Interaction of the fluctuation of the population density of sweet potato pests with changes in farming practices, climate and physical environments: A 11-year preliminary observation from South-Kivu Province, Eastern DRCongo

Abstract

Open Agriculture. 2017; 2: 495-530 determined which climatic factors may be used as best predictors of the different status of pest populations (declines, outbreaks). Farmer based data was obtained using a semi structured questionnaire administered to several of farmers. Population dynamics of sweetpotato pests were monitored year-round from 2005 to 2015 in South Kivu province, eastern DRCongo. Field monitoring (visual counts) observations (population dynamic of different soil-dwelling and surface dwelling arthropods visiting sweetpotato fields) combined with a survey of farmers' knowledge on sweetpotato pests and their practices in the management of these pests in SouthKivu Province were conducted for 11 years. Monitoring (with field observations and counts) was carried out in fields under different farming practices (monocropping and inter-cropping) in sites located at different altitudes. Similarly, data for climatic factors, for the same period, were collected from Lwiro Research center. Regression models were applied to understand the linkages between environmental factors (rainfall and temperature) and pest population dynamics. The results indicated that different varieties (local and improved ones) of sweetpotato are grown three times (3 seasons) per annum under various cropping systems (sole crop, mixed crops) in various agroecological zones at different altitudes. Various arthropod species visit the crop at its different stages of development including classically known pests (Acraea acerata, Cylas spp.) or as vectors of diseases (Bemisi tabaci, Aphis spp.). The results indicated a high fluctuation in the population density of different pests. The change in the population dynamics were characterized by gradual increase in the populations during rainy seasons followed by decline during dry seasons (hot months of the year). Significant (P<0.05) https://doi.org/10.1515/opag-2017-0054 received January 2, 2016; accepted March 19, 2017 Abstract: Sweetpotato is a major food security crop grown in eastern Democratic Republic of Congo. Its production is however limited due to high prevalence of pests and diseases among other abiotic and biotic factors. A study was designed to aid understanding the knowledge of farmers about pests and their perception about climate variability impacts, as well as documenting the phenology of sweetpotato pests (pest population dynamics) in relationship with weather factors. The paper aimed at differences were observed in the population dynamics between sole sweetpotato and mixed sweetpotato intercropping. There was a synchronization of multiple pest generations (biannual, multiannual cycles of reproduction) built up with early rains. The results indicate that rainfall and maximum temperature were critical to the survival and population built up of the pest population. High rainfall in the previous months caused increases in the population density in the subsequent months within a year. The population dynamic (seasonal occurrence) over months and years was likely to coincide ...

Screening barrier plants to reduce crop attack by sweet potato weevil (Cylas formicarius)

“…Future field work must also quantify effects on other pests including those that vector plant pathogens. Surveys have shown that intercropping systems have significantly lower pest pressure on sweet potato than monocropping systems, regardless of farmer management, climate or altitude . In smallholder systems where expensive management tools such as pesticides, pheromone disruption or crop rotation are not practical, barrier plants and intercropping offer a low‐risk and ecologically sustainable form of habitat management.…”

“…The amount of edible energy that can be produced per hectare is matched by few other crops and in some parts of the world, sweet potato is relied on to provide food when other crops fail . The high yield potential of sweet potato is often not realized in smallholder farming where poor knowledge of pests and a low availability of management options mean that little is done to manage pest attack . The sweet potato weevil, Cylas formicarius (Fabricius) is considered the most problematic pest of sweet potato as even light infestations can render roots unfit for human consumption .…”

“…sesquipedalis ) . Intercropping can suppress pests by increasing host search time by pests with confusing olfactory and visual cues, acting as a trap crop, supporting higher numbers of natural enemies and by barrier effects . Although the complexities of insect–plant interactions mean that intercropping is far from a panacea that always leads to reduced pest impact, cases where it does succeed indicate that characteristics of successful secondary plants include high structural complexity and the production of strong volatiles .…”

“…3,4 The high yield potential of sweet potato is often not realized in smallholder farming where poor knowledge of pests and a low availability of management options mean that little is done to manage pest attack. 5,6 The sweet potato weevil, Cylas formicarius (Fabricius) is considered the most problematic pest of sweet potato as even light infestations can render roots unfit for human consumption. 4,7,8 This pest is effectively controlled by a combination of sanitation, insecticides and pheromone trapping in industrial agricultural parts of the world.…”

“…16 Intercropping can suppress pests by increasing host search time by pests with confusing olfactory and visual cues, acting as a trap crop, supporting higher numbers of natural enemies and by barrier effects. 5,11 Although the complexities of insect-plant interactions mean that intercropping is far from a panacea that always leads to reduced pest impact, cases where it does succeed indicate that characteristics of successful secondary plants include high structural complexity and the production of strong volatiles. 17 Intercropping can, however, result in trade-offs in focal crop biomass and nutrient uptake 18 although these effects can be minimized by the selection of appropriate cultivars and allowing the benefits of reduced pest attack and increased land use efficiency to improve overall yield.…”