Why do thrips quickly develop resistance to pesticides? Causes and solutions

Adult thrips are very small (only about 1 mm) with thin, fringed wings, making them difficult to detect with the naked eye. Thrips (scientific name: Thrips) are one of the most damaging insect species most difficult to control today due to their rapid development of pesticide resistance. So what helps these tiny insects adapt and resist pesticides so quickly?

Youtube Video: Why Thrips Develop Pesticide Resistance So Quickly

Short life cycle, rapid reproduction leads to pesticide resistance

Thrips have a very short life cycle, only 10–20 days depending on temperature and humidity conditions. This means they grow through many generations in a short period, allowing the population to quickly evolve and adapt to pesticides. Each female thrips can lay hundreds of eggs (approximately 200–300 eggs throughout its life cycle) and the eggs are laid embedded in leaf tissue or flower buds. Thanks to such rapid reproduction, thrips populations can explode in just a few weeks. In a large population, the probability of individuals carrying pesticide resistance genes is very high. Lucky individuals possessing resistance genes will survive after pesticide application and continue to reproduce, passing on the resistance trait to the next generation. This is the process of natural selection occurring under the pressure of chemical pesticides: only resistant individuals that survive will increasingly dominate the population.

Hiding behavior helps thrips

Thrips have many biological behaviors that help them avoid the effects of pesticides. First, their eggs are laid deep inside plant tissue (leaf veins, flower buds) making it very difficult for sprays to reach and destroy the eggs. Next, thrips larvae often hide in secluded places such as closed flower buds, young leaves, and shoot crevices – places with high humidity and low light, minimizing pesticide exposure. Towards the end of their life cycle, thrips fall to the ground to pupate or hide under leaves close to the ground. Therefore, spray applications only on the canopy surface are almost ineffective against individuals in the pupal stage underground. Additionally, both adult and larval thrips are very small (only about 1mm), making it even more difficult to observe and spray their entire bodies. These characteristics help a large portion of the thrips population each time pesticides are applied, reducing the effectiveness of pest control.

Biochemical and genetic mechanisms create resistance

Pesticide resistance in thrips not only comes from their life cycle or behavior, but also from biochemical and genetic mechanisms within their bodies. Many studies have noted that some thrips individuals can produce detoxification enzymes (detoxification enzymes) in high quantities, which help break down or neutralize the active ingredient before the pesticide can affect their nervous system. The most common enzymes associated with resistance include the family of cytochrome P450 (monooxygenase) and esterase, which can metabolize pesticides into less toxic forms. In parallel, thrips can also develop point mutations on the receptors or ion channels themselves – which are the targets of pesticides. For example, mutations in the sodium ion channel (related to the mechanism of knockdown resistance to pyrethroid pesticides) or alterations in acetylcholinesterase (the target site of organophosphate and carbamate pesticides) will make the pesticide no longer effectively bind to the insect’s nervous system. Thus, thrips can simultaneously possess multiple resistance mechanisms making their chemical eradication even more complex.

Pesticide Misuse Promotes Resistance

Besides the “innate” characteristics of thrips, humans also contribute to accelerating their resistance development. The act of improper pesticide application creates significant selective pressure, helping thrips accumulate resistance. Common mistakes include:

• Repeated spraying of a single active ingredient: Continuously using one type of pesticide will allow thrips to gradually adapt to that active ingredient. 
• Not rotating pesticide groups (IRAC groups): If the mode of action is not changed, insect populations can easily develop widespread resistance to the currently used pesticide group. 
• Mixing lower than recommended doses or insufficient spraying: Reducing the dose or stopping spraying prematurely when pests temporarily subside will allow some thrips individuals to survive. These individuals are often highly resistant, and they will continue to reproduce, increasing the proportion of resistant thrips in the population. 
• Overuse of broad-spectrum pesticides: Indiscriminate use of broad-spectrum pesticides can also kill natural enemies of thrips. As a result, thrips lose their natural control agents in the ecosystem, and their populations will rebound more strongly after spraying. 

The above practices allow resistant thrips individuals to have a higher chance of survival compared to normal individuals, gradually accumulating into resistant populations. In the long run, the effectiveness of many pesticides against thrips will decrease, causing severe damage to growers.

Solutions to Limit Thrips Resistance

To combat resistant thrips, farmers and agricultural engineers should implement an Integrated Pest Management (IPM) strategy, combining multiple measures synchronously. First, it is necessary to rotate pesticides with different active ingredients and modes of action in thrips control. Avoid repeatedly spraying a single pesticide; instead, rotate pesticides belonging to different IRAC groups to reduce the risk of thrips accumulating resistance to any active ingredient. Always adhere to the recommended dosage and spraying schedule by the manufacturer; do not arbitrarily reduce the dose or stop spraying prematurely before the infestation is completely controlled. In addition to chemical measures, it is advisable to strengthen biological and cultural practices: protect and enhance natural enemies of thrips (ladybugs, predatory mites, parasitic wasps, etc.), use sticky traps to monitor and capture adult thrips, and sanitize fields after harvest to remove crop residues containing eggs and larvae. Maintaining appropriate humidity in the garden (sprinkling water when possible) is also a way to reduce thrips development in hot, dry weather conditions. Flexibly combining multiple methods helps reduce the frequency of chemical pesticide use, thereby limiting selective pressure for resistance in thrips populations.

Conclusion

Thrips are indeed a pest that is “small but mighty” for many types of vegetable crops and ornamental plants. Their pesticide resistance comes from a short life cycle, rapid reproduction, meticulous hiding habits, and complex biochemical and genetic mechanisms. However, if growers understand the causes of thrips resistance and apply appropriate control measures, we can completely control this pest. By using pesticides correctly combined with cultural and biological methods, farmers, agricultural engineers, and vegetable/flower growers can protect their crops from thrips in an effective and sustainable way..