Host Specificity of the Argentine Root-Boring Weevil, Heilipodus ventralis (Coleoptera: Curculionidae), a Potential Biocontrol Agent for Snakeweeds (Gutierrezia: Asteraceae) in Western North American Rangelands—U.S. Quarantine Tests

Native snakeweeds, especially Gutierrezia sarothrae (Pursh) Britton and Rusby and Gutierrezia microcephala (DC.) A. Gray, are among the most widespread and damaging weeds of rangelands in the western United States and northern Mexico. The genus long ago spread to southern South America, where further speciation occurred. We have found several species of insects in Argentina that damage other species of snakeweeds there and are possible candidates for biological control in North America. The first of these, the root-boring weevil, Heilipodus ventralis (Hustache), was tested in Argentina and then sent to the USDA-ARS Insect Quarantine Facility at Temple, Texas, for host specificity testing on North American plants. We tested H. ventralis on 40 species of the family Asteraceae, in 19 tests of five types, using 686 adults and 365 larvae. Host specificity increased from adult feeding, to ovipositional selection, to larval development. At Temple, adults fed mostly on 6 species of the closely related genera Grindelia, Gutierrezia, and Gymnosperma, but with substantial feeding on four other genera of the two preferred subtribes Solidagininae and Machaerantherinae and on Baccharis in the tribe Baccharidinae, with lesser feeding on the subtribe Asterinae, all in the tribe Astereae, and on 1 species in the tribe Anthemideae. Females oviposited primarily on the same 6 species but very little on plants outside the 2 preferred subtribes. Larvae developed only on 9 of the 29 U.S. plant species tested, 6 within the two preferred subtribes and on Brickellia and Aster in other tribes. Only 5 species of three genera appear to be potential true hosts of H. ventralis in North America, on which all stages of the life cycle, adult feeding, oviposition, and larval development, can take place; these are Gymnosperma glutinosum (Spreng.) Less., Gutierrezia grandis Blake, Gut. microcephala, Gut. sarothrae, and Grindelia lanceolata Nutt. None of these genera contain species of economic or notable ecological value; the few rare species appear to be protected by habitat isolation from attack by H. ventralis. H. ventralis, therefore, appears sufficiently host specific for field release in North America. This is the first introduced biocontrol agent to be approved for release in a continental area to control a native weed.     

Investigation and documentation of hybridization betweenParkinsonia aculeata andCercidium praecox (Leguminosae:Caesalpinioideae)

Morphometric, cytogenetic, geographical and ecological evidence for hybridization betweenParkinsonia aculeata andCercidium praecox is presented. Morphometric investigation using the character count procedure and cytogenetic observations confirm hybrid status. All diagnostic morphometric characters were intermediate in the hybrid. Both parents (2n = 28) show regular tetrad formation and pollen fertility greater than 94%. Hybrids have a chromosome number of 2n = 28 or 2n = 30, and display meiotic abnormalities including lagging chromosomes and micronucleus formation; less than 21% of hybrid pollen was fertile. Ecological and geographical information suggests that hybridization is occurring at increasing frequency due to the expanding range ofP. aculeata associated with cultivation as an ornamental, coupled with ecological disturbance and weediness, and the cultivation ofC. praecox and hybrids as fodder, ornamental and shade trees. Hybrid fertility and phenological observations, in conjunction with F-weighted principal component analysis, suggest that the progeny of F₁ hybrids are established. The hybrid is formally described asP. ×carterae.     

Research article: life history and host range of Prochoerodes onustaria,an unsuitable classical biological control agent of Brazilian peppertree

The life history and host range of the South American defoliator Prochoerodes onustaria (Lepidoptera: Geometridae) were examined to determine its suitability as a classical biological control agent of the invasive weed Brazilian Peppertree, Schinus terebinthifolia, in the U.S.A. Larvae were collected feeding on S. terebinthifolia in Brazil and were colonised and tested in quarantine. Life history observations indicated that 54% (n?=?63) of larvae reared on S. terebinthifolia leaves survived to adulthood and 65% of adults (n?=?34) required five instars. Development time from eclosion to adult did not differ by sex: males required 42.9?±?1.1 days and females required 41.1?±?0.9 days. No-choice host range tests were conducted on 11 species in two families (Anacardiaceae and Sapindaceae), including U.S.A. native, commercial, and ornamental species. Larvae completed development on all species, although survival differed significantly among them. Larvae fed Anacardium occidentale, Cotinus coggygria, Dodonaea viscosa, and Mangifera indica demonstrated higher survival than those on S. terebinthifolia, whereas survival was reduced among larvae fed Metopium toxiferum and Comocladia dodonaea. Consumption was significantly greater on M. toxiferum than on the other species. The results presented here suggest that P. onustaria is highly polyphagous, feeding and completing development on members of two related plant families, and is not suitable for biological control of Brazilian peppertree in the U.S.A.     

Benefits of Classical Biological Control for Managing Invasive Plants

As a result of the rapid expansion in international travel and trade over the past few decades, invasive plants have become a problem of global proportions. Plant invasions threaten the existence of endangered species and the integrity of ecosystems, and their ravages cost national economies tens of billions of dollars every year. Strategies for managing the threats posed by plant invasions involve three main tactics: prevention, eradication, and control. The effectiveness of prevention, involving enactment of legislation to prohibit the entry and spread of noxious alien plants, has been questioned. Eradication of all but the smallest, most localized weed infestations generally is not regarded as economically feasible. Conventional weed control techniques, such as mechanical and chemical controls, because they are expensive, energy and labor intensive, and require repeated application, are impractical for managing widespread plant invasions in ecologically fragile conservation areas or low-value habitat, such as rangelands and many aquatic systems. In addition, mechanical means of control disturb the soil and may cause erosion; chemical herbicides have spurred the evolution of resistance in scores of weed species and, further, may pose risks to wildlife and human health. Because of drawbacks associated with conventional weed control methods, classical biological control, the introduction of selective exotic natural enemies to control exotic pests, increasingly is being considered and implemented as a safe, cost-effective alternative to address the invasive plant problem. Worldwide, biological weed control programs have had an overall success rate of 33 percent; success rates have been considerably higher for programs in individual countries. Benefits are several-fold. Biological control is permanent, energy-efficient, nonpolluting, and inexpensive relative to other methods. Economic returns on investment in biological weed control have been spectacular in some cases, and range from an estimated benefit/cost ratio of 2.3 to 4000 or more. Although the risks involved in biological control in general are considered unacceptable by some, biological weed control in particular has had an enviable safety record. Since establishment of the stringent standards and regulatory apparatus currently in place in the United States and elsewhere, there have been no reported cases of biological weed control causing significant harm to nontarget populations or to the environment at large.     

Biological control of waterhyacinth in Sinaloa Mexico with the weevils Neochetina eichhorniae and N. bruchi

Water hyacinth (Eichhornia crassipes (Mart.) Solms.)creates severe problems in the irrigationdistricts of Mexico, particularly in westernSinaloa. Therefore water hyacinth weevils(Neochetina eichhorniae Warner and N. bruchi Hustache), imported from the USA in1993, were used to initiate a biologicalcontrol program. Precautionary screeningrevealed that some were infected with amicrosporidian so disease-free colonies wereproduced by eliminating infected breedinglines. To demonstrate effectiveness prior toopen field releases, weevils were firstreleased in cages at field sites. Weevilintensity increased to 6.3 weevils/plant after320 days when the plants were all dead ordying. More than 8,600 N. bruchi and14,500 N. eichhorniae were then releasedat various sites during January 1995 to August1996. Waterhyacinth coverage declined atBatamote reservoir (134 ha) from 95% to <3%by 1997; at the 12-ha Hilda reservoir from100% in May 1995 to 1% by March 1998; at the42.3-ha Arroyo Prieto reservoir from 100% to1% during the same interval; and at theMariquita reservoir (492 ha), the largestreservoir in the Humaya system, from 394 ha(80%)to 98.4 ha (20%).     

Best linear unbiased prediction of host-range of the facultative parasite Colletotrichum gloeosporioides f. sp. salsolae, a potential biological control agent of Russian thistle

Russian thistle or tumbleweed (Salsola tragus L.) is an introduced invasive weed in N. America. It is widely distributed in the US and is a target of biological control efforts.The fungus Colletotrichum gloeosporioides (Penz.) Penz. & Sacc. in Penz. f. sp. salsolae (CGS) is a facultative parasite under evaluation for classical biological control of this weed. Host-range tests were conducted with CGS in quarantine to determine whether the fungus is safe to release in N. America. Ninetytwo accessions were analyzed from 19 families: Aizoaceae, Alliaceae, Amaranthaceae, Apiaceae, Asteraceae, Brassicaceae, Cactaceae, Campanulaceae, Chenopodiaceae, Cucurbitaceae, Cupressaceae, Fabaceae, Malvaceae, Nyctaginaceae, Phytolaccaceae, Poaceae, Polygonaceae, Sarcobataceae, and Solanaceae and 10 tribes within the Chenopodiaceae: Atripliceae, Beteae, Camphorosmeae, Chenopodieae, Corispermeae, Halopepideae, Polycnemeae, Salicornieae, Salsoleae, and Suaedeae. These included 62 genera and 120 species. To facilitate interpretation of results, disease reaction data were combined with a relationship matrix derived from internal transcribed spacer DNA sequences and analyzed with mixed model equations to produce Best Linear Unbiased Predictors (BLUPs) for each species. Twenty-nine species (30 accessions) from seven closely-related Chenopodiaceae tribes had significant levels of disease severity as indicated by BLUPs, compared to six species determined to be susceptible with least squares means estimates. The 29 susceptible species were: 1 from Atripliceae, 4 from Camphorosmeae, 1 from Halopepideae, 2 from Polycnemeae, 6 from Salicornieae, 8 from Salsolae, and 7 from Suaedeae. Most species in the genus Salsola, which are all introduced and weedy, were very susceptible and damaged by CGS. Statistical comparisons and contrasts of BLUPs indicated that these Salsola species were significantly more susceptible than non-target species, including 15 species from relatives in the closely-related genera Bassia (=Kochia), Nitrophila, Salicornia, Sarcocornia, and Suaeda. Of the 29 susceptible species, 10 native or commercially important species in N. America were identified as needing additional tests to determine the extent of any damage caused by infection.     

Germination-Arrest Factor (GAF): 3. Determination that the herbicidal activity of GAF is associated with a ninhydrin-reactive compound and counteracted by selected amino acids

A novel, naturally-occurring herbicide (Germination-Arrest Factor, GAF), produced by Pseudomonas fluorescens WH6 and several related isolates of rhizosphere bacteria, irreversibly arrests germination of the seeds of a wide range of graminaceous species, including a number of important grassy weed species. GAF activity has been shown previously to be associated with a hydrophilic, low molecular weight compound that contains an acid group. In the present study, thin-layer chromatography (TLC) of extracts of WH6 culture filtrate demonstrated that GAF activity migrates on TLC plates with a particular ninhydrin-reactive compound. This compound was found to be present in GAF-producing P. fluorescens isolates and absent in P. fluorescens strains that lack the ability to produce GAF. Treatments, including mutagenesis, which resulted in the loss of GAF activity in culture filtrates from P. fluorescens WH6 were shown to result in the disappearance of this ninhydrin-reactive compound from extracts of WH6 culture filtrates or in alteration of its appearance on TLC chromatograms. The ninhydrin-reactivity of GAF indicates that it probably contains an amino group, as well as the acid group previously demonstrated, and suggests that GAF may be a small peptide or amino acid analog. Biological investigations motivated by this conclusion demonstrated that the effects of GAF in inhibiting the germination of seeds of annual bluegrass (Poa annua L.) could be counteracted by treatment with alanine or glutamine and, to lesser extent, by several other amino acids, suggesting that this compound may act by interfering with some aspect of amino acid metabolism or function.     

杭州西湖风景区外来杂草的调查研究

通过野外调查和文献资料的整理分析,确定杭州西湖风景区有外来杂草56种,隶属于21科44属。对西湖风景区外来杂草的种类组成、来源、分布特点进行分析,结果表明:(1)种类较多的科是菊科、苋科、豆科;(2)原产地以来源于北美洲的最多;(3)容易入侵地表裸露较大的生境;(4)发生具有季节差异;(5)种类、分布上呈动态变化。并就外来杂草近二十至三十年的变化进行了讨论。