Varietal Susceptibility and Assessment of Losses Caused by Pulse Beetle Callosobruchus Chinensis (L.) in Green Gram Under Laboratory Conditions

The susceptibility of six green gram (Vigna radiata W.) varieties and quantitative losses due to pulse beetle, Callosobruchus chinensis L., were studied under laboratory conditions. No green gram varieties were found immune. They showed different magnitude of weight loss. The lowest weight loss was observed in variety HUM-12, HUM-1 with 30.20, 31.83, respectively and lowest percent germination loss was observed in variety HUM-2, HUM-16 with 2.50, 2.70, respectively. The mean seed damage and weight loss was 8.98 and 8.26 per cent, respectively after 30 days. This was increased with the storage duration resulting in 99.99 and 48.62 per cent, respectively after 120 days of storage. The population of pulse beetle and Percent germination losses was increases with increasing storage duration.

A number of insect-pests attack the stored grains, seeds and other products.Among the important insect pests of stored grain, the pulse beetle, Callosobruchus chinensis L. (Bruchidae: Coleoptera), causes substantial losses to the pulses in the storage (Alam, 1971 and Righi-Assia et al., 2010) though the initial infestation occurs in the field itself.It causes weight loss, decreased germination potential and reduction in commercial value of the seed (Booker, 1967 andOkunola, 2003).It is a serious pest of peas, mung beans, cowpeas and lentil (Ahmed et al., 2003).In India, there are about 200 species of pest insects which cause damage to stored grains and grain products in storage.Callosobruchus chinensis L. is a major economically important pest of all pulses and causes 40-50% in losses of pulses storage (Gosh et al., 2003).Resistant cultivars/ varieties have become a crucial element in the success of many on-going insect pest management programmes.One of the most promising ways to reduce dependence on pesticides in agriculture is to plant insect resistant cultivars, which is one of the most effective, feasible, economical and environmentally safe pest management tactics (Pedigo, 1996) and fully justifies the upcoming WTO regulations.The present study was undertaken to find out green gram cultivars having resistance against pulse beetle and quantitative losses caused by pulse beetle at different storage intervals.

Test insects and maintenance
The nucleus culture of the test insect was obtained from storage laboratory, Department of Entomology and Agricultural Zoology, Institute of Agricultural Sciences, Banaras Hindu University, Varanasi.The Pulse beetle, Callosobruchus chinensis L. was used for the present experiment.A small population of C. chinensis beetle was reared and breed under laboratory conditions, on diet of the green gram seed.Initially 50 pairs of 1-2 days old adults were placed in a jar containing green gram seeds.Jars were sealed and allowed for mating and oviposition.The subsequent progenies of the beetles were used for all experiment.

Varietal Susceptibility
To study the varietal susceptibility of green gram varieties viz., HUM-1, HUM-2, HUM-6, HUM-12, HUM-16, and HUM-27 were obtained from the Department of Genetics and Plant Breeding Institute of Agricultural Sciences, BHU, Varanasi.The pulse beetle infestation is compared with local variety of green gram.

Quantitative losses
Quantitative losses caused by the pulse beetle in stored green gram were determined.The details are given as under.

Experimentation
The seeds of green gram were disinfected and cleaned.A lot of 500 g seeds were taken in glass jar of 2 kg capacity for observation of per cent seed damage, Weight loss, population build up.Four set of jars in three replications were prepared with 500 g seed in each.These jars were covered with muslin cloth.
Five pair of 0-24 hour's old adults of C. chinensis was released in each glass jar.Adults were allowed to lay eggs for multiplication.The jars were placed at the room temperature in the storage laboratory.The observations were taken at an interval of 30, 60, 90 and 120 days.

Seed Damage
Ten gram seeds were taken from the jar of each replicate.The damaged seeds were separated out from the total number of seeds taken for observation in each replication.The data taken were used for calculating the percentage of damaged seed.The following formula was used for determination of per cent damage as described by Adams and Schuten (1978).

Number of holed seeds
Total number of seeds counted X 100

Weight Loss
After removing the beetles from each jar the weight of seeds were taken separately on weighing balance from each replicate after one, two, three and four months.The per cent loss in weight was calculated by the following formula.
Percent weight loss = X 100 Where, I = Initial weight of seeds F = Final weight of seeds Population Build up of the Beetles Adults in the experimental containers were anaesthetized with chloroform and separated from experimental jars with the help of camel hair brush in an enamel tray.The adults inside the seeds were removed with the help of a needle.The total number of adults so obtained was recorded.

Germination Loss
The viability of seeds was tested after four months of storage.Each set was replicated three times.Seeds were placed on moist filter paper in Petri dishes and observed the germination of seeds.From the each set 50 seeds was collected randomly and placed in Petri dish lined with blotting paper.These Petri dishes were kept at room temperature for six days to allow sufficient time for all the seeds to germinate.Water was poured regularly to prevent drying.The number of unsprouted seeds was counted and the per cent germination loss was calculated by the formula.

Varietal Susceptibility of green gram against C. chinensis Weight losses
The per cent weight loss among different mungbean varieties was statistically significant over local varieties.The weight losses in different varieties were ranged in between30.20 to 46.06 per cent.Lowest weight loss (30.20%) was observed in HUM -12 followed by HUM -1 (31.83%) as shown in (table 1).The maximum net weight loss observed in variety HUM -16, 46.06 per cent as compare to local variety 48.60 per cent.

Germination losses
The screening of green gram varieties shows lowest per cent germination loss in HUM-2 (2.50%) and HUM-16 (2.70%).The rest of the varieties per cent germination losses were ranged between 12.33 to 30.43 per cent as compare to local variety (95.52%) after four months of storage period

Quantitative losses Seed Damage
The results of seed damage (table 2) depicted that the insect infestation caused 8.98 per cent damage after 30 days of release which increased with the storage duration resulting in almost per cent after 120 days.All the observations were found highly significant to each other.A substantial increase in damage was observed after 60 days of storage (56.58 %), whereas, it reached 90.68 per cent after 90 days of storage and in 120 days it reaches upto 99.99 per cent.The results are in conformity with Doharey et al. (1987) also observed the same trend in seed loss by C. chinensis with an initial loss of 1.35 per cent, gradually increasing to 99.91 per cent after 120 days of storage period.Similar result was found by Venkatesham et al. (2014).

Weight Loss
The per cent loss in weight of green gram increased with the advancement of storage period because of relative increase in the population of insects.The result (table 2) revealed that 8.26, 18.04, 40.25 and 48.62 per cent weight loss of grains was inflicted after 30 days, 60 days, 90 days and 120 days of insect infestation, respectively.Increase in per cent loss between 1-2 and 3-4 months was 9.78 and 8.37 per cent respectively.A highly significant variation was observed in weight loss after 30, 60, 90 and 120 days of storage.Doharey et al. (1987) reported that weight loss caused by C. chinensis was 0.62, 16.74, 25.56, and 43.26 per cent after 30, 60, 90 and 120 days of storage period, respectively.Similar results were

Population buildup of Beetles
The mean number of pulse beetles observed at different period after infestation in green gram is presented in table 3. Significant differences in population of pulse beetles at different time interval during storage in green gram was observed.The no of beetles varied from 164.86 to 3011.12 during 30 to 120 days of storage after initial infestation.The population grading increased in green gram and reached the peak level 120 days after initial infestation.Maximum beetle were 3011.12 in green gram during the fourth month storage of infested grains.Thus it showed 164.84, 1286.15,2013.57and 3011.12fold increase in beetle population after 30, 60, 90, and 120 days of storage in green gram.Daniel et al. (1977) have reported greater population buildup of C. chinensis in chickpea as compared to pigeon pea.

Germination Losses
The data on germination loss (table 3) depicted that there was adverse effect of insect infestation on germination percentage of green gram seeds after different storage periods.The loss in germination was 28.45, 76.02, 93.45 and 99.73 in green gram after 30, 60, 90 and 120 days of storage period, respectively showing a very high variation of significance.On an average 47.57per cent germination loss was experienced between first and second month.During the subsequent two months storage period, the rate of loss in germination percentage had decreased to 17.43 and 0.28 per cent.Thereafter, almost cent per cent loss was observed in the fourth month of storage.Similarly, Doharey et al. (1987) observed 5.0, 26.0, 98.0 and 100.0 per cent loss in germination by C. chinensis in black gram seeds after 30, 60, 90 and 120 days of storage period respectively.Jotwani and Sircar (1964) recorded that the germination per cent loss in 1, 2, 3 and 4 grubs developed in seeds after one two four months were 39.9, 79.5, 94.5 and 100 per cent, respectively.
Per cent germination loss =Number of unsprouted seedsNumber ofseeds kept for germination X100

Table 1 :
Screening of different green gram varieties per cent weight losses and germination losses after four months of storage ** mean of three replications; Figures in parenthesis are arc sine values

Table 2 :
Effect of the pulse beetle infestation under different storage period on seed damage and weight loss in green gram.

Table 3 :
Population buildup of C. chinensis and germination losses in green gram after different storage periods