Chilli Thrips
Thrips are small (approximately 1/15 inch long) slender insects that feed primarily on young tissue in the bud or on newly expanded leaves by sucking up sap after rasping surface cells with their mouthparts. Injured tissue dries out giving a whitish or silver-flecked appearance to wounded areas. Infestations of thrips often result in noticeable deposits of dark fecal material on infested leaf surfaces. Such deposits frequently aid in thrips detection. Concerning the control of thrips in the greenhouse, it is important to realize that thrips infesting flowers or weed hosts on the outside of the greenhouse may migrate into greenhouse ranges in vast numbers and cause rapid and serious damage. Frequently, by the time such damage is very evident, the thrips population is no longer present and control efforts are too late.
Chilli thrips can be found on over 150 plants including bananas, beans, chrysanthemum, citrus, corn, cotton, cocoa, eggplant, ficus, grape, grasses, holly, jasmine, kiwi, litchi, longan, mango, onion, peach, peanut, pepper, rose, soybean, strawberry, tea, tobacco, tomato, viburnum, etc.
Lift History of Pest Thrips
- 30 to 40 days for a complete generation
- 6, 5, and 5 days for development of egg, larva, and pupa
- Pollen doubles or triples fecundity
- Strong aggregation tendencies for flowers of Thrips and Frankliniella species
- Scirtothrips aggregate on young foliage and flowers
Reproduction in Thrips
- In most Thysanoptera, reproduction requires copulation
- Parthenogenesis common
- In most species, fertilized eggs have the full diploid number and become female; unfertilized eggs are haploid and become males
A chilli thrip.
Management of Chilli Thrips
Chilli thrips (Scirtothrips dorsalis) is an invasive species causing severe economic damage in floriculture and nursery crops and landscape plants. This new invasive species has resulted in a significant challenge to ornamental production systems and threatens established IPM programs for traditional pests.
Chilli thrips is mainly a foliage feeder and unlike western flower thrips does not feed on flower pollen. Young leaves, buds and fruits are preferred, but all above ground parts of its host plants may be attacked. Feeding damage turns tender leaves, buds, and fruits bronze in color. Damaged leaves curl upward and appear distorted. Infested plants become stunted or dwarfed, and leaves with petioles detach from the stem, causing defoliation in some plants. Feeding on buds may cause them to become brittle and drop. Chilli thrips have been reported to potentially vector a number of important plant viruses. These include peanut necrosis virus (PBNV), peanut chlorotic fan virus (PCFV), and tobacco streak virus (TSV).
Management Recommendations
- Scouting: Regular scouting is essential to detect thrips incidence and avoid economic damage. Thrips presence on the plant and in the production system (greenhouse/nursery) can be detected by tapping suspected plant material (flower or foliage) over a white sheet of paper, or by randomly placing blue/yellow sticky trap cards near plants. Thrips count on the sticky trap can be an indicator of the direction of the thrips movement/incidence as well as the efficacy of the control measures applied. Growers should apply insecticides when scouting reports identify that population density approaches levels where experience indicates action should be taken. Extension personnel can also provide advice and help determine when the grower should apply insecticide. Density levels requiring treatment (or treatment thresholds) vary based on factors including the crop, source(s) of infestation, history of viral infection, and environmental conditions.
- Sanitation: Remove weeds, old plant debris, and growing medium from within and around the greenhouse or nursery. Eliminate old stock plants, which can harbor thrips and viruses. Removing old flowers may reduce the number of western flower thrips adults and eggs. Place flowers into a sealed bag or container and dispose in a safe place immediately. Because pests are often dispersed via transport of infested materials, be careful not to carry infested plant material or debris unsealed in an open truck/vehicle.
- Exclusion: Screen greenhouse openings such as vents and sidewalls with the appropriate screen size (<0.88 mm) to exclude adult thrips from entering the greenhouse. Airflow may be obstructed with the use of screening containing small pore sizes, so the screened surface area must be increased to compensate. Check with your local Extension specialist about proper screen sizing.
- Biological Control: Several biological control agents (BCA) are available for managing thrips, including predators (i.e. Neoseiulus or Amblyseius spp., Orius spp. and Hypoaspis mites), nematodes (Steinernema feltiae), and entomopathogenic fungi (i.e. Beauveria bassiana, Isaria fumosorosea). The key for effective biological control against thrips is to release BCA early in the infestation, before they enter terminal or flower buds. BCAs will not control an existing high population of thrips before significant crop damage occurs. Some of the generalist BCA, such as Amblyseius swirskii mite, can survive and reproduce well solely by feeding on plant pollen in the absence of pest population. The prophylactic release of such predators can ensure a well-established population of predators on the plant and in the greenhouse, which may give efficient control of the arriving thrips population. Consult with your local Extension specialist about the suitable biocontrol agents available for a specific crop and pest species.
- Chemical Control: Chemicals provide a limited level of thrips control. It is important to initiate application before thrips populations increase to threshold levels. Reapply as needed based on label requirements. Use the shortest labeled interval when pest pressure is high and temperatures are warm. Insecticides’ mode of action should be rotated with each treatment or at most with each generation of thrips, unless the label indicates otherwise. The effectiveness of insecticides in managing thrips can be limited due to the insects’ evasion of treated surfaces/tissues. Thrips can evade impact of insecticides in many ways, including 1) taking refuge in weeds around the main crops, 2) laying eggs inside the host tissue (leaf, flowers, fruits), which allows next generation to survive chemical application after emergence, and 3) hiding in concealed places under the leaves, or in flowers where foliar and/or drench applications do not reach (Frank 2014). However, the most important of all is the reduced susceptibility to certain insecticides, which is a major concern for commercial growers. Frequent use of the same chemistry can bring insect pests under intense selection pressure to develop resistance against that particular insecticide. Since resistance development in arthropods is an evolutionary process and cannot be ceased, it is vital to follow recommended practices in delaying selection for insecticide resistance. In order to avoid resistance and keep thrips population under check, pest management professionals should emphasize “smart” use of insecticides, rather than weekly calendar applications during growing seasons. “Smart” use may include, but is not limited to, scouting and applying soft insecticides or biologicals as prophylactic measures early in the season. If insecticide use is necessary, three consecutive applications of insecticides should be done at the interval of 5–7 days to break the thrips generation (Frank 2014). Check the label carefully for the repeated application of an insecticide.