Tecoma stans (L.) Juss. Ex Kunth (Bignoniaceae) also known as yellow bells, has a native distribution from Northern Argentina, central America, Mexico and the Southern USA. In many warm climatic regions of the world, T. stans is commonly planted as an ornamental plant because of its yellow flowers, hence the name yellow bells, and pinnate foliage. As a result, this evergreen shrub has wide distribution in the tropical and subtropical parts of the western hemisphere. As is the case in many other parts of the world, T. stans was introduced into South Africa as an ornamental plant, but escaped cultivation and now invades roadsides, urban open spaces, watercourses, rocky sites in subtropical and tropical areas of five South African provinces; Gauteng, Mpumalanga, Limpopo, KwaZulu-Natal, Eastern Cape and neighboring countries. Tecoma stans has the potential of extending its range because its seeds are easily dispersed by wind. The purpose of this work was to carry out pre-release efficacy studies to determine the host specificity and suitability of Pseudonapomyza sp. (Diptera: Agromyzidae), a leaf-mining fly, as a biological control agent of T. stans. Available information suggests that the fly was brought to South Africa (SA) from Argentina in 2005. In that year a worker collected adult root feeding fleabeetles from T. stans and their eggs by collecting soil around the plants in the Argentinian Province of Jujuy, at San Pedro (24°12’592”S, 64°51’328”W). The soil was brought to the SA quarantine laboratory of the Agricultural Research Council, Plant Protection Research Institute (Weeds Division), Pretoria, and placed in a cage containing T. stans plants for flea-beetle larvae to emerge from the eggs. The Pseudonapomyza sp. flies which emerged from that soil were reared to produce a colony of flies used in the study reported here. The feeding behavior of Pseudonapomyza sp. adults is initiated by females which use their ovipositor to puncture holes in the leaf mesophyll and then they feed on the sap oozing from the holes. Since males have no means of puncturing the leaves, they feed from holes made by females. Eggs are laid singly into the tubular leaf punctures. Soon after hatching, the larva feeds on the leaf mesophyll tissue. As the larva feeds within the leaf it creates mines which eventually coalesce to form large blotches. The damaged leaf area reduces the photosynthetic potential of the plant especially when damaged leaves dry and fall off the plants. The potential of Pseudonapomyza sp. as a biocontrol agent is enhanced by the fact that it has a high level of fecundity and a short life cycle. As a result, its populations can build up rapidly to exert a significant impact on T. stans. Host-specificity tests undertaken on 35 plant species in 12 plant families showed that out of the 35 plant species tested, the fly was able to develop on T. stans only. Although Pseudonapomyza sp. adults fed on T. capensis, a South African indigenous ornamental shrub, no larval mines were observed on this plant. This suggests two possibilities; either females of Pseudonapomyza sp. do not oviposit on T. capensis or oviposition takes place but larvae cannot feed and develop on this plant. These studies indicate that this fly is sufficiently host-specific, and can be released against T. stans without posing any threat to either commercial or indigenous plant species grown in South Africa. Experimental designs simulating high populations of Pseudonapomyza sp. showed that the impact of leaf mining fly on T. stans can cause approximately 56 percent aboveground biomass reduction. Other concurrent studies have also showed that low and high density fly infestations can cause 23 percent and 48 percent belowground biomass reductions, respectively. Based on the available information, it appears that Pseudonapomyza sp. may have the potential to reduce the invasive capacity of T. stans in the affected areas. In order to exert more herbivore pressure on T. stans, it is suggested that agents belonging to other feeding guilds, such as root-, stem- and seed-feeding insects, be considered for release to complement the leaf-feeding of Pseudonapomyza sp. An application to release this fly in SA has been submitted to one of the two regulatory authorities.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ufh/vital:11790 |
| Date | January 2010 |
| Creators | Madire, Lulama Gracious |
| Publisher | University of Fort Hare, Faculty of Science & Agriculture |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis, Masters, MSc (Zoology) |
| Format | 84 leaves; 30 cm, pdf |
| Rights | University of Fort Hare |
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