Identity and origins of introduced and native Azolla species in Florida
- Authors: Madeira, Paul T , Center, Ted D , Coetzee, Julie A , Pemberton, Robert W , Purcell, Matthew F , Hill, Martin P
- Date: 2013
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/419313 , vital:71634 , xlink:href="https://doi.org/10.1016/j.aquabot.2013.07.009"
- Description: Azolla pinnata, an introduced aquatic fern, is spreading rapidly causing concern that it may displace native Azolla. It is now present in the Arthur R. Marshall Loxahatchee National Wildlife Refuge, the northernmost portion of the Florida Everglades. Because A. pinnata subspecies are native to Africa, Southeast Asia, and Australia, determining the actual geographic origin of the Florida exotic is important to the discovery of efficacious biological control agents. Both the exotic and native Azollas were examined using morphological and molecular criteria. Both criteria distinguished three A. pinnata subspecies with the Florida exotic matching the Australian A. pinnata subsp. pinnata. Molecular divergence between the A. pinnata subspecies indicates the three types should be considered separate species. The Florida native was characterized by both molecular and morphological methods as Azolla caroliniana. The discovery of a previously uncharacterized Ecuadorian Azolla, which appears to be a paternal ancestor of A. caroliniana, indicates that A. caroliniana is a hybrid species.
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- Date Issued: 2013
Nutrient-mediated effects on Cornops aquaticum Brüner (Orthoptera: Acrididae), a potential biological control agent of water hyacinth, Eichhornia crassipes (Mart.) Solms (Pontederiaceae)
- Authors: Bownes, Angela , Hill, Martin P , Byrne, Marcus J
- Date: 2013
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/406131 , vital:70241 , xlink:href="https://doi.org/10.1016/j.biocontrol.2013.07.023"
- Description: Environmental nutrient availability can drive and modify both plant responses to herbivory by phytophagous insects and insect feeding patterns which, in insect-weed systems, may ultimately determine whether biological control succeeds or fails. The impacts of insect biological control agents on the invasive aquatic weed, water hyacinth (Eichhornia crassipes) vary with nutrient levels in the environment. It was therefore considered important to evaluate nutrient-specific responses of E. crassipes to a grasshopper herbivore, Cornops aquaticum, prior to its release in South Africa. Both plant productivity and the response of E. crassipes to herbivory by C. aquaticum were nutrient dependent. Increases in plant biomass and leaf and ramet production were correlated with increases in nutrients in the water and plant biomass accumulation was reduced by herbivory at all three nutrient levels tested (high = 67%; medium = 100%; low = 400%). C. aquaticum nymphs fed E. crassipes leaves with the lowest nitrogen levels produced the highest biomass of frass during their development, indicating compensatory consumption. The results suggest that environmental nutrient availability will influence efficacy of C. aquaticum. They also provide further evidence that E. crassipes problems are exacerbated by an over-abundance of nutrients in aquatic environments, and that biological control would be a highly effective management tool if aquatic systems in South Africa were less polluted. Additionally, the results also show how an understanding of the fundamental responses of E. crassipes and its insect biocontrol agents to their environment can assist in determining specific management strategies or interventions according to prevailing site-specific conditions.
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- Date Issued: 2013
Overcrowding of false codling moth, Thaumatotibia leucotreta (Meyrick) leads to the isolation of five new Cryptophlebia leucotreta granulovirus (CrleGV-SA) isolates
- Authors: Opoku-Debrah, John K , Hill, Martin P , Knox, Caroline , Moore, Sean D
- Date: 2013
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/419360 , vital:71637 , xlink:href="https://doi.org/10.1016/j.jip.2012.12.008"
- Description: False codling moth, Thaumatotibia leucotreta (Meyrick) is a serious pest of economic importance to the South African fruit industry. As part of sustainable efforts to control this pest, biological control options that involve the application of baculovirus-based biopesticides such as Cryptogran and Cryptex (both formulated with a South African isolate of Cryptophlebia leucotreta granulovirus, CrleGV-SA) are popularly used by farmers. In order to safeguard the integrity of these biopesticides as well as protect against any future development of resistance in the host, we conducted a study to bioprospect for additional CrleGV isolates as alternatives to existing ones. Using overcrowding as an induction method for latent infection, we recovered five new CrleGV isolates (CrleGV-SA Ado, CrleGV-SA Mbl, CrleGV-SA Cit, CrleGV-SA MixC and CrleGV-SA Nels). Single restriction endonuclease (REN) analysis of viral genomic DNA extracted from purified occlusion bodies showed that isolates differed in their DNA profiles. Partial sequencing of granulin and egt genes from the different isolates and multiple alignments of nucleotide sequences revealed the presence of single nucleotide polymorphisms (SNPs), some of which resulted in amino acid substitutions in the protein sequence. Based on these findings as well as comparisons with other documented CrleGV isolates, we propose two phylogenetic groups for CrleGV-SA isolates recovered in this study.
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- Date Issued: 2013
The effect of herbivory by the mite Orthogalumna terebrantis on the growth and photosynthetic performance of water hyacinth (Eichhornia crassipes)
- Authors: Marlin, Danica , Hill, Martin P , Ripley, Brad , Strauss, Abram J , Byrne, Marcus J
- Date: 2013
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/419411 , vital:71642 , xlink:href="https://doi.org/10.1016/j.aquabot.2012.09.005"
- Description: Eutrophication of fresh water systems is one of the most important factors contributing to the invasion of fresh water bodies by water hyacinth, Eichhornia crassipes. The South American mite, Orthogalumna terebrantis, established on the weed in South Africa in the late 1980s, but the impact of mite herbivory on the weed has never been quantified. Water hyacinth was grown under low, medium and high nitrogen and phosphorus nutrient conditions and the effect of mite herbivory on the weed's growth was examined. Additionally, the impact of different mite herbivory intensities on the weed's photosynthetic performance was examined because herbivory may have more subtle effects on the plant than can be seen from changes in plant growth parameters. Water nutrient content had a great impact on plant growth, but growth was unaffected by mite herbivory in all levels of nutrients tested. Photosynthetic performance of water hyacinth leaves exposed to varying levels of mite herbivory was assessed by measuring net photosynthetic rate (A), leaf conductance (gl), transpiration rate (E) and intercellular CO2 concentration (Ci), and by measuring specific fluorescence parameters including maximal fluorescence (Fm), efficiency of photosystem II (Fv/Fm) and certain JIP-test parameters. Photosynthesis decreased as mite herbivory increased, but there was a positive correlation between gl, E and Ci, and the amount of leaf tissue damaged through mite feeding. The efficiency of photosystem II (PSII) decreased as mite herbivory increased, as seen in the altered fluorescence emission of mite-damaged plants, but this was not the consequence of decreased chlorophyll content. Feeding by O. terebrantis thus decreased water hyacinth photosynthetic rate and the light reaction performance, even at relatively low mite densities. These results show that the impact of a biological control agent on its host plant may not be obvious at a plant growth level, but may nonetheless affect the plant at a physiological level.
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- Date Issued: 2013
Weevil borne microbes contribute as much to the reduction of photosynthesis in water hyacinth as does herbivory
- Authors: Venter, Nic , Hill, Martin P , Hutchinson, Sarah-Leigh , Ripley, Brad S
- Date: 2013
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/423573 , vital:72073 , xlink:href="https://doi.org/10.1016/j.biocontrol.2012.10.011"
- Description: Arthropods released for weed biocontrol can have effects other than simply removing biomass and frequently decrease photosynthetic rate more than can be attributed to the mere loss of photosynthetic surface area. Some of this effect may result because biological control agents facilitate the transfer and ingress of deleterious microbes into plant tissues on which they feed. We evaluated this facilitation effect using water hyacinth (Eichhornia crassipes) and a weevil (Neochetina eichhorniae) and compared the reductions in photosynthetic rates between leaves subject to herbivory by adult weevils sterilized with 3.5% chlorine bleach, to those that were unsterilized. The results showed that weevils carried both fungi and bacteria, transferred these to leaves on which they fed, and that microbes and biomass removal contributed almost equally to the 37% decrease in photosynthetic productivity. Hence, maximising the effectiveness of using arthropods that damage leaf surfaces for biocontrol requires the presence of microorganisms that are deleterious to plants.
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- Date Issued: 2013