Diversity of Insect Fauna Associated with Summer and Monsoon Cowpea [Vigna unguiculata (L.) Walp.]

Cowpea [Vigna unguiculata (L.) Walp], an important annual legume improves the protein source in vegetarian diet. The herbaceous plant known as mini-factory of fertilizer as they fix the atmospheric nitrogen with the help of rhizobium bacteria. Cowpea is known to harbor many natural enemies of pestiferous insects, which exert a significant role in their suppression.
       
The damage by insect pests is one of the major constraints accounting for low level of yield. Cowpea crop is extensively infested by 21 insect pests from different groups cultivated during summer and monsoon season (Sardana and Verma, 1986). Some of the insects also act as vectors of various virus diseases or as defoliators, damage to flowers and pods. Cowpea crop is infested by the legume aphid (Aphis craccivora Koch), foliage beetles (Ootheca sp., Medythia spp.), the flower bud thrips (Megalurothrips sjostedti Trybom), the legume pod borer (Maruca vitrata Fabricius) and the sucking bug complex including: Clavigralla spp., Anoplocnemis spp., Riptortus spp., Mirperus spp., Nezara viridula Fab. and Aspavia armigera Linnaeus (Meena et al., 2017).
       
The different diversity indices accounts for species richness and abundance. A large number of species can increase diversity. Similarly, increasing the uniformity of individuals’ distribution among species will also increase diversity. The biodiversity studies will facilitate researchers to understand the abundance and species richness of insect fauna associated with cowpea. It gives an account to quantify the interaction between the insect pest and their associated natural enemies. This knowledge helps to understand the insect ecology, hence provides a guide for developing management tools which are area specific and result in efficient reduction in pest damage.

The biodiversity of insect fauna associated with cowpea was observed from different locations of southern Rajasthan. The insect collected from cowpea were belongs to order Lepidoptera, Coleoptera, Hemiptera, Thysanoptera and Diptera; whereas, the families comprised Agromyzidae, Aleyrodidae, Alydidae, Aphididae, Chrysomelidae, Cicadellidae, Coccinellidae, Coreidae, Geocoridae., Lycaenidae, Noctuidae, Pentatomidae, Reduviidae, Sryphidae and Thripidae. The flea beetle (Phyllotreta spp.) was first to appear at all the surveyed location and lycaenid borer (Lampides spp. and Euchrysops spp.) was last to invade the crop. Both of these insects were also recorded by Patel et al., 2010, Patient et al., 2019 and Sharma et al., 2019 from different locations.
       
During the study, it was noticed that overall species richness was more during the monsoon season as compared to summer season. It is evident from Table 1 to 3, that the total spices abundance was the maximum at Banswara during monsoon, 2019; whereas, it was the maximum for Bhilwara during monsoon, 2020. The relative diversity of aphids was the maximum on account of the clumped distribution and exponential growth (Table 1 and 2). Thrips population was not observed at Chittorgarh and Pratapgarh during summer, 2019; while it was noticed at Pratapgarh during monsoon, 2019.






       
During summer, Udaipur had the highest value of Simpson index (3.35) followed by Bhilwara (2.79), Banswara (2.45) and Chittorgarh (2.34), while, Pratapgarh (2.16) had the lowest value. The Simpson index was calculated to be highest for Banswara (6.49) followed by Bhilwara (3.40), Chittorgarh (3.35), Udaipur (3.14) and lowest diversity index was recorded for Pratapgarh (2.84) during monsoon.
       
Similarly, the highest Shannon index was recorded at Udaipur (1.67) during summer followed by Bhilwara (1.54), Banswara (1.43) and Chittorgarh (1.35). The Shannon index was lowest for Pratapgarh (1.26) during summer. The Shannon index was highest for Banswara (2.04) followed by Bhilwara (1.69), Udaipur (1.63) and Chittorgarh (1.58) during monsoon, while, the lowest value was recorded for Pratapgarh (1.46) (Table 3).
       
During summer season, Simpson index was highest for Bhilwara (4.03) followed by Banswara (3.75), Pratapgarh (3.45) and Chittorgarh (3.43), while, the highest Simpson index was observed for Bhilwara (3.96) followed by Chittorgarh (3.76), Pratapgarh (3.67), Banswara (3.61) during monsoon. The lowest Simpson index was observed for Udaipur (2.67 and 3.49) during summer and monsoon, respectively (Table 3).
       
The value of Shannon index was calculated to be highest for Bhilwara (1.81) followed by Banswara (1.76), Pratapgarh (1.56) and Chittorgarh (1.53) during the summer. Similarly, it was highest for Bhilwara (1.80) and was followed by Chittorgarh (1.76), Pratapgarh (1.75) and Banswara (1.73) during monsoon. The lowest Shannon index (1.51 and 1.71) for summer and monsoon season was recorded in cowpea grown at Udaipur (1.51 and 1.71) (Table 3).
       
The present study observed that the insect fauna in monsoon cowpea were more diverse in higher and lower levels of taxa. The present findings are more or less  in accordance with the earlier work of Pinjara (2017) who reported that Shannon diversity indices ranged from1.72 to 1.54 as per crop and location in Udaipur. As much work has not been done on comparative studies on insect pest diversity of cowpea, there is a need to initiate further research work.

From the present study it can be concluded that, the species richness and abundance of insect species was more during monsoon season as compared to that in summer. The diversity was found to be different for different locations. However, the aphid population was the most dominant species in both seasons at all the locations of southern Rajasthan.