Have you ever heard of thunderbugs? How about storm flies or corn lice? You may be thinking of big insects that are rampant in most agricultural land. However, farmers would know that thunderbugs are small, pesky insects that can damage their crops and decrease its market value. Even greenhouse owners must be aware of thunderbugs which are properly called as thrips. These tiny, slender insects must be controlled especially if you have commercial plants in your area.
Thrips is a term used both in singular and plural just like the words species or sheep. Do not be fooled by the letter “s” at the end. Whether you are referring to one insect or a swarm of insects, you will still call them thrips.
Thrips are like really small cigar-shaped insects that may or may not have wings. They come in various colors such as yellow, brown or green. They are considered tiny as their average size is only 1mm in length. The female thrips appear to be larger than male thrips. Male thrips may also appear lighter in color. Adult thrips may or may not have wings but immature thrips are all wingless. Their wings are fringed and strap-like. Their order name, Thysanoptera, is based on their fringed wings. Thysano is a Greek word for “fringe” while ptera means “wing”. Thrips’ other distinguishing feature is their asymmetrical mouthparts wherein one mandible is longer than the other. They use their mouthparts to puncture the outer layer of plants to be able to extract saps. Other thrips would use their mouthparts to puncture animal skin to extract body fluids.
Female thrips lay their eggs in plants. The whole developmental cycle of thrips mainly depend on the environmental conditions, including temperature and food availability. The eggs are almost impossible to see as they are just about 0.2mm long and kidney-shaped. Eggs may hatch in just a day or as long as several weeks. Their egg-laying may occur within 1-4 days during summer and 10-35 days within winter. Warmer weather leads to faster reproduction. Thrips technically have two larval stages plus a prepupal and pupal stage before becoming adults. It will ideally take a month to be fully-developed. Thrips can develop into an adult in just 11 days during summer time. Their short life cycle would indicate several generations growing within a year.
Since not all thrips have wings, they mainly rely on wind currents to carry them around. They can be carried by the wind for several miles. They also have the tendency to spread slowly in a certain plan or garden due to their poor flying. Their heaviest migration would occur during May and early June, when buds would bloom into flowers.
There are many predators of thrips including ladybird beetles, spiders, wasps, and pirate bugs. There is also a known fungus called Entomopthora thripidum that infects thrips. The wet season is nature’s way of controlling thrips by washing them away from plants.
Types of Thrips
Since thrips are extremely small, it is quite difficult to identify the different species. Most differentiating characteristics are only visible under the microscope. It is still best to know the different types of thrips which can be found in your flora and fauna.
The Western flower thrips is one of the well-known pest insect in agriculture. They are native to Southwestern America but have reached Europe, Australia and South America due to infested plant transportation. They are known to feed on more than 500 species of plants including most fruit, vegetable and ornamental plants. Western flower thrips are mostly female as only female thrips arise from the fertilized eggs. Males are only produced if the eggs are unfertilized. This type of thrips are known to cause damage to crops all-year round although there can be a decline in their infestation during wet season.
Onion thrips are found in foliage rather than blossoms. They are around 0.8mm to 1.00mm long and yellow or black in color. Both Western flower thrips and Onion thrips are known to host on weeds, cereals and crops such as onion. Onion thrips can cause economic loss for farmers as they reduce yields up to 60%. Thrips mostly damage young onions during their growing season. Onion thrips are also known to attach cabbages.
Rose thrips may appear like onion thrips as their difference is only visible through a microscope. They are found occasionally in roses and cucumbers. These trips mainly damage the floral petals making it less attractive and dull in color.
Banana rust thrips cause rust-colored stains on the fingers of bananas. Their feeding would not affect the taste or texture of the fruit but will appear unmarketable due to the obvious discoloration. Banana rust thrips are also known to deposit their eggs within the skins of the banana and would later feed on the banana flower buds.
Thrips bites may not be as severe as flea or mosquito bites in humans. Thrips bites cause only minor irritation on humans as they mainly feed on plant sap rather than blood. There will be no visible bites when bitten by thrips. You can easily wash away with water any thrips infection.
Thrips are known to cause visible damage to plants which leads to a decrease in the marketability of some crops. Both nymph and adult thrips would suck saps in buds, flowers and leaf tissues. This would cause discoloration and leave speckled areas on the leaves. The specks would appear gray and silver which can be unappealing for green vegetables.
If thrips continue to feed on the crops, feeding will result to leaf distortion, wilting, and browning. For example, thrips feeding on cabbage will cause brownish-gray water-like growths on the the leaf surface. It may also show black fecal material with silver mottled lesions. Although the crops are still good for harvesting, their appearance makes them unacceptable for any fresh or produce market. This will cause less profit for farmers during harvest season. Onions that have been severely damaged by thrips would appear white or straw-coloured in appearance rather than the garden green color.
Another damage that can affect greenhouse owners is the browning of petals. Thrips would cause brown or silver spots on infected flowers, especially the light-colored ones. Buds may also refuse to open making them useless for flower shops.
Thrips are also known to carry various diseases. One of the known plant disease carried by thrips is the tospovirus. Tospovirus derived its name from the first member of the virus, the Tomato spotted wilt virus (TSWV). This disease was first observed back in 1915 in Australia. Infected crops will result to spotting and wilting therefore reducing the total yield of crops. There are currently no antiviral cures developed for Tospovirus. If spotted, the infected crops should be removed and destroyed to avoid spreading across the field. Both food crops and ornamental plants can be affected by Tospovirus. It can affect tomatoes, zucchinis, watermelons, peanuts, lilies, iris, pepper, tobacco, leeks, and chives.
Thrips control is crucial for any farm or greenhouse owner who relies on their harvest for income. Most fruit and vegetable buyers would base the market value on how crop appear. A spotted tomato or discolored flower will be useless in the market.
It may be difficult to spot, control and destroy thrips but here are some important thrips control practice that you can follow.
a. Start young. Do not wait until your crops are growing before checking for thrips. Check your young plants for any possible thrips infestation. Remember that thrips can be deposited into your area through transportation. Check your newly-purchased plants before placing them in your greenhouse. Purchase sticky card traps and place among your plants for a day or two. Traps should be placed along the outer edges of your field. Examine them at least one a week. Check on the underside of the leaf or within the leaves of a developing head.
b. Stay clean. Banana farmers would cover their growing fruits with plastic to avoid any thrips from entering and feeding on their crops. Similarly, any openings in greenhouses should be covered to reduce thrips infestation. There are microscreens designed to ward off thrips. Compared to the normal screens, a microscreen would have a maximum hole size of just 0.16mm which is smaller than the average thrips size. Microscreens should be partnered with the appropriate ventilatioon system as it can reduce air flow for your plants. Clean your garden litter also.
c. Eliminate the weed. As mentioned, thrips tend to slowly infest a garden. Make sure there are no weeds around your greenhouse. Weeds can serve as houses for thrips that would later be carried by the wind into your greenhouse.
d. Spray away. Insecticides can be effective for some plants but not all. Thrips found buried inside flower buds are not reached when spraying insecticides. Some thrips have also developed resistance against common insecticides. To ensure effectiveness, check the label for registered crops. It is recommended to have at least two different insecticide classes to reduce resistance from thrips. Make sure you do a test spray to ensure your plants won’t die with the thrips.
Using insecticides and screens may be expensive for regular farmers but it is nothing compared to the possible damage thrips may cause to the crops. Poor thrips control can lead to wasted time and produce. Make sure you are diligent in keeping those pesky, little insects away. Nobody wants spotted vegetables for dinner.