IDENTIFICATION AND ASSESSMENT OF INSECT PESTS CAUSING FRUIT DROP ON Citrus sinensis L. OSBECK AND THEIR MANAGEMENT IN BENUE STATE, NIGERIA
Identification and assessment of insect pests causing fruit drop on Citrus sinensis L. Osbeck and their management was carried out in Benue State, Nigeria. A survey on the level of citrus fruit drop in the state was conducted through a semi-structured questionnaire administered to citrus farmers in the citrus producing zones A and B of the state. Three local government areas (LGAs) were randomly selected from each zone and fifteen citrus farmers from each LGA giving a total of ninety farmers. Pest identification was done through fruit culture experiment carried out in College of Agronomy Teaching and Research Farm, University of Agriculture, Makurdi in October 2014 and 2015. The experiment was a 2 x 3 factorial in a completely randomized design with four replications. Ten naturally infested orange fruits from each variety in each zone were weighed and placed in each plastic rearing box with dimension 39 cm x 27 cm x 26 cm containing sterilized moist soil securely covered with 1mm mesh net for pupation and adult insect emergence. Emerged adults were preserved for later identification. Experiment on the effect of mass trapping for the control of fruit flies was conducted in three farmers’ orchards in Aliade, Gwer East LGA of Benue State from September to November, 2014 and 2015 respectively. The experiment was a 3 x 3 factorial in a randomized complete block design replicated four times. Twelve sampled citrus trees were randomly selected in each orchard. Experiment on the effects of oviposition punctures on shelve life of sweet orange was conducted in the Department of Crop Production Laboratory, University of Agriculture, Makurdi. The experiment was a 2 x 3 factorial in a completely randomized design with four replications. The two factors were fruits and varieties as factors A and B respectively. Despite the fact that majority (86.67 %) of citrus farmers experienced citrus fruit drop in their orchards, 88.5 % of them did not know the cause of the drop. However, 47.78 % and 34.44 % of them rated citrus fruit loss to fruit flies as serious and very serious respectively with only 17.78 % as not serious. Fruit fly species identified from citrus fruit culture were: Bactrocera invadens (Drew), Ceratitis capitata (Weid) and Dacus bivittata (Biggot). B. invadens was the most abundant species and accounted for 63.70 % in Washington navel and 63.10 % in Valencia in 2014 and 2015 respectively. The varieties showed no significant difference (p>0.05) on the abundance of C. capitata and D. bivittata in 2014. In 2015 however, Ibadan Sweet variety showed significant difference (p<0.05) on the abundance of C. capitata (28.30 %) compared to other varieties. The highest percentage fruit damage was recorded in week 12 in the untreated orchard in 2014 (4.40 %) and 2015 (4.91 %) compared to mass trapping method where 2.45 % and 2.90 % were recorded in 2014 and 2015 respectively. The varieties had no significant influence(p>0.05) on the percentage fruit damage except in weeks 6, 11 and 12 of 2014 and weeks 10, 11 and 12 of 2015 where Valencia variety significantly (p<0.05) had the highest fruit damage 1.96 %, 3.19 % and 3.29 % in 2014 and 3.32 %, 3.46 % and 3.68 % in 2015 respectively. Days to various percentage fruit rot were significantly (p<0.05) influenced by varieties and oviposition punctures in 2014 and 2015. Non-infested Valencia fruits significantly delayed fruit rot (21.37 and 21.25 days) compared to fruits of Ibadan sweet(19.50 and19.00 days) and Washington navel varieties (18.62 and17.88 days) in 2014 and 2015 respectively. Therefore, in the study, citrus fruit loss to fruit flies in Benue state was rated serious by the farmers and the most abundant of these flies was B. invadens. The use of diammonia phosphate and protein hydrolysate attractant in mass trapping control method significantly reduced fruit damage to sweet orange; meanwhile, Ibadan sweet variety resisted fruit damage more than Valencia and Washington navel varieties while non-infested Valencia fruits significantly delayed fruit rot.