the potential to be a successful biological control agent.     

Field assessment of a frond-feeding weevil, a successful biological control agent of red waterfern, Azolla filiculoides, in southern Africa

Azolla filiculoides (red waterfern) is a small, floating fern native to South America, that has invaded aquatic habitats, predominantly water resevoirs in southern Africa. A frond-feeding weevil, Stenopelmus rufinasus Gyllenhal (Coleoptera: Curculionidae), was imported from Florida, USA, and released as a biological control agent against this weed in South Africa at the end of 1997. To date, 24,700 weevils have been released, which has resulted in local extinction of red waterfern at 81% of the 112 release sites. The weevil has not failed to control a single site. Several sites were, however, lost due to flooding or drainage of dams. The surface area of weed controlled totalled 203.5 ha. On average, A. filiculoides was controlled in infested sites in 6.9 (±4.3) months. The weed recolonized at 22 of the sites (through either spore germination or dispersal by waterfowl), but the weevils subsequently spread to all of these sites and successfully caused local extinction of the weed at 18 of the sites. Five years after the release of the weevil, the weed no longer poses a threat to aquatic systems in southern Africa. In comparison to other biological control programs of aquatic weeds, the program against A. filiculoides in southern Africa ranks among the most successful cases anywhere in the world.     

Host range of Ceutorhynchus assimilis (Coleoptera: Curculionidae), a candidate for biological control of Lepidium draba (Brassicaceae) in the USA

Ceutorhynchus assimilis has been selected as a potential biological control agent of Lepidium draba, which is a Eurasian invasive weed in North America. Preliminary studies indicated specificity of this weevil collected in southern France on L. draba. This result was in discord with the pest status of C. assimilis found in the literature. Host-specificity tests based both on field and laboratory experiments showed heterogeneity in the host spectrum of the weevils reared from different host-plants as determined by larval development. However, no distinguishable morphological differences could be visually detected between the populations feeding on different host-plants. All sampled populations of weevils were polyphagous as adults. Weevils reared from L. draba were specific to this plant for their complete larval development. Conversely, populations living on other wild and cultivated Brassicaceae species were not able to use L. draba as a host plant. Such differentiation is further highlighted by other biological aspects such as plant infestation rates, sex-ratio, duration of larval development, and differences in the timing of their life cycles. These results demonstrate that C. assimilis, an insect species formerly considered as a pest of Brassicaceae, is characterized by its host-range variability, with one population being potentially useful in the biological control of L. draba. Moreover, this example points to the need to test multiple populations of biological control agents in assessing risk.     

Costs of mass-producing the root weevil, Mogulones cruciger, a biological control agent for houndstongue (Cynoglossum officinale L.)

The cost of rearing the root-feeding weevil, Mogulones cruciger Herbst, to control the invasive weed houndstongue (Cynoglossum officinale L.) was determined for two managed production methods. Production in an insectary setting provides control over rearing and all adult weevils that emerge can be collected, but required facility investment and high labor input. Mass-rearing in a managed ‘field crop’ setting required less facilities and labor while the insects were multiplying, but capture of the emerged adults was challenging and labor intensive. Estimated per adult weevil production costs were $CDN 2.65 for the insectary approach, and from $CDN 0.10 to $CDN 0.14 for mass-rearing in the managed field crop setting. Even though collection of adult weevils in the field crop production system was challenging, commercial production of M. cruciger should consider use of this mass-rearing method because of its lower cost.     

Influence of release size on establishment and impact of a root weevil for the biocontrol of houndstongue (Cynoglossum officinale)

The root-boring weevil, Mogulones cruciger, was introduced into Canada to control the weed, houndstongue (Cynoglossum officinale). To optimise its use as a biocontrol agent, a 2-year study was performed in British Columbia, Canada to test if the number of M. cruciger released at sites predicted subsequent declines in weed populations. No, 100, 200, 300 or 400 weevils were released in 1999 at field sites (five replicates) corresponding to discrete populations of houndstongue separated by distances of 0.3–3 km. The sites were subsequently monitored for weevil establishment, population change, and host attack, and houndstongue population change. By 2001, M. cruciger had established at all 20 release sites and was present in low numbers in three of five control sites. The year following release, release size was positively correlated with number of adult weevils collected, their damage to host plants, and with subsequent numbers of larvae per plant. In contrast, houndstongue populations were reduced at the same rate and amount, regardless of the experimental release size, within 2 years of release. Significant release treatment×time interactions indicated that factors other than M. cruciger contributed to houndstongue reductions (e.g. drought). However, overall the addition of weevils accelerated the reductions relative to sites with no weevils added. Our study demonstrated that the lowest number within a range of release sizes typically used in weed biocontrol programmes (i.e. 100) was as effective as 200–400 weevils in achieving a consistent amount and rate of houndstongue reduction, and thus, could be implemented to optimise weevil use and achieve predictable biocontrol.     

Suppression of Boll Weevil Infestations (Coleoptera: Curculionidae) Occurring on Fallow-Season Cotton in Southern Texas by Augmentative Releases ofCatolaccus grandis(Hymenoptera: Pteromalidae)

Augmentative releases ofCatolaccus grandis(Burks) were conducted in the Lower Rio Grande Valley of Texas in an attempt to suppress infestations of boll weevil,Anthonomus grandisBoheman, occurring in stands of “fallow-season” cotton (i.e., fields in violation of the 1 September stalk destruction deadline mandated by Texas law). In each of five release sites monitored during the study period (October, 1994–March 1995), augmentative releases ofC. grandiswere accompanied by an appreciable increase in the incidence of parasitized boll weevils (primarily third-stage larvae and pupae infesting abcised cotton squares) within a relatively brief time period. The relatively high incidence of host mortality caused byC. grandisin each release site was largely indispensible (i.e., would not have occurred in the absence of the parasite) and served to destroy significant numbers of immature boll weevils that appear to have been predisposed to successfully overwinter. The potential role of parasite augmentation in the management of the overwintering boll weevil population in southern Texas is discussed.     

Field host-specificity of the mile-a-minute weevil,Rhinoncomimus latipes Korotyaev (Coleoptera: Curculionidae)

The safe practice of biological control relies, in part, on an accurate evaluation of a potential agent’s host-specificity via testing through a “filter of safety”. The results of laboratory tests may differ from those obtained in open field host-specificity tests, where agents are able to use their full range of host-selection behaviors. It was hypothesized that Rhinoncomimus latipes (Coleoptera: Curculionidae), the biological control agent released against mile-a-minute weed, Persicaria perfoliata (Polygonaceae), would not feed or oviposit on nontarget plants in a two-phase, open field setting. Ten weevils were placed at the base of each of 13 test plant species in a randomized complete block design with six replicates. Weevils placed at the base of mile-a-minute weed were marked with yellow fluorescent dust, and yellow weevils were subsequently found only on mile-a-minute. Weevils placed at the base of nontarget plants (marked with red fluorescent dust) rapidly colonized mile-a-minute weed. Three hours after release, the number of R. latipes found on mile-a-minute weed was significantly higher than predicted by a random distribution of weevils on all test plants. The likelihood of finding more weevils on mile-a-minute compared to nontarget plant species was 31.0% at 3 h and increased to 96.5% at 44 h after release. Whereas prerelease studies showed feeding at low levels on 9 of the 13 plant species tested here, under open field conditions R. latipes did not feed on any nontarget plant species and dispersed from these plants. In an open field setting, where the weevil was able to use its full range of host-selection behaviors, there was no observed risk of nontarget effects for any species tested.     

Effects of Rhinoncomimus latipes on the growth and reproduction of Persicaria perfoliata,an invasive plant in North America

Native to Asia, mile-a-minute Persicaria perfoliata, is an invasive weed in North America, and the weevil Rhinoncomimus latipes is a host-specific insect agent which occurs widely in China. We conducted a common garden experiment to compare P. perfoliata plant responses of native and invasive populations to herbivory by the weevils from different origins. We found weevils from Hunan, Hubei and Heilongjiang Provinces had strong, moderate and weak ability to suppress host plant, respectively. Weevils from Hunan and Hubei Provinces had stronger impact on the growth of both native and invasive plant populations than the weevil from Heilongjiang Province. The losses in seed output of invasive plants were also significantly greater than natives in the weevil treatments. Our results suggested that the weevil population from Hunan Province may be the most suitable for the control of mile-a-minute, while the population from Heilongjiang Province may be the least suitable due to climate matching.     

Efficacy of inoculative releases of Trichogramma ostriniae (Hymenoptera: Trichogrammatidae) against European corn borer Ostrinia nubilalis (Lepidoptera: Crambidae) in field corn

We evaluated the egg parasitoid Trichogramma ostriniae (Hymenoptera: Trichogrammatidae) to control European corn borer [Lepidoptera: Crambidae: Ostrinia nubilalis (Hübner)] in field corn in 2001 and 2002. Inoculative releases of 75,000 T. ostriniae/ha occurred in New York and Virginia in 5–10 cornfields per state when corn was at mid-whorl. Incidence of egg mass parasitism, number of stalk tunnels, incidence of ear damage, and whole-plant yield were evaluated. Parasitism of European corn borer egg masses ranged from 0 to 75% in release plots and was greater in release plots than in control plots. Individual comparisons between paired release and control plots showed no reductions in either stalk or ear damage. However, when data were combined across both years and fields, stalk and ear damage were significantly reduced in New York. In Virginia, no significant differences were detected using data obtained from one year. There were no differences in yield between release and control plots. Low densities of European corn borer, drought conditions in 1 year, and a larger plant canopy in field corn are possible reasons why T. ostriniae releases provided less control than has been observed in previous trials in sweet corn. Additional research focused on improved timing and frequency and number of releases is warranted.     

Pre-release impact assessment of two stem-boring weevils proposed as biological control agents for Alliaria petiolata

Experimental studies can be useful tools to test plant responses to herbivory and to quantify the impact of potential biological control agents prior to their release. We evaluated the per-capita effect of Ceutorhynchus alliariae and C. roberti, two stem-boring weevils currently being investigated as potential biological control agents for garlic mustard, Alliaria petiolata, in North America. Weevils were released at three different densities in individual and mixed-species treatments onto potted plants of A. petiolata. Damage by C. roberti alone and by both weevils combined caused an increase in the numbers of inflorescences produced per plant. Although plants could compensate for low levels of damage, moderate to high levels of damage by both C. alliariae and C. roberti, individually and in combination, caused a decrease in plant height and a reduction in seed output per plant. The damage inflicted by both weevil species is similar so the overall impact of both species combined can be predicted by summing the impact of each species alone. Provided they are sufficiently host specific, both weevils could be released as biocontrol agents. Because reduced seed production is necessary to suppress A. petiolata populations, both species have the potential to contribute to control of A. petiolata in North America.     

Temperature and host-plant effects on development and population growth of Mecinus janthinus (Coleoptera: Curculionidae), a biological control agent for invasive Linaria spp.

Mecinus janthinus Germar is a European stem-mining weevil that has been established in North America as a biological control agent against the invasive European weeds Linaria vulgaris P. Mill. and Linaria dalmatica (L.) P. Mill. (Scrophulariaceae). Establishment success and impact of the weevil have varied widely among sites. We investigated the hypothesis that some of this variation may be due to a lack of sufficient time for M. janthinus to develop to the adult (overwintering) stage in less favorable climates. Development time of M. janthinus was measured in L. vulgaris and L. dalmatica at four constant temperatures, and logistic regression was used to derive a model for the effect of temperature on development. Development rates were simulated using historic climate data for a site in central Alberta (where establishment was marginal on L. vulgaris) and one in southern British Columbia (where outbreaks occurred, resulting in heavy damage to L. dalmatica). The model showed that, on average, the British Columbia site had 50 more days available for the weevil to lay eggs that could reach the adult stage in time for overwintering than did the Alberta site. This may explain the more rapid population buildup at the British Columbia site. This model could be used to predict the climatic suitability of other areas for establishment of M. janthinus. An unexplained result was the very low survival rate of eggs laid in L. dalmatica under the same experimental conditions.     

Post hoc assessment of an operational biocontrol program: efficacy of the flea beetle Aphthona lacertosa Rosenhauer (Chrysomelidae: Coleoptera), an introduced biocontrol agent for leafy spurge

Mixed populations of Aphthona lacertosa and Aphthona czwalinae were released at more than 50 locations in Alberta in 1997. Two and 3 years post-release, beetle populations were primarily A. lacertosa, with A. czwalinae forming less than 0.5% of the sampled populations. Beetle densities were moderate (10–70 beetles per m²) or high (>70 beetles per m²) at 14% and more than 60% of the sampled sites in 1999 and 2000, respectively. Larger beetles had greater instantaneous egg loads (r²=0.424,P=0.003). In 2000, the largest beetles were found at moderate density sites and there was a significant negative relationship between beetle size and the time taken to accumulate a degree day threshold of 1230 (for females: r²=0.678,P=0.001). Sites with the most rapid accumulation of degree days have the greatest potential for beetle population growth based on potential fecundity. Changes in leafy spurge percent cover, stem density, and canopy height from 1997 to 2000 were assessed across sites with low (<10 beetles per m²), moderate, and high beetle densities in 2000. Sites with high beetle densities had significantly greater reductions of leafy spurge within 5 m of the release point than sites with low beetle densities (P<0.017). Damage caused by the beetles at high-density sites was often visible as a halo-shaped patch of dead leafy spurge stems. The significant overall reduction of leafy spurge within release patches makes A. lacertosa a promising biocontrol agent for leafy spurge in Alberta.     

Ecology and impact of Allorhogas sp. (Hymenoptera: Braconidae) and Apion sp. (Coleoptera: Curculionoidea) on fruits of Miconia calvescens DC (Melastomataceae) in Brazil

Two fruit-feeding insects, a gall wasp, Allorhogas sp. (Hymenoptera: Braconidae), and a beetle, Apion sp. (Coleoptera: Curculionoidea), were evaluated in their native habitat in Brazil as potential biological control agents of Miconia calvescens DC (Melastomataceae). Allorhogas sp. occurred at two out of three field sites with native populations of M. calvescens, and Apion sp. occurred at all three sites. Both species exhibited aggregated distributions among M. calvescens trees sampled at each site. Allorhogas sp. infested 9.0% and 3.8% of fruits at each of two sites. The number of larvae and pupae of Allorhogas sp. and/or an unidentified parasitoid (Hymenopetera: Eulophidae: Tetrastichinae) ranged from one to five per infested fruit. Fruits infested with Allorhogas sp. were 20% larger and had 79% fewer seeds than healthy fruits. Although adults of Apion sp. were found on leaves and inflorescences of M. calvescens at all three sites, larvae and pupae were found in fruits at only one site, where a maximum of 1.4% of fruits were infested. Fruits infested by Apion sp. contained only one larva or pupa, and were 15% smaller and had 62% fewer seeds than healthy fruits. While a variety of apionids have been used for biological control in the past, this is the first time a braconid wasp has been considered for biological control of a weed.     

Association and Synchrony ofSmicronyx guineanusVoss,S. umbrinusHustache (Coleoptera: Curculionidae), and the Parasitic WeedStriga hermonthica(Del.) Benth. (Scrophulariaceae)

Field experiments were conducted in 1992 and 1993 at Kaya, Burkina Faso, West Africa, in fields of sorghum (Sorghum bicolor) and pearl millet (Pennisetum americanum).Striga hermonthica(witchweed) was sampled weekly using a square-meter metal frame. Concurrently, adult populations of the weevilsSmicronyx guineanusVoss andS. umbrinusHustache were sampled weekly using a Univac portable suction sampler to assess the synchrony ofSmicronyxwithStriga.χ²tests for independence of the populations ofSmicronyxandStrigaindicated a good synchrony of the active stages of the life cycle of the weevils with the period of occurrence of the witchweed. The Univac portable suction sampler method was also used to determine the degree of association betweenSmicronyxandStriga.There was a positive association between the weevil and the witchweed. The percentage ofStrigaplants bearing galls caused bySmicronyxwas determined on 39 occasions and galls were found in every field visited (n = 50). The mean galling percentage ranged from 1 to 84%. A search for alternate hosts was done by sampling weevil adults on weeds surrounding the farmers' fields. NoSmicronyxadult was caught on these weeds before the emergence of volunteerStrigaplants.     

Alcidodes sedi (Col.: Curculionidae), a natural enemy of Bryophyllum delagoense (Crassulaceae) in South Africa and a possible candidate agent for the biological control of this weed in Australia

The Madagascan endemic, Bryophyllum delagoense (Crassulaceae), is a major weed in Queensland, Australia. Despite having first been recorded in Australia in the 1940s, it is far more invasive there than on the African mainland where it was introduced more than 170 years ago. This may be due to a number of factors, one of which could be the occurrence of new natural enemy associations in southern Africa. Among the insects of crassulaceous plants that have extended their host ranges, a stem-boring weevil, Alcidodes sedi, was studied to elucidate its status as a natural enemy of B. delagoense in southern Africa and as a candidate biological control agent for introduction to Australia. Laboratory studies indicated that damage inflicted by adult and larval feeding caused significant reductions in stem length and number of leaves. Preliminary host-range trials revealed that A. sedi can complete its development on other species in the Crassulaceae, including most of the introduced Bryophyllum species and some Kalanchoe species native to South Africa. Despite the oligophagous nature of A. sedi and the fact that it can complete its development on a number of ornamental species in the Crassulaceae, it should be considered a potential biological control agent in Australia. All of the native Crassulaceae in Australia are in the genus Crassula, most of which are very small and therefore unlikely to support the development of a large weevil like A. sedi. However, additional host-range trials will have to be undertaken in Australia to determine whether the weevil can be considered safe for release.     

Impact of herbivory on mile-a-minute weed (Persicaria perfoliata) seed production and viability

The monophagous weevil Rhinoncomimus latipes Korotyaev (Coleoptera: Curculionidae) has been introduced into North America as a biological control agent for the invasive vine mile-a-minute weed, Persicaria perfoliata (L.) H. Gross. This weevil has been shown to reduce the percent cover of mile-a-minute and the number of seed clusters produced, as well as altering the phenology of seed production. However, prior work has not examined the potential impact of the weevil on seed viability and numbers of seeds per cluster. When both adult and larval weevils fed on whole plants in the greenhouse, seed production and fruit maturation were delayed and both the total number of seeds and number of seeds per cluster were reduced. Overall, weevils in greenhouse cages reduced the reproductive potential of P. perfoliata by 35%. When adult weevils were confined on developing seed clusters in the field, the number of seeds produced per cluster, the weight of seeds produced, and seed viability all decreased. Overall, the number of viable seeds per cluster was reduced by 37% in the presence of adult weevils. Taken together, these findings demonstrate that this biological control agent can have important impacts on the reproductive potential of its target weed through mechanisms that have not previously been shown.     

Host specificity, establishment and dispersal of the gorse thrips, Sericothrips staphylinus Haliday (Thysanoptera: Thripidae), a biological control agent for gorse, Ulex europaeus L. (Fabaceae), in Australia

Sericothrips staphylinus was released as a biological control agent for Ulex europaeus in New Zealand and Hawaii following tests on ca. 80 plant species which showed it was narrowly oligophagous. To determine the suitability of S. staphylinus for release in Australia, further host specificity tests were conducted on 38 species and cultivars of Australian plants. These tests confirmed that S. staphylinus would feed only on U. europaeus in Australia and, following formal approval, was released in Tasmania during January 2001. To develop an optimal release strategy for S. staphylinus under Australian conditions, a field trial based on an earlier New Zealand study was conducted by replicating releases of 10, 30, 90, 270 and 810 adults. Results showed that population growth, reproduction rate and the number of S. staphylinus recovered 14 months after release can be non-linear functions of release size and establishment could be achieved with as few as 10 thrips. As S. staphylinus is easily cultured ca. 250 thrips were chosen as the minimum number for release because, based on a negative binomial model, this release size produced close to the maximum population growth. Surveys in early 2007 recovered S. staphylinus from 80% of 30 sites in Tasmania, the post release period ranging from 1 to 6 years. However, densities were low (<1 thrips/cm of tip growth) with no evidence of visible plant damage. The maximum dispersal range was 180–250 m after 38 months. At all the other sites, dispersal was estimated at less than 120 m. It is possible that S. staphylinus populations are still in the lag phase of their establishment before starting to increase rapidly and disperse. However, the survey results support a recent Tasmanian study which indicated that S. staphylinus is a sedentary, latent species characterised by steady densities and low levels of damage to its host plant. Its efficacy as a biological control agent on gorse may be restricted primarily by ‘bottom up’ effects of plant quality limiting its rate of natural increase and an inability of the thrips to reach large, damaging populations under field conditions.     

Interactive effects of light environment and herbivory on growth and productivity of an invasive annual vine, Persicaria perfoliata

Plant populations often exist in spatially heterogeneous environments with varying light levels, which can affect plant growth directly through resource availability or indirectly by altering behavior or success of herbivores. The plant vigor hypothesis predicts that herbivores are more likely to attack vigorously growing plants than those that are suppressed, for example in more shaded conditions. Plant tolerance of herbivory can also vary under contrasting resource availability. Observations suggest that damage by Rhinoncomimus latipes Korotyaev (Coleoptera: Curculionidae), introduced into the United States in 2004 as a biological control agent for mile-a-minute weed (Persicaria perfoliata [L.] H. Gross), is greater in the sun than in shade. We compared weevil densities and plant growth in paired plots in full sun or under shade cloth; a second experiment included insecticide-treated plots in sun and shade, to assess the ability of the plant to compensate for herbivore damage. Greater density of weevils and more node damage (indicating internal larval feeding) were found on P. perfoliata plants growing in sun than on those in shade. Nodes were 14% thicker in the sun, which may have provided better larval habitat. Biomass produced by plants without weevils in the sun was about twice that produced in any other treatment. Herbivory had a greater effect on plant growth in the high-light environment than in the shade, apparently because of movement into the sun and increased feeding there by the monophagous herbivore, R. latipes. Results support the plant vigor hypothesis and suggest that high weevil densities in the sunny habitats favored by P. perfoliata can suppress plant growth, negating the resource advantage to plants growing in the sun.     

原产地和入侵地紫茎泽兰对泽兰实蝇的选择性、卵巢蛋白质含量与解毒酶活性的影响

[目的] 紫茎泽兰是我国危害严重的恶性入侵杂草。比较专一性天敌泽兰实蝇对该杂草入侵前后植株的适应性,是揭示外来植物入侵后适应性机制的重要科学问题之一。[方法] 比较泽兰实蝇对原产地和入侵地紫茎泽兰植株的寄主选择性,并测定寄生于2类植株的上泽兰实蝇卵巢蛋白质含量及乙酰胆碱酯酶、羧酸酯酶、谷胱甘肽S-转移酶活性。[结果] 泽兰实蝇对原产地和入侵地紫茎泽兰的选择无显著性差异;寄生在紫茎泽兰入侵地植株上的卵巢蛋白质含量较原产地植株上更高。解毒酶活力比较表明,入侵地紫茎泽兰上泽兰实蝇的羧酸酯酶活性低于原产地上的,但谷胱甘肽S-转移酶（雌虫）活性比较则相反,乙酰胆碱酯酶活性比较均无显著性差异。[结论] 紫茎泽兰入侵后,专一性天敌泽兰实蝇的适应性有所下降,丰富了外来植物入侵机制中天敌逃逸假说的内涵。