H. van Hamburg

Selection of non-target Lepidoptera species for ecological risk assessment of Bt maize in South Africa

It is essential to assess the environmental risk that Bt maize may hold and to study its effect on species assemblages that fulfil a variety of ecosystem functions. Environmental risk assessment can be improved through the use of an ecological model which can be applied to a specific environment, so that local species can be classified functionally and prioritized to identify potential test species. Although the stem borers, Busseola fusca (Lepidoptera: Noctuidae), and Chilo partellus (Lepidoptera: Crambidae), are the target species of Bt maize in South Africa various other Lepidoptera species are also directly exposed to Bt toxin. In this paper an ecological approach was followed for selection of non-target Lepidoptera species for ecological risk assessment of Bt maize, using data collected over a two-year period on Lepidoptera biodiversity on maize. Nine primary non-target lepidopterous consumers were identified. A selection matrix was developed in which each species was ranked for its maximum potential exposure to Bt toxin by assessing its occurrence, abundance, presence and linkage to other host plants in the maize ecosystem. Non-target Lepidoptera most likely to be affected were identified and prioritized for future testing and inclusion in risk assessments. Several non-target species were prioritized for their close association with maize, general occurrence in the maize-growing regions and their potential for economic damage should they become secondary pests. Through use of the selection matrix, knowledge gaps were identified for future research and guidance for the design of ecologically realistic experiments. Non-target species populations with the highest maximum potential exposure to Bt toxin are Sesamia calamistis (Hampson) (Lepidoptera: Noctuidae), Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) and Acantholeucania loreyi (Duponchel) (Lepidoptera: Noctuidae). Eublemma gayneri (Rothschild) (Lepidoptera: Noctuidae) can be considered to be a ‘value unknown’ species in the wild. Because of their sporadic occurrence, Agrotis segetum (Denis & Schiffermüller) (Lepidoptera: Noctuidae) and Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae) are considered to be of lesser importance than H. armigera and A. loreyi, but should also be considered during preand post-release monitoring.It is essential to assess the environmental risk that Bt maize may hold and to study its effect on species assemblages that fulfil a variety of ecosystem functions. Environmental risk assessment can be improved through the use of an ecological model which can be applied to a specific environment, so that local species can be classified functionally and prioritized to identify potential test species. Although the stem borers, Busseola fusca (Lepidoptera: Noctuidae), and Chilo partellus (Lepidoptera: Crambidae), are the target species of Bt maize in South Africa various other Lepidoptera species are also directly exposed to Bt toxin. In this paper an ecological approach was followed for selection of non-target Lepidoptera species for ecological risk assessment of Bt maize, using data collected over a two-year period on Lepidoptera biodiversity on maize. Nine primary non-target lepidopterous consumers were identified. A selection matrix was developed in which each species was ranked for its maximum potential...

Developing habitat management systems for gramineous stemborers in South Africa

The stemborers Busseola fusca (Lepidoptera: Noctuidae) and Chilo partellus (Lepidoptera: Crambidae) are important pests of maize and sorghum in South Africa. A habitat management system for these pests is being developed in the Northern Province of South Africa. This management system is similar to the one used in eastern Africa, where host and non-host plants of stemborers are used to repel moths away from the main crop and attract them to highly attractive trap plants. To identify possible trap crops, a survey of wild host plants of stemborers was undertaken in the Northern Province of South Africa and several new host plants were recorded. As a possible trap crop for stemborers, various Napier grass (Pennisetum purpureum) varieties were evaluated for oviposition preference by Ch. partellus moths and subsequent larval survival on those varieties. Few larvae survived longer than 15 days after inoculation onto Napier grass plants. A survey was conducted of farming practices that would affect the adoption of habitat management strategies. The high usage of tractors for ploughing may have a negative effect on adoption of perennial intercrops in a habitat management system. The common practice of free grazing animals also reduced the fodder value and benefit of trap crops. The value of Napier grass does not only lie in its use as trap crop but also as a measure to limit soil erosion and as animal feed.RésuméLes foreurs des tiges Busseola fusca (Lepidoptera: Noctuidae) et Chilo partellus (Lepidoptera: Crambidae) sont des ravageurs importants du maïs et du sorgho en Afrique du Sud. Un système de gestion de l’habitat de ces ravageurs est en cours de développement dans la province nord de l’Afrique du Sud. Ce système de gestion est similaire à celui utilisé en Afrique de l’Est, où les plantes hôtes et non hôtes des foreurs des tiges sont utilisées pour repousser les papillons hors de la culture et les attirer vers des plantes pièges fortement attractives. Afin d’identifier de possibles cultures pièges, on a entrepris une enquête sur les plantes hôtes sauvages des foreurs des tiges dans la province nord de l’Afrique du Sud et plusieurs nouvelles plantes hôtes ont été trouvées. Plusieurs variétés d’herbes à éléphants (Pennisetum purpureum), pouvant jouer le rôle de culture piège pour les foreurs des tiges ont été évaluées pour tester la préférence ovipositionelle des adultes de C. partellus ainsi que la survie larvaire ultérieure. Très peu de larves survivent plus de 15 jours après l’infestation sur les plants d’herbe à éléphants. Une enquête a été conduite sur les pratiques culturales qui pourraient influencer l’adoption de stratégies de gestion de l’habitat. L’utilisation importante des tracteurs pour labourer pourrait avoir une influence négative sur l’adoption de cultures associées pérennes dans un système de gestion de l’habitat. La pratique courante du libre pâturage des animaux réduit également la valeur du fourrage et le bénéfice des cultures pièges. La valeur de l’herbe à éléphants ne se résume pas seulement dans son utilisation comme culture piège mais aussi comme un moyen de limiter l’érosion du sol et comme fourrage.

Effect of stubble treatment on the post-diapause emergence of the grain sorghum stalk borer, Chilo partellus (Swinhoe) (Lepidoptera: Pyralidae)

Abstract The effect of conservation tillage and stubble treatment in winter on the survival of overwintering populations of Chilo partellus (Swinhoe) was studied in a grain sorghum field near Brits, Transvaal, South Africa. More moths emerged from the untreated plot ( c . 226 000/ha) than from the slash or slash and remove plots ( c . 75 000/ha) and from the slash, remove and plough ( c . 49 000/ha). It is concluded that conservation tillage or the other treatments of stubble in winter as commonly practised by farmers in South Africa do not control the overwintering populations of C. partellus . Complete destruction of stubble in winter is recommended.

The relative abundance of maize stem borers and their parasitoids at the Tshiombo irrigation scheme in Venda, South Africa

Abstract Maize is an important resource in many small-scale farming areas in South Africa and especially on irrigation schemes in the Limpopo Province where this crop is cultivated under irrigation in sub-tropical conditions. The aim of this study was to determine the moth flight patterns, species distribution, infestation levels and parasitism levels of maize stem borers at the Tshiombo irrigation scheme in Venda. Moth flight patterns were monitored by means of sex pheromone traps over a 2.5-year period. The incidence of damaged plants and infestation levels were monitored by means of destructive sampling at 4–6 week intervals over a 15-month period. Moth flight patterns were erratic and although peaks were observed, the period of peak activity differed between seasons. The stem borer population was dominated by Chilo partellus which made up between 65–99% of the total number of larvae collected at each planting date. Busseola fusca and Sesamia calamistis made up between 0–16% and 0–31% of the population respectively. The most important parasitoid was Cotesia sesamiae and the average level of parasitism over species was 10%. The average level of parasitism ranged between 0–34, 0–7 and 0–3% for C. partellus, B. fusca and S. calamistis respectively.

Comparative Diversity of Arthropods on Bt Maize and Non-Bt Maize in two Different Cropping Systems in South Africa

ABSTRACT The biodiversity of an agroecosystem is not only important for its intrinsic value but also because it influences ecological functions that are vital for crop production in sustainable agricultural systems and the surrounding environment. A concern about genetically modified (GM) crops is the potential negative impact that such crops could have on diversity and abundance of nontarget organisms, and subsequently on ecosystem functions. Therefore, it is essential to assess the potential environmental risk of the release of a GM crop and to study its effect on species assemblages within that ecosystem. Assessment of the impact of Bt maize on the environment is hampered by the lack of basic checklists of species present in maize agroecosystems. The aims of the study were to compile a checklist of arthropods that occur on maize in South Africa and to compare the diversity and abundance of arthropods and functional groups on Bt maize and non-Bt maize. Collections of arthropods were carried out during two growing seasons on Bt maize and non-Bt maize plants at two localities. Three maize fields were sampled per locality during each season. Twenty plants, each of Bt maize and non-Bt maize, were randomly selected from the fields at each site. The arthropods collected during this study were classified to morphospecies level and grouped into the following functional groups: detritivores, herbivores, predators, and parasitoids. Based on feeding strategy, herbivores and predators were further divided into sucking herbivores or predators (piercing-sucking mouthparts) and chewing herbivores or predators (chewing mouthparts). A total of 8,771 arthropod individuals, comprising 288 morphospecies and presenting 20 orders, were collected. Results from this short-term study indicated that abundance and diversity of arthropods in maize and the different functional guilds were not significantly affected by Bt maize, either in terms of diversity or abundance.

Ant assemblages at three potential breeding sites for the Brenton blue butterfly, Orachrysops niobe (Trimen)

Conservation of South Africas butterflies is critically dependent on knowledge of their ecology. Many endangered species are in the family Lycaenidae and have a more-or-less obligate relationship with a particular species of ant. An ecosystem capable of hosting such butterfly species must also be able to sustain substantial populations of the host ant. The Brenton blue, Orachrysops niobe, is one of the most endangered South African butterflies, and is known only from one site in the Western Cape. Ant assemblages were investigated at this site and two other ecologically similar sites where the host plant of O. niobe, Indigofera erecta, also occurs, but O. niobe was absent. The ant assemblages differed significantly, with the host ant of O. niobe, Camponotus baynei, only occurring at the Brenton site where the butterfly was breeding. Vegetation composition, structure and microclimate differed at the three sites and these appear to be key factors in determining the ant assemblages that a site will support. The two sites where C. baynei was absent had a history of recent fire, which contributed to the vegetation changes and deprived the ant of dead wood for nesting. The invasive Argentine ant, Linepithema humile, was not detected at any of the study sites, and the reasons for this are discussed.

The vegetation of ash disposal sites at Hendrina Power Station. II: Floristic composition

An important component of any ecosystem is the species it contains. Species also serves as good indicators of the ecological condition of a system. A list of all species collected during the three-year period was therefore compiled together with their life form spectra. The floristic composition of the ash disposal area at Hendrina Power Station was also compared with the floristic composition of an adjacent natural grassland. A total of 278 species were identified of which 151 occurred on the ash disposal sites and 163 in the natural grassland. Of all the species, 35 occurred in both areas of which most were annual pioneer species. The species composition and life form spectra of the two areas were considerably different. Therophytes were, for example, more abundant on the ash disposal areas. The reconstruction of an ecosystem on ash disposal sites with a species composition similar to that of the natural grassland will require far more financial inputs and habitat amelioration than is presently the situation.

The vegetation of ash disposal sites at Hendrina power station I: Phytosociology

A phytosociological study was conducted as an initial assessment of the vegetation on ash disposal sites to determine the community structure of vegetation and how the communities were related based on their species composition and habitat characteristics. The Braun-Blanquet survey and data analysis method was used to identify and classify plant communities on ash disposal sites and an adjacent natural grassland. Releves were compiled in 113 survey plots. The TWINSPAN classification algorithm was used as first approximation and results were subsequently refined using Braun-Blanquet procedures. The DCA ordination technique was also used to determine the relationship between communities and whether gradients exist in the study area, α-diversity between communities are statistically compared using the Shannon diversity indices and species richness. The natural grassland sites, rehabilitated ash disposal sites and unrehabilitated ash disposal sites formed three separate communities. The two sub-communities that are described on rehabilitated ash disposal sites are distinguished mainly with respect to age of rehabilitation and level of disturbance. Community structure, on a variant level, is largely determined by different treatments (seed mixtures and soil preparations) that were used in the rehabilitation of the ash disposal sites. Plant communities on recently rehabilitated sites are similar to plant communities on dumps of domestic refuse on some of the disposal sites. Based on the variants described, three homogenous areas on the old rehabilitated sites, which were rehabilitated more than three years ago, can be identified. Vegetation is relatively homogenous and variants are closely related. Differences in rehabilitation treatment, age of rehabilitation and man-made disturbances were some of the important factors determining the establishment of different communities on ash disposal sites. Statistically significant differences are found in the diversity of vegetation studied on a community and variant level. Associations on the ash disposal areas are strongly based on the dominance of particular species rather than specific indicator species.