| dc.description.abstract | The study was conducted to determine the pest status, spatio-temporal distribution and host preference of major
insect pests of citrus at Jaintapur, Sylhet during May to October 2014. Three type citrus orchards viz. Mandarin,
Sweet orange and Jara lebu were selected randomly from five locations viz. Citrus Research Station, Dowdic,
Bagerkhal, Lamashampur and Utlarpar of two Unions viz. Nijpat and Fatehpur in Jaintapur, Sylhet. In each
location, four plants were tagged randomly and five canopy directions of each plant viz. north, south, east, west
and central were considered from the middle canopy of the plant. One twig from each canopy direction was
selected randomly and infested leaves were counted at 21days interval from 50 leaves of the selected twig and
infested fruits were also counted from 25 fruits of each canopy direction. Insect pest status, distribution, host
preference and seasonal abundance of major insect pests were determined on the basis of leaf and fruit infestation
(%). Insects were considered major pests when leaf infestation reached to 30% or >30% and when fruit infestation
reached to 25 or >25%. Insects were considered minor pests when leaf and fruit infestation was <30% and <25%
respectively. A total of 13 insect pests were found to attack Mandarin, Sweet orange and Jara lebu at Jaintapur,
Sylhet. Among them 5 species viz. Lemon butterfly, Citrus leafminer, Asian citrus psyllid, Citrus red mite and
Spined citrus bug were found as major pests. The average leaf infestation (Mean±SD) was 37.44±3.07% for
Lemon butterfly, 55.36±2.99% for Citrus leaf miner, 52.62±2.34% and 60.40±1.97% for Asian citrus psyllid and
Citrus red mite respectively. Besides, the average fruit infestation (Mean±SD) was 29.95±1.35% for Citrus red
mite and 34.63±3.00% for Spined citrus bug. The distribution of major insect pests on both leaves and fruits were
almost similar across the study sites, but the canopy directions had significant influence on the abundance of
major insect pests. The maximum average leaf infestation (45.18±3.66%) by Lemon butterfly was found in north
canopy and minimum (32.44±2.19%) in south canopy. The maximum average leaf infestation (64.70±3.38%) by
Citrus leaf miner was found in north canopy and minimum (49.12±2.13%) in east canopy. The maximum average
leaf infestation (60.88±2.45%) caused by Asian citrus psyllid was found in north canopy and minimum
(47.92±2.22%) in east canopy. The maximum average leaf infestation (64.48±2.46 %) by Citrus red mite was
found in north canopy and minimum (53.90 ± 1.82 %) in central canopy. The maximum average fruit infestation
(45.96±1.86%) and (39.28±1.41%) by Citrus red mite was found on Jara lebu and Mandarin respectively in north
canopy, while maximum (34.04±1.08%) fruit infestation on Sweet orange was found in east canopy. The
minimum average fruit infestation (22.68±0.94%), (16.16±1.17%) and (20.44±0.80%) by Citrus red mite was
found on Jara lebu, Mandarin and Sweet orange respectively in central canopy. The maximum average fruit
infestation (28.44±3.87%) and (54.92±4.08%) by Spined citrus bug was found on Jara lebu and Mandarin
respectively in north canopy, while maximum (44.28±3.50%) fruit infestation on Sweet orange was found in east
canopy. The minimum average fruit infestation (10.76±1.90%), (31.92±2.73%) and (27.56±2.56%) by Spined
citrus bug was found on Jara lebu, Mandarin and Sweet orange respectively in central canopy. Lemon butterfly
preferred most (47.58±2.54%) the leaves of Sweet orange and least (20.78±4.52%) the leaves of Jara lebu. Citrus
leaf miner preferred most (56.50±3.18 %) the leaves of Jara lebu and least (53.52±3.22%) the leaves of Mandarin.
Asian citrus psyllid preferred most (58.46±1.82%) the leaves of Jara lebu and least (43.34±2.90%) the leaves of
Mandarin. Citrus red mite preferred most (63.96±1.89%) the leaves of Jara lebu and least (57.48±1.74%) the
leaves of Mandarin. Citrus red mite also preferred most (35.28±1.39%) the fruits of Jara lebu and least
(27.16±1.43%) the Mandarin. Spined citrus bug preferred most (40.00±3.36%) the fruits of Mandarin and least
(22.76±2.63%) the Jara lebu. The infestation of Lemon butterfly ranged from 30.06 to 42.56% during May to
October 2014, with maximum (42.56±5.20%) during September to October and minimum (30.06±7.5%) in May.
The infestation of Citrus leaf miner ranged from 52.00 to 61.80%, with maximum (61.80 ± 1.20%) in May and
(61.80±1.11%) in October. The infestation of Citrus leaf miner was minimum (52.00±1.11%) in June. The
infestation of Asian citrus psyllid ranged from 46.70 to 56.46%, with maximum (56.46±4.90%) in August and
minimum (46.70±4.27%) in May. The infestation of Spined citrus bug ranged from 19.08 to 47.44%, with
maximum (47.44±3.00 %) in September and minimum (19.08±1.77%) in May. In case of leaf, the infestation of
Citrus red mite ranged from 59.40 to 64.30%, with maximum (64.30±1.98%) in September and minimum
(59.40±2.20%) in July. In case of fruit, the infestation ranged from 31.04 to 35.04%, with maximum
(35.04±1.03%) in May and minimum (31.04±1.25%) in July. Spatio-temporal distribution was closely related
with temperature and relative humidity and flushes of new leaves as well as maturity of fruits. The host preference
of Lemon butterfly ranked as Sweet orange>Mandarin>Jara lebu. On the other hand, the host preference of Citrus
leaf miner, Asian citrus psyllid and Citrus red mite ranked as Jara lebu>Sweet orange>Mandarin. The host
preference of Spined citrus bug ranked as Mandarin>Sweet orange>Jara lebu. | en_US |
