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Biology of the Eggfruit and Shoot Borer (EFSB), Leucinodes orbonalis Guenee (Crambidae) on the Garden Egg, Solanum gilo Raddi

A. Onekutu, A.A. Omoloye and J.A. Odebiyi
 
ABSTRACT
The eggfruit and shootborer (EFSB), Leucinodes orbonalis (Crambidae), is a major exotic pest of garden egg, Solanum gilo, causing enormous shoot and fruit damage in Nigeria. Information of the biology is required for effective management of this field pest. Life history of EFSB was studied on susceptible variety Lv Makurdi at 27±3°C and 85±4% RH data on developmental period of immature stages and reproductive parameters and sex ratio were collected. Developmental stages consist of an egg, five larval instars, pupa and adult. Developmental periods observed were eggs (5.93 days), 1st instar (1.00 day), 2nd instar (1.16 days), 3rd instar (1.48 days), 4th instar (2.63 days), 5th instar (4.46 days), pupa (11.2 days), female (4.14 days) and male (4.31 days). The reproductive parameters observed were incubation period (5.93 days), pre-oviposition period (1.19 days), oviposition period (2.71 days) and post-oviposition period (3.75 days). The Male to Female ratio was 1:2 and actual fecundity and potential fecundity per female were 123 and 207 eggs , respectively. Laboratory studies reveal that EFSB, Leucinodes orbonalis will complete its life cycle in 28.17 days.
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A. Onekutu, A.A. Omoloye and J.A. Odebiyi, 2013. Biology of the Eggfruit and Shoot Borer (EFSB), Leucinodes orbonalis Guenee (Crambidae) on the Garden Egg, Solanum gilo Raddi. Journal of Entomology, 10: 156-162.

DOI: 10.3923/je.2013.156.162

URL: http://scialert.net/abstract/?doi=je.2013.156.162
 
Received: April 12, 2013; Accepted: May 13, 2013; Published: June 24, 2013

INTRODUCTION

Leucinodes orbonalis Guenee(Crambidae) is the most damaging pest of Solanum gilo (Solanum aethiopicum), S. melongena, S. macrocarpon and other related vegetables. It is regarded as the most obnoxious and destructive pest of the eggplant, S. melongena in all Asia (Butani and Jotwani, 1984; Chattopadhyay, 1987; Tewari and Sandana, 1987; AVRDC, 1995; Rashid et al., 2008), contributing more than 80% loss in marketable yield (Ali et al., 1994; Dhankar, 1988; Raju et al., 2007). L. orbonalis is active throughout (Raju et al., 2007) and is a major constraint to the production of eggplant world over (Dhankar, 1988; Rahman et al., 2006).

Occurrence was first reported in India (Dhankar, 1988), which is considered the centre of origin and diversity of the eggplant, S. melongena. It is therefore possible that the insect also is native to India, where it is considered as a primary pest of eggplant (AVRDC, 1995; Sarker et al., 2006). EFSB damage is caused by the larva which feeds inside the fruit and at the same time leave large exit holes when leaving to pupate, reducing the market value of the fruits and rendering them unfit for human consumption (Alam et al., 2003). The damage by this borer starts at seedling stage and continues till the last harvest of fruits. At the early stage of plant growth, the larva bores into petioles and midribs of large leaves and young shoots, sealing the entry points with their frass, continues to feed within the stem (Butani and Jotwani, 1984), eventually leading to drooping and withering of the shoot (Alam and Sana, 1962). At a later stage, the larva bores into the flower buds and fruits through the calyx, leaving no visible sign of infestation (Butani and Jotwani, 1984). This leads to secondary infection by certain bacteria causing further deterioration of the fruits and making them unfit for human consumption (Islam and Karim, 1994). The insect has been reported a number of crops such as S. tuberosum (potato), S. lycopersicum and some other Solanaceous crops (Dhankar, 1988). Other hosts include sweet potato, Ipomea batatas (L.), S. indicum L, S. myriacanthum Dunal, S. torvum (turkey berry) and S. nigrum L (black nightshade) (CABABSTRACTS, 2007). The Biology of Leucinodes orbonalis has been widely studied on the eggplant in different parts of the world and has been found to be highly varied. In this study the biology on the garden egg, Solanum gilo is reported.

MATERIALS AND METHODS

Studies were conducted using the susceptible local variety of S. gilo in the Entomology Research Laboratory of the Department of Crop Protection and Environmental Biology, University of Ibadan under the laboratory conditions of 27-32°C and 85-92% relative humidity and 12:12 h photoperiod.

Culture of L. orbonalis: A batch of 100 infested fruits of S. gilo were kept in plastic rearing cage till emergence. Three pairs of day-old adults were introduced into the oviposition cages containing young shoot of S. gilo inserted in glass vials for 24 h. The eggs deposited were transferred into separate rearing cages containing un-infested fruits of S. gilo.

Life cycle study
Developmental biology of L. orbonalis:
A batch of 400 day old eggs on excised S. gilo shoots taken from the culture were incubated in 15 cm diameter petri-dishes in the laboratory. A random sample of 10 eggs were taken daily for observation till eclosion. At eclosion, the larvae were transferred to fresh un-infested fruits of S. gilo in plastic rearing cages after observation. Thereafter, 10 fruits each were dissected daily and larvae recovered were preserved in 70% alcohol in glass vials. Larval development was monitored till the onset of pupation. Pupae were placed in emergence cages laid with moist filter paper and observed for emergence. Temperature and relative humidity records were also taken. The egg, immature larvae, pupae and teneral adults collected were examined, morphometric data such as head capsule measurements (width), body length and body width of all the larvae collected were taken daily using an Olympus SZ-HTR Stereo binocular microscope fitted with an ocular micrometer.

Frequency distribution of the head capsules measurements were grouped and plotted to represent the number of larval instars in the life cycle of the moth. The groupings were then subjected to analysis of variance (ANOVA) to confirm the reliability of the groupings. The head capsule measurements were also tested for conformity to Dyar’s rule using a t-test.

For the determination of pre-pupal, pupal period, adult emergence and sex ratio and longevity of adults, 5th instar larvae were collected monitored over a period for pupation, adult emergence and senescence. The pre-pupal period, pupal period, longevity for both the male and female insects were determined by taking records from the first day of emergence for both mated and unmated male and female insects.

Reproductive biology of L. orbonalis: Ten freshly cut shoots of S. gilo inserted in glass vials filled with water plugged with cotton wool were placed individually in a rearing cage and a pair of newly emerged male and female EFSB adults introduced into them. The set-up was replicated thrice and arranged on the laboratory benches. The set up was observed daily and data on pre-oviposition, oviposition and incubation periods together with fecundity were collected. Also the total number of hatched and unhatched eggs were counted and the percentage hatched estimated using the formula given below:

Statistical analysis: Head capsule measurements were grouped and the groups subjected to Analysis of Variance (ANOVA). The groupings of head-capsule measurements were also tested for conformity to Dyar’s rule using a t-test.

RESULTS

Developmental biology of Leucinodes orbonalis guenee: At a room temperature of 27-32°C and relative humidity of 85-92% inside plastic cages kept in the laboratory. Developmental stages consist of one egg, five larval instars, pupa and adult. The mean life cycle of Leucinodes orbonalis on Solanum gilo fruits from egg to adult was 28.17 days with a range of 24-46 days at fluctuating ambient temperature and 85-92% relative humidity.

The head capsule width increased with successive instars, with a mean growth rate of 1.41 Table 1 and 2 shows the analysis of variance of the larval head capsule measurements. There was a significant (p<0.05) difference significant difference between the larval instars. Measurements also showed that the five groupings were significantly different from each other. Head-capsule measurements falling within the range of any of the groups in Table 1 belongs to that group at a confidence level greater than 95%.

Description of the stages in the life cycle of Leucinodes orbonalis guenee reared on Solanum gilo egg: The freshly laid creamy eggs were flat and oval shaped with mean length of 0.94 and 0.5 mm wide (Table 3). The eggs were laid singly or in batches on the foliage, most of which were on the ventral surface of young leaves. The creamy white egg gradually turns pinkish red before eclosion. Average incubation period was 5.9 days with a range of 4-7 days (Table 3).

Table 1: Head capsule measurements of larval instars of Leucinodes orbonalis

Table 2: Analysis of variance for head capsule measurements

Newly hatched larva was cream to brownish pink in colour, it was cylindrical with a conspicuous head and had between 9 or 10 abdominal segments, with mean head capsule measurement of 0.45 mm, a mean body width of 0.47 mm and an average body length of 4.19 mm, while the second instar larva had an head capsule measurement (0.74 mm), developmental period (1.16 days), body width (0.90 mm) and a body length (6.98 mm) (Table 3). For the third instar, head capsule measurement was 1.06 mm, developmental period (1.48 days), body width (1.38 mm) and body length (11.10 mm). The fourth instar larva had a mean developmental period of 2.63 days, head capsule measurement (1.44 mm) body width (1.71 mm) and body length (16.58 mm). The head-capsule measurement of the fifth instar larva was 1.73 mm, developmental period(4.46 days), body width (2.15 mm), while the mean body length was 18.44 mm (Table 3).

The fifth instar larva spins a cocoon around itself to turn into the pupa which at first is white but gradually darkens and becomes dirty brown. The mean developmental period of the pupa was 11.2 days (Table 3), while the mean length and width were 13.9 mm and 5.48 mm, respectively.

The mean developmental period from egg to adult was 28.17 days (Table 3). Morphologically, the adult L. orbonalis is white with a pale brown or black spots at the back of the thorax and abdomen. Its wings are white with a pinkish or bluish tinge and are ringed with small hairs along the apical and anal margins. The forewings have several black pale and light brown spots. It measures 20-22 cm when its wings are widely spread. The female appears slightly bigger than the male, because of a broader abdomen and wider wingspan. The male had a wingspan of 21.59 mm, mean body length of 13.26 mm, while the mean body width was 4.20 mm. The adult female on the other hand had a wingspan of 24.33 mm, mean body length of 14.17 mm, while the mean body width was 4.59 mm.

Reproductive biology of Leucinodes orbonalis guenee: Oviposition started a day after emergence. Freshly laid eggs are creamy and cylindrical and are laid singly usually but are sometimes found in batches. On the average were 123 eggs were laid per female per day with a range of 72-207 eggs (Table 4). A mean pre-oviposition period of 1.19 days was recorded for the moth, oviposition period was 2.71 days and the mean post oviposition period recorded was 3.75 days.

Table 3: Developmental period (days) and body measurements(mm) of the life stages

Table 4: Reproductive parameters, longevity and sex ratio of Leucinodes orbonalis reared on Solanum gilo garden egg fruits in plastic cages

The average lifespan of a mated male and female were 4.31 and 4.14 days, with a range of 3-7 and 2-6 days, respectively (Table 4). The unmated male and female had a lifespan of 4.7 and 5.8 days, with a range of 2-8 and 2-9 days, respectively. The sex ratio was 1:2 in favour of the female moth (Table 4). Morphologically, the adult L. orbonalis is white with a pale brown or black spots at the back of the thorax and abdomen. Its wings are white with a pinkish or bluish tinge and are ringed with small hairs along the apical and anal margins. The forewings have several black pale and light brown spots. It measures 20-22 cm when its wings are widely spread.

DISCUSSION

Effective control of the EFSB L. orbonalis requires a thorough knowledge of its reproductive and developmental biology. From laboratory observations, the creamy white eggs are laid singly on the ventral surface of the leaves, very close to the veins. Fecundity on average is 123 eggs per female. Lall and Ahmed (1965) however recorded between 92.5 and 233 eggs per female while Singh and Singh (2003) reported a fecundity of 175 eggs per female in Meghalaya, India. An incubation period of 5.93 days was recorded in this study which compared with incubation periods of 5.4, 5.65, 4.30 days reported by Mehto et al. (1983), Singh and Singh (2003) and Jat et al. (2002), respectively.

Pre-oviposition and oviposition periods of 1.19 and 2.71 days observed agrees with the findings of Mehto et al. (1983), who reported pre-oviposition and oviposition periods of 1.2-2.1 days and 1.4-2.9 days and Singh and Singh (2003) who reported 1.35 and 2.09 days. The result also confirms Harit and Shukla (2005) report who observed pre-oviposition and oviposition periods of 1.45 and 2.1 days, respectively.

Larval and pupal developmental periods were 10.71 and 11.2 days, respectively. The larval period was much shorter than observations made by Mehto et al. (1983), Baang and Corey, (1991) and Singh and Singh (2003) who reported developmental periods of 17.5, 15.0 and 18.6 days, respectively. Jat et al. (2002) on the other hand reported a larval period 12.83 days. The pupal developmental period of 11.2 days recorded seems to agree with the findings of Mehto et al. (1983), Baang and Corey (1991), Jat et al. (2002) and Singh and Singh (2003).

The development of L. orbonalis is affected by location, altitude and agroecological characteristics. It varies from place to place and from season to season. As temperature increases and humidity decreases, fecundity increases and the duration of the life-cycle decreases.

The male and female insects had a lifespan of 4.31 and 4.14 days which varied considerably from the records of Mehto et al. (1983), Baang and Corey (1991), Jat et al. (2002), Singh and Singh (2003) and Harit and Shukla (2005). They reported male and female lifespan of 1.5-2.4 and 2.0-3.9 days, 4.0 and 7.5 days, 1.82 and 3.0 days, 3.53 and 5.80 days, 3.53 and 5.51 days, respectively. The total developmental period from egg to adulthood was 28.17 days, which is very different from 25.8 days and 27.07 days reported Jat et al. (2002) and Kumar and Johnsen (2000), respectively. Singh and Singh (2003) and Harit and Shukla (2005) on the other hand reported total developmental period of 36.82 days and 42.5 days, respectively. The duration of the total developmental period is dictated to a great extent by temperature. Patel et al. (1988) observed a significant difference in the incidence of L. orbonalis in plants transplanted at different periods in Gujarat, India.

The differences observed might be attributed to location, altitude and agroecological characteristics Kumar and Johnsen (2000) and Jat et al. (2002) found a positive correlation between the degree of infestation and maximum temperature. Ghosh and Senapati (2009) reported increased L. orbonalis activity during the summer and rainy season and caused 49.5-81% damage to fruits.

CONCLUSION

This investigation recorded a total developmental period of 28.17 days for the eggfruit and shootborer, L. orbonalis (Crambidae) on one of its most susceptible host S. gilo. It consist of an egg, five larval instars, pupal and adult stages. The female lays an average of 123 eggs and a, male:female ratio of 1.2.

ACKNOWLEDGMENT

We want to thank the Management and staff of the National Horticultural Research Institute, Idi Ishin, Ibadan for the support this research. A special appreciation to Dr V.C Umeh, Mrs Tairu, Mr Daniel, Mr Thomas and a number of support staff of the Institute rendered all the needed assistance particularly at the early stage of the research.

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