Farmer's Weekly (South Africa)
The future of Tuta absoluta control
As the tomato leaf miner feeds on a wide range of species, its natural enemies are likely to continue increasing, says Bill Kerr.
The tomato leaf miner ( Tuta absoluta), which originates in South America, has spread to most tomato-producing countries, increasing from 3% to 60% global infection in just 10 years.
This pest causes havoc wherever it goes. In Nigeria, for example, it resulted in an 80% crop loss in 2016.
Some farmers, desperate to get
T. absoluta under control, have caused additional harm. By spraying harsh chemicals, they have eradicated a host of predators, including the natural enemies of whitefly, another tomato pest. This has resulted in whitefly outbreaks and curly stunt virus, of which whitefly is a vector.
HOME-GROWN SUCCESS
I recently had a visit by an entomologist from the Agricultural Research Council who is working on the tomato leaf miner and fall armyworm. He collected a number of parasitoids and predators from my tunnels, including Macrolophus bugs. He had no record of the latter being present in South Africa. These are used in Europe to control the tomato leaf miner and supposedly do not thrive above 30°C. Clearly, my population of Macrolophus is more heattolerant, as my tunnels are particularly hot. The good news is that these bugs are easy to rear in the laboratory.
The entomologist also collected Diadegma and Nesidiocoris wasp parasitoids and a great number of minute egg parasites that still have to be identified. Genes will be extracted from all these for proper classification.
He had been travelling the country looking for potential natural enemies of T. absoluta and managed to find only one parasitoid, and that was in the Eastern Cape.
What is particularly pleasing for me (and excellent news for other growers) is that there is no more T. absoluta activity in my tunnels; control is now at 100%. There is not a single lesion on any new growth on existing tomatoes, or on tomatoes planted later.
I haven’t sprayed for pests for three successive years; despite this,
T. absoluta damage has steadily declined. This proves beyond doubt that effective biocontrol is possible.
Moreover, none of the pest’s natural enemies were introduced; they came in naturally, which bodes well for the future.
T. absoluta feeds on a great many weed and plant species; this supports an increase in its natural enemies, which in turn prey on a range of other plant pests. I am thus optimistic that there will be little or no damage next season in my tunnels. It appears, in any case, that mine is the first case of complete biological control of T. absoluta in the country.
COMPLETE CONTROL
The same results have been obtained elsewhere with other leaf miners, including Liriomyza huidobrensis. This pest started off by destroying a number of crops, but was then brought under control by parasitoids in two years. The trick, of course, is to avoid using harsh chemicals. I suspect this will be the case with the tomato leaf miner as well. It is likely that several control species will be required, as is the case on my property.
Beneficial insects will be bred by companies and institutions for release in tomato productions.
In Spain, the parasitoid Necremnus tutae started in one tunnel and then spread naturally around the country, providing effective control.
Unfortunately, success has not been achieved in rearing this wasp ‘in captivity’, as it were, but it seems unnecessary in any case.
Bill Kerr is a vegetable specialist and breeder. Email him at farmersweekly@caxton.co.za. Subject line: Vegetable production.
THERE IS NO MORE TOMATO LEAF MINER ACTIVITY IN MY TUNNELS; CONTROL IS NOW AT 100%