ABSTRACT

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.

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INTRODUCTION

Sweet orange (Citrus sinensis L. Osbeck) is a tropical to semi-tropical evergreen, small flowering tree, growing to about five to eight metres (5 m-8 m) tall (Umesh, 2009). Oranges are classified into two: sweet and sour orange. Sweet orange is one of the important fruit crops of the world, occupying third position among the sub-tropical fruits (Tariq et al., 2007) and the second largest by production volume next to banana (FAO, 2006; Mohammed, 2013). Oranges probably originated from south-East Asia and were cultivated in China by 2500 B.C. (Nicolasi et al., 2008). Today it is grown almost all over the world as a source of food for humans because of its high nutritional values, source of vitamins and other uses (Etebu and Nwauzoma, 2014). Citrus is widely cultivated in tropical as well as sub-tropical African countries. Whereas fresh fruit for the market is produced preferably in sub-tropical climate (South Africa and Mediterranean climate e.g. Tunisia, Egypt, Morocco and Libya), citrus for juice is predominantly produced in tropical climates probably because of the possibility of higher sugar content.(Mohammed, 2013).

Government policy on the promotion of citrus production in Africa as reported by Mohammed, (2013) is quite encouraging as the sector has got attractive and multiple social and economic advantages. It is one of the most important commodities in tropical Africa being a source of foreign currency, raw material for agro-industries and source of employment (Mohammed, 2013). Apart from the above benefits, citrus are the main source of important phytochemical nutrients and for long have been valued for their wholesome nutritious and antioxidant properties (Etebu and Nwauzoma, 2014). Other biologically active, non-nutrient compounds found in citrus fruits such as soluble and insoluble dietary fibers are known to be helpful in reducing the risk of cancers and many chronic diseases like arthritis, obesity and coronary heart diseases (Crowel, 1999; Liu et al., 2000; Djousse et al., 2004).

Adewale et al. (1996), reported that citrus is one of the most important and among top ten widely cultivated fruit crops in Nigeria. The production of citrus in Nigeria is more concentrated in the Guinea and Sudan Savanna zones of the country (Olaniyan, 2004) with Benue State giving the highest annual production of the commodity (Avav and Uza, 2002).

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Citrus species are attacked by many pests and diseases incurring expenditures worth one hundred and sixty million USA dollars to avoid what sometimes can develop into total loss (Parra et al., 2004). Some of the arthropods that are harmful to this crop include: mite species, fruit flies, scale insects, aphids, etc. (Parra et al., 2004).

Fruit flies (Diptera: Tephritidae) are the world’s worst pest of fruits (Heaven, 2006). They are present in most countries and attack many types of fruits as well as fruiting vegetables, ornamentals and nuts. Feeding by fruit fly larvae (maggots) damage the fruits internally causing premature ripening, dropping and rotting of the fruits. Up to 100 % of the fruits may be damaged by fruit flies when infestations are not controlled (Heaven, 2006). It is globally estimated that direct and indirect losses caused by fruit flies is over two million USA dollars per annum (Christiane et al., 2009). Umeh et al. (2008) reported that there has been a lot of neglect of the fruit fly menace for a long time in Africa and consequently, huge resources running into millions of USA dollars are constantly being lost. Therefore, studies about fruit flies are mandatory in all the countries in which fruit production is commercially explored since these insects are the key pest in the fruit plantations.

Fruit flies apart from causing losses in horticultural produce across the world are a major quarantine concern for most countries (Benard et al., 2011). With the increasing globalization of trade as reported by Stanway et al. (2001) and the export promotion drive initiated by the government of the Federal Republic of Nigeria, there is a serious need for production of good quality fruits that meet the standard of export market and quarantine regulations. The above was confirmed by Oliver, (2002) and Stephenson et al. (2003) who reported that fruit flies pose a major quarantine concern which is currently monitored through regional surveillance programs. Stephenson et al. (2003) and Li et al. (2010) also reported that fruit flies cause direct losses to many fresh fruits and some vegetables resulting in adverse impacts on trade and economies of many countries. Mohammed et al. (2012) also reported that fruit flies seriously affect the production and exportation of various fruits especially Mango and Citrus.

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Due to concealed nature of damage by fruit fly, insecticide spray seems not to be effective. Moreover, the use of insecticides on the consumable products are being discouraged due to their toxic residues and pollution of the environment (Qamer et al., 2003).

In Africa south of the Sahara, particularly in Nigeria, limited research work has been carried out on identifying and controlling fruit flies of economic importance to the horticultural industry (Umeh et al., 2008). The authors also reported that majority of citrus farmers are neither aware of ideal citrus production practices nor acquainted with efficient fruit fly control options.

The availability of fruit fly food attractants and readily made traps in Nigeria is scarce. It is therefore necessary to explore the efficacy of easily available food attractant commonly known as fertilizer by farmers (DAP) used in locally fabricated trap for fruit fly capture.

Despite the economic, nutritional and health benefits of citrus, unfortunately according to Ortese et al. (2012), there have been limited studies involving crucial aspects of citrus production in Benue state. Studies in pest and disease aspects of the production are also scanty. In Benue state, there is insufficient information on the abundance, effective control measure and effects of fruit flies infestation on the shelve life of citrus fruits.

The aim of this study is to collect, identify and control insect pests responsible for sweet orange fruit drop in the state with the following objectives:

i.            To survey and ascertain the level of citrus fruit drop in some orchards in Benue state.

ii.             To collect and identify the major insect pest responsible for fruit drop of citrus in orchards.

iii.             To study the abundance of the major identified pest in the orchjards.

iv.            To examine the effectiveness of mass trapping as a control measure for the pest.

v.      To study the effects of oviposition puncture on shelve life of citrus fruits.       .

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LITERATURE REVIEW

Agriculture and Nigerian Economy

In the pre-independence era, the agricultural sector made the highest contribution to the Gross Domestic Product (GDP) of Nigeria and agricultural export crops like cocoa, groundnuts, cotton, rubber, palm oil and palm kennel accounted for about 65 – 75 % of Nigeria’s foreign exchange earnings, providing source of revenue for the federal and state governments through export of products and sales taxes (Ekwundare,1973).

However, the oil boom era of 1970s which resulted in extensive exploration and exportation of petroleum caused the neglect of the agricultural sector and the over dependence of Nigeria on a mono-economy crude oil base. Petroleum production and export play a dominant role in Nigeria’s economy and account for about 90 % of her gross earnings. This dominant role has pushed agriculture, the traditional mainstay of the economy, since the early fifties and sixties to the background (Odularu, 2007).

The recent decline in the price of crude oil that fell by 44 % (Lutz, 2015) resulting to one of the worst fall in the price of oil in recent history is a good signal to deviate from the mono-cultural crude oil based economy and diversify into other sectors of Nigerian economy especially agriculture. Improving productivity and quality of fruits and vegetables generally enhances food security, employment and trade opportunities. Sweet oranges (Citrus sinensis L. Osbeck) are one of the most important fruit crops of the world, occupying third position among the sub-tropical fruits (Tariq et al., 2007). In terms of production volume, citrus ranks after banana as the world second fruit corps with more than 108 million tonnes (FAO Statistics, 2006; Mohammed, 2013).

Description

Sweet orange is a small evergreen tree of about 7.5 m high and in some cases up to 15 m tall (Etebu and Nwauzoma, 2014). It belongs to the family Rutaceae and sub-family Aurantioide. Orange produces evergreen leave of different shapes ranging from elliptical to oblong to oval, 6.5 cm – 15 cm long and 2.5 cm – 9.5 cm wide often with winged petiols (Etebu and Nwauzoma, 2014). It bears fragrant white flowers either singly or in whorls of six, about 5 cm

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wide with five petals and 20 – 25 yellow stamens (Etebu and Nwauzoma, 2014). The authors also reported that the fruit which may be globose or oval is 6.5 to 9.5 cm wide and ripens to orange or yellow in color. The skin of the fruit consists of an epidermis of epicuticular wax with numerous small aromatic oil glands that gives it its peculiar smell.

Economic Importance of Orange

Orange is grown almost all over the world as a source of food for humans due to its high nutritional values, source of vitamins and other uses (Etebu and Nwauzoma, 2014). Economically, oranges are important fruit crops with an estimated sixty (60) million metric tonnes produced worldwide as at 2005 for a total value of nine billion dollars (Etebu and Nwauzoma, 2014). Of this total, about fifty percent (50 %) came from Brazil and United States of America (Goudeau et al., 2008; Bernard et al., 2010). The global citrus hectarage according to FAO Statistic (2009) was nine million hectares with production put at 122.3 million tonnes, ranking sweet orange first among all the fruit crops (Xu et al., 2013).

Mohammed (2013), reported that citrus production has attractive and multiple social and economic advantages. It is one of the most important commodities in tropical Africa as source of foreign currency, raw material for Agro-industries and source of employment (Mohammed, 2013). Also, citrus are the main source of important phytochemical nutrients and for long have been valued for their wholesome nutritious and antioxidant properties (Etebu and Nwauzoma, 2014). These phytochemicals have been linked to many positive effects on human health, including coronary heart diseases, diabetes, high blood pressure, cataract digestive diseases and obesity (Liu et al., 2000; Djousse et al., 2004).

Citrus Pests

Citrus species are attacked by many pests and diseases reducing yields, fruit quality, affecting trade values and export opportunities. The arthropods that comprise the harmful entomofauna in citrus include mite species (Tetrancychidae), fruit flies (Tephritidae), scale insects (Coccidae) and others that transmit disease such as Aphids (Aphidiodae), leafhoppers (Cicadellidae) and leaf miners (Gracillariidae) (Parra et al., 2004).

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Fruit Flies (Diptera: Tephrididae)

Fruit flies Tephritid species have caused tremendous losses in fruit and vegitable production and imposed limits on local and export markets in several countries (Christane et al., 2004; Stephenson et al., 2003). Bernard et al. (2011) reported that there were about 4, 500 species of fruit flies worldwide. In the pacific area alone, Allwood, (2000) reported that there were 350 species of which at least 25 species were regarded as being of major economic importance. White and Elson-Harris (1994), stated that the family Tephritidae includes 4,000 species made up of 500 genera. Out of the 500 genera, five of them are considered of worldwide economic importance (Rega et al., 2004). These include Anastrepha, Bactrocera, Ceratitis, Dacus