Total 25 species of flower visiting insects from 14 different families and 6 orders were observed during the experiment. They belonged to order Hymenoptera (15 spp.), Lepidoptera (5 spp.), Hemiptera (1 sp.), Diptera (2 spp.), Coleoptera (1 sp.), Thysanoptera (1 sp.), respectively (Table 1). Among the order Hymenoptera, the families Apidae (6 spp.), Megachilidae (7 spp.), Halictidae (1 sp.) and Scoliidae (1 sp.) were recorded. Among the 25 insect species recorded on the flowers of the pigeon pea, 8 species belonging to orders Lepidoptera, Coleoptera, Thysanoptera and Hemiptera were harmful and were not considered for further studies and study was mainly concentrated on the insect pollinators of pigeon pea (Table 1). Pollination efficiency ranking was based on the overall pollination rate, foraging behaviour and abundance. Highest pollination efficiency was observed for Megachile disjuncta
which was followed by Xylocopa latipes
and Megachile bicolor
. Pollinators of Apis sp.
were not found to be true pollinator on the investigation of body adhered pollens. Flower morphology had been observed to play a greater role in the pollination effectiveness of the insects. This results were in accordance to (Singh, 2016)
Table 1: Pollination scores, preferred variety and efficiency rankings of different pollinator species (pooled over years).
Among the varieties, PA-441 was most preferred by three species such as Apis mellifera
, Xylocopa latipes
, Megachile bicolor
whereas UPAS-120 and PA-421 were preferred by two species each (Table 1). Keeping the efficiency rating in the mind, UPAS-120 was preferred by the most efficient pollinator and PA-441 was also preferred by two efficient pollinators. Thus this two varieties were largely benefitted by the insect pollinations (Table 2). There was also highest nectar volume recorded with these two varieties which were significantly higher than the rest of the varieties. Nectar volume is also known to be a factor for the attraction of the insect pollinators. It was also observed in the study that mean abundance followed the same trend of the nectar volume present in the flower. Higher abundance of pollinators resulted in significantly higher percentage of cross pollination and correspondingly higher fertilization rate in the varieties. However, effect of insecticides on the nectar volume was found non-significant. On the other hand, insecticides had affected the pollinator abundance and consequently affected the percent cross pollination and fertilization. Mean abundance of pollinators was found highest with Deltamethrin 2.8 EC followed by Quinalphos 25 EC and Indoxacarb 15.8 EC (Table 2).
Table 2: Effect of varieties and different insecticides on nectar volume, mean abundance of pollinators, % cross pollination and % fertilization of pigeon pea (pooled over years).
In order to evaluate the effect of insecticides on the abundance of pollinators, species wise pre-treatment and post treatment abundance readings were compared side by side (Table 3). Deltamethrin 2.8 EC was found to have significantly negative impact on A. florea
and X. latipes
; other pollinators were not affected or positively affected. Lufenuron 5.4 EC was having net negative impact on the abundance of A. dorsata
, A. florea, M. bicolor
and M. disjuncta
. Indoxacarb 15.8 EC was found to reduce the abundance of A. dorsata
, X. latipes
and M. disjuncta
Quinalphos 25 EC was found to have significantly negative impact on the abundance of A. dorsata, A. mellifera, A. florea, X. latipes
and M. disjuncta
(Table 3). These results well justify the trends in Table 2.
Table 3: Effect of insecticides on abundance of bee pollinators, data pooled over years (No. /m2/5 min).
Economic yield and yield attributes such as pods/plant, seeds/pod were found to be significantly affected by both the factors. However, effect on the 100 seed weight was found to be unaffected by the levels of insecticide as it was varietal character. Highest yield was recorded from UPAS-120 (1181.3 kg/ha) followed by PA-441 (1160.1 kg/ha). Among insecticidal treatments highest yield was recorded from Deltamethrin 2.8EC (1219.8 kg/ha). Number of pods as well as number of seeds per pod was determined by the fertilization percentage and hence followed the same trend. UPAS-120 and PA-441 were observed to have highest pods/plant and seeds/pod. Among insecticides, Deltamethrin 2.8 EC with the least negative impact on pollinators had highest pods/plant and seeds/pod. On the contrary, treatments having lower pods/plant and seeds/pod were having higher 100 seed weight due to the more availability of photo synthates to the seeds.