Temporal variation of aquatic insects biodiversity in selected rice fields of Saran district of Bihar

 

Nabab Ali¹, Equabal Jawaid

¹Research Scholar, Jai Prakash University, Chapra (Bihar)

²Department of Zoology, ZA Islamia PG College,Siwan (Bihar)

 

Abstract:

Rice is a major food crop of India. The rice cultivation has maintained its priority status in the agricultural sector of the country. The intensive management practices adopted by the practitioners have resulted in genetic erosion, thus affecting the species composition of the rice field ecosystems. There is obvious difference in species composition and community structure in upland and lowland rice fields and lowland fields has minimum pests affecting production of yield per hectare. This paper presents a work carried out on the biological diversity of lowland rice field ecosystems of India, and proposes the need for conservation strategies to ensure the sustainability of these rice growing ecosystems in the long run.

 

 

 

INTRODUCTION:

The vegetative and reproductive stages of rice crop are represented by aquatic phase of the rice field while the semi aquatic and terrestrial dry phases correspond to the grain ripening stage. Therefore, a rice-field ecosystem undergoes through three major ecological phases: aquatic, semi-aquatic and terrestrial dry phase during a single crop cycle (1). Each of these phases supports a particular type of fauna and flora. Resultantly the rice field has the greatest biodiversity as compared to the other tropical rain fed systems (2).

 

The biodiversity of fauna and flora of rice fields has characteristic of rapid colonization as well as rapid reproduction and growth of organisms. These organisms colonize rice fields by resting stages in soil, by air and via irrigation water (1, 3). The fauna inhabiting the vegetation, water and soil sub-habitat of rice field are dominated by invertebrates. Those that inhabit the vegetation are generally insects and spiders. In relation to the rice crop, the fauna in rice field include pests, their natural enemies (predators and parasitoids) and neutral forms etc. The organisms inhabiting the rice field ecosystem can be considered as opportunistic biota with high resilience stability as they holds the ability to recover rapidly from various disturbances, including chemical inputs (4).

 

A rice field is frequently disturbed by farming practices i.e., tillage, irrigation, crop establishment and agrochemical application. Traditional rice systems were sufficiently multifaceted ecosystems and did not involve the use of chemical fertilizers, maintained a moderate but stable yield for thousands of years because a rich array of micro-organisms and other invertebrates enabled them to maintain soil fertility by generation of nutrients through recycling for rice cultivation in contrast to modern rice cultivation (5-7).

 

However, the current state of knowledge about insect biodiversity associated with rice crop is inadequate and a lot of research is waiting to be done in this field. The changes to the insect biodiversity associated with rice crop would be evaluated with greater precision and confidence in coming decades. Moreover, this study aims not only to establish a baseline data on species richness and distributions to which future surveys and conservation activities could be related but also to assess differences from place to place, under different management systems, or from present to future.

 

MATERIALS AND METHODS:

The insects were collected with the help of insect net and evaluated for different community parameters during the study period (8, 9) which are described as:

 

Shannon-Weaver diversity index (H) was used to determine which sample has more abundant species. A species diversity study takes into account the number of species (species richness) and the importance of individuals in species evenness. Shannon's index accounts for both abundance and evenness of the species present. The proportion of species i relative to the total number of species (p_i) was calculated, and then multiplied by the natural logarithm of this proportion (ln p_i). The resulting product was summed across species, and multiplied by -1. H is a more reliable measure as sampling size increases. The addition of the calculation of evenness (J) or equitability (EH) was also applied. Shannon's equitability (EH) was calculated by dividing H by Hmax (here Hmax = lnS). J=EH =H/H max = H/ ln S

 

The evenness index measures how evenly species are distributed in a sample. When all species in a sample are equally abundant an evenness index will be at its maximum, decreasing towards zero as the relative abundance of the species diverges away from evenness (Sebastian et al, 2005). It means evenness assumes a value between 0 and 1with 1 being complete evenness i.e., a situation in which all species are equally abundant. Simpson's diversity index (D) was used to determine which sample has more rare species. It is a simple mathematical measure that characterizes species diversity (rarity) in a community as

 

S=(1-D) = 1 - ∑[  n_i (n_i-1)/ N (N-1)]

 

where pi is the proportional abundance of the ith species and is given by p_i= n_i /N, i= 1,2 ,3,…….S and  n_i is the number of individuals of i^th species and N is the known total number of individuals for all S species in the population. Simpson’s index varies from 0 to 1 and gives the probability that two individuals drawn at random from an infinitely large population belong to the different species. For a given species richness (S), evenness (J) increases as D decreases, and for a given evenness, D decreases as richness increases.

 

In order to represent number of abundant species in samples and also to represent species maximum in abundance Hill’s diversity numbers were used. In equation form, Hill’s diversity numbers are

 

H_α = (∑ p_i^α) ^1/(1-α)

where pi is the proportion of individuals belonging to ith species. Hill shows that the 0th, 1st and 2nd order of these diversity numbers (i.e., A=0, 1 and 2) coincide with three of the most important measures of diversity. Hills diversity numbers are Number 0: N₀=S, where S is the total number of species, so, N₀ is the number of all species in the sample regardless of their abundance,  Number 1: N₁=eH, where H is the Shannon’s index and _N1 is the measure of number of abundant species in the sample. N₁   will always be intermediate betweenN₀ and N_2, and Number 2: N₂=1/λ, where λ is Simpson’s index and N₂ is the number of species maximum in abundance in a sample.

 

The species richness was also calculated to determine whether the sampling sites had been sufficiently sampled or not.

 

RESULTS AND OBSERVATIONS:

Temporal variation in insect faunal diversity in the Site 1:

The values for S, N, H, D, J were 125, 1026, 3.061, 0.135, 0.554 at pre-nursery; 172, 1840, 3.814, 0.055, 0.652 at nursery; 195, 2950, 4.088, 0.043, 0.685 at tillering-booting; 193, 1480, 4.269, 0.033, 0.716 at flowering-milking; 184, 1045, 4.234, 0.039, 0.716 at grain ripening stage of rice crop (Table 1).

 

In the Site 1, insect species richness and abundance increased with crop age and reached maximum at tillering-booting stage in the months of July-August and then declined gradually towards crop maturity. The value of (H) increased from pre-nursery stage and reached at its maximum at flowering-milking stage in the month of September and then decreased slightly at grain ripening stage. It means highest number of abundant species N1 (i.e. 88 species in which 30 species were maximum in abundance) was in the month of September (Table 5). The number of rare species (D) was maximum at pre-nursery stage and indicated that most of the species in the month of May (pre-nursery stage) were present in very low number because they had just started to invade the fields where puddling operations had been started. This result was also supported by the fact that at pre-nursery stage abundant species (N1) were least (21) as compared to other crop stages.

 

For LIP system the values for S, N, H, D, J were 104, 5560, 3.103, 0.110, 0.580 at pre-nursery; 152, 9994, 3.870, 0.0519, 0.676 at nursery; 175, 18090, 3.896, 0.049, 0.665 at tillering-booting; 170, 9800, 4.104, 0.034, 0.704 flowering-milking; 162, 5800, 4.193, 0.036, 0.725 at grain ripening stage, respectively. But in case of HIP the values for S, N, H, D, J were 79, 4414, 2.706, 0.195, 0.535 at pre-nursery; 148, 8850, 3.509, 0.066, 0.645 at nursery; 140, 11572, 4.120, 0.038, 0.730 at tillering-booting; 140, 4806, 4.139,  0.043, 0.734 at flowering-milking; 130, 4700, 3.955,  0.050,  0.711  at grain ripening stage, respectively (Table 2).

 

Temporal variation in insect faunal diversity in the Site 2:

The values for S, N, H, D, J were 120, 748, 3.554, 0.068, 0.648 at pre-nursery; 173, 1635, 3.634, 0.063, 0.621 at nursery; 204, 3596, 3.986, 0.037, 0.663 at tillering-booting; 208, 1360, 4.338, 0.029, 0.719 at flowering-milking; 188, 1380, 4.030, 0.051, 0.679 at grain ripening stage of rice crop, respectively (Table 3).

 

The values for S, N, H, D, J in case of LIP system were 99, 536, 3.363, 0.082,  0.635 at pre-nursery; 146, 930, 3.497, 0.082, 0.615 at nursery; 182, 1722, 3.963,  0.040, 0.672 at tillering-booting; 185, 866, 4.233, 0.032, 0.716 at flowering-milking; 159, 811, 3.871, 0.055, 0.671 at grain ripening stage, respectively. However, in case of HIP the values for S, N, H, D, J were 76, 205, 3.491, 0.080, 0.694 at pre-nursery; 124, 706, 3.498, 0.070, 0.634 at nursery; 150, 1675, 3.804,  0.046, 0.667 at tillering-booting; 149, 494, 4.237, 0.032, 0.743 at flowering-milking; 135, 569, 4.005, 0.051, 0.714 at grain ripening stage, respectively (Table 4).

 

Temporal variation in insect faunal diversity in the Site 3:

The values for S, N, H, D, J were 118, 927, 3.063, 0.114, 0.560 at pre-nursery stage; 172, 1674, 3.491, 0.093, 0.597 at nursery; 201, 4546, 4.01, 0.042, 0.669 at tillering-booting; 210, 1530, 4.195, 0.037, 0.694 at flowering-milking; 204, 1050, 4.425, 0.028, 0.736 at grain ripening stage, respectively (Table 5).

 

In the Site 3 the values for S, N, H, D, J in case of LIP system were 89, 629, 2.754, 0.145, 0.532 at pre-nursery; 151, 1024, 3.208, 0.122, 0.561 at nursery; 185, 2522, 4.092, 0.033, 0.692 at tillering-booting; 196, 941, 4.028, 0.048, 0.675 at flowering-milking; 183, 692, 4.163, 0.038, 0.705 at grain ripening stage, respectively. In case of HIP the values for S, N, H, D, J were 87, 299, 3.376, 0.076, 0.653 at pre-nursery; 125, 650, 3.694, 0.063, 0.669 at nursery; 154, 2023, 3.713, 0.073, 0.648 at tillering-booting; 152, 590, 4.130, 0.036, 0.722 at flowering-milking; 147, 358, 4.575, 0.020, 0.805 at grain ripening stage, respectively (Table 6).

 

Table 1: Temporal variation in insects associated with rice crop agro-ecosystem in the Site 1.

 

Table 2: Spatio-temporal variation in insect associated with LIP & HIP rice crop agro-ecosystems in the Site 1.

Table 3: Temporal variation in insects associated with rice crop agro-ecosystem in the Site 2.

 

Table 4: Spatio-temporal variation in insects associated with LIP & HIP rice crop agro-ecosystems in the Site 2

 

Table 5: Temporal variation in insects associated with rice crop agro-ecosystem in the Site 3.

 

Table 6: Spatio-temporal variation in insects associated with LIP & HIP rice crop agro-ecosystems in the Site 3.

 

Table 7. Overall temporal variation in insects associated with rice crop agro-ecosystem in the Site 1.

 

Table 8: Overall spatio-temporal variation in insect associated with LIP & HIP rice crop agro-ecosystems.

 

 

Overall temporal variation in insect faunal diversity in the Sites:

In the Sites, the overall values for S, N, H, D, J were 180, 2698, 3.345, 0.099,  0.568 at pre-nursery; 225, 5150, 3.788, 0.061, 0.620 at nursery; 241, 11100, 4.162, 0.034, 0.673 at tillering-booting; 244, 4352, 4.464, 0.025, 0.721 at flowering-milking; 242, 3490, 4.394, 0.033, 0.710 at grain ripening stage, respectively (Table 7).

 

In the Site 1 the overall values for S, N, H, D, J in case of LIP system were 155, 1750, 3.242, 0.104, 0.565 at pre-nursery; 210, 2914, 3.696, 0.069, 0.612 at nursery; 230, 6254, 4.161, 0.035, 0.679 at tillering-booting; 236, 2782, 4.382, 0.028,  0.711 at flowering-milking; 229, 2080, 4.295,  0.036, 0.701 at grain ripening stage, respectively. In case of HIP the values for S, N, H, D, J were 133, 945, 3.368,  0.094,  0.603, at pre-nursery; 175, 2240, 3.760, 0.058, 0.641 at nursery; 202, 1560, 4.032, 0.040, 0.672 at tillering-booting; 202, 1564, 4.439, 0.025, 0.739 at flowering-milking; 195, 1398, 4.401, 0.032, 0.738 at grain ripening stage, respectively (Table 8).

 

DISCUSSIONS:

The change in diversity with respect to passage of time or along a time scale is called temporal diversity (10, 11). Rice crop during a single cropping season passes through different crop/ecological stages (generally corresponding to a particular month of the growing season) supporting a special type of insect fauna associated with that particular type of crop stage or habitat (1, 4, 11).

 

The rarity decreased as the crop age increased with minimum at flowering-milking stage. This might be due to the drastic effects by application of agrochemicals (in the end of August or in the start of September) on some sensitive species causing their mortality. As a consequence only abundant species left behind and thus resulted into lower value of rare species. There was, then, a slight increase in the rarity at grain ripening stage in the month of October. The fact was that as the rice crop reached at its maturity, many species including a number of tourist species, visited rice fields to utilize this special type of man-made aquatic habitat for many purposes and contributed to increase in rarity.

 

Besides this at grain ripening stage, the species left for rice crop because of drastic changes in plant and soil which made rice crop less favorable for many species ultimately there was an increase in the rarity of species as compared to flowering-milking stage. The values of (J) also depicted that evenness increased gradually from pre-nursery to grain ripening stages of rice crop gradually with its maximum value (72%) at flowering milking and grain ripening stages. At tillering-booting stage rarity was high for LIP as compared to that for HIP. This could be due to HIP practices, especially due to the use of insecticides in the end of August, which did not allow all species to behave in the same manner and affected deleteriously to most of sensitive species resulting into disappearance of these low populated species and consequently number of abundant species at tillering-booting stage in HIP system increased. Due to harms (unfavorable conditions) of intensive farming system sensitive species avoided from HIP system and their population did not increase in abundance and remained below a certain level and contributed to more number of rare species.

 

In the Site 2 the values of S, N, H, D, N1 and N2, changed almost in the same manner as for the Site 1. The insect fauna of rice crop behaved almost in the same manner for both of the sites. However, the values of (J) responded in a different way in comparison with Site 1. These fluctuated throughout the crop stages. However, the species at all crop stages were distributed with almost equal evenness with highest (71%) at flowering-milking stage.

 

The differences in values of (H) between LIP and HIP systems were significant (P<0.05) at pre-nursery & grain ripening stage for HIP and at tillering-booting stage for LIP. However, these differences were non-significant (P>0.05) at nursery and flowering milking stages. The value of (D) was high at almost all crop-stages (except at tillering-booting) for LIP system with highest at pre-nursery and lowest at flowering-milking stage. This indicated that LIP had more number of rare species. The species in LIP system, as a result, were distributed with comparatively low evenness with lowest value of 61% at nursery stage. Similarly, the number of abundant species and species maximum in abundance were also high at almost all crop stages (except at tillering-booting stage) for HIP system with highest value of 69 species among which 30 were maximum in abundance at flowering-milking stage.

 

 

The value of (D) was highest at pre-nursery stage which decreased gradually with crop age. This indicated that rarity decreased with crop age with lowest at grain ripening stage indicating that at this stage most of the species were present in fairly good number. The value of (J) also increased continuously from pre-nursery to grain ripening stage reflecting that even distribution of species increased as the crop progressed and at grain ripening stage evenness reached at its maximum with 73% even distribution of species. From these results it is evident that Site 3 was different from the other two sites because in Site 3 diversity followed a uniform and smooth pattern.

 

The species richness and H increased as the rice grew towards maturity with the maximum at flowering-milking stage and then there was a slight decline at grain ripening stage due to availability and scarcity of aquatic insects in studied rice fields (Figure 1).

 

Figure 1: Comparison of community structure in the Rice Crop ecosystems.

 

These changes in values of (D) indicated that number of rare species decreased as crop matured because with the passage of time all the invading species started to increase their population in rice crop habitat and hence the (J) increased with crop age. The results are in accordance with studies of (12), (13) and (14).

 

It is evident from observations that the values of S, H, J, N1 and N2 increased at site 2 with crop age and reached at their maximum at flowering-milking stage of the rice crop in September for both HIP and LIP systems and then declined at grain ripening stage in October. The species abundance also increased with crop age and was maximum at tillering-booting stage in July-August for both of the systems and then declined towards crop maturity (Figure 2).

 

Figure 2: Comparison of insect species (a) richness and (b) abundance in LIP & HIP rice fields.

 

 

The number of rare species (D) decreased with crop age and was minimum at flowering-milking stage, it then increased slightly at grain ripening stage. These results suggested that maximum number of insect species utilized rice crop agro-ecosystem as a habitat at flowering-milking stage. The values of (H) indicating abundant species in sampled population for both of the systems were also maximum at flowering-milking stage. It is clear that at flowering-milking stage due to high number of abundant species the number of rare species was less. Almost at all crop stages (except at tillering-booting stage) the species were distributed with high evenness for HIP. Similarly, N1 and N2 were also higher at flowering-milking stage. The differences among the values of (H) at all crop stages were significant (P<0.05) in favor of HIP system except for tillering-booting stage.

 

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Received on 27.02.2023       Modified on 06.03.2023 Accepted on 10.03.2023      ©A&V Publications All right reserved Research J. Science and Tech. 2023; 15(1):57-63. DOI: 10.52711/2349-2988.2023.00011