Carryover of Callosobruchus maculatus (Fab.) in Pigeon Pea Seeds from Field to Storage and its Management by Smearing Oil on Seeds

Legumes, part of the Fabaceae family, are vital in Indian agriculture for nitrogen fixation, soil enrichment and nutrition. Pigeonpea (Cajanus cajan) holds a prominent position in Indian agriculture as a second most vital legume crop. Possessing drought tolerance and nitrogen-fixing ability, Pigeonpea plays a crucial role in sustainable farming practices (Sarkar et al., 2020). Pigeonpea (Cajanus cajan) cultivation in India is often challenged by various pest attacks, with Callosobruchus maculatus being a significant threat. C. maculatus, commonly known as the pulse beetle, is a notorious pest that inflicts severe damage to Pigeonpea seeds during storage. Female pulse beetles lay eggs on mature Pigeonpea pods or seeds and upon hatching, the larvae bore into the seeds, feeding on their contents (Khavilkar and Dalvi, 1984). To mitigate C. maculatus infestations, several integrated pest management strategies are employed. These include the use of chemical insecticides during storage, fumigation with carbon dioxide, Edible oils also play a crucial role in the management of C. maculatus infestations in pigeonpea seeds. The importance of edible oils in this context lies in their ability to deter and control C. maculatus infestations during storage, preserving the quality and nutritional value of Pigeonpea seeds (Khalequzaman et al., 2007). This investigation aimed to focus on the status of carryover of pest from fields to storehouses causing infestations and pest management by application of edible and non edible oils on grain surface to confer if it is a viable option for future grain storage in storehouses.

Rearing of Callosobruchus maculatus
 
The pulse beetle, C. maculatus, was cultured on cowpea in controlled lab conditions (27±1°C temperature, 70±1% RH). adult beetles from infested grains were placed in open plastic containers with disinfested cowpea. After egg-laying, adults were removed and newly emerged ones were released onto fresh cowpea/moong bean for mating and oviposition. This cycle was repeated every 15 days to ensure a steady supply of insect stages for research.
 
Carryover of C. maculatus from fields to storage
 
The Pigeonpea grains were collected from farm threshing floors of ICAR- IIFSR, Modipuram Meerut and from those grains 100 g seed was divided equally into 4 treatments classifying the infestation carried from field, from storehouse, from field + storehouse and a control. Hundred grams of freshly harvested seeds of pigeonpea with pre-measured moisture content were taken in plastic containers (5x10 cm). For checking field infestations, the container was covered with muslin cloth tightened with rubber band and kept in the laboratory. Another sample of hundred grams of Pigeonpea seed were taken and examined for bruchid infestation. Further it was fumigated for zero infestation carried from the field. It was kept without covering with muslin cloth in the University storehouse to know about the infestation occurring in storehouse. Further hundred grams of freshly harvested seeds were taken in a plastic container which was kept open in the storehouse to find out Field + storage combined infestation. In number four treatment which was control, egg free seeds (same as treatment number two) were taken in plastic container and covered with muslin cloth and tightened with rubber band to avoid oviposition in store house. Observations were recorded after a generation of the insect. The experiments were replicated five times. This experiment was repeated in the next year also the same season for confirmation. Following observations were recorded-
1. Seeds having eggs on per fifty randomly selected seeds from each treatment.
2. Total number of insect damaged seeds from per fifty randomly selected seeds in each treatment.
 
Control of Callosobruchus maculatus with some oils
 
The evaluation was conducted with linseed, mustard, soybean, rice bran, safflower, castor, mahua and neem oil each at concentrations of 0.20, 0.50 and 1.00 ml per 100 g of seeds. An untreated control was kept for comparison. The experiment was conducted under room temperature with an average temperature of 26°C and relative humidity of 83.5 per cent. The grain moisture was 10.50 per cent before the release of freshly emerged beetles. 100 g of seed of each treatment as weighed by electronic balance (400 g total for four replications of a treatment) was taken for each proportion of an oil in plastic containers separately. Required quantities of each oil for 400 g of seed (i.e. 0.20, 0.50 and 1.00 ml per 100 g of seed) were measured with a 1. 00 ml micropipette with graduation up to 0.01 ml. and mixed with the seeds of pigeonpea variety T-21 by shaking thoroughly to get uniform smearing of seeds. Five pairs of newly emerged beetles were then released in each container. The following nine treatments, including an untreated control, were used. The beetles were removed from the container after five days.
 
Treated seed samples of treatments (T-1 to T-9) were kept for 3 months to observe the residual efficacy of different oils smeared with pigeonpea against C. maculatus F. Five pairs of freshly emerged beetles were then released after 3 months. Following observations were recorded.
 
Mean oviposition
 
By counting total number of eggs laid on per 50 randomly selected seeds in each treatment replication.
 
Mean number of adult beetles emerged
 
By counting the total number of adult beetles that emerged after completion of one generation in each treatment replication.
 
Mean seed damage
 
By calculating the percentage of seed damage on 50 randomly selected seed in each treatment replication. Similar observations were recorded at 3 months after releasing five pair of adult beetles.

Carry over of the Callosobruchus maculatus from the field to storage
 
Mean no. of eggs laid
 
During the year 2020-2021 and 2021-2022 after the harvesting and threshing of pigeonpea grains were collected observations were recorded on the different treatments on the following parameters.
 
Mean number of eggs laid on per 50 randomly selected seeds from each treatment were recorded after five days of infestation in store house. During second year’s observations (2021-22), oviposition was recorded more than the first year’s observations(2020-21), due to favourable weather conditions for biological activity of the pest during the period of investigation. Treatments differed significantly in the experiments of both years. Maximum oviposition was observed on freshly harvested seeds kept openly in store house (T3) (16.88 eggs/50 seeds) from field and store house followed by eggs laid in store house (T2) (10.00 eggs/50 seeds). Taking an average of both the years of experimentation eggs came from field with pigeonpea seeds (T1) were found 6.63 eggs/50 seeds which was less than other sources. Whereas, in control oviposition was recorded as zero (Table 1). Patnaik (1984), observed that the C. maculatus.  infest pigeonpea seeds in the standing crop as well as store of pigeonpea. Dharne et al., (1984) recorded 1.33 to 3.61 eggs of C. maculatus after 25 days of harvest.


 
Extent of seed damage
 
In experiment of both years (2020-21,2021-22), mean per cent of seed damage was recorded after completion of one generation on different samples of Pigeonpea seeds. In second year’s observations (2021-22), more seed damage was observed than the first year. Maximum seed damage (5.75%) was noticed in T3 which occupied infestation from both sources i.e, field and store. Treatment 2 (3.75%) was next in order. Infestation came from only field (T1) showed least seed damage (2.25%). Percentage of seed damage was nil in control. These observations were recorded on the basis of circular hole made by the bruchids to emerge out from seed (Table 2). Patnaik (1984), reported that pulse beetle is active in field as well as store. Dharne et al., (1984), recorded per cent seed damage ranged from 30 to 93 per cent on freshly harvested Pigeonpea seeds kept in laboratory. These findings support our present findings.

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Control of Callosobruchus maculatus with edible and non-edible oils
 
Immediately after oil smearing of seed
 
Mean number of eggs laid by C. maculatus 5 days after oil smearing of seeds
 
All the oil treatments provided significant protection to the grain when compared to control. Rice bran oil conceded minimum protection to the grains compared to other oil treatments. Neem and mahua oils were highly effective and significantly better at protection than soyabean, safflower and linseed oil treatment (Table 3). Mustard and castor oil offered slightly lesser protection when compared to neem and mahua, the findings are corroborated by Krishnamurthy and Rao (1944), who also reported inhibition effect of vegetable oil treatments of seeds on egg laying due to the fact that eggs could not be properly adhered on oily surface of seeds. Complete inhibition of egg laying of the pest by seed, treatment with some oils was also reported by other workers.
 


Among three levels of oil treatment 1.00 ml oil applied per 100 g seed was found most effective and significantly better performing than both lower levels, among lower levels 0.20 ml per 100 g seed provided lesser protection than 0.50 ml per 100 g seed. Interaction of oils and their levels of application were not significant.
 
Number of adult beetles emerged after one generation
 
It was observed that with neem oil treatment least number of beetles emerged, which was significantly superior over rest of the oil treatments (Table 3). Mahua oil was superior over soybean, safflower, linseed and rice bran oils. Among all the oils, most beetle emergence was observed with rice-bran oil. However, all the oil treatments were significantly superior over control on the basis of the beetle emergence. Singh (1976), also reported that the population buildup of the pest was checked by treatment with neem and groundnut oils.
 
Similar observations were also made by Mummigatti and Ragunathan (1977), Schoonhoven (1978). Interaction between oils and their levels of application were also found to be significant 0.50 and 1.00 ml oil per 100 g seed levels of neem and mahua oils showed no emergence of beetles being best treatment. Also, mustard and soybean oils at 1.00 ml. level recorded nil emergence. Least effectiveness was observed with 0.20 ml level of rice-bran oil. Levels of oils were also found to be significant. Best effectiveness was observed with 1.00 ml, level, which was at par with 0.50 ml. level, both levels being significantly superior over 0.20 ml level.
 
Extent of seed damage after one generation
 
Effectiveness of different oils increased with their successive higher doses. With lower doses of 0.20 ml oil per 100 g seed. Castor, mahua and neem oil proved more desirable, neem oil providing best effectiveness (Table 3). However, at this level rice-bran oil offered least protection. At 0.50 and 1.00 ml levels all the oils were equally effective in controlling the pest except rice-bran oil at 0.50 ml per 100 g seed and 1.00 ml per 100 g seed.  

The results are corroborated by (Sharma et al., 2018) who reported that Neem oil @ 10 ml/kg completely inhibited the oviposition, adult emergence and seed damage. All the oils and inert materials prevented egg laying, reduced population build-up of beetles and minimized the seed damage when compared to control.
 
Residual effect of different oil treatments three months after oil smearing of Pigeonpea seeds
 
Mean no of eggs laid
 
Neem oil was found most effective followed by mahua, mustard and linseed oil.  Soybean oil treatment was, superior to rice-bran and safflower oils but inferior to all other oil treatments (Table 4). The interaction between type of oils and their levels of application were not registered as significant. The findings are confirmed by Raghvani et al., (2003) who concluded that neem, sesame and groundnut oils at 10 ml/kg seed and Karanja oil at 5 ml/kg seed provided more than 94% protection for up to four months of storage. Singh et al., (1996) reported neem oil @ 0.5 per cent to be the most effective to provide cent percent protection against C. maculatus in green gram for long term.
 
Number of adult beetles emerged
 
Neem oil treatment was most effective followed by mahua oil treatment. Linseed oil and mustard, were inferior to neem and mahua oils and superior to other oil treatments. Rice Bran oil was least effective and significantly inferior to rest of the oil treatments (Table 4). 1.00 ml oil per 100 g seed showed minimum emergence of adult beetles and was significantly superior to 0.20 ml 0.50 ml oil per 100 g seed level. 0.20 ml. level showed maximum emergence and was significantly inferior to both the levels the results are confirmed by Reddy et al., (1999).  Stating that oils caused a significant reduction in oviposition and adult emergence. Neem oil at one per cent level gave the best protection, followed by palmolein, karanja and mahua oils. Fluctuations in untreated control observations in case of oil smearing may be the result of temperature changes as the experiment was carried out at room temperature and due to season change at the time of carrying out residual activity.


 
Lal and Raj (2012), in their studies revealed neem, eucalyptus, sunflower and castor oil at 0.1 and 0.3 per cent (v/w) as safest and most effective concentration of oils to minimize the incidence of C. maculatus on Pigeonpea based on its reduced fecundity, adult emergence and delayed development. However, their investigations registered no adverse effect on seed germination for up to 120 DAT (DAT= Days after treatment).
 
Extent of seed damage
 
Neem, mahua and mustard oil treatments were highly effective providing protection to grain against damage. Castor oil yielded results inferior than linseed, neem, mahua and mustard oils but superior to other oil treatments (Table 4). Rice-bran oil was least effective and inferior to other oil treatments. Fluctuations in untreated control observations in regard to observations taken 3 months before residual effect observation be resulted due to temperature changes as the experiment was carried out at room temperature and due to season change at the time of carrying out residual activity. Amongst the three levels of oil application seed damage was progressively less with increasing levels of oil application. 0.50 ml. level was superior to 0.20 ml. level but inferior to 1.00 ml. level. 1.00 ml. level was superior to both the lower levels. Singh (2017) reported that neem seed kernel powder at 2.0 per cent when admixed to the Pigeonpea and mung bean gave protection against C. maculatus, which corresponds to our findings.

Findings emphasize the critical role of storage conditions in managing Callosobruchus maculatus infestations in Pigeonpea seeds, ensuring their quality and marketability, this study highlights the significance of management of Callosobruchus maculatus infestations in stored pigeonpea seeds. This approach comes across as a promising, eco-friendly and sustainable strategy to manage C. maculatus infestations, ensuring the preservation of seed quality and marketability. All oil treatments were significantly better than the control. Neem, mahua and mustard oils showed the highest effectiveness with no seed damage. Castor and linseed oils were also effective. Findings suggest the potential of neem and mahua oils as promising alternatives for grain protection in agriculture at a dose of 1.00 ml/ 100 g seed, outperforming lower levels. Rice-bran oil performed least effectively, hence, rice bran oil is not ideal for grain protection.

All the authors declare that there is no conflict of interest.