Bionomics and Chemical Control of Ietranychus Ludeni Zacher Infesting cowpea under South Gujarat Condition
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Date
1999-03
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Entomology Department, N. M. College of Agriculture Gujarat Agricultural University, Navsari
Abstract
Investigations were carried out from May, 1997 to July, 1998 on
"Bionomics and chemical control of Tetranychus /wkni Zacher (Acari :
Tetranychidae) infesting c.owpea under South Gujarat condition" in field as well
as in laboratory, Deprubnent of Entomology, Gujarat Agricultural University,
Navsari. Studies on the biology of T. /udeni were carried out in laboratory at
room temperature (29.2 I °C average temperature and 79.00% average relative
humidity) during May to June, 1997. Both the sexes of T.ludeni passed through
five stages viz., egg, larva, protonymph, deutonymph and adult. Three active
feeding immature stages (larval and two nymphal) were each followed by a short
period of quiscence. Various stages of both the sexes, their shape, sizes, colour,
moulting, sexual behaviour etc. are descnbed in detail. The incubation period of
eggs (irrespective of sexes) varied from 2.33 to 4.00 days (2.99 ± 0.44 days) .
•
There was 93 to 97 per cent hatching of eggs. The average developmental periodsin days for larva, protonymph and deutonymph were 1.00 ± 0.35, 0.69 ± 0.30 and
0.86 ± 0.24 in case of male and 1.14 ± 0.29, 0.79 ± 0.31 and 0.97 ± 0.27 in case of
female. The combined larval-nymphal periods were on an average 5.07 ± 0.36
days and 5.82 ± 1.18 days for male and female, respectively. The mated females
laid on an average of 53.84 ± 3.96 eggs during their average ovipositional period
of 5.77 ± 0.56 days, whereas unmated females laid on an average 35.73 ± 3.83
during their average ovipositional period of 7.16 ± 0.95 days. The pre-
oviposition and post-oviposition periods were 0.81 ± 0.65 and 0.94 ± 0.35 days,
respectively for mated female and 1.57 ± 0.36 and 1.45 ± 0.34 days, respectively
for unmated female. The unmated male (4.40 ± 0.80 days) and unmated female
(9.24 ± 0.92 days) lived longer than mated male (2.02 ± 0.77 days) and mated
female (6.74 ± 0.84 days). Mated female produced male and female progeny in
ratio of I :4.59, whereas unmated female invariably gave rise to male progeny.
Under life-table studies of T.ludeni when reared on cowpea leaf
under laboratory condition, the net reproductive rate (Ro) was 34.41
female/female/generation in a precise generation time of 16.16 days. The innate
capacity for increase, finite rate of increase, weekly multiplication and
hypothetical F2 females were 0.2190 female/female/day, 1.66 female/female/day,
34.15 and 1184.05, respectively. On reaching the stable age-distribution, the
contribution of various stages viz., egg, larva, protonymph, deutonymph and adult
were to the tune of 69.82, 15.92, 7.78, 3.76 and 2.72 per cent, respectively.
As regard to impact of mating and age of female on oviposition, the
rate of oviposition following mating reached peak by 3rd day of adult life, while
in case of unmated female it reached peak by 4th day of adult life. The unmated
female produced fewer eggs (35.73 ± 3.83) than mated females (53.84 ± 3.96)
despite the fact that the unmated female lived longer (7.16 ± 0.95 days) than
mated female (5.77 ± 0.56 days). Study on the effect of webbing on ovipositionrevealed that individual female (r1udem) with web spun laid consistently higher
number of eggs than the individual with removal of web spun.
Two
phytophagous
Polyphagotarsonemus
latus
mites
viz.,
T.ludeni
(Tetranychidae),
Banks (Tarsonemidae) and predatory
mite,
Amblyseius (Euseius) als/oniae Gupta (Phytoseiidae) were recorded on cowpea in
the region. The incidence of red spider mite (T.ludem) commenced from 13th
standard week (STW) being peak during 20th STW (May), whereas tarsonemid
mite (P.la/us) appeared on the crop from 12th STW and attained peak during 18th
STW (April). As regard to distribution pattelll of mite on the plant, T.ludeni
preferred top canopy leaves followed by middle and lower canopy leaves. Similar
trend was observed in case of P.latus. Spider mite, T.ludeni prefelled lower
surface as compared to upper surface of the leaf. The incidence of predatory mite,
A.alstoniae commenced from 13th STW being peak during 20th STW (May). The
maximum density of spider mite, T.ludeni was recorded on late sown crop (23rd
March) followed by 16th and 9th March sown crop, while early sown crop (9th
February) had least incidence followed by 16th February sown crop. Further, peak
incidence of spider mite on different dates of sowing was concentrated at 20th and
21st STW (May). Unlike spider mite, the maximum density oftarsonemid mite,
th
P. latus was recorded on early sown crop (9 February) sown crop followed by
rd
16th February and 9th March sown crop. Whereas, late sown crop (23 March)
had least incidence followed by 16th March sown crop. The peak incidence for
different dates of sowing except 16th and 23rd March sown crop was
concentrated at a period corresponding to 17th to 19th STW (April-May). The
predatory mite was higher on those crops which also harboured higher population
of prey mite.
Interaction study between prey mite (T.ludeni and P.latus) and
predatory mite (A. (E.) alstoniae) showed significant positive correlation. Inregard to influence of abiotic factors, the population of T.ludeni showed
significant positive correlation with temperatures (maximum, minimum and
average) and sunshine hours. The build up of P.latus was positively correlated
with temperatures (maximum and average) and sunshine hours. The predatory
mite, A.alstoniae showed a significant positive correlation only with temperatures
(maximum, minimum and average). The joint contribution of all abiotic factors
(temperatures, relative humidities, sunshine hours and rainfall) on the build up of
T.ludeni, P.lotus and A.alstoniae were significant indicating 71.0, 68.0 and 74.0
per cent variation in population, respectively.
In field evaluation of chemical pesticide including botanical
(Neemark, Repelin and NSKE) and microbial (Bt.) pesticides, dicofol,
monocrotophos, endosulfan and methyl-o-demeton were highly effective in
reducing mite popUlation (67.64 to 79.09% reduction). However, the predatory
mite markedely diminished in the plots treated with monocrotophos, methyl-o-
demeton and dicofol (62.48 to 68.02% reduction) and to a lower degree in case of
endosulfan (30.61% reduction). Spark was most toxic to predatory mite but was
found less effective against prey mite. NSKE was least toxic to predatory mite but
was least effective against prey mite. Mite predator also diminished in the plot
treated with plant product (Neemark and Repe1in), endosulfan and microbial
pesticide (Bt.), but to a lower extent (27.33 to 39.54% reduction) and gave
appreable control of spider mite (42.02 to 70.90% reduction) which can be
manipulated and offers great scope in Integrated Pest Management Stratagies
against cowpea mite, T.ludeni.
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Citation
KAMLESHKUMAR CHIMANBHAI PATEL_32604