TY  - BOOK
AU  - Sreshma, M
AU  - Haseena Bhaskar (Guide)
TI  - Susceptibility of Tetranychus okinawanus Ehara (Prostigmata: Tetranychidae) infesting ornamental plants to novel acaricides 
U1  - 632.6 
PY  - 2021///
CY  - Vellanikkara 
PB  - Department of Agricultural Entomology, College of Agriculture
KW  - Agricultural Entomology
KW  - Tetranychus okinawanus Ehara
KW  - Prostigmata
KW  - Tetranychidae
N1  - M Sc
N2  - Spider mites of the family Tetranychidae are well-known agricultural and 
horticultural pests that feed on a wide variety of plants, including vegetables, fruit trees, 
and ornamentals. Many traditional insecticides and acaricides have been used to 
manage mite pests for several decades. The widespread usage of acaricides around the 
world has facilitated development of resistance in different mite species, making mite 
management challenging. As a result, many novel acaricides with distinct chemical 
structures and modes of action have been developed and marketed for mite control.
However, after a few years of use, mite populations developed resistance to these newly 
introduced compounds too.
The spider mite species, Tetranychus okinawanus, recently recorded on an 
ornamental plant Adenium in Thrissur district, for the first time in India, has now 
emerged as the predominant species of mite infesting ornamental plants in Kerala.
Recently, several growers reported inefficacy of the commonly used novel acaricides 
against mite pests in many ornamental crops, suggesting that the mite populations might 
have developed resistance to acaricides. Hence a study was carried out to investigate 
the status of acaricide resistance in Tetranychus okinawanus infesting Adenium in 
horticultural nurseries and also to elucidate the biochemical mechanism involved in 
development of resistance.
Purposive surveys were conducted in six commercial horticultural nurseries in 
Thrissur district viz., National Rose Garden, Mangadan Botanical Garden, Ayyappa 
Nursery, Saranamayyappa Nursery, Pooja Gardens and Nursery, and Manalur Adenium 
Garden and samples of spider mite infesting Adenium were collected. Mites were 
maintained as separate isoline cultures assigning unique accession numbers as NrAd1, 
MgAd2, AyAd3, SyAd4, PjAd5 and MnAd6. Morphological characterisation of the 
slide mounted mite specimens from the isoline cultures was carried out to confirm the 
species identity as T. okinawanus. Susceptibility of the six field populations to three 
acaricides viz., spiromesifen, fenazaquin and dicofol was evaluated in the laboratory, in 
comparison with the reference susceptible population maintained without exposure to 
any acaricides in the laboratory, following toxicological bioassay.
Susceptibility studies with fenazaquin revealed that the accession NrAd1 
recorded the highest LC50 value (27.85 ppm) and has developed moderate level of 
resistance (14.38-fold) to fenazaquin. This was followed by PjAd5 (9.70-fold), AyAd3 
(4.06-fold), MnAd6 (3.78-fold), and SyAd4 (3.23-fold). The lowest resistance ratio was 
recorded by the accession MgAd2 (1.66). The toxicity studies of spiromesifen also 
recorded low to moderate levels of resistance in different populations of T. okinawanus. 
The accession NrAd1 recorded highest resistance ratio of 27.31 followed by PjAd5
(7.18), MnAd6 (3.94), AyAd3 (1.78), MgAd2 (1.42) and SyAd4 (1.06). However, the 
mite populations showed only low level of resistance to dicofol, recording resistance 
ratios in the range of 3.65 to 1.22. 
Biochemical basis of acaricide resistance in different populations of T. 
okinawanus was investigated by estimating the activity of detoxifying enzymes such as 
carboxyl-esterase, cytochrome P450 and glutathione S- transferase. Carboxyl-esterase
enzyme showed an enhanced activity of 1.03 to 3.52-fold, while cytochrome P450
monooxygenases recorded 1.01 to 2.08-fold higher activity in the field collected 
populations, compared to the susceptible population. The level of these detoxifying 
enzymes was found to be higher in the accession NrAd1, which also recorded the 
highest resistance ratio in the study. However, the activity of glutathione S-transferase 
(GST) did not differ significantly among the field populations and also with susceptible 
population, indicating that GST is not a contributing factor in the development of 
resistance in T. okinawanus against spiromesifen, fenazaquin and dicofol.
The study recorded development of resistance in the spider mite, T. okinawanus
on Adenium to spiromesifen and fenazaquin, in the horticultural nurseries in Thrissur 
district, Kerala for the first time in the world. The significant role of the detoxifying 
enzymes, carboxyl-esterases and cytochrome P450 monooxygenases in imparting 
resistance in T. okinawanus to the two novel acaricides, fenazaquin and spiromesifen
was also confirmed in the study. The study demands formulation of a suitable resistance
management strategy in horticultural nurseries in the state for suppressing or delaying 
resistance development in mite populations
UR  -  https://krishikosh.egranth.ac.in/handle/1/5810198038
ER  -