Frankliniella is a genus of tiny insects, commonly known as thrips. These minute organisms are widespread global plant pests. The genus was first identified in 1910 and encompasses approximately 230 species. Many species are polyphagous, meaning they feed on a wide variety of plants, making them concerns in both agricultural and horticultural settings.
Identifying Frankliniella
Frankliniella species are small, slender insects, typically ranging from 1 to 2 millimeters in length, though males are usually smaller than females. Their bodies can vary in color, appearing yellow, brown, or nearly black, with color often influenced by temperature and geographic location. Adult Frankliniella have two pairs of narrow, fringed wings, which assist in their movement.
A common species is the Western Flower Thrips, Frankliniella occidentalis. This species typically has an elongated body, with adult females often being mainly yellow with a brown patch on each abdominal segment, while males are consistently pale yellow. Their antennae have eight segments, with segments three and four possessing forked sense cones. These insects are frequently found in flowers and within leaf axils, where they feed and lay eggs.
Damage to Plants
Frankliniella species inflict damage on plants by rasping the plant surface and sucking out sap from ruptured cells. This feeding causes symptoms such as silvery or bronzed streaks and patches on leaves and petals. Damaged tissue can turn brown and die, reducing the plant’s vigor and overall health. Small black specks of thrips excrement often accompany these feeding marks.
Feeding on young tissues like growing tips and flower buds often leads to distorted growth, including deformed leaves, curled shoots, and misshapen or aborted flowers. This cosmetic and structural damage can reduce the marketability and yield of crops. Beyond direct feeding damage, Frankliniella species are known for their ability to transmit plant viruses, particularly tospoviruses like Tomato Spotted Wilt Virus (TSWV) and Impatiens Necrotic Spot Virus (INSV). Nymphs acquire the virus by feeding on infected plants for at least 30 minutes, and once infected, they can transmit the virus as adults for their entire lifespan, even with brief feeding periods of 15 minutes. Virus transmissions can result in widespread symptoms such as leaf necrosis, ring spots, stunting, and even plant death, posing an economic threat to various crops worldwide.
Control Strategies
Managing Frankliniella infestations involves a combination of strategies, often guided by integrated pest management (IPM) principles. Cultural practices are a primary element, beginning with thorough inspection of new plant material, such as cuttings or seedlings, for signs of thrips or damage before introduction to the main growing area. Quarantining new plants for a few days and monitoring them closely can prevent the spread of pests. Proper sanitation, including removing alternate host plants and weeds, helps disrupt their life cycle and reduce populations.
Physical and mechanical controls also manage Frankliniella. Sticky traps, particularly blue or yellow ones, are used for monitoring thrips populations and can help in mass trapping to reduce adult numbers. The addition of species-specific aggregation pheromones or kairomone lures to traps can increase their effectiveness. Overhead irrigation or misting plants in the morning can create an unfavorable environment, discouraging thrips activity.
Biological control methods utilize natural enemies to suppress thrips.
- Predatory mites, such as Amblyseius swirskii, Neoseiulus cucumeris, Amblydromalus limonicus, and Iphiseius degenerans, are commercially available and feed on thrips larvae.
- Predatory bugs like Orius insidiosus are effective against both nymph and adult thrips.
- Entomopathogenic fungi, such as Beauveria bassiana and Metarhizium anisopliae, can infect and kill thrips.
- Parasitic nematodes like Steinernema feltiae target thrips in the soil during their pupal stages.
Chemical control, while sometimes necessary, presents challenges due to Frankliniella’s tendency to hide in cryptic plant parts and rapid development of insecticide resistance. Resistance has been reported to several classes of insecticides, including:
- Carbamates
- Organophosphates
- Pyrethroids
- Neonicotinoids
This resistance is often due to enhanced metabolic detoxification by enzymes like cytochrome P450 monooxygenases. When chemical control is used, it is important to rotate insecticides with different modes of action to delay resistance development and to follow label recommendations for application. Combining these approaches within an IPM framework offers sustainable and effective long-term management of Frankliniella infestations.