By Gilbert Mwijuke
Global warming has significantly increased the number of invasive tomato insect pests in Uganda over the past forty years, according to a study that was recently published in Heliyon, an international all-science journal.
The study by researchers N’dakpaze Gno-Solim Ela, Daniel Olago, Amwata Dorothy Akinyi and Henri E.Z. Tonnang found that because of the current unprecedented rise in global temperatures, new invasive tomato pests have been regularly discovered in Uganda and many other parts of Africa.
During the study, it was found that there had been a significant increase in temperatures in Kampala and Namutumba districts over the past 40 years – by 0.049 °C and 0.037 °C per year, respectively. Mbale – the other Ugandan district in which the study was conducted – recorded the least increase in temperatures of 0.002 °C per year.
“Such an increase may have a drastic impact on insect pests which are essentially poikilothermic species with a high level of temperature-dependency for their development and life history. The highest proliferation of some insect pests occurs at the highest temperatures and lowest relative humidity.
Moreover, pest response to increasing temperatures has an impact on the amount of damage to crop yields,” the study says.
The authors of the study, which is titled Assessment of the effects of climate change on the occurrence of tomato invasive insect pests in Uganda, noted that the rise of invasive insect pests in Uganda was aided by wind owing to the positive relationship between wind speed and pest data.
The trends of wind speed during the study period amplified between 1981 and 2020. Data used in the study indicated an increased rate of 0.05 miles per hour and 0.003 miles per hour in Kampala and Namutumba, respectively.
“The relationships among wind speed, temperature, rainfall variables, and pest occurrence were positive in Kampala and Namutumba. The positive relationships observed in Mbale were among wind speed, humidity, rainfall and pest occurrence. The associations among all studied climate variables and pest occurrence were significantly correlated in the three districts, except for humidity in Kampala, wind speed, temperature, and humidity in Mbale,” the study says.
The latest Intergovernmental Panel on Climate Change report indicates that global temperatures will increase by 2 °C by the end of this century. Eastern Africa’s climate, which is characterised by dry seasons that follow humid spells, is favourable for insect invasion and spread, the study says.
The research
The authors of the new study collected data from the European and Mediterranean Plant Protection Organisation (EPPO), the Global Biodiversity Information Facility (GBIF) and the Centre for Agriculture and Bioscience International (CABI), which house billions of records collected globally since the 1900s.
“The annual averages of these bioclimatic variables were used to match the number of invasive pests recorded annually. The native species that were endemic to Uganda were excluded from the analysis,” the researchers said.
After the elimination of native species, which were clearly categorised in the databases as “native Ugandan species”, the researchers found that the total number of the invasive species that have been introduced into the country increased from 17 in 1981 to 38 in 2020. Some of the invasive pests cited by the study include leaf miner and thrips – and about 80 per cent of them were found in Kampala.
“This was expected as the Kampala agricultural produce markets are central to all the agricultural products originating across the country, hence many pests also become introduced and centralised in Kampala.
Additionally, this could be attributable to the fact that the capacity to identify, record, and report these pests could be higher in Kampala than in other parts of the country,” the study says.
Data from the European and Mediterranean Plant Protection Organization indicated that there is no native insect pest species that has entirely disappeared from Uganda.
Tomato pests threat to smallholder farmers
While efforts have been made to limit introduction of new pests, climate change and climatic variability remain a very big challenge – and this threatens smallholder farmers by making them more vulnerable to pests’ invasion and new diseases.
This is an especially big challenge for a country like Uganda where agriculture plays a pivotal role in many people’s livelihoods. In Mbale and Namutumba districts where part of the study was conducted, for instance, tomato production is the main source of income for smallholder farmers, and yields have been reducing steadily in these areas for the past three decades, the study says.
That said, tomato remains the most widely grown vegetable in Uganda and there has been an increase of about four per cent in tomato production in Uganda per year since 1972, but the use of pesticides has also increased, with 57 per cent of farmers applying pesticides to their tomatoes, mainly targeting insects.
“The challenge is that within the newly colonised eco-zones, there are no proper natural enemies that will slow down the progression of those invasive pests,” the study says.
