Integrating biological control and botanical pesticides for management of Plutella xylostella

A large number of different plant species have natural pesticidal properties, and man has made use of this since early times. By applying plant extracts to other susceptible plant species the defence of the susceptible plant is improved. This thesisfocuseson the possibility of integrating botanical pesticides with biological control for management of the diamondback moth, Plutella xylostella , inSouth Africa Twenty-one species of primary parasitoids have been collected from P. xylostella in the field inSouth Africa. Biological control therefore provides a natural control technique. However, biological control alone is insufficient to provide adequate protection and requires integration with other control techniques. Plant products from the Meliaceae family have been widely used to control insect pests, particularly products from the neem tree, Azadirachta indica . The neem tree does not grow inSouth Africabut the closely related syringa tree Melia azedarach is a widespread invasive plant found throughout the country. In this thesis I make use of a commercial neem product, Neemix 4.5 ® , and aqueous leaf extracts derived from the syringa tree.The neem- and syringa- derived botanical pesticides had adverse effects on the development, reproduction and survival of P. xylostella . These botanical pesticides also reduced feeding and oviposition, which are important factors in pest control. However, if a botanical pesticide is to be combined with biological control it must not hamper natural enemies. The neem- and syringa- derived botanical pesticides did not have a directly negative impact on the survival of Cotesia plutellae or Diadromus collaris two of the most abundant natural enemies found in South Africa. In a glasshouse, a significantly higher proportion of P. xylostella larvae were parasitised by C. plutellae on plants that been treated with the syringa extract than on control plants. Results from a choice test in a windtunnel showed that C. plutellae was attracted significantly more often to cabbage plants treated with the syringa extract than to the control plants. Headspace analysis revealed that treatment of cabbage with syringa extracts caused an increased emission of volatiles by the cabbage plants. This may explain the increased attraction of C. plutellae to plants that had been treated with the syringa extract. It was important to verify results from the laboratory under more realistic conditions in the field. We did not find a difference in P. xylostella infestation levels between the treated and the control plants in the field. However, the damage on plants treated with the botanical pesticides was significantly lower. Therefore, it seems that reduced feeding by P. xylostella larvae was a more important factor in the reduction of damage than the actual population density. The proportion of P. xylostella larvae that had been parasitised was significantly higher on the treated plants than on the control plants. Direct observations showed that plants that had been treated with neem- and syringa- derived pesticides were still visited by parasitoids. Therefore these botanical pesticides do not appear to interfere with parasitoid foraging. I assessed the possibility for introducing this control method to the rural farming community inSouth Africa. Syringa trees are invasive plants found throughoutSouth Africaand therefore provide a free local resource for the botanical pesticide. Results indicated that the use of syringa extracts could be introduced. Water is the main factor limiting the introduction of this technique in more arid environments. Results presented in this thesis indicate that biological control and the use of botanical pesticides derived from the neem and syringa trees can be integrated for the management ofP. xylostella. However, mammalian toxicity and residual effects still require extensive investigation before any further recommendations can be made

Integrating biological control and botanical pesticides for management of Plutella xylostella

A large number of different plant species have natural pesticidal properties, and man has made use of this since early times. By applying plant extracts to other susceptible plant species the defence of the susceptible plant is improved. This thesisfocuseson the possibility of integrating botanical pesticides with biological control for management of the diamondback moth, Plutella xylostella , inSouth Africa Twenty-one species of primary parasitoids have been collected from P. xylostella in the field inSouth Africa. Biological control therefore provides a natural control technique. However, biological control alone is insufficient to provide adequate protection and requires integration with other control techniques. Plant products from the Meliaceae family have been widely used to control insect pests, particularly products from the neem tree, Azadirachta indica . The neem tree does not grow inSouth Africabut the closely related syringa tree Melia azedarach is a widespread invasive plant found throughout the country. In this thesis I make use of a commercial neem product, Neemix 4.5 ® , and aqueous leaf extracts derived from the syringa tree.The neem- and syringa- derived botanical pesticides had adverse effects on the development, reproduction and survival of P. xylostella . These botanical pesticides also reduced feeding and oviposition, which are important factors in pest control. However, if a botanical pesticide is to be combined with biological control it must not hamper natural enemies. The neem- and syringa- derived botanical pesticides did not have a directly negative impact on the survival of Cotesia plutellae or Diadromus collaris two of the most abundant natural enemies found in South Africa. In a glasshouse, a significantly higher proportion of P. xylostella larvae were parasitised by C. plutellae on plants that been treated with the syringa extract than on control plants. Results from a choice test in a windtunnel showed that C. plutellae was attracted significantly more often to cabbage plants treated with the syringa extract than to the control plants. Headspace analysis revealed that treatment of cabbage with syringa extracts caused an increased emission of volatiles by the cabbage plants. This may explain the increased attraction of C. plutellae to plants that had been treated with the syringa extract. It was important to verify results from the laboratory under more realistic conditions in the field. We did not find a difference in P. xylostella infestation levels between the treated and the control plants in the field. However, the damage on plants treated with the botanical pesticides was significantly lower. Therefore, it seems that reduced feeding by P. xylostella larvae was a more important factor in the reduction of damage than the actual population density. The proportion of P. xylostella larvae that had been parasitised was significantly higher on the treated plants than on the control plants. Direct observations showed that plants that had been treated with neem- and syringa- derived pesticides were still visited by parasitoids. Therefore these botanical pesticides do not appear to interfere with parasitoid foraging. I assessed the possibility for introducing this control method to the rural farming community inSouth Africa. Syringa trees are invasive plants found throughoutSouth Africaand therefore provide a free local resource for the botanical pesticide. Results indicated that the use of syringa extracts could be introduced. Water is the main factor limiting the introduction of this technique in more arid environments. Results presented in this thesis indicate that biological control and the use of botanical pesticides derived from the neem and syringa trees can be integrated for the management ofP. xylostella. However, mammalian toxicity and residual effects still require extensive investigation before any further recommendations can be made

Impact of botanical pesticides derived from Melia azedarach and Azadirachta indica on the biology of two parasitoid species of the diamondback moth

The effect of two botanical pesticides was tested on two species of parasitoids, Cotesia plutellae and Diadromus collaris. Aqueous leaf extracts from the syringa tree, Melia azedarach and commercial formulations from the neem tree, Azadirachta indica, Neemix 4.5 were investigated in the laboratory and in a glasshouse. No direct negative effect was recorded on the longevity of the parasitoid species. However, hind tibia length was found to be significantly shorter in male C. plutellae that emerged from Plutella xylostella that had been exposed to syringa extracts. Whether this negatively affects the fitness of male C. plutellae remains unknown. The impact of the botanical extracts on the fitness of D. collaris could not be investigated because the pesticides resulted in a high mortality of P. xylostella hosts. In the glasshouse a significantly higher proportion of P. xylostella were parasitised by C. plutellae on plants treated with botanical pesticides than on the control plants. However, there were no significant differences between the treatments for the proportion of P. xylostella parasitised by D. collaris. Results indicate that these botanical pesticides have the potential to be combined with biological control programs for P. xylostella. [KEYWORDS: Botanical pesticides ; Melia azedarach ; Azadirachta indica ; Cotesia plutellae ; Diadromus collaris ; Plutella xylostella]

Impact of botanical pesticides derived from Melia azedarach and Azadirachta indica on the biology of two parasitoid species of the diamondback moth

The effect of two botanical pesticides was tested on two species of parasitoids, Cotesia plutellae and Diadromus collaris. Aqueous leaf extracts from the syringa tree, Melia azedarach and commercial formulations from the neem tree, Azadirachta indica, Neemix 4.5 were investigated in the laboratory and in a glasshouse. No direct negative effect was recorded on the longevity of the parasitoid species. However, hind tibia length was found to be significantly shorter in male C. plutellae that emerged from Plutella xylostella that had been exposed to syringa extracts. Whether this negatively affects the fitness of male C. plutellae remains unknown. The impact of the botanical extracts on the fitness of D. collaris could not be investigated because the pesticides resulted in a high mortality of P. xylostella hosts. In the glasshouse a significantly higher proportion of P. xylostella were parasitised by C. plutellae on plants treated with botanical pesticides than on the control plants. However, there were no significant differences between the treatments for the proportion of P. xylostella parasitised by D. collaris. Results indicate that these botanical pesticides have the potential to be combined with biological control programs for P. xylostella. [KEYWORDS: Botanical pesticides ; Melia azedarach ; Azadirachta indica ; Cotesia plutellae ; Diadromus collaris ; Plutella xylostella

Integration of biological control and botanical pesticides : evaluation in a tritrophic context

The plant kingdom is by far the most efficient producer of chemical compounds, synthesising many products that are used in defence against herbivores. Extracts made from some plants, particularly extracts from plants within the Meliaceae (mahogany) family, have been shown to have insecticidal properties. We investigated the potential of these extracts and the possibility of integrating botanical pesticides with biological control of the diamondback moth, Plutella xylostella. Sub-lethal doses of botanical extracts were prepared from leaves of the syringa tree (Melia azedarach) and commercial preparations (Neemix 4.5®) from the neem tree (Azadirachta indica). In "no-choice" tests, bioassay trays were used to test the impact of three different doses on first- instar larvae. In "choice" tests, half a leaf was treated with extract and the other half left untreated. The impact that these extracts had on natural enemies was investigated using two parasitoid species, Cotesia plutellae and Diadromus collaris. Results indicated that these extracts had a significantly negative impact on first-instar larvae of P. xylostella. However, the extracts had no direct negative impact on their parasitoids. Therefore, it appears that biological control and botanical pesticides can be combined to control P. xylostella

Behavioural responses of diamondback moth Plutella xylostella (Lepidoptera: Plutellidae) to extracts derived from Melia azedarach and Azadirachta indica

The impact of three different doses of botanical insecticide derived from the syringa tree, Melia azedarach and the neem tree, Azadirachta indica was tested on the behaviour of the diamondback moth, Plutella xylostella (Linnaeus). Both botanical insecticides had a significant impact on larval behaviour. At higher doses the extracts showed feeding deterrent activity, with larvae preferring the untreated sides of cabbage leaves and consuming less of the treated half of cabbage leaves. The botanical insecticides had less of an effect on the oviposition behaviour of P. xylostella moths. In laboratory and glasshouse trials, significantly fewer eggs were oviposited on the plants that had been treated with syringa extracts. Therefore, the syringa extracts appear to have a repellent effect. In contrast, when exposed to the neem extracts the moths did not discriminate between control plants and treated plants. Behavioural observation indicated that, despite the lower number of eggs oviposited on cabbage treated with syringa extracts, the moths chose cabbage treated with the highest dose of syringa more often than they chose control cabbage plants. Similar observations were found in cabbage plants treated with neem, moths chose the medium dose more often than they chose the control. Oviposition and feeding deterrent properties are important factors in pest control, and results from this study indicate that botanical insecticides have the potential to be incorporated into control programmes for P. xylostella in South Africa. [KEYWORDS: Plutella xylostella ; Azadirachta indica ; Melia azedarach ; insecticides ; plant extracts ; South Africa ; control and damage control]

Impact of botanical extracts derived from Melia azedarach and Azadirachta indica on populations of Plutella xylostella and its natural enemies: A field test of laboratory findings

Differences between results from ecological laboratory studies and what actually happens in the field can be large. Therefore, field experiments are essential to validate laboratory findings. In previous laboratory trials we investigated the impact of aqueous leaf extracts from the syringa tree, Melia azedarach L. (Meliaceae) and commercial formulations from the neem tree, Azadirachta indica Juss. (Meliaceae), Neemix 4.5®, on the biology and behaviour of the diamondback moth Plutella xylostella and two of its most abundant parasitoids, Cotesia plutellae and Diadromus collaris. In the laboratory we had demonstrated that these botanical extracts had adverse effects on survival, fecundity, development, oviposition and feeding of P. xylostella, but no direct negative effects on the survival and foraging of the parasitoids. In the current study, we verified the importance of these previous laboratory findings through field experiments. We treated cabbage plants in the field with the neem product and syringa extract and assessed the infestation levels of P. xylostella and the parasitism rates by natural enemies. Infestation levels of P. xylostella were similar in the plots treated with the botanical extracts and the control plots. However, the damage in the treated plots was significantly lower than in the control plots, indicating that reduced feeding by P. xylostella was a more important factor in the reduction of damage than the actual population density. The proportion of marketable cabbages was significantly higher in the treatments than in the control. The proportion of parasitoids found emerging from P. xylostella was also significantly higher in the treated plots than in the control plots and direct observations indicated that parasitoids still visited cabbage plants that had been treated with the botanical extracts.