Exploring the prevalence of Tetranychus urticae and T. turkestani in Turkish cotton fields and their endosymbiotic bacteria relationships
Beneath the scorching Turkish sun, in the sprawling cotton fields of Aydın province, a silent war rages on the undersides of leaves. The combatants are tiny—smaller than a pinhead—but their impact is enormous. Spider mites, nearly invisible to the naked eye, puncture plant cells and suck out the life-giving contents, leaving behind telltale yellow spots that eventually turn fiery red as leaves desiccate and die. For cotton farmers, these red spots signal declining yields and economic losses.
Recent research has revealed an invisible dimension to this conflict: symbiotic bacteria that live inside the mites, potentially enhancing their ability to survive chemical attacks.
Understanding these relationships has become crucial for Turkish agriculture, as cotton remains a vital fiber crop and cornerstone of the nation's economy, contributing substantially to export revenues and supporting local communities 1 .
Nearly invisible pests causing significant agricultural damage
A vital crop for Turkey's economy and agricultural sector
Uncovering complex relationships between pests and their bacterial allies
Spider mites represent one of the most destructive pest groups afflicting cotton worldwide. These minute arachnids (not insects!) thrive in hot, dry conditions, making sun-drenched cotton fields an ideal environment. They typically colonize the undersides of leaves, forming dense colonies protected by fine silken webbing 1 .
The feeding damage begins subtly with scattered yellow spots on leaves where mites have pierced individual plant cells. As feeding continues, the yellow spots multiply and coalesce, eventually turning reddish due to the destruction of chlorophyll. Severe infestations lead to premature leaf desiccation and abscission, and can even cause shedding of bolls and flowers, directly impacting cotton yield and quality 1 .
| Mite Species | Percentage | Color Form |
|---|---|---|
| Tetranychus urticae | 57.1% | Red form |
| Tetranychus turkestani | 39.3% | - |
| Tetranychus urticae | 3.6% | Green form |
Data source: 1
Identifying spider mites requires painstaking work under magnification. Researchers collect approximately 20 leaves from each field, storing them carefully for transport to the laboratory. The identification process involves both morphological and molecular approaches 1 .
For morphological analysis, adult female and male mites are mounted on microscope slides using Hoyer's medium, a specialized clearing solution that makes their tiny anatomical features visible. Scientists examine key characteristics such as body shape, the structure of genital organs, and patterns of body setae (hairs) under high-powered microscopes 1 .
To confirm morphological identifications, scientists turn to genetic analysis. DNA is extracted from individual mites using the SDS sodium acetate method. Researchers then employ a multiplex PCR technique that amplifies specific regions of the ITS gene in the mite's DNA, producing different fragment sizes for T. urticae (739 bp) and T. turkestani (950 bp) 1 .
This molecular confirmation is crucial because some mite species are virtually indistinguishable based on morphology alone but may differ significantly in their biology and resistance to control measures 1 .
One of the most fascinating aspects of recent spider mite research has been the investigation of endosymbiotic bacteria—microorganisms that live inside the mites' bodies and form mutually beneficial relationships. These bacteria can influence many aspects of their hosts' physiology, including reproduction, nutrition, and potentially, pesticide resistance 1 .
Four bacterial genera have received particular attention in spider mite research:
The potential role of endosymbionts in pesticide resistance represents a paradigm shift in how we think about pest control. Some bacteria within arthropod microbiomes can actually degrade pesticides, effectively providing their hosts with a built-in detoxification service. While this protective role is well-established in some insect systems, research into spider mite endosymbionts is still unfolding 1 .
The development of resistance to acaricides (chemicals designed specifically to kill mites) has become a critical issue in Turkish agriculture. Spider mites possess biological characteristics that make them particularly prone to developing resistance: very short life cycles, high reproductive rates, and arrhenotokous reproduction 2 .
In strawberry production areas, which face similar spider mite challenges, resistance monitoring has revealed alarming trends. Studies of T. urticae populations from Turkish strawberry fields found resistance ratios to pyridaben exceeding 450-fold in some populations, with most populations showing significant resistance 2 .
Resistance in spider mites develops through two primary mechanisms:
Recent research has uncovered striking differences in resistance patterns between the two dominant mite species in cotton fields. A 2024 study examined resistance ratios of T. urticae (red form) and T. turkestani to commonly used acaricides in Aydın province, with dramatic results 4 :
| Acaricide | T. urticae RF Resistance Ratio | T. turkestani Resistance Ratio | Resistance Status |
|---|---|---|---|
| Abamectin | 187.1-223.66 fold | Susceptible | T. urticae: Resistant T. turkestani: Susceptible |
| Hexythiazox | 156.31-168.25 fold | 164.34-182.39 fold | Both: Resistant |
| Etoxazole | 409.58-517.20 fold | Susceptible | T. urticae: Resistant T. turkestani: Susceptible |
| Spiromesifen | 981.77-1246.11 fold | Susceptible | T. urticae: Resistant T. turkestani: Susceptible |
Data source: 4
The Aydın studies found a relationship between detoxification enzymes and resistance in the mite populations. Esterase activity was highest in resistant populations of T. urticae, while glutathione-S-transferase (GST) activity was elevated in both resistant T. urticae and one T. turkestani population 4 .
With chemical control becoming increasingly unreliable, researchers have been exploring biological alternatives, particularly the use of predatory mites. These natural enemies can be highly effective against spider mites without the resistance development associated with chemical acaricides.
In Mersin province, studies on strawberry fields identified several predatory mite species that naturally keep spider mite populations in check. The most common beneficial species included Neoseiulus californicus and Phytoseiulus persimilis, along with Amblyseius swirskii, Amblyseius andersoni, and several others belonging to the Phytoseiidae family 3 .
Data source: 3
Recent research has revealed that the effectiveness of predatory mites can be influenced by the physical characteristics of cotton plants. A 2023 study investigated the performance of Phytoseiulus persimilis against T. urticae on six different cotton varieties with varying leaf hairiness (trichome density) 8 .
The researchers found that the predatory mites exhibited a Type II functional response on all cotton varieties, regardless of trichome density. However, prey consumption capacity on protonymphs was significantly higher on varieties with lower trichome density (Gloria and Lima) compared to varieties with higher trichome density (Edessa and ST-468) 8 .
This suggests that plant breeding programs could potentially develop cotton varieties that simultaneously discourage pest mites while encouraging their natural enemies—a win-win scenario for sustainable pest management 8 .
| Research Material | Primary Function | Application in Mite Research |
|---|---|---|
| Hoyer's medium | Microscopic mounting medium | Clearing and preserving mites for morphological identification |
| SDS sodium acetate method | DNA extraction | Isolating genetic material from individual mites for molecular analysis |
| Multiplex PCR primers | DNA amplification | Simultaneously detecting and differentiating mite species |
| Specific primers (UrtF, TurkF, TetCR) | Species identification | Amplifying species-specific DNA fragments in the ITS region |
| Enzyme assay reagents | Metabolic activity measurement | Quantifying detoxification enzyme levels (esterases, GSTs, P450s) |
| Acaricide formulations | Bioassays | Determining resistance levels in field populations |
Researchers collected samples from the major cotton-producing districts of Germencik, Kocarli, Nazilli, and Soke during June, July, and August of 2020-2021. They examined approximately 220 fields ranging from 2 to 50 hectares, collecting about 20 mite-infested leaves from each field 1 .
The collected mites were carefully mounted on microscope slides and identified using taxonomic keys. In total, 2,512 slides were prepared and examined under light microscopy to determine species composition 1 .
DNA was extracted from representative mites using the SDS sodium acetate method. A multiplex PCR approach was employed to amplify the ITS region of the mites' DNA, producing species-specific fragment sizes that confirmed the morphological identifications 1 .
The researchers screened the mite populations for four endosymbiotic bacteria (Wolbachia, Rickettsia, Cardinium, and Spiroplasma) using molecular methods to detect the presence of bacterial DNA 1 .
Additional bioassays were conducted to determine resistance levels to various acaricides, and enzyme assays were performed to measure activity levels of detoxification enzymes 4 .
The intricate relationships between spider mites, their endosymbiotic bacteria, and the cotton plants they infest represent a microcosm of the complex ecological challenges facing modern agriculture. The research in Aydın province has revealed that the most abundant mite species, T. urticae red form, possesses dramatically higher resistance to multiple acaricides compared to T. turkestani—a finding with immediate implications for cotton farmers 4 .
As research continues to unravel the complex interactions between mites, their microbial partners, and the cotton ecosystem, one thing becomes increasingly clear: solutions to agricultural challenges often lie in understanding not just the visible players, but the invisible ones as well.