Effect of weather parameters on population dynamics of Coccinellids on different crop ecosystems

Ladybeetles are of great significance as biological control agents, as they are predaceous on several groups of insect pests, including aphids, coccids, adelgids and aleyrodids. Ninety percent of the known 4200 coccinellid species are predaceous (Iperti and Paoletti, 1999). A particular set of environmental conditions is required for coccinellids for their survival and multiplication. The population build up of any insect is very closely associated with various environmental factors prevailing during a periods. Coccinellid predators usually aggregate in patches of high prey abundance, but their relative abundance often changes in space and time due to unpredictable condition of extrinsic and intrinsic factors (Majumder et al., 2013). The present study was carried out to establish the relationship between populations of three important species of ladybird beetle with abiotic factors of environment.

Ladybeetles are of great significance as biological control agents, as they are predaceous on several groups of insect pests, including aphids, coccids, adelgids and aleyrodids. Ninety percent of the known 4200 coccinellid species are predaceous (Iperti and Paoletti, 1999). A particular set of environmental conditions is required for coccinellids for their survival and multiplication. The population build up of any insect is very closely associated with various environmental factors prevailing during a periods. Coccinellid predators usually aggregate in patches of high prey abundance, but their relative abundance often changes in space and time due to unpredictable condition of extrinsic and intrinsic factors (Majumder et al., 2013). The present study was carried out to establish the relationship between populations of three important species of ladybird beetle with abiotic factors of environment.
The seasonal incidence of three dominant coccinellid beetles was studied at Pundibari(Lat. 26 0 19'86" N,Long. 89 0 23'53" and elevation of 43 meter above MSL) under the sub-Himalayan Terai ecological conditions of West Bengal during 2015-16 and 2016-17. The population of Coccinell a transversalis and Cheilomenes sexmaculata was monitored fortnightly on Brinjal whereas; the population of Coccinella septempunctata was monitored in the wheat field. The observations were recorded by random sampling of 25 plants from each crop. The weather data were collected from the meteorological unit of the University. To establish the relationship between populations of predatory coccinellids with abiotic factors, simple linear correlation coefficients (r) were derived between the pooled mean population of coccinellids incidence and various abiotic parameters pooled over two years. The data were statistically analyzed using OPSTAT software package.
The lady bird beetle, Coccinella transversalis appeared in 49 th SMW (i.e., 1 st fortnight of December) (0.8/ plant) on Brinjal, Cheilomenes sexmaculata from 1 st SMW (i.e., 1 st fortnight of January) (0.23/plant) on Brinjal and Coccinella septempunctata from 3 rd SMW (i.e., 2 nd fortnight of January (0.11/plant) on wheat crop (Fig. 1). The highest population of Coccinella transversalis was recorded on 7 th SMW (2.58/plant), Cheilomenes sexmaculata on 7 th SMW (1.95/plant), when average maximum temperature was 28.2 o C, minimum temperature was 11.9 o C, relative humidity was 91 per cent. The highest population of Coccinella septempunctata on wheat was observed in 11 th SMW (1.72/ plant) when temperatures were slightly higher and humidity was lower. In a similar type of studies Hugar et al., (2008) reported that aphidophagous predator (Coccinellids) viz., Coccinella septempunctata, Coccinella transversalis, Cheilomenes sexmaculata appeared from last week of January to first week of March (0.20 to 1.55 Coccinellids per plant). Vermora et al. (2010) also observed that the incidence Correlation coefficients (r) between Coccinella transversalis and weather parameters revealed that minimum relative humidity had highly significant negative correlations with the occurrence of Coccinella transversalis on Brinjal(-0.775), Cheilomenes sexmaculata on Brinjal(-0.837) and Coccinella septempunctata on wheat (-0.849). All other weather parameters had non-significant association with all the three lady bird beetle population. Kalasariya and Parmar (2018) also reported non-significant correlation of lady bird beetle in mustard with most of the weather parameter at Junagadh, Gujarat. Saha et al. (2018) reported that coccinella in cucumber in Bihar was positively correlated with temperature and negatively correlated with humidity.

Effect of weather parameters on population dynamics of Coccinellids on different
The abiotic factors were mostly found to have little influence on the population of coccinellids. Only the relative humidity was found to influence the population greatly. Probably the coccinellids population was more dependent on the population of their respective host insect and fluctuated according to their prey density.

ACKNOWLEDGEMENT
Authors are thankful to the Head, Department of Agril. Entomology, UBKV, Pundibari, West Bengal for providing the necessary facilities for conducting the research work.