Insect diversity and abundance
For assessing the diversity of different insect pests of mungbean, survey in Jaisalmer revealed that mungbean crop received the infestation of Spotted pod borer (
Maruca testulalis), pod borer (
Helicoverpa armigera), blister beetle (
Lydomorphus angusticollis), looper (
Chrysodexis sp.), sphinx moth caterpillar, leaf folder, whitefly (
Bemicia tabaci), thrips (
Megalurothrips usitatus) and leaf miner, of these major pests were thrips, pod borer and spotted pod borer (Fig 1). Spotted pod borer was initially found to feed on the growing shoots later infested the pods.
Helicoverpa was first seen on the leaves of mungbean then on the developing pods. Blister beetle was also observed as voracious and devastating pest but was sporadic in nature; In mungbean, spotted pod borer and American pod borer appeared in the second fortnight of July (0.05 and 0.06 larvae) and reached peak (1.02 and 1.01 larvae) in the first fortnight of September. Mean pod damage was observed to be 20.93 per cent which ranged from 12.8 to 41.90 per cent at various locations. Thrips was seen (0.51 thrips) in the second fortnight of July and recorded maximum (4.3 thrips) in the first fortnight of September (Table 1 and 2).
Verma and Saxena (1987) reviewed the insect-pests of mung and enlisted about 99 species of insect pests under 68 genera.
Atactogaster orientalis,
M.
lactivirens and
P.
costalis were reported as new records.
Nimchang et al., (2018) recorded 23 insect-pests in mungbean.
Duraimurugan and Tyagi (2014) recorded the pest spectra on mungbean comprising of 35 species during
kharif season. Broad mite (
Polyphagotarsonemus latus), blister beetle
(Mylabris pustulata), spotted pod borer (
Maruca vitrata) and Bean flower thrips (
M.
usitatus) recorded as the pests of major status during
kharif season at Kanpur location.
Khan et al., (2018) observed richness of aphid, flea beetle and pod borer on mungbean. Grey weevil (
Myllocerus maculosus), black weevil (
Cyrtozemia cognata), jassid (
Empoaska kerri) pod borer (
Lampides boeticus) and white fly (
Bemisia tabaci) were reported as pests in arid region (
Verma and Henry, 1988). They observed mean percent pods damage varying from 2.66 to 29.33 by
L.
boeticus with mean damage of 6.94 per cent at different locations.
Soundararajan and Chitra (2017) recorded legume pod borer larva during
kharif (0.33-3.75/plant) season. As a consequence of canal irrigation, many minor insects have assumed significance in the last two decades and damage to several crops has increased (
Vyas, 1996). Due to strip cultivation of forage with legumes,
C.
pucta exclusive pest of grasses has established on legumes as well (
Verma, 1979).
Cydia ptychora is a less known pod borer of mungbean, but 45% pod with 73% grain damage was observed when grown as companion crop with
Cenchrus sp. grass strips (
Verma, 1986).
Yadav et al., (2020) recorded the spotted borer,
M.
vitrata, chickpea pod borer,
H.
armigera, Bihar hairy caterpillar,
Spilosoma obliqua and leafhopper,
E.
kerri as major pests in Western U.P.
Relative density and diversity index
RD of major insect pests
i.
e. spotted pod borer, American pod borer and thrips recorded to be 10.77, 13.26 and 48.32 percent, respectively. Minor insects were also recorded in numerous proportions (Table 1). A diversity index is a quantitative measure that reflects how many different types (such as species) there are in a dataset (a community). Shannon’s diversity index recorded in this study was 1.45 altogether. It is irrefutable that insects significantly contribute to ecological prosperity and play a crucial role in agroecosystems
(Vijayababu et al., 2016). Studies have shown that the populations of insects population profile are governed by vegetation, abiotic factors and other meteorological factors
(Pinheiro et al., 2002). Vegetation is a major factor in the diversity and composition of insects and any changes to the environment are likely to affect the distribution and relative abundance of insects (
Kerchev el al., 2012;
Patil et al., 2016). The type of vegetation in a given area or habitat has a direct impact on the distribution of insects (
Selvi and Dayana, 2015). The diversity of the entomofauna is highly influenced by weather factors. Temperature, precipitation and relative humidity influence the seasonal activities of insects (
Danks and Key, 2006). There is a strong correlation between rainfall and insect abundance, which may have an impact on the insects numbers (
Selvi and Dayana, 2015).
Relationship of mungbean insect pests with weather parameters
Incidence of
Maruca (0.17 larvae /plant),
Helicoverpa borer (0.63 larvae /plant) and thrips (2.43 thrips) started in the first fortnight of August. Population increased gradually with peak period of incidence of spotted pod borer and thrips coincided with the second fortnight of August while
Helicoverpa attained peak in first fortnight of September (Table 3).
Verma and Saxena (1987) reviewed the insect-pest of mung and enlisted about 99 species of insect including
A.
orientalis,
M lactivirens and
P.
costalis as new records from 68 genera.
Mylocerus maculosus, black weevil (
C.
cognata), jassids, pod borer
L.
boeticus and
B.
tabaci were reported as pests in arid region (
Verma and Henry, 1988).
Mean maximum temperature exhibited mild effect on the decrease of spotted pod borer and increase of
Helicoverpa and thrips population while mean minimum had moderate effect. Mean Maximum and mean minimum relative humidity demonstrated strong significant positive effect on the population of these pests. Sunshine hours demonstrated significant negative relationship of relative humidity with the spotted pod borer as well as thrips population and negative relationship with
Helicoverpa.
Duraimurugan and Tyagi (2014) in mungbean recorded strong negative correlation of flower thrips with mean relative humidity (r= - 0.66) and positive correlation with maximum (r= 0.39 in mungbean) and minimum temperature which are in agreement with the present study. Rainfall recorded a strong negative correlation with the incidence of bean flower thrips (r = -0.78) and spotted pod borer (r = -0.83). There was positive correlation with maximum (r= 0.39) and minimum temperature (r= 0.83) supporting the present study. The present findings outcome are supported by
Kurly and Singh, (2021) who recorded that RH and temperature had positive and rainfall had negative influence on defoliators. In contrast to the present investigation,
Sujatha and Bharpoda, (2017) reported a significant positive association with bright sunshine hours on thrips (r = 0.69*).
Gehlot and Prajapat, (2021) recorded negative correlation of sucking insect pests with rainfall.
