Chemotype variation of the weed Melaleuca quinquenervia influences the biomass and fecundity of the biological control agent Oxyops vitiosa

Host plant nutritional and non-nutritional variability can have a significant effect on herbivore populations by influencing survival, larval performance, and fecundity. The effect of chemical and physical variation of the leaves of two chemotypes of the weed Melaleuca quinquenervia was determined on the biomass and fecundity of the biological control agent Oxyops vitiosa (Coleoptera: Curculionidae). M. quinquenervia chemotypes were distinguished by the principal terpenoids E-nerolidol and viridiflorol using gas chromatography and mass spectroscopy. Not only were the terpenoid profiles of the two chemotypes different but the viridiflorol leaves had greater toughness (1.2-fold) and reduced nitrogen (0.7-fold). When the larvae and adults were fed leaves of the E-nerolidol chemotype increased adult biomass (1.1-fold) and fecundity were found (2.6- to 4.5-fold) compared with those fed leaves of the viridiflorol chemotype. Regardless of the larval diet, when adults were fed the E-nerolidol chemotype leaves they had greater egg production compared with those adults fed the viridiflorol leaves. Moreover, adult pre-oviposition period was extended (1.5-fold) when individuals were fed the viridiflorol leaves compared with those fed the E-nerolidol leaves. By rearing the O. vitiosa weevil on the more nutritious chemotype plants these results assisted in the mass production and establishment of the M. quinquenervia biological control agent.     

Post-biological control invasion trajectory for Melaleuca quinquenervia in a seasonally inundated wetland

The recruitment and mortality of Melaleuca quinquenervia seedlings were evaluated over a 3-year period in a seasonally inundated wetland in the western Everglades region. The mean (±SE) density of seedlings/saplings m^?1 declined from 64.8 (±4.5) to 0.5 (±0.2) over the 3 years, a population reduction of 99.2%. Four distinct water regimes characterized this site: dry, dry to wet transition, flooded, and wet to dry transition. Seedling recruitment was highest in the dry to wet transition and lowest in the flooded water regime, while mortality was highest under flooded and dry water regimes. The mean estimate of population growth (λ) across water regimes was 0.64 ± 0.05 indicating negative population growth. Elimination of introduced insect herbivores using insecticides did not reduce mortality of recruited M. quinquenervia seedlings/saplings indicating that direct herbivory was not responsible for the decline in seedling density. On the other hand, a mean of only 0.2 (±0.03) viable seeds m^?2 d^?1 fell into the plots, an amount considerably lower than in previous studies. We submit that change in the invasion trajectory M. quinquenervia was most likely caused by reduced seed inputs from aerial seed banks depleted by insect herbivory rather than direct herbivory on seedlings. This may indicate a fundamental alteration of M. quinquenervia population dynamics ultimately resulting in a less invasive and, therefore, less ecologically damaging species.     

Biology, distribution and host-range of the sawfly,Lophyrotoma zonalis (Hym. pergidae), a potential biological control agent for the paperbark tree,Melaleuca quinquenervia

Since its introduction into southern Florida at the beginning of this century, the Australian paperbark tree,Melaleuca quinquenervia (Cav.) S. T. Blake, has become a major economic and environmental pest. A project to develop biological control agents for this tree in Australia began in 1986. Among a number of potential agents, a defoliating sawfly,Lophyrotoma zonalis (Rohwer) (Hymenoptera: Pergidae), was selected for further study. The larvae of this sawfly are conspicuous defoliators ofMelaleuca trees in northern Queensland. We collected these sawflies from Cairns to Mackay in northern Queensland, and they are also known from the Northern Territory and New Guinea. The life-cycle from egg to adult takes about 12 weeks. The egg, larval and pupal stages are parasitized by dipteran and hymenopteran parasites. We conducted 2234 larval no-choice feeding tests on 46 plant species from 20 families. Although feeding occurred on 35 of these plant species,M. quinquenervia and its close relative,M. leucadendra (L.) L., were preferred. In oviposition tests, larvae only emerged from egg cases laid onM. quinquenervia andM. leucadendra. Our extensive field surveys of nearly 70 tree species foundL. zonalis eggs and larvae only on several closely relatedMelaleuca species. The potential effectiveness of this sawfly as a biocontrol agent is discussed and estimated using the Goeden-Harris scoring system. Quarantine studies of this insect began in Florida in early 1994.     

Laboratory life history and field observations of Poliopaschia lithochlora (Lower) (Lepidoptera: Pyralidae), a potential biological control agent for Melaleuca quinquenervia (Myrtaceae)

Abstract  Melaleuca quinquenervia (Cav.) S.T. Blake, Australian broad-leaved paperbark, has become a serious weed in southern Florida. Poliopaschia lithochlora (Lower) is a promising candidate as a potential biological control agent, and this study describes laboratory and field observations of the life history of this moth. Eggs are laid in small batches, mainly on the surface of leaves, and larvae are voracious leaf feeders, concealed in tubes that are usually found in small colonies attached to leaves and stems. Larvae move from these tubes to feed on surrounding leaves, and saplings and suckers are frequently defoliated. Prepupae form sealed bulbs in the larval tubes in which they pupate. Adult females are mainly active and oviposit at night. Development from egg to adult occurs in approximately 80 d. Field populations appear to be regulated by several egg and larval parasites. Because this moth severely damages saplings and suckers of M .  quinquenervia , prefers low-lying humid sites, and can be successfully mass reared, it is rated highly for its potential as a biological control agent.     

Chemical basis of host selection and plant resistance in oligophagous insects

Recent investigations of the Colorado potato beetle and the alfalfa weevil reveal many similarities in their modes of host selection. Many plant chemicals influence their behavioral responses and physiological processes. Chemical stimuli influencing host finding and acceptance or rejection of plants include attractants, repellents, sign stimulants, feeding stimulants and deterrents. Both species are highly sensitive to deterrent chemicals present in many plants. Feeding stimulants are indispensible for these insects and are supplied by both primary nutrients (i.e. sugars, amino acids, phospholipids and potassium salts) and secondary plant substances. The important role played by different plant chemicals in host selection and plant resistance is discussed.

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Zusammenfassung Neuere Untersuchungen am Kartoffelkäfer und am Luzerneblattnager förderten viele Übereinstimmungen in der Art ihrer Wirtswahl zu Tage. Viele Pflanzenstoffe beeinflussen ihre Verhaltensweisen und physiologische Prozesse. Chemische Reize, welche die Auffindung des Wirtes, Annahme oder Ablehnung der Pflanzen beeinflussen, umfassen Attractants, Repellents, Signalstoffe, Fraß-Stimulatoren und Abschreckstoffe. Beide Arten sind hochempfindlich gegenüber abschreckenden Verbindungen in vielen Pflanzen. Fraß-Stimulatoren sind für beide Insekten unabdingbar notwendig und werden sowohl von primären Nährstoffen (wie Zucker, Aminosäuren, Phospholipiden und Natriumsalzen) wie von sekundären Pflanzenstoffen gestellt. Die bedeutsame Rolle, welche Pflanzenstoffe bei der Wirtswahl und der Resistenz der Pflanzen spielen, wird diskutiert.

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Journal paper No. ...., Utah Agricultural Experiment Station, Logan, Utah.     

Initial impacts and field validation of host range for Boreioglycaspis melaleucae Moore (Hemiptera: Psyllidae), a biological control agent of the invasive tree Melaleuca quinquenervia (Cav.) Blake (Myrtales: Myrtaceae: Leptospermoideae)

Invasion of south Florida wetlands by the Australian paperbark tree, Melaleuca quinquenervia (Cav.) S.T. Blake (melaleuca), has caused adverse economic and environmental impacts. The tree's biological attributes and favorable ambient biophysical conditions combine to complicate efforts to restore and maintain south Florida ecosystems. Management requires an integrated strategy that deploys multiple biological control agents to forestall reinvasion and to supplement other control methods, thereby lessening recruitment and regeneration after removal of existing trees. This biological control program began during 1997 when an Australian weevil, Oxyops vitiosa (Pascoe), was released. A second Australian insect, the melaleuca psyllid (Boreioglycaspis melaleucae Moore), first introduced during 2002, has also widely established. After inoculation of the psyllid in a field study, only 40% of seedlings survived herbivory treatments compared with 95% survival in controls. The resultant defoliation also reduced growth of the surviving seedlings. A weevil-induced decline at a site comprised mainly of coppicing stumps had slowed after a 70% reduction. Psyllids colonized the site, and 37% of the remaining coppices succumbed within 10 mo. The realized ecological host range of B. melaleucae was restricted to M. quinquenervia; 18 other nontarget plant species predicted to be suboptimal or nonhosts during laboratory host range testing were unaffected when interspersed with psyllid-infested melaleuca trees in a common garden study. Evaluations are ongoing, but B. melaleucae is clearly reducing seedling recruitment and stump regrowth without adversely impacting other plant species. Manifestation of impacts on mature trees will require more time, but initial indications suggest that the psyllid will be an effective supplement to the weevil.     

Decline in exotic tree density facilitates increased plant diversity: the experience from Melaleuca quinquenervia invaded wetlands

The Australian tree Melaleuca quinquenervia (melaleuca) formed dense monocultural forests several decades after invading parts of Florida and the Caribbean islands. These dominant forests have displaced native vegetation in sensitive wetland systems. We hypothesized that native plant diversity would increase following recent reductions in density of mature melaleuca stands in south Florida. We therefore examined data on changes in melaleuca densities and plant species diversity derived from permanent plots that were monitored from 1997 to 2005. These plots were located within mature melaleuca stands in nonflooded and seasonally-flooded habitats. Two host-specific biological control agents of melaleuca, Oxyops vitiosa and Boreioglycaspis melaleucae, were introduced during 1997 and 2002, respectively. Also, an adventive rust fungus Puccinia psidii and lobate-lac scale Paratachardina pesudolobata became abundant during the latter part of the study period. Overall melaleuca density declines in current study coincided with two to four fold increases in plant species diversity. The greatest declines in melaleuca density as well as the greatest increases in family importance values and species diversity indices occurred in nonflooded as compared to seasonally-flooded habitats. Most pioneer plant species in study sites belonged to Asteraceae, Cyperaceae, Poaceae, and Ulmaceae. The rapid reduction in melaleuca density and canopy cover during the study period may be attributed to self-thinning accelerated by the negative impact of natural enemies. Densities of other woody plants, particularly Myrica and Myrsine, which were sparsely represented in the understory by a few suppressed individuals also declined during the same period, possibly due to infestation by the generalist lac-scale. These findings indicate that natural-enemy accelerated self-thinning of melaleuca densities is positively influencing the native plant diversity and facilitating the partial rehabilitation of degraded habitats.     

Simplicillium chinense: a biological control agent against plant parasitic nematodes

Simplicillium chinense (Snef5) was isolated from Antheraea pernyi pupae and identified by morphological and molecular methods. Culture filtrates of Snef5 showed a high level of nematicidal activity. It is the first time to report that S. chinense can be used as a biological control agent against plant parasitic nematodes.     

Quarantine host range studies with Lophyrotoma zonalis, an Australian sawfly of interest for biological control of melaleuca, Melaleuca quinquenervia, in Florida, U.S.A.

The Australian melaleuca tree, Melaleuca quinquenervia (Cav.) S. T. Blake (Myrtaceae), has naturalized in southern Florida,U.S.A., and is now one of that regions most important weeds.Primarily a weed of wetlands, it also infests neighboring drierareas. Current efforts to restore the South Florida ecosystem arethreatened by the continuing range expansion of melaleuca andother weeds. In an effort to supplement the current chemical andcultural control methods for melaleuca, a search for potentialbiological control agents was begun in Australia in 1986. Thesawfly, Lophyrotoma zonalis, was determined after extensive fieldand laboratory studies to have potential as a biological controlagent. Larvae of L. zonalis eat leaves and occasionally defoliatelarge trees in Australia. Host range studies were conducted in aFlorida quarantine facility with native and cultivated plantspecies. Multi-choice and no-choice oviposition tests wereconducted with 36 species in the Myrtaceae and with 18 species inother families. Larvae developed to prepupae and adults from theeggs oviposited on 23 species of Myrtaceae only on 3 species ofbottlebrushes, Callistemon. Medium-sized larvae were tested forfeeding on bouquets of plant cuttings and on potted plants. Theyare the stage that might wander from defoliated trees. Noticeablefeeding, but much less than on melaleuca, was restricted to theMyrtaceae, except for a few individual larvae that fed on waxmyrtle, Myrica cerifera. Medium-sized larvae became prepupae onlyon Melaleuca decora (73%) and on wax myrtle (10%). However,neither species received eggs in the oviposition tests. Thesestudies confirmed the narrow host range of L. zonalis aspreviously reported from field and laboratory studies inAustralia.     

Herbivore-induced plant volatiles mediate host selection by a root herbivore

In response to herbivore attack, plants mobilize chemical defenses and release distinct bouquets of volatiles. Aboveground herbivores are known to use changes in leaf volatile patterns to make foraging decisions, but it remains unclear whether belowground herbivores also use volatiles to select suitable host plants. We therefore investigated how above- and belowground infestation affects the performance of the root feeder Diabrotica virgifera virgifera, and whether the larvae of this specialized beetle are able to use volatile cues to assess from a distance whether a potential host plant is already under herbivore attack. Diabrotica virgifera larvae showed stronger growth on roots previously attacked by conspecific larvae, but performed more poorly on roots of plants whose leaves had been attacked by larvae of the moth Spodoptera littoralis. Fittingly, D. virgifera larvae were attracted to plants that were infested with conspecifics, whereas they avoided plants that were attacked by S. littoralis. We identified (E)-β-caryophyllene, which is induced by D. virgifera, and ethylene, which is suppressed by S. littoralis, as two signals used by D. virgifera larvae to locate plants that are most suitable for their development. Our study demonstrates that soil-dwelling insects can use herbivore-induced changes in root volatile emissions to identify suitable host plants.     

Rapid molecular technique for identification of a biological control agent Rhodosporidium diobovatum

The purpose of this study was to develop a rapid molecular technique for identification of the biological control agent, Rhodosporidium diobovatum. DNA from all yeast cultures described below was extracted, amplified by PCR using primers specific to septate fungi, and fixed to nylon membranes. Using sequence information obtained from the GenBank database, Rhodosporidium diobovatum-specific oligonucleotides were designed and, after labeling with digoxigenin-d-UTP, were used as probes in a dot-blot hybridization assay. After preliminary testing, two probes were selected for further study. For probe RD3, a positive reaction was obtained at 38, 42 and 48°C with R. diobovatum in pure culture. Other yeast isolates such as Rhodosporidium toruloides, R. fluviale, R. babjevae, R. sphaerocarpum, R. kratochvilovae, R. azoricum, Pichia anomala, and some common greenhouse pathogens tested gave a negative result. The other probe (RD1) reacted with two species, R. diobovatum and R. babjevae at 42°C. The present dot-blot assay can be used reliably to identify the biocontrol agent, Rhodosporidium diobovatum, from pure culture and plant tissue.     

Rhizobia as a biological control agent against soil borne plant pathogenic fungi

Rhizobia promote the growth of plants either directly through N2 fixation, supply of nutrients, synthesis of phytohormones and solubilization of minerals, or indirectly as a biocontrol agent by inhibiting the growth of pathogens. The biocontrol effect of rhizobia is due to the secretion of secondary metabolites such as antibiotics and HCN. Siderophore production in iron stress conditions provides rhizobia an added advantage, resulting in exclusion of pathogens due to iron starvation.     

Consequences of Melaleuca quinquenervia Invasion on Soil Nematodes in the Florida Everglades

The tree Melaleuca quinquenervia invades all types of habitats of South Florida leading to up to 80% loss of aboveground diversity. To examine impacts on the belowground ecosystem, we investigated the composition and diversity of nematodes from soils dominated by the invasive tree and compared them with soils supporting native plant communities at six locations across the Florida Everglades over three years. Despite the significant differences in soil type, hydrology, and native plant composition of the sites, there were consistent differences in nematode communities between soil environments under the native and invaded plant communities. The total abundance and diversity of nematodes in soils dominated by M. quinquenervia was 60% and 80% of adjacent soils under native plants. Fungal-feeding and plant-parasitic nematodes were twice as abundant under native plants as under M. quinquenervia. Nematode communities under M. quinquenervia were bacterivore-dominated, while under native vegetation plant-parasite dominated. The overall diversity of nematodes was 20% lower under the exotic than under native plants, with plant parasites being 36% and fungivores being 30% less diverse. Soil moisture, % of Ca, Mg, and clay particles and total soil C and N were greater in M. quinquenervia soils, but plant-available concentrations of P, K, Ca, and Mg as well as CEC were reduced. Overall, data suggests that the invasion process may modify soil biotic and abiotic conditions that in turn promote the advancement of the exotic M. quinquenervia and displacement of the native plants.     

Nesaecrepida infuscata: a biological control agent of the invasive plant Mimosa pigra

Mimosa pigra L. is a serious weed of wetlands of Australia, Asia and Africa. A suite of established biocontrol agents have been introduced in Australia and some Asian countries, but better control is needed. Nesaecrepida infuscata (Schaeffer) (Coleoptera: Chrysomelidae) is a common insect on M. pigra in tropical America. The larvae develop on the roots while the adults feed on the leaves. As both roots and leaves of M. pigra are relatively undamaged in the introduced range, this species has potential to limit the growth, survival and seed production. Furthermore, it is abundant in the dry season and so inflicts damage when most other agents are not active. In host specificity tests, larvae did not develop on any of the 65 test plant species other than M. pigra. Adult feeding on test plant species other than M. pigra was minimal. Based on these results, this insect has been released in Australia.     

The molecular genetic basis of plant adaptation

How natural selection on adaptive traits is filtered to the genetic level remains largely unknown. Theory and quantitative trait locus (QTL) mapping have provided insights into the number and effect of genes underlying adaptations, but these results have been hampered by questions of applicability to real biological systems and poor resolution, respectively. Advances in molecular technologies have expedited the cloning of adaptive genes through both forward and reverse genetic approaches. Forward approaches start with adaptive traits and attempt to characterize their underlying genetic architectures through linkage disequilibrium mapping, QTL mapping, and other methods. Reverse screens search large sequence data sets for genes that possess the signature of selection. Though both approaches have been successful in identifying adaptive genes in plants, very few, if any, of these adaptations' molecular bases have been fully resolved. The continued isolation of plant adaptive genes will lead to a more comprehensive understanding of natural selection's effect on genes and genomes.     

The use of molecular assays to identify plant pathogenic organisms vectored by biological control agents

The planthopper Prokelisia marginata VanDuzee (Homoptera: Delphacidae) has beenconsidered for the biological control of theweed Spartina alterniflora Loisel(Poaceae) in Willapa Bay, Washington, U.S.A. Prokelisia marginata is a stenophagousphloem-feeding insect with the potential totransmit bacterial plant diseases that could bemoved by less-specific vectors to other plantspecies. Initial assays with PCR primers thatare putatively specific for phytoplasmas gavepositive results in Spartina. However,subsequent analyses did not indicate thetransmission of the pathogen by theplanthopper. We sequenced the 16S ribosomalRNA (rRNA) gene of the bacterial species thatgave positive results in PCR. Comparisons withsequences available in GenBank suggested thatthe positive results using the putativelyspecific PCR primers were due to the presenceof such bacteria as Pseudomonas, Holomonas, Vibrio, and Acinetobacter. We did not find phytoplasmasin either Spartina or the planthopperP. marginata.     

Mechanisms underlying host plant selection by Holcocerus hippophaecolus adults

We determined the mechanisms underlying host selection by adults of the seabuckthorn carpenterworm, Holcocerus hippophaecolus Hua, Chou, Fang et Chen. Four sea buckthorn (Hippophae rhamnoides L.) subspecies (varieties) with different degrees of resistance to H. hippophaecolus were chosen for artificial insect infection in cages. The results showed that olfactory and visual cues are very important for the selection of host plants by H. hippophaecolus, but that olfactory stimuli play a more vital role in this process. The relative abundance of branches and leaves had no effect on the likelihood that adults landed on plants from four subspecies (varieties), but did influence landing rates within the same subspecies (varieties). When considering only the most resistant sea buckthorn subspecies (varieties), the presence of luxuriant branches and leaves led to lower landing rates. These results provide a theoretical basis for the understanding of H. hippophaecolus damage to sea buckthorn and the means to implement effective measures of control.     

Reticulate evolution in the natural range of the invasive wetland tree species Melaleuca quinquenervia

The Melaleuca leucadendra complex (broad-leaf paperbarks; Myrtaceae) is a dominant component of the tropical and sub-tropical biota of Australia, particularly in wetlands of high conservation significance. In Florida and other parts of the Americas, however, one member of the group (Melaleuca quinquenervia) is a serious ecological and economic weed. Understanding the relationships and evolution of the group is integral to both conservation and biocontrol efforts. Although the complex is currently considered to include up to 14 species, there has been some concern over taxonomic boundaries within the complex because most species are circumscribed only by combinations of characters, each of which also occurs in other species. Here, DNA sequence data derived from the chloroplast and two nuclear regions are used to explore the relationships of M. quinquenervia. We find little evidence for clear species boundaries within the M. leucadendra complex in general, with regional sharing of chloroplast haplotypes across morphologically defined taxa, indicating asymmetrical introgression or retention of ancestral haplotypes (lineage sorting). Phylogenies were further confounded by the recovery of multiple copies of both nuclear regions sequenced (ITS and rpb2) from many individuals. There was no clear evidence of polyploidy or pseudogenes, but multiple duplications of rpb2 could not be ruled out. Parsimony networks of the nuclear ITS region show some clustering of haplotypes by morphospecies but there is also evidence of both hybridisation and recombination. Signals of introgression were also evident in rpb2, supporting an hypothesis of recent or ongoing gene flow between M. quinquenervia and other members of the M. leucadendra complex. Both relaxed and fixed molecular-clock dating estimate the introgression to have occurred sometime within the past seven million years (95% CI: 0.7-18). The New Caledonian population of M. quinquenervia appears to have been established by dispersal from Australia during this period. M. quinquenervia is found to have alleles closely related to multiple different morphotaxa within the M. leucadendra complex, suggesting considerable past introgression into this taxon from some other members of the M. leucadendra complex, and this has implications for biocontrol efforts. The M. leucadendra complex appears to reflect early to intermediate stages of speciation, possibly driven by different ecologies.