No description available.

In order that the citrus industry in South Africa may be commercially developed to the greatest possible extent it is of importance that certain basic ecological problems should be investigated. Until the complex relationships between the host plant, the insect pests and their parasites and predators are known, the results of applications of either chemical or biological control must be largely a matter of chance. A certain amount of rather generalised work in this connection has already been done in South Africa, principally by Carnegie (1955), Smithers (1953) and Whitehead (1948) in the Eastern Cape Province and by Steyn (1954) in the Transvaal. The first three of these workers were content to determine which species of insects occurred in citrus orchards and made some attempts to study the biology of certain predators. Steyn went a little further when he correlated ant activity with scale insect infestations. Without doubt the most economically important insect pests of citrus are the scale insects (Homoptera: Coccoidea). Introduction, p. 1.

[Introduction] In the Western Cape Province the mealybug, Planococcus citri (Risso), was first reported on vines in 1930 by Joubert (1943a). By 1935 this mealybug had spread to the Hex River Valley, and subsequently to all the main table grape producing areas of the Western Cape Province. At present Pl. citri is the most important insect pest of the table grape industry and can, if not effectively controlled, result in a loss of at least five per cent of the export table grape crop (Kriegler, 1954). Some preliminary work on the natural enemies of Pl. citri on vines was carried out by Stubbings in 1948, but no further work of this nature has been undertaken in this area since then. The fact that the natural enemies can be an effective check to this mealybug on vines in the Western Cape Province has been known for a number of years (Potgieter, 1937; Hattingh, 1943; Joubert, 1943a; Myburgh, 1951). The present work is an attempt to obtain some basic knowlege of the population fluctuations of the insects concerned in this biological control. Surveys undertaken have shown that there is a complex of primary, secondary and possibly tertiary Hynenopterous parasites associated with Pl. citri. The presence of hyperparasites reduces the efficiency of the primary parasitic Hymenoptera. The usefulness of these primary parasites is further reduced as they only occur in effective numbers for a short period of the year. On the other hand, although attacked by some parasites, the numerous coccinellids found preying on Pl. citri are of more importance in reducing the mealybug populations, as they are present on the vines in effective numbers for the greater part of the year.

No description available.

This study focuses on the effective biocontrol agent Chilocorus nigritus (Fabricius). Its behaviour and ecology were compared with other Chilocorus spp. where appropriate, to elucidate why this species is such an effective biocontrol agent, and how to improve methodology for its deployment as a natural enemy. An artificial diet for C. nigritus was developed, but was still sub-optimal. Asterolecanium miliaris (Boisduval) was a suitable prey for all life stages of C. nigritus and the adults of Chilocorus bipustulatus (Linnaeus) and Chilocorus infernalis Mulsant, but was inadequate for larvae of the last two species. Adult weight, measured at one day after adult eclosion, was an appropriate indicator of the effects of larval treatment on their development and on the fitness of subsequent adults. There was no improvement in culture vigour due to a behavioural response of individuals within one generation to fluctuating as opposed to constant temperature. starvation for between 10h and 24h was appropriate for standardisation of hunger. Measuring feeding rate at a range of static temperatures did not reflect differences in the climatic adaptations of six Chilocorus spp., but mortality rates at increasingly high temperatures were useful. Chilocorus spp. showed little ability to choose between prey species. Prey substitutions adversely affected adults and larvae. Introduction of adults was the most effective method for field establishment. Giant bamboo Dendrocalamus giganteus Munro was a valuable site for field releases of C. nigritus, but less useful for C. bipustulatus and C. infernalis. Counter to assumptions on which interference models have been based, no significant intraspecific interference, reducing predatory efficiency, was observed. Visually prominent features on the horizon and a specific leaf shape, were attractive to foraging C. nigritus. The location of prey patches by adults was facilitated by prey odour, but not so for larvae. Adults detected individual prey olfactorily and visually over short distances, but physical contact was required for detection by larvae. Prey location by larvae and adults was facilitated by alterations in movement patterns in response to prey consumption. Differences in prey detection and the effects of prey substitutions, between the life stages, were related to field behaviour. The relevance to biological control, of responses to rearing conditions and feeding and foraging behaviour, was investigated. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1991.

Ball State University LibrariesLibrary services and resources for knowledge buildingMasters ThesesThere is no abstract available for this thesis.

AbstractScientists trying to find biological controls for insect pests are hamperedd by the absence of rapid methods for screening organisms such as bacteria for potential pathogenicity. An organism must grow in the gut of the insect to be pathogenic. By using radioisotopes as tracers a quick method of screening potential insect pathogens may be developed.Escherichia coli and Sarcina flava were used as known nonpathogens and Bacillus thuringiensis was used as a known pathogen. In this work an attempt was made to verify the presence of bacteria in specific tissues of the insects.European corn borer larvae were fed 1-C14 palmitic acid and labeled E. coli, S. flava and B. thuringiensis. Parasaggital sections were made of the corn borers and radioautograms were made of the sections. Grain counts over a 2,000 u2 area were made of various tissues and compared.There was a statistically significant difference in the distribution of label in corn borer larvae fed labeled bacteria as compared to corn borers fed 1-C14 palmitic acid. Label tended to incorporate into fatty tissue in the corn borers.If this technique can be used to positively demonstrate the establishment of selected bacteria in the gut of the insect then it may be possible to use such methods to screen for potential insect pathogens and give insight into the mechanisms which result in the death of insects.Ball State UniversityMuncie, IN 47306

This study investigated effects of insect growth regulators (IGRs), recommended for use on citrus in southern Africa, on non-target organisms, particularly species of Coccinellidae in and around three citrus estates in the lowveld region of Swaziland, i.e. Tambuti, Tambankulu and Tunzini estates. Some of the species are important predators of citrus pest insects. The distribution of coccinellids within an agricultural land mosaic and factors affecting this distribution pattern were also investigated. Results showed that coccinellid densities and species diversity were lowest in the natural veld surrounding the orchards. In contrast, citrus orchards had the highest coccinellid densities and diversity. River borders, along the Great Usuthu river, had intermediate densities and diversity. While temperature, relative humidity and ground insolation had no significant effect on coccinellid population densities, the presence / absence of prey (host plant), on the other hand, was an important factor. This was the case both for phytophagous and predatory coccinellid species. These showed close patterns of distribution with their respective host plants or prey species. Economically important species, such as Rodolia spp., were restricted to the orchards, while other species, especially those whose economic role is uncertain, such as Cheilomenes lunata and Scymnus spp., were found in most habitat types. Coccinellid population densities were assessed during four treatment programmes: 1) an integrated pest management (IPM) programme where no IGRs were used, 2) a programme where any of the recommended IGRs were to be applied, 3) conventional pesticide programme, and 4) an orchard which did not receive any chemically treatment over the last four years (at Tambankulu estate only). Significant differences between treatment programmes were observed at all three estates, when only economically important coccinellid species were assessed. Orchards under an IPM programme (with no IGRs) were found to have significantly higher population densities compared to those in IGR-treated or under a conventional pesticide regime. The untreated orchard at Tambankulu, however, had significantly higher coccinellid densities of economically important species and higher overall population densities than any of the managed orchards. Of the three estates assessed, Tunzini had significantly higher population densities of all beneficial coccinellids, (excluding the untreated orchard at Tambankulu). Natural vegetation around Tunzini and Tambuti contributed to the higher coccinellid densities compared to Tambankulu, which was surrounded by other agricultural land. Laboratory and field experiments on two non-target species, the ladybird Chilocorus nigritus (Fabricius) (all stages) and the moth Bombyx mori (Linnaeus) (larval stage) assessed specific IGR effects, if any. Three IGRs, buprofezin, teflubenzuron (both chitin synthesis inhibitors) and pyriproxyfen (a juvenile hormone analogue) were used. All three pesticides are currently recommended for use on citrus in southern Africa and were tested at the recommended dosages. Laboratory experiments showed that all three IGRs have a negative impact on both non-target species. When B. mori received direct applications, there was larval mortality as a result of the failing to complete moulting or dying immediately after moulting. In addition, no larvae were able to pupate after having fed on contaminated leaves. In the case of C. nigritus, larvae fed IGR-treated scale or sprayed with buprofezin suffered significantly higher mortality than controls, while IGR effects on those sprayed with, or fed scale-treated with, pyriproxyfen or teflubenzuron were not significant. No adults however, emerged from any pupae in any of the treatment groups. All three IGRs had ovicidal activity on C.nigritus eggs. Adult fecundity in both field and laboratory experiments was not affected significantly after exposure to any of the three IGRs. In field experiments, the proportion of larvae of the moth and ladybird that developed up to the reproductive adult stage, after exposure to buprofezin, was not significantly different from the control. This was not the case for pyriproxyfen and teflubenzuron. Buprofezin was therefore found to be the least detrimental of the three IGRs tested. Minimal drift was observed when a knapsack sprayer was used. However, there was spray drift up to 32m (the furthest distance assessed here) where commercial sprayers were used. This suggests that pesticide drift from orchards to adjacent areas would have serious implications for biological diversity in the river borders and rivers adjacent to the estates. The sensitivity of the non-target species to the IGRs tested needs serious consideration, as it indicates a broader spectrum of activity for the compounds than what is promoted. Additionally, natural control may be affected. This is because the timing of IGR applications and increasing coccinellid populations coincide, resulting in a reduced pool of coccinellid predators. This study emphasised the importance of an appropriately heterogenous landscape to maximise habitat availability for the coccinellids. Although the economic role of the multihabitat coccinellid species recorded here is unknown, they nevertheless clearly contribute to citrus pest control. Such a mosaic landscape, in conjunction with IPM, with no IGR use, promotes ecological diversity and controls pests with minimum disruption to biodiversity. The use of IGRs in citrus thus needs carefiil reconsideration in light of the non-target effects observed on the two species, especially the valuable predatory species, C. nigritus. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1998.

Glucose was present in substantially greater concentrations in whole body extracts of fourth instar Aedes aegypti L. larvae than was trehalose; in contrast, trehalose was more abundant than glucose in haemolymph extracts. Preliminary studies suggested that infection of Ae. aegypti by the entomopathogenic digenean Plagiorchis elegans Rudolphi alters the carbohydrate metabolism of fourth instar larvae. Within 24 hours of cercarial penetration, total body extracts of infected fourth instar larvae exhibited decreased trehalase activity, increased trehalose-6-phosphatase activity, and an accumulation of trehalose in comparison to uninfected larvae. Concentrations of glucose, glycogen and lipids, and the activity of glycogen phosphorylase a were similar in extracts of infected and control larvae. The predominant fatty acids, in both control and infected larvae, were C 18:0, C 18:1 and C 18:3. There were no significant differences in the types and proportions of fatty acids found in control and infected larvae. Parasitic infection is discussed in terms of impaired trehalose metabolism.

This project investigated the impact of bird predation on insect pest populations within two cornfields of Southwestern Quebec. Birds were excluded from portions of these fields through the use of bird-proof netting. Rhopalosiphum maidis, Ostrinia nubilalis, Agrotis spp. and Sphenophorus spp. were all found at greater densities in plots where birds were excluded as compared with the non covered plots. Only the adult Diabrotica longicornis population was not reduced by birds. Results significantly suggest that birds can reduce insect pest populations. Bird visits in cornfields with respect to distance from field edge, type of edge habitat and corn phenology were also studied. Red-winged Blackbird, Song and Chipping Sparrows and American Robin were the most frequently observed bird species inside cornfields. Early in the summer, birds tended to stay closer to the field edge, especially when composed of mature coniferous trees. Different bird species visited the cornfields at specific periods during corn development.