Nitrogen fertilisation improves growth of Chromolaena odorata (Asteraceae) and the performance of the biological control agent, Pareuchaetes insulata (Erebidae)
- Authors: Uyi, Osariyekemwen O , Zacharariades, Costas , Hill, Martin P
- Date: 2016
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/416880 , vital:71393 , xlink:href="https://doi.org/10.1080/09583157.2015.1118615"
- Description: Recent studies have demonstrated, through their contrasting results, that relationships between nitrogen levels in host plants and phytophagous insect performance are not simple. This study examined the effect of varying fertilisation regimes on the invasive alien plant, Chromolaena odorata (L.) (Asteraceae) and the response of a specialist folivore (a biological control agent), Pareuchaetes insulata (Walker) (Lepidoptera: Erebidae). C. odorata plants were treated with 3 different levels of fertilisation and plant characteristics were measured within 2–3 months of fertiliser application. Leaves from each of the three treatments were fed to newly hatched larvae until pupation in order to determine the effect of nitrogen fertilisation on herbivore performance metrics such as survival, development time, fecundity and longevity. High and medium fertilisation significantly increased foliar nitrogen concentrations, basal stem diameter, leaf length, shoot height and above-ground biomass of C. odorata plants relative to low fertilisation. When individuals of P. insulata were fed on leaves from medium- or high-fertilisation treatments, they developed faster, grew to a larger size (by 8%) and achieved higher fecundity (19–22%) than leaves from the low-fertilisation treatment. The results suggest that in mass-rearing, increased production of this biological control agent will occur in high- or medium-fertilised plants.
- Full Text:
- Date Issued: 2016
Screening of entomopathogenic fungi against citrus mealybug, Plannococcus citri (Hemiptera: Pseudococcidae)
- Authors: Chartier Fitzgerald, Veronique , Hill, Martin P , Moore, Sean D , Dames, Joanna F
- Date: 2016
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/407059 , vital:70333 , xlink:href="https://hdl.handle.net/10520/EJC195093"
- Description: Planococcus citri (citrus mealybug) is a common and damaging citrus crop pest which has proven difficult to control using conventional methods, such as chemical pesticides and insect growth regulators, particularly late in the citrus growing season. The virulence of two entomopathogenic fungal species was studied in laboratory bioassays against the crawlers and adults of P. citri. Isolates of Metarhizium anisopliae and Beauveria bassiana, collected from citrus orchards in the Eastern Cape Province in South Africa, were verified using and molecular techniques. Mealybug bioassays were performed in 24-well plates. Beauveria bassiana (GAR 17 B3) and M. anisopliae (FCM AR 23 B3) isolates both resulted in 67.5 % mortality of mealybug crawlers and B. bassiana (GB AR 23 13 3) resulted in 64 % crawler mortality with concentrations of 1 x 107 conidia/ml. These three isolates were further tested in multipledose bioassays to determine the median lethal concentration (LC50), which were 5.29 x 105conidia/ml for the M. anisopliae isolate (FCM AR 23 B3), 4.25 x 106 conidia/ml for B. bassiana (GAR 17 B3), and 6.65 x 107 conidia/ml B. bassiana (GB AR 23 13 3) for crawlers, respectively. The results of this study suggested that two isolates (M. anisopliae FCM AR 23 B3 and B. bassiana GAR 17 B3) showed potential for further development as biological control agents against citrus mealybug. Further research would be required to determine their ability to perform under field conditions.
- Full Text:
- Date Issued: 2016
Temperature-dependent performance and potential distribution of Pareuchaetes insulata, a biological control agent of Chromolaena odorata in South Africa
- Authors: Uyi, Osariyekemwen O , Zachariades, Costas , Hill, Martin P , McConnachie, Andrew J
- Date: 2016
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/418067 , vital:71505 , xlink:href="https://doi.org/10.1007/s10526-016-9760-1"
- Description: Despite the release of about 1.9 million individuals of Pareuchaetes insulata (Walker) (Lepidoptera: Erebidae) in KwaZulu-Natal for the biological control of Chromolaena odorata (L.) King and Robinson (Asteraceae) in South Africa, the moth probably only established at one of the 30 release sites and its population level is generally low in the field. To determine whether climate incompatibility in South Africa is responsible for the poor performance of P. insulata, the effects of temperature on life-history traits were investigated under several constant temperatures. Although a degree-day model estimated between 3.9 and 10.0 generations of the moth per year in the weed’s invaded range, survival and fecundity declined while development time was prolonged at constant temperatures below 25 °C, indicating that both direct and indirect negative impacts of low winter temperatures, such as increased mortality, slow development and reduced fecundity as well as exposure to natural enemies, may partly explain the poor performance of P. insulata in South Africa.
- Full Text:
- Date Issued: 2016
Two in one: cryptic species discovered in biological control agent populations using molecular data and crossbreeding experiments
- Authors: Paterson, Iain D , Mangan, Rose , Downie, Douglas A , Coetzee, Julie A , Hill, Martin P , Burke, Ashley M , Downey, Paul O , Henry, Thomas J , Compton, Stephen G
- Date: 2016
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/424877 , vital:72191 , xlink:href="https://doi.org/10.1002/ece3.2297"
- Description: There are many examples of cryptic species that have been identified through DNA-barcoding or other genetic techniques. There are, however, very few confirmations of cryptic species being reproductively isolated. This study presents one of the few cases of cryptic species that has been confirmed to be reproductively isolated and therefore true species according to the biological species concept. The cryptic species are of special interest because they were discovered within biological control agent populations. Two geographically isolated populations of Eccritotarsus catarinensis (Carvalho) [Hemiptera: Miridae], a biological control agent for the invasive aquatic macrophyte, water hyacinth, Eichhornia crassipes (Mart.) Solms [Pontederiaceae], in South Africa, were sampled from the native range of the species in South America. Morphological characteristics indicated that both populations were the same species according to the current taxonomy, but subsequent DNA analysis and breeding experiments revealed that the two populations are reproductively isolated. Crossbreeding experiments resulted in very few hybrid offspring when individuals were forced to interbreed with individuals of the other population, and no hybrid offspring were recorded when a choice of mate from either population was offered. The data indicate that the two populations are cryptic species that are reproductively incompatible. Subtle but reliable diagnostic characteristics were then identified to distinguish between the two species which would have been considered intraspecific variation without the data from the genetics and interbreeding experiments. These findings suggest that all consignments of biological control agents from allopatric populations should be screened for cryptic species using genetic techniques and that the importation of multiple consignments of the same species for biological control should be conducted with caution.
- Full Text:
- Date Issued: 2016
Agathis bishopi (Hymenoptera: Braconidae) as a potential tool for detecting oranges infested with Thaumatotibia leucotreta (Lepidoptera: Tortricidae)
- Authors: Zimba, Kennedy J , Hill, Martin P , Moore, Sean D , Heshula, Unathi
- Date: 2015
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/423955 , vital:72108 , xlink:href="https://doi.org/10.1007/s10905-015-9526-0"
- Description: In South Africa, Thaumatotibia leucotreta is a key pest of citrus impacting its production and trade. Detection of newly infested fruit by visual inspection is challenging and poses a risk of packing infested with healthy fruit for export. Agathis bishopi is a larval endoparasitoid of T. leucotreta, attacking early larval instars. Understanding how A. bishopi parasitoids locate fruit infested with their host is of interest for developing an efficient detector for T. leucotreta infested fruit. The response of female adult A. bishopi parasitoids to olfactory and visual cues associated with T. leucotreta infested fruit were evaluated using a Y-tube olfactometer and flight tunnel. Agathis bishopi parasitoids were strongly attracted to infested fruit over healthy fruit, either when only olfactory or combinations of visual and olfactory cues were offered. Among the four synthetic compounds tested, D-limonene and ocimene elicited a strong attraction to parasitoids with response rates of 92 % and 72 % respectively. A blend of four synthetic compounds simulating T. leucotreta infested fruit odour equally elicited strong attraction to parasitoids (84 % response rate). Attraction of parasitoids to infested fruit cues was heightened by prior experience, suggesting the occurrence of associative learning. Results from this study indicate that A. bishopi parasitoids mainly rely on olfactory cues in host habitat location and that D-limonene and ocimene are the major attractants in infested fruit volatiles. These findings and the potential for manipulating A. bishopi for detection of infested fruit in the packhouse are discussed.
- Full Text:
- Date Issued: 2015
Agathis bishopi, a larval parasitoid of false codling moth Thaumatotibia leucotreta: laboratory rearing and effect of adult food on parasitism and longevity
- Authors: Zimba, Kennedy J , Moore, Sean D , Heshula, LU , Hill, Martin P
- Date: 2015
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/406985 , vital:70328 , xlink:href="https://hdl.handle.net/10520/EJC185849"
- Description: Agathis bishopi (Nixon) (Hymenoptera: Braconidae) is a koinobiont larval endoparasitoid of false codling moth (FCM), Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae), a pest of economic importance on citrus in South Africa. In the field Agathis bishopi was found to parasitise up to 34 % of FCM larvae in fruit, reflecting reasonable biocontrol potential. Improving the rearing of A. bishopi would therefore complement the existing biocontrol strategies for FCM. In several parasitic wasps, sugar concentration and feeding duration has been shown to influence parasitism and longevity. However, their effect on parasitism and longevity of A. bishopi is unknown. In the present study a rearing protocol for A. bishopi is described, including evaluation of the effects of honey concentration on parasitoid longevity. On average, 18.2%of FCM larvae in rearing containers were parasitised under the rearing protocol described. Cotton wool, instead of paper towelling, as honey carrier for feeding parasitoids in rearing containers significantly increased parasitism and yield of offspring. Furthermore, longevity significantly increased with higher concentrations of honey. Maximum lifespan duration for male and female parasitoids was achieved when parasitoids were fed on 36 % (w/v) honey. Results from this study indicate that A. bishopi requires a sufficient concentration of sugar, coupled with frequent and prolonged feeding on a cotton wool substrate, in order to achieve maximum parasitism and longevity. Such information provides a basis for optimising mass-rearing and longevity of A. bishopi and parasitism of FCM in orchards.
- Full Text:
- Date Issued: 2015
Baculovirus-based strategies for the management of insect pests: a focus on development and application in South Africa
- Authors: Knox, Caroline M , Moore, Sean D , Luke, Garry , Hill, Martin P
- Date: 2015
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/416829 , vital:71389 , xlink:href="https://doi.org/10.1080/09583157.2014.949222"
- Description: There is growing concern among governments, scientists, agricultural practitioners and the general public regarding the negative implications of widespread synthetic chemical pesticide application for the control of crop pests. As a result, baculovirus biopesticides are gaining popularity as components of integrated pest management (IPM) programmes in many countries despite several disadvantages related to slow speed of kill, limited host range and complex large scale production. In South Africa, baculoviruses are incorporated into IPM programmes for the control of crop pests in the field, and recent bioprospecting has led to the characterisation of several novel isolates with the potential to be formulated as commercial products. This contribution will provide an overview of the use of baculoviruses against insect pests in South Africa, as well as research and development efforts aimed at broadening their application as biocontrol agents. Challenges faced by researchers in developmental projects as well as potential users of baculoviruses as biopesticides in the field are also discussed.
- Full Text:
- Date Issued: 2015
Beauveria and Metarhizium against false codling moth (Lepidoptera: Tortricidae): a step towards selecting isolates for potential development of a mycoinsecticide
- Authors: Coombes, Candice A , Hill, Martin P , Moore, Sean D , Dames, Joanna F , Fullard, T
- Date: 2015
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/405757 , vital:70203 , xlink:href="https://hdl.handle.net/10520/EJC167505"
- Description: False codling moth, Thaumatotibia leucotreta Meyrick (1912) (Lepidoptera: Tortricidae), can cause both pre- and post-harvest damage to citrus fruit. Not only can this result in reduced crop yield, but more importantly because of the moth's endemism to sub-Saharan Africa, it is classified as a phytosanitary pest by many export markets. An entire consignment of citrus may be rejected in the presence of a single moth (Moore 2012). Since the bulk of citrus fruit production in South Africa is exported, the control of T. leucotreta is critical (Citrus Growers Association, South Africa 2012). Traditionally, control has been achieved through the use of chemical insecticides; however, residue restrictions, resistance development and concerns about environmental pollution have substantially reduced the dependence on chemical pesticides in citrus. Research on T. leucotreta control has therefore focused on the use of biological organisms (e.g. parasitoids and viruses), which are used as control agents within an integrated pest management (IPM) programme in citrus. These biological control agents, however, only targeted the aboveground life stages of the pest, not the soil-dwelling life stages (late fifth instars, prepupae, pupae), which is the subject of this contribution (Moore 2012).
- Full Text:
- Date Issued: 2015
Comparisons of isotopic niche widths of some invasive and indigenous fauna in a South African river
- Authors: Hill, Jaclyn M , Jones, Roy W , Hill, Martin P , Weyl, Olaf L F
- Date: 2015
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/423711 , vital:72088 , xlink:href="https://doi.org/10.1111/fwb.12542"
- Description: Biological invasions threaten ecosystem integrity and bio-diversity, with numerous adverse implications for native flora and fauna. Established populations of two notorious freshwater invaders, the snail Tarebia granifera and the fish Pterygoplichthys disjunctivus, have been reported on three continents and are frequently predicted to be in di-rect competition with native species for dietary resources.
- Full Text:
- Date Issued: 2015
DNA-based identification of Lepidoptera associated with citrus in South Africa
- Authors: Marsberg, Tamryn , Hill, Martin P , Moore, Sean D , Timm, A E
- Date: 2015
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/405782 , vital:70205 , xlink:href="https://hdl.handle.net/10520/EJC167513"
- Description: A number of insects, primarily Lepidoptera, cause damage to citrus in South Africa. A major limitation to the management and control of these pests is their correct identification. The aim of this study was to develop a database of gene sequences to aid in the identification of these Lepidoptera. Multiple specimens of 12 species were sequenced for the ~650 bp of the cytochrome oxidase I gene. These sequence data were supplemented and validated using sequences available in public databases. Results showed that each species could be unambiguously identified, and neighbour-joining analysis based on K2P distances formed highly supported, distinct clusters for each species, i.e. the maximum intraspecific genetic distance was less than that of the minimum interspecific genetic distances. Thus, this data set provides a molecular means to successfully identify the most important Lepidoptera associated with citrus in South Africa.
- Full Text:
- Date Issued: 2015
Genetic and biological characterisation of a novel Plutella xylostella granulovirus, PlxyGV-SA
- Authors: Abdulkadir, Fatima , Knox, Caroline M , Marsberg, Tamryn , Hill, Martin P , Moore, Sean D
- Date: 2015
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/417971 , vital:71498 , xlink:href="https://doi.org/10.1007/s10526-015-9666-3"
- Description: Plutella xylostella granulovirus (PlxyGV) has been isolated from insect populations in many countries and is considered a potential biopesticide for sustainable control of P. xylostella (L.) (Lepidoptera: Plutellidae). Several PlxyGV isolates have been genetically characterised, and the full genome sequence of PlxyGV-Japan is available for comparison with novel isolates. A South African PlxyGV was recently recovered from an overcrowded laboratory P. xylostella colony and identified as a genetically distinct isolate by sequencing of the granulin gene and restriction endonuclease (REN) analysis of genomic DNA. In this report, PlxyGV-SA was further characterised by PCR amplification and sequencing of egt, lef-8 and lef-9 genes, and several amino acid substitutions were observed. The PstI REN profile of PlxyGV-SA was different from that of PlxyGV-Japan in terms of band size and number, thereby confirming its novel genetic identity. Surface dose bioassays showed that PlxyGV-SA is pathogenic to neonate but not late instar larvae at the same and higher virus doses, indicating that a biopesticide should be targeted at early larval stages in the field.
- Full Text:
- Date Issued: 2015
Host searching and oviposition behaviour of Agathis bishopi (Hymenoptera: Braconidae), a larval parasitoid of false codling moth, Thaumatotibia leucotreta (Lepidoptera: Tortricidae): a potential proxy indicator for fruit infestation
- Authors: Zimba, Kennedy J , Heshula, LU , Moore, Sean D , Hill, Martin P
- Date: 2015
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/407019 , vital:70330 , xlink:href="https://hdl.handle.net/10520/EJC195073"
- Description: Agathis bishopi (Nixon) (Hymenoptera: Braconidae)is an arrhenotokous larval endoparasitoid of Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae) (Gendall 2007; Hofmeyr et al. 2015) commonly known as false codling moth (FCM), a major pest of citrus in South Africa (Moore et al. 2004; Malan et al. 2011). Under field conditions, A. bishopi was identified attacking more than 34% of FCM larvae in fruit, showing good biocontrol potential (Gendall 2007). Preference by A. bishopi for parasitising the early instars of its concealed host suggests that the parasitoid has strong natural host location ability (Sishuba 2003; Gendall 2007).
- Full Text:
- Date Issued: 2015
The effect of long-distance transportation on the fitness of irradiated false codling Moth (Lepidoptera: Tortricidae) for use in a sterile insect release program
- Authors: Nepgen, Eugene S , Hill, Martin P , Moore, Sean D
- Date: 2015
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/423835 , vital:72098 , xlink:href="https://doi.org/10.1093/jee/tov246"
- Description: The effect of cold immobilization and long-distance transport of irradiated Thaumatotibia leucotreta (Meyrick) on the flight ability of male (?) and female (/) moths, the longevity of male and female moths, and the realized fecundity of mating pairs CIM (chilled irradiated moths) / CIM?, CIM/ NIP (nonirradiated pupae) ?, NIP/ CIM?, and NIP/ NIP? was examined to improve application of the sterile insect technique (SIT). Adult moths treated with 150 Gy of gamma radiation were immobilized with cold temperature between 4 and 6C inside a polyurethane cooler box and transported for 12 h by road from Citrusdal, Western Cape Province, to Addo, Eastern Cape Province. Nonirradiated moths were transported as pupae inside a cardboard tray and removed by hand after which male and female pupae were separated and placed inside containers for eclosion. Male and female moths were individually placed inside petri dishes to determine longevity or paired with irradiated and nonirradiated counterparts to evaluate realized fecundity before incubation in 100% darkness at 25C and 75% relative humidity. Flight tests were conducted indoors at 25C by release of individual moths per hand. A significant decrease in flight ability and longevity of irradiated false codling moth was found after handling, cold immobilization, and transport, although critically, realized fecundity was not affected. Because of the impact of long-distance transport on quality of the released insects as well as the efficacy of SIT, comprehensive protocols for this critical step in the process need to be developed for a pestiferous insect with phytosanitary status such as false codling moth.
- Full Text:
- Date Issued: 2015
The nocturnal larvae of a specialist folivore perform better on C hromolaena odorata leaves from a shaded environment
- Authors: Osariyekemwen O. Uyi , Costas Zachariades , Hill, Martin P , Conlong, Desmond
- Date: 2015
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/424855 , vital:72189 , xlink:href="https://doi.org/10.1111/eea.12321"
- Description: Increasing evidence suggests that individuals of the same plant species occurring in different micro-habitats often show a degree of phenotypic and phytochemical variation. Consequently, insect herbivores associated with such plant species must deal with environment-mediated changes or variability in the traits of their host plants. In this study, we examined the effects of habitat condition (shadedvs. full-sun habitats) on plant traits and leaf characteristics of the invasive alien plant, Chromolaenaodorata (L.) King and Robinson (Asteraceae). In addition, the performance was evaluated in two generations of a specialist folivore, Pareuchaetes insulata (Walker) (Lepidoptera: Erebidae: Arctiinae), on leaves obtained from both shaded and full-sun habitats. The study was done in an area where the insect was introduced as a biological control agent. Leaves growing in shade were less tough, had higher water and nitrogen content, and lower total non-structural carbohydrate, compared with leaves growing in full sun. Plants growing in shade had longer leaves and were taller, but above-ground biomass was significantly reduced compared with plants growing in full sun. In both generations (parents and offspring), P. insulata developed faster and had larger pupal mass, increased growth rate, and higher fecundity when reared on shaded foliage compared with full-sun foliage. Although immature survival and adult longevity did not differ between habitats, Maw’s host suitability index indicated that shaded leaves were more suitable for the growth and reproduction of P. insulata. We suggest that the benefits obtained by P.insulata feeding on shaded foliage are associated with reduced toughness and enhanced nitrogen and water content of leaves. These results demonstrate that light-mediated changes in plant traits and leaf characteristics can affect insect folivore performance.
- Full Text:
- Date Issued: 2015
A promising biological control agent for the invasive alien plant, Pereskia aculeata Miller (Cactaceae), in South Africa
- Authors: Paterson, Iain D , Mdodana, Lumka A , Mpekula, Ongezwa , Mabunda, Bheki D , Hill, Martin P
- Date: 2014
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/416806 , vital:71387 , xlink:href="https://doi.org/10.1080/09583157.2014.919439"
- Description: Pereskia aculeata Miller (Cactaceae) is an invasive alien plant from Central and South America that has become a problematic environmental weed in South Africa. A potential biological control agent, the stem-wilter, Catorhintha schaffneri Brailovsky and Garcia (Coreidae), was collected in southern Brazil and imported into quarantine in South Africa. Field host range data suggested that C. schaffneri has a host range restricted to P. aculeata. No-choice nymph survival tests were then conducted on 27 test plant species in 9 families. Survival to the adult stage was only recorded on P. aculeata and the closely related Pereskia grandifolia Haw. (Cactaceae). Mortality was significantly higher on P. grandifolia with only 3% of the nymphs reaching the adult stage compared with 74% on P. aculeata indicating that P. aculeata is the primary host plant. P. grandifolia is native in South America and is of no agricultural importance in South Africa so any feeding on P. grandifolia in South Africa would have no negative environmental or economic consequences. In other tests, adult survival on P. aculeata [25.8 days (SE ± 3.74)] was significantly longer than on other test plant species [4.3 days (SE ± 0.36)] further confirming the host specificity of the species. Impact studies conducted in quarantine indicated that C. schaffneri is damaging to P. aculeata, significantly reducing the number of leaves and the shoot lengths of plants, even at relatively low insect densities. C. schaffneri is safe for release in South Africa and is likely to be a damaging and effective agent.
- Full Text:
- Date Issued: 2014
Comparison of the biology of geographically distinct populations of the citrus pest, Thaumatotibia leucotreta (Meyrick)(Lepidoptera: Tortricidae)
- Authors: Opoku-Debrah, John K , Hill, Martin P , Knox, Caroline M , Moore, Sean D
- Date: 2014
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/405769 , vital:70204 , xlink:href="https://hdl.handle.net/10520/EJC160246"
- Description: Baculovirus biopesticides are an important component of integrated pest management programmes worldwide. One such example is the Cryptophlebia leucotreta granulovirus (CrleGV) which is used for the control of false codling moth, Thaumatotibia (= Cryptophlebia) leucotreta (Meyrick) (Lepidoptera: Tortricidae), a pest of citrus and other crops in South Africa. A potential problem associated with constant application of viral biopesticides is the differing susceptibility to the virus observed between different geographic populations of the insect host. This could be related to a number of factors, including biological performance and fitness of the target insect population. This study compared a variety of phenotypic traits between geographically distinct T. leucotreta populations collected from the Addo, Marble Hall, Citrusdal and Nelspruit regions of South Africa, and reared under laboratory conditions for several generations. Traits including pupal mass, female fecundity, egg hatch, pupal survival, adult eclosion and developmental time were used as parameters to measure biological performance and fitness. Insects from the Citrusdal region of the Western Cape exhibited significantly lower pupal mass, female fecundity, egg hatch, pupal survival, adult eclosion and the longest duration in larval and pupal development compared to the other colonies investigated. This is the first study to report differences in the performance of laboratory reared T. leucotreta from different geographic locations, and the findings may have important implications for the application of viral biopesticides for the control of this pest in South Africa.
- Full Text:
- Date Issued: 2014
Effect of water trophic level on the impact of the water hyacinth moth Niphograpta albiguttalis on Eichhornia crassipes
- Authors: Canavan, Kim N , Coetzee, Julie A , Hill, Martin P , Paterson, Iain D
- Date: 2014
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/423740 , vital:72090 , xlink:href="https://doi.org/10.2989/16085914.2014.893225"
- Description: Eutrophication contributes to the proliferation of alien invasive weed species such as water hyacinth Eichhornia crassipes. Although the South American moth Niphograpta albiguttalis was released in South Africa in 1990 as a biological control agent against water hyacinth, no post-release evaluations have yet been conducted here. The impact of N. albiguttalis on water hyacinth growth was quantified under low-, medium- and high-nutrient concentrations in a greenhouse experiment. Niphograpta albiguttalis was damaging to water hyacinth in all three nutrient treatments, but significant damage in most plant parameters was found only under high-nutrient treatments. However, E. crassipes plants grown in high-nutrient water were healthier, and presumably had higher fitness, than plants not exposed to herbivory at lower-nutrient levels. Niphograpta albiguttalis is likely to be most damaging to water hyacinth in eutrophic water systems, but the damage will not result in acceptable levels of control because of the plant's high productivity under these conditions. Niphograpta albiguttalis is a suitable agent for controlling water hyacinth infestations in eutrophic water systems, but should be used in combination with other biological control agents and included in an integrated management plan also involving herbicidal control and water quality management.
- Full Text:
- Date Issued: 2014
Thaumatotibia leucotreta and the Navel orange: ovipositional preferences and host susceptibility
- Authors: Love, C N , Hill, Martin P , Moore, Sean D
- Date: 2014
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/423811 , vital:72095 , xlink:href="https://doi.org/10.1111/jen.12126"
- Description: False codling moth, Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae), presents a significant threat to the South African citrus industry. To limit income loss due to direct larval damage or from fruit rejection due to the phytosanitary status of this pest, additional pre-harvest control techniques are required for Navel oranges, which are known to be susceptible to T.leucotreta damage. A number of Navel orange cultivars have been developed, and differences in female T. leucotretaovi positional preference and susceptibility of cultivars to larval penetration are known to exist. Navel orange cultivars were grouped according to time of maturity (early, mid- and late season). Female T.leucotreta were subjected to choice and no-choice tests with these cultivars, measured by oviposition. Host susceptibility was tested by allowing neonate T. leucotreta larvae to penetrate the different Navel cultivars. In the early maturing group, Fischer Navels were least preferred for oviposition and the least susceptible to larval penetration. The mid- and late season maturing groupings showed limited differences in oviposition preference, although host susceptibility did appear to be an important factor in assessing the vulnerability of fruit to T. leucotreta. Despite being widely planted in South Africa, the mid-season Palmer Navels were highly susceptible to larval penetration, while for the late season cultivars, Cambria and Glen Ora Late were the least susceptible to T. leucotreta. As a result of these laboratory trials, it is recommended that farmers increase cultivation of Fischer Navels as the principal early season cultivar, avoid Palmer Navels in favour of other mid-season maturing cultivars and give preference to the late maturing Cambria and Glen Ora Late cultivars, to limit T. Leucotreta damage.
- Full Text:
- Date Issued: 2014
The effect of sap-sucking by Falconia intermedia (Hemiptera: Miridae) on the emission of volatile organic compounds from the leaves of Lantana camara varieties
- Authors: Heshula, Lelethu U , Hill, Martin P
- Date: 2014
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/406141 , vital:70242 , xlink:href="https://hdl.handle.net/10520/EJC150957"
- Description: Evidence from more than 100 plant species has confirmed that plants emit volatile organic chemicals (VOC) in response to herbivory (Karban and Baldwin 1997; Dicke et al. 2003; Arimura et al. 2005). Feeding-induced plant responses may result in higher levels of volatiles, and different bouquets of compounds being emitted by plants following herbivore damage (Wei et al. 2006). The emission of volatile chemicals may be beneficial to plants in two ways; undamaged plants may interpret the chemical signals from damaged plants and in turn prime themselves for defence (Arimura et al. 2000; Dicke et al. 2003; Agrawal 2005), or volatiles emitted by damaged plants may attract natural enemies of the herbivores, which may reduce further damage to the plants (Tumlinson et al. 1993; De Moraes et al. 1998; Dicke and Vet 1999).
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- Date Issued: 2014
The herbivorous arthropods associated with the invasive alien plant, Arundo donax, and the native analogous plant, Phragmites australis, in the Free State Province, South Africa s
- Authors: Canavan, Kim N , Paterson, Iain D , Hill, Martin P
- Date: 2014
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/406155 , vital:70243 , xlink:href="https://hdl.handle.net/10520/EJC155690"
- Description: The Enemy Release Hypothesis (ERH) predicts that when plant species are introduced outside their native range there is a release from natural enemies resulting in the plants becoming problematic invasive alien species (Lake and Leishman 2004; Puliafico et al. 2008). The release from natural enemies may benefit alien plants more than simply reducing herbivory because, according to the Evolution of Increased Competitive Ability (EICA) hypothesis, without pressure from herbivores more resources that were previously allocated to defence can be allocated to reproduction (Blossey and Notzold 1995). Alien invasive plants are therefore expected to have simpler herbivore communities with fewer specialist herbivores (Frenzel and Brandl 2003; Heleno et al. 2008; Heger and Jeschke 2014).
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- Date Issued: 2014