Browsing by Author "Mudavanhu, Pride"
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- ItemBiologically based methods for pest management in agriculture under changing climates : challenges and future directions(MDPI, 2012) Chidawanyika, Frank; Mudavanhu, Pride; Nyamukondiwa, CasperThe current changes in global climatic regimes present a significant societal challenge, affecting in all likelihood insect physiology, biochemistry, biogeography and population dynamics. With the increasing resistance of many insect pest species to chemical insecticides and an increasing organic food market, pest control strategies are slowly shifting towards more sustainable, ecologically sound and economically viable options. Biologically based pest management strategies present such opportunities through predation or parasitism of pests and plant direct or indirect defense mechanisms that can all be important components of sustainable integrated pest management programs. Inevitably, the efficacy of biological control systems is highly dependent on natural enemy-prey interactions, which will likely be modified by changing climates. Therefore, knowledge of how insect pests and their natural enemies respond to climate variation is of fundamental importance in understanding biological insect pest management under global climate change. Here, we discuss biological control, its challenges under climate change scenarios and how increased global temperatures will require adaptive management strategies to cope with changing status of insects and their natural enemies.
- ItemGlobal climate change as a driver of bottom-up and top-down factors in agricultural landscapes and the fate of host-parasitoid interactions(Frontiers Media, 2019-03-28) Chidawanyika, Frank; Mudavanhu, Pride; Nyamukondiwa, CasperThe global climate is rapidly changing and the evidence is increasingly manifesting across various biological systems. For arthropods, several studies have demonstrated how changing climates affect their distribution through phenological and physiological responses, largely focusing on various organismal fitness parameters. However, the net-effect of the changing climate among ecological communities may be mediated by the feedback pathways among interacting trophic groups under environmental change. For agroecosystems, the maintenance of the integrity of trophic interactions even under climate variability is a high priority. This is even more important in this era where there is advocacy for sustainable agriculture, with higher emphasis on environmentally benign methods. For this reason, pest management in food production systems using biological control (especially use of parasitoid antagonists) has come to the forefront. In this review, we give an overview of the diversity of physiological responses among host insect and parasitoid populations and how this may influence their interactions. We highlight how climate change may modify bottom-up and top-down factors among agroecosystems with a particular focus on plant-insect host-parasitoid tritrophic interactions. We also outline how habitat management may influence arthropod population dynamics and how it can be manipulated to improve on-farm climate resilience and parasitoid conservation. We wrap-up by highlighting how the application of knowledge of conservation biodiversity, designing of multifunctional resilient landscapes, and evolutionary physiology of arthropods under thermal stress may be used to improve the fitness of mass-reared parasitoids (in or ex situ) for the improvement in efficacy of parasitoids ecosystem services under thermally stressful environments.
- ItemMating compatibility and competitiveness between wild and laboratory strains of Eldana saccharina (Lepidoptera : Pyralidae) after radiation treatment(Florida Entomological Society, 2016) Mudavanhu, Pride; Addison, Pia; Carpenter, James E.; Conlong, Des E.The efficacy of the sterile insect technique (SIT) applied as part of area-wide integrated pest management (AW-IPM) depends on efficient transfer of sperm carrying dominant lethal mutations from sterile males to wild females. Success or failure of this strategy is therefore critically dependent on quality and ability of sterile males to search for and copulate with wild females. The African sugarcane borer, Eldana saccharina Walker (Lepidoptera: Pyralidae) is an economic pest of sugarcane targeted for control in South Africa using an AW-IPM approach with a SIT component. As part of further steps towards development of the technique, levels of mating competitiveness and compatibility were assessed by observing the extent to which individuals from different populations interbreed when confined together under both laboratory and semi-field conditions. Three types of pair-wise competition experiments were conducted: non-irradiated laboratory adults vs. non-irradiated wild adults, irradiated (200 Gy) laboratory adults vs. non-irradiated wild adults, and non-irradiated laboratory adults vs. irradiated (200 Gy) laboratory adults. Data from these tests were used to generate indices for mating performance and measuring sexual compatibility between strains. Irrespective of trial location, wild moths did not discriminate against irradiated or laboratory-reared moths, indicating no negative effects on acceptability for mating due to laboratory rearing or radiation treatment. In general, irradiated males mated significantly more than their wild counterparts regardless of the type of female, which indicated that they were still as competitive as their wild counterparts. The mating indices generated showed no evidence of incipient pre-mating isolation barriers or sexual incompatibility with the wild strain. Data presented in this paper therefore indicate that there is scope for further development of the SIT as an addition to the arsenal of tactics available for AW-IPM of this economic pest.
- ItemPerformance of sterilized Eldana saccharina Walker (Lepidoptera: Pyralidae) adults in mating and cage trials : further steps towards its control using the Sterile Insect Technique(Stellenbosch : Stellenbosch University, 2012-12) Mudavanhu, Pride; Conlong, D. E.; Addison, Pia; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.The sugarcane borer, Eldana saccharina Walker (Lepidoptera: Pyralidae) is the most limiting factor in the South African sugar industry with losses to this insect pest estimated to be at least ZAR60 million per annum. Because of its cryptic nature as well as the fact that E. saccharina is both indigenous to Africa and occurs on several host plants, attempts to control or eradicate it using several available methods have not been very successful. However, the sterile insect technique (SIT) is one of the newer control methods that can be incorporated into an area-wide integrated pest management (AW-IPM) programme to achieve better control or eradication. The implementation of the SIT program needs to go through a series of well-researched phases in order to be successful. In the first of this multi-phase project, it was determined that E. saccharina is susceptible to ionizing radiation, and is thus a suitable candidate for the SIT development against it and that a sub-sterilizing dose of 200 Gy is sufficient to induce F1(inherited) sterility in male and complete sterility in female moths respectively. The results presented here are discussed in the context of further development of the SIT as an addition to the arsenal of tactics in an AW-IPM programme against E. saccharina. Based on these initial findings, the study examined the lek and mating behavior of male moths subjected to three radiation doses (150, 200, 250 Gy) against normal non-irradiated/fertile moths. Both mass-rearing and irradiation of E. saccharina led to a quantitative departure of male mating behavior away from that exhibited by their wild counterparts. However, treated males are still able to form leks and mate with wild females. Male E. saccharina irradiated at all three doses tested were found to be as active and competitive as wild males, but in some of the traits measured, performance diminished significantly with an increase in the radiation dosage. In general, the performance of moths treated at 200 Gy did not differ significantly from that of moths treated at 150 Gy and therefore the former dose is ideal for SIT development since it results in a lower residual F1 fertility than the latter. The level of mating competitiveness and compatibility was assessed under both laboratory and semi-field conditions in pairwise comparisons consisting of laboratory reared vs. wild (L-W), 200 Gy irradiated vs. wild (S-W) and laboratory reared vs. irradiated moths (L-S). Based on the results from the more robust field cage assays, the mating indices generated indicated that the mass-reared E. saccharina strain produced in South Africa has not yet evolved sexual behaviours suggestive of incipient pre-mating isolation barriers with local wild strains. Wild moths did not discriminate against either the partially sterile or laboratory reared moths and most importantly, the irradiated males mated significantly more than their wild counterparts regardless of the type of female. The irradiated insects could therefore achieve the purpose for which they are intended upon release into the field. Third, the critical thermal limits (CTLs) to activity at high and low temperatures (i.e. critical thermal maxima “CTmax” and minima “CTmin”) of different E. saccharina strains/treatments were investigated under standard experimental conditions. The effect of laboratory rearing and increasing radiation dosage on thermal tolerance of the adult stage of E. saccharina was explored. There were highly significant differences between the laboratory-reared and wild strain and also between non-irradiated and irradiated strains in both CTmax and CTmin. Laboratory reared E. saccharina moths were more heat tolerant compared to wild moths for both genders while in the case of CTmin, the reverse was true. Irradiation had a negative effect on both CTmax and CTmin. Moths treated at the lowest radiation dose were more cold and heat tolerant than those treated at higher dosages thereby reinforcing the importance of lower dosages rather than those that induce full sterility against E. saccharina. In general, gender effects on the CTLs were non-significant. Pilot sterile male releases in shade house trials to measure the impact of sustained releases of partially sterile adult males at an over-flooding moth ratio of 10T: 1U (treated to untreated),were conducted to measure their efficacy to stop E. saccharina incursions and suppress populations prior to testing in pilot studies under true season-long and area wide conditions. Results from the current study demonstrated that releasing partially irradiated (200 Gy) adult male moths at the afore mentioned release rate significantly reduced sugarcane stalk damage as well as lowered the number of fertile progeny from F1to succeeding generations in a stable E. saccharina population initiated in a cage house. There were more damaged internodes per stalk in the control than in the sugarcane receiving regular releases of partially sterile male moths. Overall, there were significantly more undamaged stalks in the treated sugarcane than the untreated control. Furthermore, there were significantly more larvae per stalk retrieved from the control compared to the treated sugarcane suggesting that the sustained release of steriles was efficacious in reducing emergence of fertile larvae in the succeeding generations. The results of this study indicate that there is considerable scope for the SIT against E. saccharina.