DETERMINATION OF PEST STATUS, DISTRIBUTION, HOST PREFERENCE AND SEASONAL ABUNDANCE OF MAJOR INSECT PESTS OF CITRUS IN SYLHET

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.