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Early indications of attack by L. orbonalis are the result of larval feeding on flowers, flower buds and young shoot tips and stems. Final-instar larvae bore into the fruits. Infested fruits are characterized by small entrance holes closed by dried excrement. Wilting may occur in severe infestation. L. orbonalis causes yield loss, weakens plants and the fruits produced by infested plants may be unsuitable for consumption. Damage is most severe when a substantial population has built up over several generations.
A significant difference in the incidence of L. orbonalis was observed in plants transplanted at different periods in Gujarat, India (Patel et al., 1988). Asari and Nair (1972) investigated the use of deterrents in Kerala, India.
Jat et al. (2002) found a positive correlation between the degree of infestation and maximum temperature; no correlation was observed with minimum temperature. Relative humidity had no effect on fruit infestation in the first year but there was a positive correlation in the second year.
Different concentrations of nitrogen, phosphorus and potassium fertilizers to the soil of aubergine fields in India (Chaudhary and Kashyap, 1987). Significant differences in pest incidences were observed between fertilized and unfertilized plots.
In West Bengal, India, Karmakar and Bhattacharya (2000) showed that the pest population can be maintained at well below the economic injury level (0-11.75 L. orbonalis Guen./plot) using mechanical methods of control.
In Orissa, India, Patnaik et al. (1998) found that an increase in yield was due to applications of fertilizer rather than insecticides.
The effect of intercropping coriander as a single line, double line or border crop with aubergine on infestation by L. orbonalis was compared with untreated and cypermethrin-treated monocrop aubergine treatments during the 1995-96 and 1996-97 cropping seasons at Gazipur, Bangladesh. The highest cost-benefit ratio was obtained from plots which had single line coriander with aubergine as an intercrop, followed by the aubergine-coriander double line intercrop, aubergine-coriander border crop and cypermethrin-treated monocrop aubergine treatments. Intercropping coriander with aubergine may be useful in IPM programmes against L. orbonalis by reducing fruit infestation and the amount of insecticide used by farmers (Khorsheduzzaman et al., 1997).
Gupta et al. (1999) intercropped four spice crops (fennel, omum, coriander and nigella) with brinjal. Significantly lower infestations were recorded on shoots (2.01%), fruits (16.86%), and on the basis of weight (18.10%) and minimum larval population (43.20)/100 fruits, when three rows of nigella were planted between rows of aubergine, compared to the other treatments including the monocrop. Although the monocrop showed the greatest yield (173.79 quintal/ha), intercropping with fennel gave the highest return for aubergine (Rs. 9451/ha) and significantly reduced pest infestation.
Several varieties of aubergine have been evaluated for resistance against infestation by L. orbonalis. Resistance in varieties SM 17-4, PBR 129-5 and Punjab Barsatiby was attributed to a large number of small fruits per plant with shorter inter/intracluster distance, late fruiting and a longer fruiting period (Dilbagh-Singh et al., 1991). Biochemical characters, such as total sugars and free amino acids, were positively correlated with fruit infestation, and polyphenol content was negatively correlated with attack (Darekar et al., 1991). Bajaj et al. (1989) suggested that the presence of glycoalkoids in association with phenolic compounds was responsible for the resistance in variety SM-17-4.
In Himachal Pradesh, India, Chaudhary and Sharma (2000) found that the aubergine variety Arka Kesav had a fruit borer incidence of 2.88 compared to 5.64 in variety SM 6-6.
The highly resistant aubergine variety, Sm-202, had tightly arranged seeds in the mesocarp (Lal, 1991). Mishra et al. (1988) attributed resistance in long-fruited varieties to thick fruit skin and closely packed vascular bundles in the pulp.
Of eight aubergine cultivars studied in the field in Jammu and Kashmir, India, none were found to be absolutely tolerant of L. orbonalis (Sharma et al., 1998). The cultivars Pusa Purple Cluster, Muktakeshi and Pusa Purple Round were graded as tolerant, and Pusa Kranti, Arkakusmakar, BR-112, Neelam Round and Pusa Purple Long as moderately tolerant, on the basis of shoot infestation. However, on the basis of fruit infestation (number and weight), the cultivars Arkakusmakar and Pusa Purple Cluster were ranked as tolerant, whereas cultivars Muktakeshi and BR-112 were susceptible. Pusa Kranti, Pusa Purple Long, Pusa Purple round and Neelam Round were highly susceptible.
When 1-month-old seedlings of Solanum macrocarpon M4 lines (10 Kr-P7-20, 5 Kr-P7-33, 5 Kr-P22-4, 5 Kr-P21-2, 5 Kr-P38-6 and 10 Kr-P2-10), S. macrocarpon (control) and S. melongena cv. Pusa Purple Long (PPL) were transplanted in the field in India, the shoots and fruits of cv. Pusa Purple Long were infested with L. orbonalis but none of the shoots and only a low percentage of the fruits of M4 lines and the control were infested (Babu et al., 1999). The presence of a tough calyx cover and a high phenolic content in the M4 lines and in the control was thought to contribute to resistance to L. orbonalis.
Behera et al. (1999) studied genetic diversity in aubergine for resistance to L. orbonalis in India. They found clusters in 12 genotypes and the genotype Solanum indicum in cluster iii was highly resistant. Awasthi (2000), who also studied 12 aubergine genotypes in Madhya Pradesh, India, found the lowest percentage of fruit infestation in genotypes Nurki (27%) and CH-150-16-4-1 (32%).
Panda (1999) studied 174 varieties of aubergine in the field in Bhabaneswar, India. None of the entries was immune to larval attack of shoots and fruits. The mean percentage of shoot infestation varied from 1.61 to 44.11% and fruit damage varied from 8.5 to 100%. Maximum shoot damage was recorded 75 days after treatment (DAT), with maximum fruit damage recorded at 76-121 DAT and 99-114 DAT in susceptible and resistant cultivars, respectively. Thus, early fruiting varieties are more liable to fruit attack by L. orbonalis. Leaf hair density and the number of shoots per plant played a role in restricting shoot damage. Morphological characteristics such as a tight calyx and long fruits, increased resistance of the fruits to attack. L. orbonalis attack of fruits was also restricted by tightly packed seeds in the mesocarp, a low content of water, nitrogen and potassium, and a high phosphorus content. It is suggested that resistant cultivars such as Pitala Local 1 and Sambalpur Local should be grown in order to minimise the incidence of L. orbonalis.
Vinod-Sharma et al. (2001) and Sridhar et al. (2001) found a correlation between the form and structure of fruits and the degree of infestation by L. orbonalis.
Behera et al. (2002) studied the resistance of interspecific crosses (between Solanum incanum, S. indicum, S. gilo and S. melongena cultivars Annamalai, Aushey and Pusa kranti) and the resultant hybrids in New Delhi, India. Different results where obtained in terms of infestation, pollen fertility and sterility; Solanum indicum was found to be immune to fruit infestation.
A number of authors have reported on the parasitoids and pathogens found to attack L. orbonalis (see Natural Enemies). Some laboratory tests have been undertaken but there have been no large-scale field tests.
Janardar-Singh et al. (1974) conducted laboratory tests on L. orbonalis using an entomophilic nematode.
Due to the variable regulations around (de-)registration of pesticides, we are for the moment not including any specific chemical control recommendations. For further information, we recommend you visit the following resources:
L. orbonalis causes important yield loss but there are few detailed accounts of losses.
Tewari and Rao (1989) developed a sequential sampling plan to identify the economic injury level for aubergine in Bangalore, India; the economic injury level was equivalent to 6% infestation.
Naresh et al. (1986b) reported 12.28-95.24% damaged fruits in Haryana, India during 1982-83; loss in fruit weight ranged from 13.28 to 88.89%.
Borer infestation of the top shoots of brinjal was 73.3% at the beginning of September and peaked at 86.6% in the third week of September at 2.9 borers/plant in Uttar Pradesh, India (Singh et al., 2000). Infestation moved to the flowers and fruits reaching 66.6% of fruit by the end of October. Fruit infestation decreased (with a small peak in the third week of November) until 0% infestation was recorded at the start of December. Temperature was positively, and relative humidity negatively, correlated with the multiplication of the pest. Losses caused by the borer to fruits was 21.3%. Total loss was 48.3%, of which 45.9% was avoidable and 2.4% unavoidable. The economic injury level of L. orbonalis on fruits and on shoots was calculated as 0.67 and 0.91%, respectively.
In Orissa, India, the peak infestation periods were later with maximum shoot and fruit infestations occurring on November 15-21 and December 13-19, respectively (Tripathi et al., 1996).