The tomato leaf miner, Tuta absoluta, originally from South America, feeds voraciously on tomato plants and is a serious threat to production and profit in the sector, regardless of whether the crop is grown under cover or in open fields.
The highly adaptable insect has been able to advance rapidly across territories, and pick up resistance to pesticides along the way. Because of this chemical resistance, biological controls are seen as an additional, essential, weapon in the fight against Tuta absoluta.
DESCRIPTION AND LIFE CYCLES
The leaf miner has a temperature dependent, 24 to 38 day reproductive cycle. It can’t operate if the temperature is under 9°C. Very unfortunately, the destructive, caterpillar (larval) stage does not advance into the next stage, of the cycle, while there is still food around.
A single female moth deposits her eggs on plants. She can lay 250 eggs in her lifetime. The hatchling caterpillars begin their ghastly and destructive job of mining the leaves, stems and fruit of tomato plants. Caterpillars (larvae) may have a couple of growing phases before they pupate in the soil, leaf mines or old leaves.
Tuta absoluta can overwinter as an egg, a pupa or a moth.
The grey-brown adult moth forages at night and hides out during the day. With a size of 6mm it has a 10mm wingspan. The male is darker than the female.
The young, yellowish caterpillars are 0,5 mm long and mature caterpillars are yellow-green with a black band behind the head. The light-brown pupae are 6 mm long.
Although they prefer the leaves and stems of the plant, caterpillars are also found in the fruit and under the fruit crown. Leaf mines look like irregular tomato fruit gives bacteria and fungi access and the opportunity inflict more damage.
Agronomists advise clearing of all crop residues. One doesn’t want to provide survival shelters for insects. Mass trapping with baited pheromone traps takes out the males, attracted by the sex signals of the pheromone to a sticky end on the surface of the trap. Mass trapping should be carried out before planting.
Where populations are reasonably low (10 captures/week) the sticky, pheromone baited traps work well as a maintenance regime, set at 30 to 40 traps per hectare.
The lure and kill approach combines sticky traps and insecticide; a little, slow release insecticide in combination with the pheromone lures insects onto the sticky pans. The traps are functional for six weeks.
Apply recommended chemicals 10 days after planting and re-apply a different chemical to kill off survivors. Tuta absoluta is resistant to pyrethroids and methamidophos; imadocloprid, indoxocarb and deltamethrin are said to be effective.
Biocontrols include egg parasitoids and predatory insects. The microbe, Bacillus thunbergiensis, will also kill larvae. Biological controls may be sourced from one of many reputable biocontrol operations, most of which are based in Europe with agencies in southern Africa.
There have been some good results with Neem seed extract applied to the underside of the leaf as a contact killer, and to the soil, as a systemic insecticide.
Practice sensible farming methods and aim for the healthiest possible plants by following the rules of irrigation, fertilisation and a debris free environment. Learning recognition of the pest at any stage of its life cycle can help stop the devastating destruction of Tuta absoluta.