Catherine W. Gitau

Tri-Trophic Insecticidal Effects of African Plants against Cabbage Pests

Botanical insecticides are increasingly attracting research attention as they offer novel modes of action that may provide effective control of pests that have already developed resistance to conventional insecticides. They potentially offer cost-effective pest control to smallholder farmers in developing countries if highly active extracts can be prepared simply from readily available plants. Field cage and open field experiments were conducted to evaluate the insecticidal potential of nine common Ghanaian plants: goat weed, Ageratum conyzoides (Asteraceae), Siam weed, Chromolaena odorata (Asteraceae), Cinderella weed, Synedrella nodiflora (Asteraceae), chili pepper, Capsicum frutescens (Solanaceae), tobacco, Nicotiana tabacum (Solanaceae) cassia, Cassia sophera (Leguminosae), physic nut, Jatropha curcas (Euphorbiaceae), castor oil plant, Ricinus communis (Euphorbiaceae) and basil, Ocimum gratissimum (Lamiaceae). In field cage experiments, simple detergent and water extracts of all botanical treatments gave control of cabbage aphid, Brevicoryne brassicae and diamondback moth, Plutella xylostella, equivalent to the synthetic insecticide Attack® (emamectin benzoate) and superior to water or detergent solution. In open field experiments in the major and minor rainy seasons using a sub-set of plant extracts (A. conyzoides, C. odorata, S. nodiflora, N. tabacum and R. communis), all controlled B. brassicae and P. xylostella more effectively than water control and comparably with or better than Attack®. Botanical and water control treatments were more benign to third trophic level predators than Attack®. Effects cascaded to the first trophic level with all botanical treatments giving cabbage head weights, comparable to Attack® in the minor season. In the major season, R. communis and A conyzoides treatment gave lower head yields than Attack® but the remaining botanicals were equivalent or superior to this synthetic insecticide. Simply-prepared extracts from readily-available Ghanaian plants give beneficial, tri-trophic benefits and merit further research as an inexpensive plant protection strategy for smallholder farmers in West Africa.

Evolution of a Polydnavirus Gene in Relation to Parasitoid–Host Species Immune Resistance

CrV1, a polydisperse DNA virus (polydnavirus or PDV) gene contributes to the suppression of host immunity in Cotesia genus parasitoids. Its molecular evolution was analyzed in relation to levels of resistance in the sympatric host species. Natural selection for nonsynonymous substitutions (positive Darwinian selection) was observed at specific amino acid sites among CrV1 variants; particularly, between parasitoid strains immune suppressive and nonimmune suppressive to the main resistant stem borer host, Busseola fusca. In Cotesia sesamiae, geographic distribution of CrV1 alleles in Kenya was correlated to the relative abundance of B. fusca. These results suggest that PDV genes evolve through natural selection and are genetically linked to factors of suppression of local host resistance. We discuss the forces driving the evolution of CrV1 and its use as a marker to understand parasitoid adaptation to host resistance in biological control.

Biology of the bark beetle Ips grandicollis Eichhoff (Coleoptera: Scolytinae) and its arthropod, nematode and microbial associates: a review of management opportunities for Australia.

The five‐spined bark beetle, Ips grandicollis, is an exotic pest in Australia that preferentially attacks stressed pine trees, including Pinus radiata D. Don, but it can also attack healthy trees. The beetle has been present in Australia for 70 years, feeding principally on logging debris, with occasional outbreaks resulting in damage to plantations. Attack on trees stressed by drought, fire or storm damage leads to occasional significant losses. In recent years, I. grandicollis has been observed to attack ‘trap trees’ treated with herbicide to make them attractive to Sirex noctilio Fabricius as part of a successful biological control programme against this wood wasp. Ips grandicollis is able to tolerate a wide range of climatic conditions, and has an extensive geographical range (limited by host tree plantings). The economic impact of I. grandicollis is exacerbated by adults vectoring a fungus, Ophiostoma ips (Rumbold) Nannfeldt, which discolours the outer sapwood and contributes to tree death. Nematodes also are also associated with I. grandicollis, both in the body cavity and under the elytra. The dominant nematode is Contortylenchus grandicolli Massey, which is found internally, in haemocoel, the gut and the head region of the majority of adult beetles. Mites and bacteria are also associated with I. grandicollis but their biology is not well known. Since the first detection of I. grandicollis in Australia, various bio‐control and other management strategies have been tested. While a better understanding of the microbial and nematode associates of I. grandicollis may yield novel approaches for the management of this exotic pest, semiochemical‐based disruptants offer more immediate scope, particularly for protecting small areas of high value trees such as trap tree plots.

Entomopathogenic fungi of the oil palm pest, Zophiuma butawengi (Fulgoromorpha: Lophopidae), and potential for use as biological control agents

Oil palm, Elaeis guineensis Jacq., is an important cash crop in Papua New Guinea. Production is currently under threat from Finschhafen disorder caused by the planthopper Zophiuma butawengi (Heller), a native pest of coconut. The need for a non‐chemical strategy to manage Z. butawengi is high because the industry is committed to sustainable production. One possible option is the development of biological control using entomopathogenic fungi, and this study aimed to assess the scope for such a technology. Field collections extending over three regions of West New Britain in the 2010 monsoon season yielded 38 mycosed cadavers. Only three yielded entomopathogenic fungi: two of Hirsutella citriformis Speare and one each of Metarhizium flavoviride var. minus Rombach, Humber and D.W. Roberts, and Purpureocillium lilacinum (Thom) Luangsa‐ard, Houbraken, Hywel‐Jones and Samson. The pathogenicity of each isolate to Z. butawengi was confirmed in a laboratory study. M. flavoviride var. minus killed Z. butawengi significantly more rapidly over the course of a 15‐day period, and day 7 mortality was significantly greater than in water or nil control treatments. Given this pathogenic fungus was readily culturable and congenerics are used in other biological control treatments, it merits further investigation as a potential inundative entomopathogenic agent against Z. butawengi.

Description and biological parameters of Ooencyrtus isabellae Guerrieri and Noyes sp. nov. (Hymenoptera: Chalcidoidea: Encyrtidae), a potential biocontrol agent of Zophiuma butawengi (Heller) (Hemiptera: Fulgoromorpha: Lophopidae) in Papua New Guinea

The planthopper Zophiuma butawengi (Heller) (= Z. lobulata Ghauri) is a serious pest of coconut and oil palm in Papua New Guinea, causing palm decay known as Finschhafen disorder. Recently, two dominant species of parasitoids emerged from egg masses of this pest, namely Parastethynium maxwelli (Girault) (Hymenoptera: Mymaridae) and an undescribed species of Ooencyrtus Ashmead (Hymenoptera: Encyrtidae). The latter species, here described, appears to be a potential biocontrol agent of Z. butawengi especially in the New Britain Province of Papua New Guinea. Biological features of the new species, i.e. development time and adult longevity, were also calculated to give information that could help in its use in biological control programmes.

Maintenance of Specialized Parasitoid Populations by Polydnaviruses

Publisher Summary This chapter discusses how polydnaviruses are linked to the process of specialization in braconid and ichneumonid wasps and are hence very good markers of wasp specialization. It also reviews how they are involved in host adaptation and specialization. The parasitoid lifestyle requires an intense specialization at different steps of the life-cycle. As a consequence, most parasitic wasps are specialized and can successfully parasitize very few host species. This host specificity makes them one of the most used biological control agents against insect pests. Unraveling specialization and defining host range within a species or among morphologically identical species might be problematic without the use of molecular markers. Expanding the host range of a given parasitoid increases the cost. From the hosts point of view, the cost of developing defense mechanisms could be higher than the cost of parasitism and more specialized parasitoids take advantage of that situation.