Tomato pinworms

Tomato pinworms naturally occur in the hot agricultural areas. These tomato eating worms are primarily a greenhouse problem. In addition to their namesakes, tomato pinworms feed only on Solanaceous plants; that is, members of the nightshade family, such as tomatoes, eggplant and potato. As tiny worms on tomato plants, these insects can do tremendous crop damage.

Key: TPW is a short form of Tomato Pin Worm

Tomato pinworm identification

 

In warmer climes, the tomato pinworms spend the winter as pupae at the soil’s surface. Where the winter weather is too cold for survival, the pupae hide in the dirt floors and plant detritus of the greenhouse.

The small grey-brown moths lay their eggs on the underside of leaves during the night and because of their tiny size, the eggs are hardly noticeable. Because of this, tomato pinworm control rarely begins at this stage. It’s not until the larval stages that damage begins to mount and when the worms in tomato’s leaves leave their tunnels behind, the evidence is clear.

 

During the next stage of development, the tomato eating worms drill pinholes into the stems, buds and fruit and eat the flesh until they are ready to pupate or move on to the next stage of development. While leaf damage is of little importance, the damage to the fruit crop can be devastating. In areas where the moths are prevalent, growers must be vigilant with tomato pinworm control because these tiny insects multiply at a remarkable rate and can produce up to eight generations a year.

Damage to the crop

 

The tomato pinworm attacks both the leaves and fruits of tomato. Tunnelling or mining by larvae in the leaves is the most common type of injury. Initially, the mine is long and narrow, but it later widens to become blotch-shaped. Older larvae may fold the leaf over itself, or knit 2 leaves together, between which they continue to feed, causing large blotches. In severe infestations, all leaves on a plant are attacked giving the crop a burnt appearance. More direct damage is caused to the crop when the older larvae may penetrate nearby fruits by burrowing under the calyx into the fruit. Very small pinholes are left at the points of entry, which are often marked by the presence of a small amount frass or droppings. Points of entry under the calyx are inconspicuous and can easily be overlooked during packing. Larvae may also bore into the sides of tomato fruits in heavily-infested crops.

 

Stages of its life

 

Eggs

Eggs are laid scattered, or in small groups of 3-7, mainly on the upper leaves, and on both upper and lower leaf surfaces. The egg is oval in shape and very tiny (approximately 0.4 mm long). Its colour is pearly white at first, and then becomes pale yellow before hatching. The egg stage lasts from four to eight days at 22-240C.

 

Larva

The larva molts 4 times. The newly-hatched larva is tiny (about 0.7 mm long), with a black or dark brown head capsule, and a cream-colour body. The fully-grown larva is 6-8 mm long, and has brownish to purplish markings along the body. Tomato pinworm larvae are characteristically very active and wriggle when touched. The larval stage lasts 10 days at 24-260C.

 

Pupa

Pupation takes place within a loosely-spun cocoon in several possible locations including under debris on the ground, just under the soil surface, within the folds of leaves, on strings supporting tomato plants, or, rarely, in the fruits. The pupa is spindle-shaped; greenish at first, but soon changes to a dark chestnut brown colour. The pupal stage lasts 8-20 days depending on temperature.

 

Adult

The adult resembles a clothes moth in size and colour. It is greyish-brown in colour and is 6-8 mm long. Adults live for about 7-9 days at 24-260C, and for about 23 days at 130C.

 

How to control tomato pinworms?

The first step toward tomato pinworm control is cultural. End of season clean-up is essential for the prevention of future contamination. Garden debris should be cleared and burned and the soil should be turned under to deeply bury any overwintering pupae of the tomato eating worms.

For the following planting season, carefully inspect all hothouse grown seedlings before transplanting them into the bed to avoid transfer of the eggs. Continue to survey the foliage after transplant for the mines and folded leaf shelters that indicate and infestation. Conduct weekly inspections until signs of the worms on tomato plant’s leaves are discovered. If you find two or three worms on tomato plants in each row, it’s time to apply treatment. Pheromone traps have been used effectively in larger field plantings, but are impractical for smaller homestead gardens.

Once evidence of the worms in tomatoes is discovered, chemical treatment is called for. Broad spectrum insecticides can be used successfully to kill the tiny worms on tomatoes but must be applied at regular intervals throughout the season. If crops continue to show signs of damage, the narrow spectrum insecticide abamectin can be used, but this is rarely necessary in the home garden.

For the organic gardener, garden cleanliness is a must. Remove brown and curled leaves daily and pick any visible worms by hand.

And lastly, for those wondering is it harmful to ingest a pinworm from a tomato, the answer is a resounding no! Tomato pinworms are infectious only to Solenaceous plants and NOT to humans. While it might give you the willies to see half of one after you have bitten into a tomato, tomato pin worms are not poisonous to people.

 

Control strategies

 

Use of a combination of techniques is the best approach for managing TPW. Such techniques are as follows:

1. Monitoring is key to detecting initial populations and preventing any build-up. This is most efficiently done by weekly inspection of pheromone traps that are placed in the greenhouse throughout the season to detect male adults. Place traps at the same height as the tops of the plants. Note that the pheromone lures placed in the traps must be replaced regularly according to the manufacturer's instructions.
2. Sanitation - Thorough clean up of an infested crop is essential to preventing, or at least minimizing, carryover of populations to the next crop. Ensure that all crop debris is properly destroyed by burning or burying deeply. Adults cannot emerge normally if the pupal stages are buried at least 7-9 cm in the soil.
3. Physical Hand Removal - By regularly inspecting the crop from the very start, and hand removing and destroying infested leaves, a build-up in a population could be prevented or at least minimized.
4. Disinfest Crates - Ensure crates or boxes are properly disinfested before moving them from one operation to another. Adults, infested leaves, or fruits resting in crates can serve as a source of infestation.
5. Biological Control - Studies at the Greenhouse and Processing Crops Research Centre in Harrow, Ontario, indicate that some Trichogramma species hold promise as a biological control agent for TPW, but should be integrated with other control options.
6. Mating Disruption - Slow release of the TPW sex pheromone into the atmosphere serves to confuse male TPW in their search for female TPW. This confusion results in the disruption of mating. When TPW populations in a greenhouse are low, and when there are no neighbouring sources of infestation, use of mating disruption is effective in suppressing populations of TPW.
7. Light traps - Tomato pinworm adults are attracted to lights and commercially-available light-traps can assist in reducing adult populations.