The diamondback moth, Plutella xylostella (L.), (Lepidoptera: Plutellidae) and its biological control in the Eastern Cape Province, South Africa
- Authors: Smith, Tamara Jane
- Date: 2003
- Subjects: Plutellidae Plutellidae -- South Africa -- Eastern Cape Insect pests -- Biological control -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5626 , http://hdl.handle.net/10962/d1004742
- Description: The diamondback moth, Plutella xylostella (L.), is a pest on crucifer crops worldwide, damaging the leaves, florets and seed pods of many crucifers including cabbage, cauliflower, broccoli and canola. It has been controlled using broad-spectrum insecticides, but this has led to a rapid build-up of insecticide resistance. In the Grahamstown area of the Eastern Cape Province, South Africa, diamondback moth showed resistance to cypermethrin (a pyrethroid) on commercially grown cabbages. Therefore it is imperative that other methods of control be adopted, including both cultural control and biological control using parasitoids, and that these are incorporated into an Integrated Pest Management (IPM) programme. The diamondback moth and its parasitoids were monitored weekly from April 1997 to November 1999 at three sites near Grahamstown. One site was a commercial farm with an active insecticide spraying program; the others were unsprayed. Infestation levels were highest during spring (September to November) and autumn (March to May). Nine species of parasitoids were associated with the diamondback moth, with abundances being highest over spring and early summer (September to December). Cotesia plutellae (Kurdjumov) dominated the sprayed site, while the unsprayed sites yielded a complex of parasitoids, including C. plutellae, Diadegma mollipla (Holmgren), Diadromus collaris Gravenhorst and Oomyzus sokolowsldi (Kurdjumov). Parasitism levels ranged between 10 and 90%. There was a large amount of site-to-site and year-to-year variation. Parasitoids were an effective mortality factor against the diamondback moth. The effects of temperature on development and mortality, and of field size and non-crop plants on the distribution of diamondback moth and its parasitoids, were investigated. The results show that high temperatures can depress pest populations, and that the size and surroundings of fields can be manipulated to improve cultural control of the diamondback moth. Suggestions for effective rPM in the Eastern Cape Province include a reduction in insecticide applications, the use of bioinsecticides, for example Bacillus thuringiensis Berliner (Bt) and the encouragement of indigenous parasitoids by planting suitable nectar sources. Cultural control methods are also important and involve removal of cabbage refuse after harvest, management of wild crucifers around cabbage fields, scouting and monitoring the moth population and determining the optimal field size to assist with control by parasitoids.
- Full Text:
- Date Issued: 2003
- Authors: Smith, Tamara Jane
- Date: 2003
- Subjects: Plutellidae Plutellidae -- South Africa -- Eastern Cape Insect pests -- Biological control -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5626 , http://hdl.handle.net/10962/d1004742
- Description: The diamondback moth, Plutella xylostella (L.), is a pest on crucifer crops worldwide, damaging the leaves, florets and seed pods of many crucifers including cabbage, cauliflower, broccoli and canola. It has been controlled using broad-spectrum insecticides, but this has led to a rapid build-up of insecticide resistance. In the Grahamstown area of the Eastern Cape Province, South Africa, diamondback moth showed resistance to cypermethrin (a pyrethroid) on commercially grown cabbages. Therefore it is imperative that other methods of control be adopted, including both cultural control and biological control using parasitoids, and that these are incorporated into an Integrated Pest Management (IPM) programme. The diamondback moth and its parasitoids were monitored weekly from April 1997 to November 1999 at three sites near Grahamstown. One site was a commercial farm with an active insecticide spraying program; the others were unsprayed. Infestation levels were highest during spring (September to November) and autumn (March to May). Nine species of parasitoids were associated with the diamondback moth, with abundances being highest over spring and early summer (September to December). Cotesia plutellae (Kurdjumov) dominated the sprayed site, while the unsprayed sites yielded a complex of parasitoids, including C. plutellae, Diadegma mollipla (Holmgren), Diadromus collaris Gravenhorst and Oomyzus sokolowsldi (Kurdjumov). Parasitism levels ranged between 10 and 90%. There was a large amount of site-to-site and year-to-year variation. Parasitoids were an effective mortality factor against the diamondback moth. The effects of temperature on development and mortality, and of field size and non-crop plants on the distribution of diamondback moth and its parasitoids, were investigated. The results show that high temperatures can depress pest populations, and that the size and surroundings of fields can be manipulated to improve cultural control of the diamondback moth. Suggestions for effective rPM in the Eastern Cape Province include a reduction in insecticide applications, the use of bioinsecticides, for example Bacillus thuringiensis Berliner (Bt) and the encouragement of indigenous parasitoids by planting suitable nectar sources. Cultural control methods are also important and involve removal of cabbage refuse after harvest, management of wild crucifers around cabbage fields, scouting and monitoring the moth population and determining the optimal field size to assist with control by parasitoids.
- Full Text:
- Date Issued: 2003
The biology of a facultative hyperparasitoid, Tetrastichus Howardi Olliff (Hymenoptera : Eulophidae), and its potential as a biocontrol agent of lepidopterous stem borers
- Authors: Moore, Sean Douglas
- Date: 1993
- Subjects: Eulophidae , Hymenoptera , Cephidae -- Biological control , Pests -- Biological control
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5649 , http://hdl.handle.net/10962/d1005331 , Eulophidae , Hymenoptera , Cephidae -- Biological control , Pests -- Biological control
- Description: The gregarious pupal endoparasitoid, Tetrastichus howardi Olliff (Hymenoptera: Eulophidae), was introduced into South Africa as a biocontrol agent against the maize and the sorghum stem borers, Busseola fusca Fuller and Chilo partellus Swinhoe. Preovipositional behaviour, ovipositional behaviour, development, fertility, sex-ratio, and longevity were studied in the laboratory. A complex courtship behaviour was observed, however 35.3% of females were mated before emergence from the host pupa. Preoviposition period ranged from 100 mins up to 5 days. Host searching time in Petri dishes was shorter for lepidopteran pupae than for their parasitoid pupae, and shortest when T. howardi had previously experienced the host. Duration of oviposition was significantly longer in the lepidopteran pupae than in the smaller tachinid puparia. T. howardi showed no difference in preference for hosts of different ages. The lepidopteran hosts were preferred to their parasitoids. If T. howardi had previously experienced a certain host its pereference for that host tended to increase, but not significantly. When reared on a certain host, the preference for that host did increase. The parasitoid was able to discriminate between parasitzed and unparasitzed pupae although this ability developed only 2 days after the pupa was parasitized. Cotesia sesamiae Cameron, the main indigenous parasitoid of B. fusca and C. partellus, was not attacked by T howardi. The total duration of development from egg deposition to the adult stage ranged from 18 to 26 days at 24°C and 60% RH. Emergence of adults began after first light, mean emergence time in winter being 09h00. Emergence rate of T. howardi from parasitized hosts, and mortality rate of parasitized hosts, was higher for C. partellus and H. armigera than for Eldana saccharina Walker and Palexorista laxa Curran. This decreased for C. partellus and H. armigera when superparasitized. A strong correlation existed between total parasitoids emerging from a host and percentage of females. When a lepidopteran pupa was parasitized by a single T. howardi female, 55 progeny emerged of which 94% were females. Larger females showed greater fertility and also produced a higher percentage of females. Younger hosts were more suitable for development of T. howardi. Females lived for 5.4 to 52.5 days, and males lived for 3.1 to 28.6 days, depending on presence or absence of food, water and hosts. Reasons for releasing T. howardi in the field are discussed. Only 2 recoveries of parasitized C. partellus pupae were made from the field.
- Full Text:
- Date Issued: 1993
- Authors: Moore, Sean Douglas
- Date: 1993
- Subjects: Eulophidae , Hymenoptera , Cephidae -- Biological control , Pests -- Biological control
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5649 , http://hdl.handle.net/10962/d1005331 , Eulophidae , Hymenoptera , Cephidae -- Biological control , Pests -- Biological control
- Description: The gregarious pupal endoparasitoid, Tetrastichus howardi Olliff (Hymenoptera: Eulophidae), was introduced into South Africa as a biocontrol agent against the maize and the sorghum stem borers, Busseola fusca Fuller and Chilo partellus Swinhoe. Preovipositional behaviour, ovipositional behaviour, development, fertility, sex-ratio, and longevity were studied in the laboratory. A complex courtship behaviour was observed, however 35.3% of females were mated before emergence from the host pupa. Preoviposition period ranged from 100 mins up to 5 days. Host searching time in Petri dishes was shorter for lepidopteran pupae than for their parasitoid pupae, and shortest when T. howardi had previously experienced the host. Duration of oviposition was significantly longer in the lepidopteran pupae than in the smaller tachinid puparia. T. howardi showed no difference in preference for hosts of different ages. The lepidopteran hosts were preferred to their parasitoids. If T. howardi had previously experienced a certain host its pereference for that host tended to increase, but not significantly. When reared on a certain host, the preference for that host did increase. The parasitoid was able to discriminate between parasitzed and unparasitzed pupae although this ability developed only 2 days after the pupa was parasitized. Cotesia sesamiae Cameron, the main indigenous parasitoid of B. fusca and C. partellus, was not attacked by T howardi. The total duration of development from egg deposition to the adult stage ranged from 18 to 26 days at 24°C and 60% RH. Emergence of adults began after first light, mean emergence time in winter being 09h00. Emergence rate of T. howardi from parasitized hosts, and mortality rate of parasitized hosts, was higher for C. partellus and H. armigera than for Eldana saccharina Walker and Palexorista laxa Curran. This decreased for C. partellus and H. armigera when superparasitized. A strong correlation existed between total parasitoids emerging from a host and percentage of females. When a lepidopteran pupa was parasitized by a single T. howardi female, 55 progeny emerged of which 94% were females. Larger females showed greater fertility and also produced a higher percentage of females. Younger hosts were more suitable for development of T. howardi. Females lived for 5.4 to 52.5 days, and males lived for 3.1 to 28.6 days, depending on presence or absence of food, water and hosts. Reasons for releasing T. howardi in the field are discussed. Only 2 recoveries of parasitized C. partellus pupae were made from the field.
- Full Text:
- Date Issued: 1993
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