Thrips
Thrips Facts
Common names: Thrips, Thunderflies
Scientific names: Thysanoptera
Thrips suck the sap from many plants.
Thrips are active all year round in greenhouses and are most active April to September.
Symptoms include:
- Mottled leaves
- Silvery white discolouration on upper leaves
- Distorted growth
- Onion Thrips can transmit diseases
Non-Chemical Treatments include:
- Sticky strips
- Attracting predators to the site
- Nematodes
Due to the thrips ability to transmit viruses, it is important to monitor your crops for thrips and detect them as early as possible. The classic method for doing this is by using adhesive traps. These traps are blue in colour, because thrips are strongly attracted to blue. The traps should be examined every few days using a magnifying glass to see if any thrips (usually winged adults) have become stuck to them.
About Thrips
Thrips Lifecycle
A typical Thrips will lay up to 100 eggs at a rate of one or two per day. These are often laid on the younger leaves or in flower buds of host plants. Eggs hatch into nymphs which; like the adult insects, feed by sucking sap. There are two feeding nymphal stages before they go into pre-pupal and pupal stages.
These non-feeding stages take place in the soil and/or in sheltered places on the host plant. The feeding nymphs are entirely wingless; wing buds are present on the pre-pupal and pupal stages, although wings are not fully formed until the adult thrips emerge.
The length of the lifecycle varies and is affected by temperature. Under ideal conditions the life cycle is completed in 24-35 days and thrips in glasshouses may continue breeding throughout the year. Thrips on garden plants usually have two or three generations a year but may have more during hot summers. Outdoor thrips overwinter as adults or nymphs, either in the soil or concealed on the host plant.
The adult thrip eats a varied diet based mainly on pollen, but the larvae feed on plant tissues and it is the larvae that are responsible for the majority of plant damage. The larvae suck the liquid from plant cells, mainly from the leaves, but also the petals, shoots and fruits. Early symptoms include an almost transparent or clear discolouration of the leaf with black dots (which are caused by faecal secretions). They have rasping, sucking mouth parts that look like combs and make a soup from the tissue which is then sucked up. Usually, the top layer of the tissue is undisturbed and a window of clear tissue is seen in the middle of the area of discolouration.
Certain toxic substances are present in the saliva of thrips, some deformations may occur in the shoots or flowers of affected plants. In cases of very severe infestation, the leaves may dry up entirely. At the same time, some thrips like Frankliniella occidentalis secrete a few drops of a substance when they are threatened by predators. These excretions contain decyl acetate and dodecyl acetate – pheromones that serve as a warning signal for other nearby thrips.
