Description
Tetranychus truncatus Ehara, 1956. J. Faculty Sci. Hokkaido Univ. Ser. VI, Zool., 12: 507.
Materials examined (not types) India
5♂ ♂ , TNAU-Coimbatore, Tn-GN-007-011, 09.ix.2023 and 6♀♀, TNAU- Coimbatore, Tn-GN-001-006, 09.ix.2023 on
Arachis hypogaea. The specimens are retained in the Acarology laboratory, Department of Agricultural Entomology, Tamil Nadu Agricultural University Coimbatore, TN, India.
Diagnosis
Female
Body, idiosoma length excluding gnathosoma (v2-f2) 332-370 µm, width (sc2-sc2) 204-289 µm (Plate 2a and 2b). The mites were red in colour (Plate 1).
Dorsum
Idiosomal setae longer than the interval between their longitudinal bases and gradually tapers distally (Plate 3a). Dorsal striae between setae
e1-e1 mixed longitudinal and oblique; dorsal striae between setae
f1-f1 longitudinal; dorsal striae between setae
e1 and
f1 transverse, forming a diamond-shape medially (Plate 3b); ventral striae without lobes; pregenital striae entire, unbroken (Plate 3c). Peritreme hook 27-28 μm long with slightly expanded bulbous tip forming a distinct ‘U’ shaped (Plate 2e). Dorsal setae of prodorsum barbed. Opisthosomal setae long, pubescent (except setae
h2, h3 thin, smooth. Empodia with 6 proximoventral hairs, empodia I-IV each with a spur (>2 μm long) (Plate 6a); tarsus I with sockets of 4 tactile setae proximal to proximal pair of duplex setae; D
duplex 24-26 (Plate 2d); tarsus III with 1 proximal tactile seta.
Gnathosoma (Palp)
Terminal sensillum or spinneret (eupathidion
su ζ), equal in length and breadth with a pit at tip (Plate 4b) and slightly shorter (5 μm) than both eupathidia
ul'
ζ and
ul"
ζ (6 to 9 μm) (Plate 4c); dorsal sensillum (solenidion w), slightly taller (6.1 μm) than, terminal sensillum and tapering distally (Plate 4a). Trochanter is glabrous, palpal chaetotaxy is from trochanter to tibia, 0-1 (
dPFe)-1 (
l"
PGe)-3 (
dPTi, l'
PTi, l"
PTi). The dorsal seta (
dPFe), on the femur is long and thin.
Legs
Setal counts:
cx 2,2,1,1;
tr 1,1,1,1;
fe 10,6,4,4;
ge 5,5,4,4;
ti 10,7,6,7;
ta 18,16,10,10. Tarsus I with two sets of duplex setae (solenidion on proximal 55-63, solenidion on distal 85-93), 1 solenidion, 3 eupathidia and 10 tactile setae; with 4 tactile setae proximal and 1 solenidion adjacent, to proximal duplex setae (Plate 2d).
Male (n=5)
Body, idiosoma length excluding gnathosoma (v2-f2) 197-210 µm, width (sc2-sc2) 145-156 µm (Plate 2c). Colour in life red.
Dorsum
Peritreme with hook (length of hook 26-28) and slightly enlarged bulbous tip. Striae on prodorsum finely spaced. Dorsal setae of prodorsum barbed and slender. Opisthosomal setae long and pubescent (except setae
h2, h3 thin, smooth).
Venter
Setae thin, mostly smooth (generally anterior setae smooth, posterior setae barbed).
Gnathosoma (Palp)
Eupathidia (
ul'
ζ,
ul"
ζ) approximately equal in size (Plate 5c and 5d), solenidion w slightly shorter (Plate 5b). Terminal sensillum or spinneret (eupathidion
su z), twice as long as wide (4.1 in length and 2.7 in width) (Plate 5a). The trochanter is glabrous, palpal chaetotaxy is from trochanter to tibia, 0-1 (
dPFe)-1 (
l"
PGe)- 3 (
dPTi, l'
PTi, l"
PTi). The femoral seta
d is formed as a short, stout, partly sunken spine-like process exhibiting sexual dimorphism.
Legs
Setal counts:
cx 2,2,1,1;
tr 1,1,1,1;
fe 10,6,4,4;
ge 5,5,4,4;
ti 13,7,6,7;
ta 20,16,11,11. Tarsus I with two sets of duplex setae (proximal solenidion 47-51, distal solenidion 59-61), 3 solenidia, 3 eupathidia and 10 tactile setae; with 4 tactile setae and 3 solenidia proximal to proximal set of duplex setae; Empodia I-IV each with obvious dorsal spur 4 μm long; empodia I and II claw-like (uncinate) (Plate 6c and 6d), empodia III and IV each with proximoventral hairs long and free (Plate 6b).
Aedeagus
Aedeagus with terminal knob, anterior and posterior projection short and pointed; flat to slightly convex dorsal surface and a medial indentation (Plate 6e).
Remarks
The infestation was high during the summer months. Symptom of damage caused by
T. truncatus, is more similar to that of other
Tetranychus spp. and is hard to differentiate unless proper mounting of the specimens and careful examination of the morphological characters done particularly that of male aedeagus. Reports of
T. truncatus from North-western Himalayan regions of Jammu and Kashmir and Himachal Pradesh by
Rather (1983) claims to be the first report of this species in India. Despite
Gupta and Gupta (1994) stating it could be
T. urticae, which was known to infest Dahlia. Nearly two decades later,
Srinivasa et al., (2012) reported
T. truncatus to infest
Morus sp. from Karnataka. In Kerala,
T. truncatus was reported by
Bennur et al., (2015) on vegetable crops; on cucumber and amaranthus grown in polyhouses by Lenin and Bhaskar, 2016; on cowpea, pumpkin, tapioca, banana and Dahlia by
Arunima (2017); on banana (Nendran) by
Bhaskar and Lenin, 2018. Recently
T. truncatus was recorded on marigold, cock’s comb and rose from different localities of Thrissur district, Kerala by
Prakash et al., (2022).
Hosts
Occurrence of
T. truncatus has been recorded from 104 host plant species, of which major reports have been on
Morus sp (
Migeon and Dorkeld, 2023). In India, reports of incidence and damage has been given by
Srinivasa et al., (2012) and
Prakash et al., (2022).
Distribution
Tetranychus truncatus has so far been reported from 14 countries including India
viz., Japan, China, Korea, Bangladesh, Indonesia, Phillipines, Taiwan, Thailand, Vietnam, Iran, Guam, Burkina Faso and Northern Mariana Is. In India, reports of its occurrence have been claimed from Karnataka and Kerala (
Migeon and Dorkeld, 2023).
Molecular characterization of Tetranychid mites
Molecular sequence analysis was performed to supplement the morphological description and taxonomic identity of tetranychid mites based on the sequence information obtained for the Internal Transcribed Spacer region 2 (ITS2). ITS2 gene, the most commonly used species-specific primer, was amplified, yielding an amplicon size of ~620 bp (Fig 1). The PCR products were purified and sequenced. The resulting sequences were searched against GenBank nucleotide database for deriving their annotation using nBLAST program. The results of BLAST analysis showed that
Tetranychus truncatus, had 99 per cent similarity with GENBANK sequences (Fig 2).