Penuballi Swathi
Acaricide resistance in spider mites (Acari: Tetranychidae) Infesting major crops of Central Kerala - Vellanikkara Agricultural Entomology, College of Agriculture 2025 - xiii,158p
Ph.D
Spider mites (Acari) inhabit a wide array of environments and pose significant threat to a variety of commercially grown vegetable crops and ornamental plants. Chemical management measures using synthetic acaricides remains the primary means of mite management, globally. However, the repeated use of chemical pesticides has led to the development of resistance in mite populations, including resistance to acaricides with novel modes of action, resulting in control failures. TetranychustruncatusEhara and Tetranychusgloveri Banks are the predominant spider mite pests on vegetable crops and ornamental plants in Kerala. Mite management in vegetable fields and horticultural nurseries of Kerala primarily relies on synthetic acaricides like spiromesifen, fenazaquin and diafenthiuron. Increased instances of control failures, despite the application of recommended doses of these acaricides, have recently been reported by the farmers and nursery owners. Sole dependence on acaricides for a prolonged period might have resulted in the reduced susceptibility of mite populations to commonly used acaricides. Hence, a study was carried out to investigate the susceptibility of the field populations of T. truncatus and T. gloveri to commonly used acaricides, the possible development of cross /multiple resistance and to elucidate the underlying mechanisms of resistance. Purposive sampling surveys were conducted across commercial horticultural nurseries, vegetable fields and tissue culture (TC) hardening units in central Kerala (Thrissur, Ernakulam, Palakkad and Malappuram) to collect spider mite populations. Isoline cultures of eight T. truncatus populations collected on marigold (Mg1Tr) and vegetable crops (Cp1Pt, Cu1Pt, Ok1Pt, Am2Pt, Am3Vt, Cp2Tv and Am4Tv), and nine T. gloveri populations collected on adenium (Ad1Rg and Ad2Sd), gerbera (Gr1Pt), dahlia (Da1Vt), anthurium (An1Bv) and tissue culture banana (Bn3Tr, Bn2Kn, Bn1Gn and Bn4Ak) were maintained in the laboratory with unique accession numbers. The laboratory maintained populations of T. truncatus (SST) for more than 10 years (>300 generations) and T. gloveri (SSO) for more than six years (>180 generations), without exposure to acaricides were designated as susceptible reference populations. The laboratory bioassay of T. truncatus with fenazaquin showed moderate levels of resistance in the populations on amaranthus (Am2Tr- 39.70 folds) and marigold (Mg1Tr- 25.60 folds) populations from Thrissur, cucumber from Pattambi (Cu1Pt- 12.90 folds) and amaranthus from Vyttila (Am3Vt- 10.50 folds). The other populations collected on amaranthus from Tavanur (Am4Tv) and on okra (Ok1Pt), and cowpea (Cp1Pt) from Pattambi, recorded low levels of resistance (RR 3.70- 7.90 folds). Among the T. gloveri populations, adenium population from National Rose Garden, Thrissur (Ad1Rg- 57.20 folds) and TC banana population from Kannara (Bn2Kn- 41.04 folds) recorded high levels of resistance to fenazaquin, while the mite populations collected on TC banana plants from Vyttila (Bn1Gn- 15.72 folds) and Thrissur (Bn3Tr- 15.80 folds), and on dahlia from Vyttila (Da1Vt- 13.31 folds) recorded moderate level of resistance. Other T. gloveri populations collected on gerbera, anthurium and adenium showed only low levels of resistance. Tetranychustruncatus collected on marigold (81.90 folds) and amaranthus (79.75 folds) from Thrissur recorded very high levels of spiromesifen resistance. The amaranthus population from Vyttila (Am3Vt- 33.41 folds); cowpea (Cp1Pt-25.16 folds) and okra (Ok1Pt- 25.83 folds) populations from Pattambi, showed moderate levels of resistance, while populations on cowpea (RR 07.08) and amaranthus (RR 05.90) collected from Tavanur recorded low levels of resistance. Susceptibility studies of T. gloveri with spiromesifen showed that the population on adenium from National Rose Garden (76.33 folds) and on TC banana from Kannara (71.33 folds) exhibited high levels of resistance. Populations collected on TC banana from Vyttila (30.33 folds), Thrissur (28.17 folds) and Anakkayam (13.79 folds) recorded moderate levels of resistance. The populations collected on the ornamental plants viz., dahlia (24.33 folds), anthurium (19.08 folds) and adenium (17.25 folds) also recorded moderate levels of resistance to spiromesifen. Low to moderate levels of resistance to diafenthiuron were recorded in T. truncatus (1.94- 17.56 folds) and T. gloveri (1.95- 15.57 folds), where marigold population from Thrissur (17.56 folds) and adenium population from National Rose Garden (15.57 folds) recorded significantly higher levels of resistance, respectively. Tetranychustruncatus and T. gloveri populations with resistance to fenpyroximate showed moderate levels of cross-resistance to fenazaquin and the propargite resistant populations showed cross resistance to diafenthiuron. However, the field populations recorded only low levels of multiple resistance to chlorfenapyr and hexythiazox (acaricides with different modes of action) in T. truncatus (1.20- 5.40 folds; 1.00- 1.50 folds) and T. gloveri (1.10- 2.35 folds; 2.08- 12.00 folds). Assay of detoxification enzymes in T. truncatus and T. gloveri showed significantly elevated activities of carboxylesterase (CarE) (1.27-2.27fold; 1.59-2.10 folds), cytochrome P450 monooxygenase (CytP450) (1.36- 4.98 folds; 1.08-3.10 folds), and glutathione S-transferase (GST) (1.00- 2.12 folds; 1.09- 1.98 folds) in resistant populations. The highest activity of detoxifying enzyme was recorded in T. truncatus population on marigold for CytP450. The study on differential gene expression and sequence variation of the CYP392E10 gene (encodes CytP450 enzyme) in the spiromesifen and fenazaquin resistant marigold population of T. truncatus showed a lower CT value with 7.61 folds higher gene expression than the susceptible population. Sequence analysis of CYP392E10 gene in the resistant population showed four single nucleotide polymorphisms (SNPs), where T is substituted by A (256th, 676th and 1356th) and A is replaced with G (708th position). The alignment of amino acid sequences of the susceptible and resistant T. truncatus populations showed substitution of Lleucine with methionine at 86th position and phenylalanine with isoleucine and lysine at 226th and 452nd positions, respectively. This study reports alarming levels of acaricide resistance in the spider mites, T. truncatus and T. gloveri in central Kerala, to commonly used acaricides. The mite species were also found to have developed significant levels of cross resistance to many unexposed acaricides. However, significantly low level of multiple resistance to the acaricides, chlorfenapyr and hexythiazox suggests their suitability as alternatives to commonly used acaricides in mite management. The study highlights the role of detoxifying enzymes and the overexpression of the related gene, particularly CytP450 in the development of resistance against commonly used acaricides (fenazaquin, spiromesifen and diafenthiuron). The study also provides new insights into the resistance mechanisms in the mite species in response to sustained acaricide pressure, exhibiting metabolic and target-site insensitivity, which further needs functional validation.
Agricultural Entomology
Acaricide resistance, Acari: Tetranychidae
632.96 / PEN/AC Ph.D
Acaricide resistance in spider mites (Acari: Tetranychidae) Infesting major crops of Central Kerala - Vellanikkara Agricultural Entomology, College of Agriculture 2025 - xiii,158p
Ph.D
Spider mites (Acari) inhabit a wide array of environments and pose significant threat to a variety of commercially grown vegetable crops and ornamental plants. Chemical management measures using synthetic acaricides remains the primary means of mite management, globally. However, the repeated use of chemical pesticides has led to the development of resistance in mite populations, including resistance to acaricides with novel modes of action, resulting in control failures. TetranychustruncatusEhara and Tetranychusgloveri Banks are the predominant spider mite pests on vegetable crops and ornamental plants in Kerala. Mite management in vegetable fields and horticultural nurseries of Kerala primarily relies on synthetic acaricides like spiromesifen, fenazaquin and diafenthiuron. Increased instances of control failures, despite the application of recommended doses of these acaricides, have recently been reported by the farmers and nursery owners. Sole dependence on acaricides for a prolonged period might have resulted in the reduced susceptibility of mite populations to commonly used acaricides. Hence, a study was carried out to investigate the susceptibility of the field populations of T. truncatus and T. gloveri to commonly used acaricides, the possible development of cross /multiple resistance and to elucidate the underlying mechanisms of resistance. Purposive sampling surveys were conducted across commercial horticultural nurseries, vegetable fields and tissue culture (TC) hardening units in central Kerala (Thrissur, Ernakulam, Palakkad and Malappuram) to collect spider mite populations. Isoline cultures of eight T. truncatus populations collected on marigold (Mg1Tr) and vegetable crops (Cp1Pt, Cu1Pt, Ok1Pt, Am2Pt, Am3Vt, Cp2Tv and Am4Tv), and nine T. gloveri populations collected on adenium (Ad1Rg and Ad2Sd), gerbera (Gr1Pt), dahlia (Da1Vt), anthurium (An1Bv) and tissue culture banana (Bn3Tr, Bn2Kn, Bn1Gn and Bn4Ak) were maintained in the laboratory with unique accession numbers. The laboratory maintained populations of T. truncatus (SST) for more than 10 years (>300 generations) and T. gloveri (SSO) for more than six years (>180 generations), without exposure to acaricides were designated as susceptible reference populations. The laboratory bioassay of T. truncatus with fenazaquin showed moderate levels of resistance in the populations on amaranthus (Am2Tr- 39.70 folds) and marigold (Mg1Tr- 25.60 folds) populations from Thrissur, cucumber from Pattambi (Cu1Pt- 12.90 folds) and amaranthus from Vyttila (Am3Vt- 10.50 folds). The other populations collected on amaranthus from Tavanur (Am4Tv) and on okra (Ok1Pt), and cowpea (Cp1Pt) from Pattambi, recorded low levels of resistance (RR 3.70- 7.90 folds). Among the T. gloveri populations, adenium population from National Rose Garden, Thrissur (Ad1Rg- 57.20 folds) and TC banana population from Kannara (Bn2Kn- 41.04 folds) recorded high levels of resistance to fenazaquin, while the mite populations collected on TC banana plants from Vyttila (Bn1Gn- 15.72 folds) and Thrissur (Bn3Tr- 15.80 folds), and on dahlia from Vyttila (Da1Vt- 13.31 folds) recorded moderate level of resistance. Other T. gloveri populations collected on gerbera, anthurium and adenium showed only low levels of resistance. Tetranychustruncatus collected on marigold (81.90 folds) and amaranthus (79.75 folds) from Thrissur recorded very high levels of spiromesifen resistance. The amaranthus population from Vyttila (Am3Vt- 33.41 folds); cowpea (Cp1Pt-25.16 folds) and okra (Ok1Pt- 25.83 folds) populations from Pattambi, showed moderate levels of resistance, while populations on cowpea (RR 07.08) and amaranthus (RR 05.90) collected from Tavanur recorded low levels of resistance. Susceptibility studies of T. gloveri with spiromesifen showed that the population on adenium from National Rose Garden (76.33 folds) and on TC banana from Kannara (71.33 folds) exhibited high levels of resistance. Populations collected on TC banana from Vyttila (30.33 folds), Thrissur (28.17 folds) and Anakkayam (13.79 folds) recorded moderate levels of resistance. The populations collected on the ornamental plants viz., dahlia (24.33 folds), anthurium (19.08 folds) and adenium (17.25 folds) also recorded moderate levels of resistance to spiromesifen. Low to moderate levels of resistance to diafenthiuron were recorded in T. truncatus (1.94- 17.56 folds) and T. gloveri (1.95- 15.57 folds), where marigold population from Thrissur (17.56 folds) and adenium population from National Rose Garden (15.57 folds) recorded significantly higher levels of resistance, respectively. Tetranychustruncatus and T. gloveri populations with resistance to fenpyroximate showed moderate levels of cross-resistance to fenazaquin and the propargite resistant populations showed cross resistance to diafenthiuron. However, the field populations recorded only low levels of multiple resistance to chlorfenapyr and hexythiazox (acaricides with different modes of action) in T. truncatus (1.20- 5.40 folds; 1.00- 1.50 folds) and T. gloveri (1.10- 2.35 folds; 2.08- 12.00 folds). Assay of detoxification enzymes in T. truncatus and T. gloveri showed significantly elevated activities of carboxylesterase (CarE) (1.27-2.27fold; 1.59-2.10 folds), cytochrome P450 monooxygenase (CytP450) (1.36- 4.98 folds; 1.08-3.10 folds), and glutathione S-transferase (GST) (1.00- 2.12 folds; 1.09- 1.98 folds) in resistant populations. The highest activity of detoxifying enzyme was recorded in T. truncatus population on marigold for CytP450. The study on differential gene expression and sequence variation of the CYP392E10 gene (encodes CytP450 enzyme) in the spiromesifen and fenazaquin resistant marigold population of T. truncatus showed a lower CT value with 7.61 folds higher gene expression than the susceptible population. Sequence analysis of CYP392E10 gene in the resistant population showed four single nucleotide polymorphisms (SNPs), where T is substituted by A (256th, 676th and 1356th) and A is replaced with G (708th position). The alignment of amino acid sequences of the susceptible and resistant T. truncatus populations showed substitution of Lleucine with methionine at 86th position and phenylalanine with isoleucine and lysine at 226th and 452nd positions, respectively. This study reports alarming levels of acaricide resistance in the spider mites, T. truncatus and T. gloveri in central Kerala, to commonly used acaricides. The mite species were also found to have developed significant levels of cross resistance to many unexposed acaricides. However, significantly low level of multiple resistance to the acaricides, chlorfenapyr and hexythiazox suggests their suitability as alternatives to commonly used acaricides in mite management. The study highlights the role of detoxifying enzymes and the overexpression of the related gene, particularly CytP450 in the development of resistance against commonly used acaricides (fenazaquin, spiromesifen and diafenthiuron). The study also provides new insights into the resistance mechanisms in the mite species in response to sustained acaricide pressure, exhibiting metabolic and target-site insensitivity, which further needs functional validation.
Agricultural Entomology
Acaricide resistance, Acari: Tetranychidae
632.96 / PEN/AC Ph.D