Biology and devouring propensity of lady bird beetle , Coccinella septempunctata Linnaeus on rapeseed-mustard aphid , Lipaphis erysimi Kaltenbach

An experiment was conducted to study the biology and devouring propensity of Coccinella septempunctata Linnaeus in the laboratory at 25 ± 1°C and 65 ± 5% relative humidity (RH) on mustard aphid, Lipaphis erysimi (Kalt.) infesting rapeseed-mustard crop during the rabi cropping seasons of 2009 to 2010 and 2010 to 2011. The mean fecundity was 378.00 ± 26.51 eggs/female while ovipositional period, size of egg cluster, incubation period, percentage of grub emergence, larval period, pupal period, total developmental period (egg to adult), mating period and adult longevity were 4.32 ± 0.26, 9.00 ± 0.21, 99.00 ± 0.49, 4.50 ± 0.29, 94.65 ± 0.68, 11.15 ± 0.50, 5.60 ± 0.18, 25.57 ± 1.20, 49.43 ± 39.79 and 122.93 ± 4.05 days respectively. The mean devouring propensity of grubs and adult was 53.11 ± 1.46 and 86.20 ± 1.34 aphids per day per individual, respectively.


INTRODUCTION
Rapeseed-mustard, Brassica juncea (Linnaeus) is one of the important cruciferous oilseed crops cultivated all over India but its yield is largely affected by number of insect pests.Out of these, the mustard aphid, Lipaphis erysimi Kalt is the most dreaded insect, infesting the crop right from seedling stage to maturity.The losses in yield caused by mustard aphid ranged from 9 to 95% at different places of India (Singh et al., 1980;Singh et al., 2012).The bio-control agents like coccinellid and chrysopid have been reported to be effective for controlling the aphids, L. erysimi (Shukla et al., 1990;Singh and Singh, 2013).Among different predators and parasitoids, lady bird beetle, C. septempunctata Linn. is the most important groups of entomophagous predator preying upon wide variety of aphid species and reported as potential predator of aphids and manage the pest population in the field (Agarwala et al., 1987;Afroz, 2001;Pandey and Khan, 2002;Bilashini and Singh, 2009).In evolving eco-friendly strategy using the bio-agents for the management of mustard aphid, C. septempunctata could be a potential predator.
For the effective use of predaceous coccinellids in the integrated pest management programme, a complete investigation on their bio-ecology and predation potential are of utmost importance.The present study was, therefore, carried out to gather relevant information with particular reference to biology and devouring propensity of lady bird beetle on rapeseed-mustard aphid eastern *Corresponding author.E-mail: kuldeepsingh153@gmail.com.Tel: 09235132023, 09889230797.region of Uttar Pradesh.

MATERIALS AND METHODS
The experiment was conducted in the departmental laboratory, Department of Agricultural Entomology, U.P. Autonomous College, Varanasi (U.P.).20 pairs of C. septempunctata were collected from the experimental fields of the same institution and reared in the laboratory at 25 ± 1°C and relative humidity 65 ± 5% on mustard aphid in the specimen jars (15L × 15 W × 25 H) during the Rabi cropping seasons of 2009 to 2010 and 2010 to 2011.The experiment was replicated 10 times for each set during both the crop seasons.
The mustard twigs infested with mustard aphid were provided as food.The eggs were collected from the specimen jars and reared in other jars till they become adults.The males and females were collected from this stock culture and kept separately in petri dishes (15 cm dia) for mating.The mated females individually were allowed to oviposit in separate petridishes (15 cm dia) containing mustard aphid and observations on fecundity and oviposional period were recorded.Twenty freshly laid eggs were kept individually in separate petri dishes (15 cm dia) having moistened filter paper at the bottom.These filter papers were replaced daily to avoid contamination till hatching and the incubation period was recorded.Soon after hatching, the grubs were provided with mustard aphid as food, at least 3 times the number of aphids it had consumed on the previous day.
The numbers of aphids left uneaten were counted next morning.The final instar grubs were provided with additional mustard leaves as a shelter for pupation.The emergence of adults were observed, and also their longevity.The daily consumption of adults on mustard aphid was also recorded till death to find out devouring propensity.Observations were also recorded on the duration of different instar and their devouring propensity, pupal period and adult longevity.

RESULTS AND DISCUSSION
It was studied that, the freshly laid were small, cigar shaped and shiny deep yellow, and turned light grey just before hatching.It is clearly documented from the Table 1 that, the average incubation period was 4.60 ± 0.31 and 4.40 ± 0.26 days during 2009 to 2010 and 2010 to 2011 respectively with means as 4.50 ± 0.29 days which are similar to that of Agarwala and Saha (1986).The average duration of first, second, third, and fourth instar grubs were 2.45 ± 0.13 and 3.30 ± 0.10, 2.20 ± 0.09 and 2.65 ± 0.13, 2.15 ± 0.12 and 2.45 ± 0.14, and 3.20 ± 0.13 and 3.90 ± 0.16 days during 2009 to 2010 and 2010 to 2011 respectively.The total grub period was recorded as 10.00 ± 0.47 and 12.30 ± 0.53 days respectively, with mean period of first, second, third and fourth instars being 2.86 ± 0.12, 2.38 ± 2.43 ± 0.11, 2.30 ± 0.13 and 3.55 ± 0.14 days and total grub period was as 11.15 ± 0.50 days.Agarwala and Saha (1986) and Behera et al. (1999) reported 12.6 and 9.35 ± 0.20 days grub period of C. septempunctata on aphids.
The average pupal period was recorded as 6.50 ± 0.20 and 4.70 ± 0.15 days during 2009 to 2010 and 2010 to 2011 respectively while mean was 5.60 ± 0.18 days.Agarwala and Saha (1986) reported the pupal period was 6.4 days on Aphis gossypii and Singh et al. (2009) reported 5.35 ± 0.15 days on L. erysimi.The adults copulated/mated after 5.80 ± 0.26 to 6.20 ± 0.31 days of emergence, during 2009 to 2010 and 2010 to 2011 respectively with an average of 6.00 ± 0.29 days.The copulation taking place during daytime and night, and this lasted for an average of 48.60 ± 37.21 and 50.25 ± 42.37 min during the first and second year of study respectively with an average 49.43 ± 39.79 min and ranges from 3 to 130 min.
The females started oviposition after 6.20 ± 0.30 and 6.40 ± 0.42 days of mating with an average of 6.30 ± 0.36 days in between the range of 4.00 to 7.00 days and eggs laid in clusters of 8 to 100 eggs/cluster.These results are in corroboration with those of Singh and Malhrotra (1979), Behera et al. (1999), Petro and Behera, (2005) and Singh et al. (2009).The adult females laid an average of 360.75 ± 25.71 and 395.25 ± 27.31 eggs during 2009 to 2010 and 2010 to 2011, respectively while mean fecundity was 378.00 ± 26.51.Behera et al. (1999) reported fecundity as 330.80 ± 22.41 eggs.The average longevity of adults were 120.25 ± 3.75 and 125.60 ± 4.35 during 2009 to 2010 and 2010 to 2011, respectively, while mean was 122.93 ± 4.05 days.Saha (1987) reported the adult longevity of Menochilus sexmaculatus from 80 to 112 days.
The life cycle from egg to adult completed in 25.38 ± 1.14 and 25.75 ± 1.25 days during 2009 to 2010 and 2010 to 2011, respectively, while mean was 25.57 ± 1.20 days.Agarwala and Saha (1986) and Behera et al. (1999) reported total life cycle as 24.20 and 16.02 days respectively, which is in accordance with the present study.
It is inferred that, C. septempunctata had better longevity and high predatory potential/devouring propensity against the mustard aphid and it could be concluded that, it might play a suitable role in biointensive Integrated Pest Management programmes (Table 2).

Table 2 .
Devouring propensity of C. septempunctata Linnaeus on rapeseed-mustard aphid, L. erysimi Kalt.The mean female adult's consumption was 87.54 ± 1.36 aphids per day.The average consumption of adults was 85.98 ± 1.38 and 86.43 ± 1.29 aphids per day during 2009 to 2010 and 2010 to 2011, respectively with a mean of 86.20 ± 1.34 aphids per day.These findings are similar to that of