Martin P. Hill

A Review of the Biological Control Programmes on Eichhornia crassipes (C.Mart.) Solms (Pontederiaceae), Salvinia molesta D.S.Mitch. (Salviniaceae), Pistia stratiotes L. (Araceae), Myriophyllum aquaticum (Vell.) Verdc. (Haloragaceae) and Azolla filiculoides Lam. (Azollaceae) in South Africa

Biological control against water hyacinth, Eichhornia crassipes (C.Mart.) Solms (Pontederiaceae), salvinia, Salvinia molesta D.S.Mitch. (Salviniaceae), water lettuce, Pistia stratiotes L. (Araceae), parrots feather, Myriophyllum aquaticum (Vell.) Verdc. (Haloragaceae), and red water fern, Azolla filiculoides Lam. (Azollaceae) has been ongoing in South Africa since the release of the first biological control agent on water hyacinth in 1974. This review provides an account of progress for the period from 1999. Post-release evaluations over the last three years have shown that, with the exception of water hyacinth, all of these problematic aquatic plants have been suppressed effectively using classical biological control. In eutrophic water bodies at high elevations that experience cold winters, an integrated approach, that includes herbicide application and augmentive biological control, is required against water hyacinth. The grasshopper Cornops aquaticum (Brüner) (Orthoptera: Acrididae: Leptysminae) has recently been released as a new agent for water hyacinth, and Megamelus scutellaris Berg (Hemiptera: Delphacidae) and Taosa longula Remes Lenicov (Hemiptera: Dictyopharidae) are being considered for release on water hyacinth. The longterm management of alien aquatic plants in South Africa relies on the prevention of new introductions of aquatic plant species that could replace those that have been controlled, and, more importantly, on a reduction in nutrient levels in South Africas aquatic ecosystems.

The impact and control of alien aquatic vegetation in South African aquatic ecosystems

Water hyacinth, water lettuce, salvinia, parrots feather and red water fern are South American aquatic plant species that have become invasive in aquatic ecosystems in South Africa. The lack of indigenous natural enemies and the presence of nutrient rich waters have contributed to their invasiveness. The impacts of dense mats of these weeds include the reduction in quality and quantity of water for urban, agricultural and industrial uses, an increase in siltation of rivers, dams and wetlands, a reduction in water surface area for recreation, clogging of irrigation canals and pumps, drowning of livestock and severe deterioration of aquatic biodiversity. Biological control offers a sustainable management tool for all five species and significant success has been achieved in the control of these weeds. However, the long-term management of alien aquatic vegetation relies on the prevention of other species entering South Africa and, more importantly, the reduction of nutrients entering aquatic ecosystems.

The influence of climate on the establishment and success of the biocontrol agent Gratiana spadicea, released on Solanum sisymbriifolium in South Africa

Abstract The tortoise beetle Gratiana spadicea (Klug) (Coleoptera: Chrysomelidae) was released as a biological control agent for the South American weed, Solanum sisymbriifolium Lamarck (Solanaceae), in South Africa. Many of the releases were carried out in the high altitude regions (Highveld). However, the insect failed to establish at some sites, and where establishment was confirmed, its impact has been variable. Cold winters were blamed for the insects nonestablishment or for the variable success at some sites. This hypothesis was tested by comparing the climate in the native range of beetles with that of the release sites in South Africa and by exposing different life stages of the beetle to the extremes of temperature and humidity, typical of winters at these sites. Climate comparison indicated that moisture stress would be expected at the high elevation release sites. The lower lethal humidity for the eggs was calculated to be 56.6% RH. Humidity at the high elevation release sites dropped below this value every month, creating potential moisture stress for the eggs. Humidity had no significant effect on the survival of G. spadicea pupae. The critical minimum temperature (CT min ) of the adult beetles was 4.9±1.3 ° C (n=20) and 6.8±1.3 ° C (n=20) for the larvae. The calculated LT 50 of the adult beetles was −7.1 ° C (n=120;−9.1 to −5.3 ° C ) , while eggs and larvae survived 2-h exposure to −10 ° C . Although the beetle is tolerant of temperature extremes experienced at the Highveld sites, this area was shown to be a marginal habitat for the beetles because of humidity stress.

Predicting the distribution of Eccritotarsus catarinensis, a natural enemy released on water hyacinth in South Africa

Water hyacinth [Eichhornia crassipes (Mart.) Solms (Pontederiaceae)] is the most damaging aquatic weed in South Africa, where five arthropod biological control agents have been released against it. The most recent introduction of Eccritotarsus catarinensis (Carvalho) (Heteroptera: Miridae) has failed to establish permanent populations at a number of sites in South Africa where water hyacinth is a problem. Cold winter temperatures at these sites are assumed to be the reason for these establishment failures. This assumption was tested by investigating the thermal physiology of the mirid, then incorporating these data into various predictive distribution models. Degree‐day models predict 3–14 generations per year at different localities in South Africa, and five generations at a Johannesburg site where the mirid failed to overwinter. The inability to develop sufficiently rapidly during winter months may hinder overwintering of this insect, which was predicted to develop through only one generation during the winter months of April to August in Johannesburg. A CLIMEX model also showed that cold stress limits the mirids ability to overwinter in the interior of the country, while determination of the lower lethal limit (–3.5 °C) and critical thermal minimum (1.2 ± 1.17 °C) also indicated that extreme temperatures will limit establishment at certain sites. It is concluded that E. catarinensis is limited in its distribution in South Africa by low winter temperatures.

The effect of largemouth bass Micropterus salmoides on aquatic macro-invertebrate communities in the Wit River, Eastern Cape, South Africa

Fish predation is one of the driving forces of freshwater invertebrate community structures, with alien predators having a pronounced effect. A quantitative assessment of aquatic invertebrates in the Wit River, Sundays River catchment, Eastern Cape, South Africa, was undertaken to assess the impact of the alien fish Micropterus salmoides on their relative abundance and community structure. Communities in the stones-in-current and marginal vegetation biotopes were sampled in the presence and absence of M. salmoides in late summer (February–April) 2008. Results suggest that the presence of M. salmoides does have an impact on indigenous macroinvertebrate fauna and communities. Community structure in the stones-in-current biotopes did not differ significantly between sections of the river with or without fish. However, there was a significant difference in community structure in marginal vegetation between sections of river. In sections with M. salmoides several large or conspicuous taxa (Odonata, Hemiptera and Coleoptera) were significantly reduced (p < 0.05) or even absent, while cryptic/inconspicuous taxa (Trichoptera, Leptoceridae and Mollusca, Physidae) were significantly more abundant (p < 0.05).

The effect of water hyacinth, Eichhornia crassipes (Martius) SolmsLaubach (Pontederiaceae), on benthic biodiversity in two impoundments on the New Year's River, South Africa

Water hyacinth, Eichhornia crassipes (Martius) Solms-Laubach (Pontederiaceae), forms thick mats that affect water resource utilisation, but little is known about its impacts on biodiversity in aquatic ecosystems. The benthic invertebrate community and algal biomass were sampled under water hyacinth mats and in water hyacinth-free water over a 13-month period, using artificial substrates in New Years Dam, Eastern Cape Province, South Africa. The number of families per substrate (U = 796.5, P < 0.001), number of individuals per substrate (U = 620.5, P < 0.001), Shannon-Weiner Diversity Index (U = 1 038, P < 0.001), Margalefs Richness index (U = 1 136, P < 0.002), Pielous Evenness Index (U = 1 230, P < 0.001) and chlorophyll a (U = 678, P < 0.01) were all significantly lower under water hyacinth mats than in water hyacinth-free zones. Similarly, multivariate analyses showed more diversity in invertebrate communities in open water than under water hyacinth. Thus, the control of water hyacinth is important, in order to prevent both ecological and economic impacts of biodiversity loss.

Overcrowding of false codling moth, Thaumatotibia leucotreta (Meyrick) leads to the isolation of five new Cryptophlebia leucotreta granulovirus (CrleGV-SA) isolates.

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.

Regulation and Risk Assessment for Importations and Releases of Biological Control Agents Against Invasive Alien Plants in South Africa

The importation and release of biological control agents against invasive alien plants in South Africa are subject to regulation by the Department of Agriculture, Forestry and Fisheries (DAFF), under its Agricultural Pests Act, and by the Department of Environmental Affairs (DEA), initially under its Environment Conservation Act, subsequently under the National Environmental Management Act and eventually, as soon as the relevant regulations have been developed, under the National Environmental Management: Biodiversity Act. Peer review, both within South Africa, and with colleagues in other countries, has helped to ensure the integrity of the science and practice of weed biological control in South Africa. This paper traces the development of the regulatory system from the first weed biological control project in 1913, through a dispensation when importations and releases were authorized by DAFF only to a dual regulatory system involving two government departments. Inappropriate legislation, lack of knowledge about biological control amongst the relevant authorities and the costs of employing compulsory private consultants are some of the reasons for significant delays that have become a feature in the authorization of biological control agent releases. These delays have set back several control programmes. Holding agents in quarantine while awaiting decisions ties up expensive space and staff time and increases the risk of losing colonies through accidents or decreased genetic vigour. It seems likely that changes in legislation within DEA will streamline the regulatory process in the near future.

Natural enemies from South Africa for biological control of Lagarosiphon major (Ridl.) Moss ex Wager (Hydrocharitaceae) in Europe

The non-native invasive plant, Lagarosiphon major (Hydrocharitaceae) is a submersed aquatic macrophyte that poses a significant threat to water bodies in Europe. Dense infestations prove difficult to manage using traditional methods. In order to initiate a biocontrol programme, a survey for natural enemies of Lagarosiphon was conducted in South Africa. Several phytophagous species were recorded for the first time, with at least three showing notable promise as candidate agents. Amongst these, a leaf-mining fly, Hydrellia sp. (Ephydridae) that occurred over a wide distribution causes significant leaf damage despite high levels of parasitism by braconid wasps. Another yet unidentified fly was recorded mining the stem of L. major. Two leaf-feeding and shoot boring weevils, cf. Bagous sp. (Curculionidae) were recorded damaging the shoot tips and stunting the growth of the stem. Several leaf-feeding lepidopteran species (Nymphulinae) were frequently recorded, but are expected to feed on a wide range of plant species and are not considered for importation before other candidates are assessed. The discovery of several natural enemies in the country of origin improves the biological control prospects of L. major in Europe.

What Determines the Number of Juvenile Instars in the Tropical Grasshopper Cornops aquaticum (Leptysminae: Acrididae: Orthoptera)?

Cornops aquaticum (Bruner) is host specific on Eichhornia spp. and Pontederia spp. (Pontederiacae). Its present distribution ranges from Mexico to Argentina. The number of juvenile instars (5-7) apparently mirrors the photoperiod and temperature pulses of different climatical conditions in the respective geographical regions. Based on life-history data, three working hypotheses are proposed for forthcoming studies. These will test whether the varying number of juvenile instars represents a phenotypic plasticity of a single genotype or an adaptation that is genetically fixed, due to an evolutionary relationship of the host with its host-plant.