The complexity of the behaviour of neonate Eldana saccharina Walker (Lepidoptera: Pyralidae) larvae and the limited information on their response to the morphological characteristics of South African sugarcane varieties was the primary justification to study antixenotic/antibiotic effects on larval behaviour. Laboratory experiments were conducted with stalk segments in plastic jars inoculated with larvae and in a metal cage covered with gauze. In jars, the larvae were observed until they penetrated the stalks. After 14 days, the stalks were dissected and larvae weighed. In all varieties, larvae moved directly to the node after inoculation and penetrated the stalk through leaf scars and buds. No significant differences in larval mass were observed among varieties. In cage experiments different parts of the node, namely the rind below the wax band; the bud; and the root primordia were tested. There was a clear indication that rind hardness and the budscale properties are associated with varietal resistance and only affect early instars. The experiments were repeated using whole cane plants in a glasshouse. The results were similar to those of laboratory experiments. In the Insect Rearing Unit, scraped waxes from different varieties were incorporated into the diet. Larval masses from different diets showed significant differences among varieties, but they did not conform to the known resistance ratings, as cane varieties N12 and N21 showed high susceptibility, instead of resistance. Dispersal behaviour of neonates shortly after hatching was investigated in 'mobility experiments' conducted on live cane plants. Mobility is important because the more time neonates spend wandering around on the stalk surface or on exposed parts of the plant, the more vulnerable they are to predation and other adverse factors that may reduce their survival. Experiments to test stalk penetration by larvae on the node showed that neonates required a softer food source before attacking the hard nodal parts. Second and third instar larvae were used subsequently to the mortality of all neonates fed on the rind, which in turn resulted in non-significant differences, suggesting that feeding on debris and/or leaves is critical to the survival and penetration of larvae into the sugarcane stalk. Incorporation of the characteristics tested in these experiments aims to reduce the number of larvae that penetrate the stalk and to expose them for longer on the surface where their numbers may be controlled by predators and insecticides. The resistant varieties used in these experiments have high fibre and less sugar, but newer varieties, such as N29 and N33 incorporate both high resistance and high sucrose yield, which are the two key elements for optimised sugar production. Chemical characteristics of the plants need to be taken into consideration as high sucrose is seldom found in fibrous varieties. Leaf sheath tightness is another characteristic that would go well with leaf sheath hairiness, because though not tested in this work-would make it difficult for the larvae to get to the smooth adaxial surface of the leaf. The hardness of trichomes is another feature that needs to be investigated, because a variety may have dense, but soft pubescence that does not repel even the most sensitive larvae, neonates. At present, integrating plant resistance with cultural control, i.e. field hygiene etc. is cost-beneficial for the sugar industry. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 2002.

This study investigated aspects of the breeding biology, ecophysiology, morphology, over-wintering and population dynamics of the pre-imaginal stages of members of the Anopheles gambiae complex in northern Natal, South Africa, Investigation of the breeding biology, concentrated on breeding site utilisation by the different members of the Anopheles gambiae complex. Surveillance personnel were unable to locate the breeding sites of Anopheles arabiensis and postulated that location and description of these would offer a unique opportunity for control. The difficulty in locating the breeding sites of An. arabiensis at certain localities was found to be a product of their low density, presumably as a result of the intra-domiciliary, residual insecticide spray programme. The effect of temperature on larval physiology and adult morphology was investigated. terms of their implications Anopheles gambiae complex. The findings are discussed in for anopheline taxonomy and the The effect of temperature on larval growth rates was investigated in both the field and laboratory. The finding of this part of the study indicate that the larval stages play an important role in the over-wintering of populations within the region. The control implications of these findings and winter breeding site localisation are discussed. A theory for the so called 'late season transmission i.e. Apri-May, within the province and southern Africa is proposed. The population dynamics of An. merus were investigated, together with the effect of abiotic factors such as temperature, salinity and rainfall. The effect of sampling bias due to factors such as behavioural avoidance were studied. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1991.

No description available.

The sea louse (Lepeophtheirus salmonis), whose larvae are planktonic and disseminated in the water column, is an economically important parasite of Atlantic salmon (Salmo Salar). The effect of temperature (5, 10, 15°C), diet (larvae alone, larvae plus phytoplankton), and bivalve size (small, medium, large) on the amount of L. salmonis larvae ingested by various species of filter-feeding bivalves (Pacific oysters, Pacific scallops, blue/Gallo’s mussel hybrids, basket cockles) was examined in a series of laboratory experiments. Four separate temperature/diet experiments were conducted (one for each species) in which large bivalves were individually placed in 2-L containers holding 750 ml of aerated, filtered seawater and fed one of three treatment diets: (1) phytoplankton: ~7.1 x 104 cells ml-1 of Isochrysis sp. (Tahitian strain, TISO); (2) sea lice larvae: ~431 larvae (mostly nauplii); and (3) phytoplankton and larvae (at the levels mentioned above). There was also a control treatment of phytoplankton and larvae, but no bivalve. After feeding for 1 h, the bivalve soft tissues were excised and preserved, the digestive system was dissected, and sea lice larvae were removed and counted to provide direct evidence of ingestion. The larvae remaining free swimming in the container were iv preserved and counted. The proportion missing from the container was used to estimate ingested larvae in statistical analyses. Two additional experiments investigating the effect of bivalve size (small, medium, large) on the ingestion of sea lice larvae were conducted with Pacific oysters and Pacific scallops. The heights for oysters (anterior-posterior axes) were 19.2, 44.2, and 84.0 mm, and scallops (dorsal hinges to ventral margins) were 40.3, 64.1, 102.7 mm. The methodology for the size experiments was as previously described for the temperature/diet experiments with the following changes: (1) the diet of larvae alone was not used; (2) the mean number of larvae in each container was ~498; (3) the mean concentration of TISO added to each container was ~7.8 x104 cells ml-1, and (4) the mean water temperature was 10.4°C. The data for the four temperature/diet experiments indicate that all four bivalve species ingested sea lice larvae, whether their diet included phytoplankton or not, and that temperature had no significant effect. The data for the two size experiments indicated that all three sizes of oysters and scallops ingested sea lice larvae and that there was a significant size effect. Large shellfish consumed a significantly greater proportion of the sea lice larvae than the small shellfish. Bivalves grown at salmon net pens as part of an IMTA (Integrated Multi-Trophic Aquaculture) system may be able to reduce the number of sea lice larvae as well as being an additional crop of market value. Future research, conducted at a commercial scale at a salmon farm, is warranted in order to determine if bivalves can serve in this role. / Graduate

No description available.

Common snook (Centropomus undecimalis) is a relatively new species for aquaculture; considered as a recreational species and not commercial. The aim of this study was to develop common snook larval rearing techniques for stock enhancement. Common snook culture has two main bottlenecks, broodstock management and larval culture. High mortality during the first 6 days is the main limitation for successful larval survival. Broodstock management of common snook is still developing and the only source of common snook eggs is from wild broodstock. Securing a regular supply during the natural spawning was essential to reach the main objective. Finding the optimal spawning sites, as well as optimal spawning time was achieved. Results showed Terra Ceia, Longboat and Cayo Costa to be the best sites for wild broodstock collection. The onset of spawning was triggered by a rise in water temperature. During the 4 years of this study spawning started at the end of May and finished in September. Total capture results and egg quality results, such as fertilization, hatching rate and lipid analysis, indicated June and July as the peak months during the spawning season. Common snook follow a lunar spawning cycle. Results showed that one to three days after the new and full moon were the peak spawning periods and therefore the best days to capture wild stock. Common snook egg lipid composition fits the general marine fish fatty acid composition with saturated fatty acids predominating. On the other hand, the omega 3, omega 6 (n-3/n-6) ratio was lower than the typical marine fish and arachidonic acid values were significantly higher than other marine species. This egg fatty acid profile will be helpful in the future to compare it with captive spawned eggs for egg quality purposes. Description of the common snook embryonic and larval development for the first 14 days was carried out. This has strengthened knowledge for this species’ development, and should provide a helpful tool to identify common snook embryos and larvae in the wild. Novel improvements to existing common snook larval culture protocols were implemented. Larval lipid analysis throughout development, and high mortality around day 6 post hatching, suggested that common snook larvae were dying of starvation. Gross morphological development and ultra-structure findings in the digestive and eye system development during the first three days indicated that day 2 post hatching larvae were capable of capturing and digesting food. Additionally, larval nutritional improvements were made, increasing the larval survival. The most significant ones were: finding a smaller and more nutritional prey (SS type rotifers and copepods), finding an optimal stocking and feeding density and the importance that green water technique has on larval survival. Overall, larval success was improved from a zero percent survival during the first 14 days to a 2% survival rate.

Reduced access to atmospheric oxygen greatly increased early instar Aedes aegypti mortality. Data suggest that death was by drowning mainly because slow swimming speed and low visual acuity delayed larvae from finding access to air. Late instar larvae experienced developmental delays when food depletion in the immediate vicinity of the breathing site forced them to forage farther away. As the distance between feeding and breathing sites increased, feeding efficiency of fourth instars may have declined enough to reduce their pupation success and to cause increased pupal mortality, reduced adult emergence and sex ratio skewed in favour of males among emerging functional adults. Thus reduced access to atmospheric oxygen at the pre-imago level may reduce the vectorial capacity of emerging adult population.

No description available.

No description available.

In 1931, Mungomery stated "whitegrubs have been for years past, and still are, the worst insect problem confronting the sugar industry". This statement remains true to this day, with canegrubs costing the Australian sugar industry A$7.22 million in lost production and in use of insecticides. The development of a sugarcane cultivar with resistance to canegrub attack would be a valuable addition to the recently implemented canegrub management program. This thesis examined the possibility that natural inhibitors derived from canegrubs could be incorporated in sugarcane to reduce or prevent its destruction by canegrubs. The research described here demonstrated that canegrub haemolymph contains inhibitors with activity against commercially purified enzymes and serine proteases found in crude midgut extracts. A cDNA encoding a potential canegrub protease inhibitor (DA10 12) belonging to the Ascaris family was cloned, but it did not have activity against the major canegrub midgut proteases. This protein does, however, still have potential for modification into a serine protease inhibitor suitable for use as a novel insect resistance transgene. The possibility of using haemolymph derived inhibitors as novel antimetabolites in a canegrub management strategy based on transgenic plants was also explored. The findings suggest that proteins with properties similar to those of DA10 12 will require the presence of a signal peptide and/or codon optimisation for successful expression in sugarcane. The research outlined in this thesis is the first investigation of protease inhibitors in the haemolymph of scarab larvae, and is the first report of an Ascaris family inhibitor that does not inhibit a serine protease.