Assessment of diversity and relative abundance of insect fauna associated with Triticum aestivum from district Sialkot, Pakistan

2.1 Study area

The Sialkot is a city in the north east of Punjab, Pakistan. It has a population of 2.7 million that lives in an area of 3016 sq. km, thus, having an estimated density of 903/sq. km. With the help of meteorological center, data regarding average temperature, average rainfall and relative humidity were gathered during 2017 as 25.6 °C, 36 mm and 44.8% respectively (Table 1). The sampling period was from the beginning of January 2017 to June 2017. Selection of sampling site was carried out by considering GC Women University, Sialkot Pakistan as zero point and fixing an area of up to 50 km from this point. Four sampling sites Sambriyal, Dallowali, Wario and Kanpur were selected randomly within 50 km from GC Women university, Sialkot on any side (Fig. 1). The wheat variety MILLAT-2011 was used in these fields. Sampling was conducted fortnightly during this period and each sampling session comprised of three hours in the afternoon until sunset. Data regarding irrigation system, fertilizers, fungicides, herbicides and pesticides was collected and record was kept for further analysis (Table 2).

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Fig. 1

Map of sampling locations of district Sialkot, Pakistan.

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2.2 Collection and preservation of insects

Two fields of wheat crops were selected at each sampling site. Insects were collected by sweep net method. This method was used towards length of the field and from the center of the field by making the figure of eight on one-acre field (Maalik et al., 2013). A total of 50 sweeps were selected while moving in field 20 horizontally and 30 diagonally. Collected specimens were preserved in glass vials containing 70% alcohol as preservative with few drops of glycerin. Labeling was done with date, time of sampling, location, field number and number of samples (Inayat et al., 2011).

2.3 Identification of collected specimen

The collected specimens were identified up to species level by consulting available, classification-based information in the “Fauna of British India” by Talbot (1978), Borror and Delong (2005). This was also confirmed from online electronic keys present on different web sites, Museum of the Department of Agri-Entomology, UAF (University of Agriculture Faisalabad) and Entomological Research institute, Jhang road Faisalabad. All the institutes were taken into consideration for the purpose of identification. Sampled insects were classified as a predator or a prey after verification from the literature (Inayat et al., 2010).

2.4 Statistical analysis

The collected data was subjected to Microsoft Office 2007 at the level of significance α < 0.05. Relative abundance of sampled data was calculated using Microsoft Excel 2007. Following tests were carried out to find results at different levels.

3.1 Diversity and relative abundance of various species

A total of 896 specimens were sampled from wheat field of district Sialkot. The pooled-up data of 2017 showed insect fauna comprising 15 (predator and preys/pests) species belonging to 9 families and 5 orders (Table 3). Collected insects belong to Homoptera (37%), Coleoptera (30%), Diptera (14%), Lepidoptera (10%) and Hymenoptera (9%) (Fig. 2). Overall, highest number of specimen (37%) belonged to family Aphididae while Chrysomelidae showed lower number of specimens (3%) (Fig. 3). S. graminum (157 specimens), C. septempunctata (106 specimens), Rhopalosiphum padi (L.) (96 specimens) and D. noxia (82 specimens) were dominant species, whereas, Ischiodon scutellaris (Fabricius) (27 specimens), Chrysolina hyperici (Forster) (26 specimens) and Coccinella hieroglyphica (L.) (17 specimens) were minimum recorded species.

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Fig. 2

Percentage proportion of insect sampled from wheat field by sweep method of district Sialkot, Pakistan.

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Fig. 3

Families of insect sampled from wheat field by sweep method of district Sialkot, Pakistan.

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Number of insects increases from February (125 specimens) to March (332 specimens) which gradually decreases in April (308 specimens) followed by May (79 specimens) and June (52 specimens), whereas, they were absent in January (Table 4). Overall, maximum aphids were recorded in March but remained low in April. Aphids vanished from fields during May and June. A variation in number of Musca domestica (L.) and Culex pipiens (L.) was recorded from February to June. The number of beetles was at its peak in April but least number was recorded in June (Fig. 4).

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Fig. 4

Month-wise diversity of selected insect fauna sampled from wheat field by sweep method of district Sialkot, Pakistan.

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The highest relative abundance of collected fauna was recorded in March (37.05%) followed by April (34.37%) while it was least in June (5.80%). Relatively, S. graminum was the most dominant species (17.52%) followed by C. septempunctata (11.83%). The most abundant order was Homoptera contributing 37.38% in the collected data followed by Coleoptera 30.23%, Diptera 13.38%, Lepidoptera 9.59% and Hymenoptera 9.37% (Table 5).

3.2 Trophic guilds

Identified insect fauna were assigned as carnivore, herbivore and omnivore based on their food habits (Table 6). The carnivorous guild was dominated by the orders Coleoptera followed by Hymenoptera and Diptera. Sampled data showed that C. septumpuctata was the most dominant predator. Other collected predators/carnivores were C. hieroglyphica, Coccinella undecimpunctata (L.), Cheilomenes sexmaculata (Fabricius), Polistes olivaceus (De Geer) and I. scutellaris. The herbivorous guild was dominated by order Homoptera followed by Lepidoptera. The numerically most captured preys/herbivores in the wheat fields were S. graminum, D. noxia and R. padi.

3.3 Predator prey association

Presence of prey and their predators are interdependent on each other. Highest Predator prey interaction was observed between C. septempunctata (larva) and D. noxia (R² = 0.945) followed by S. graminum (R² = 0.895) and R. padi (R² = 0.819) C. septempunctata showed significant association with most of its preys like D. noxia (R² = 0.912) followed by S. graminum (R² = 0.872) and R. padi (R² = 0.793) (Fig. 5). C. undecimpunctata showed strongest association with R. padi (R² = 0.806). C. sexmaculata was also significantly associated with S. graminum (R² = 0.741) (Table 7).

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Fig. 5

Simple linear regression showing predator prey association between selected species of insects.

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3.4 Shannon diversity index

Significant results were recorded for Diversity (H′ = 2.64), Evenness (E = 0.822) and Dominance (D = 0.08) of insect fauna of wheat fields (Table 8). Comparatively, results showed the highly significant diversity in April (H′ = 2.592) followed by March (H′=2.566), May (H′=2.343), June (H′=2.272) and February (H′=2.270) (Table 9, Fig. 6).

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Fig. 6

Analysis of diversity of five months of wheat crop by applying Shannon diversity index.

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3.5 Canonical correspondence analysis (CCA)

Maximum number of species were significantly associated with rainfall and temperature (Fig. 7). C. sexmaculata and C. undecimpunctata were significantly associated with rainfall. Temperature was significantly associated with C. sexmaculata, Spodoptera exigua (Hubner) and Spodoptera litura (Fabricius).

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Fig. 7

Canonical correspondence analysis (CCA) showing association of insect species (cones) with environmental factors (arrows) in the wheat fields of district Sialkot, Pakistan. Key to species: C. se (C. septempunctata), C. un (C. undecimpunctata), C. hi (C. hieroglyphica), C. se (C. sexmaculata), C. hy (C. hyperici), S. gr (S. graminum), R. pa (R. padi), D. no (D. noxia), A. ce (A. cerana), P. ol (P. olivaceus), S. ex (S. exigua), S. li (S. litura), C. pi (C. pipiens), M. do (M. domestica), I. sc (I. scutellaris).

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4.1 Diversity and relative abundance of various species

This study highlights the richness, abundance and diversity of the insect fauna in Sialkot. The number of sampled insects showed numerical variations in different months. Identified orders were also reported by Ruby et al. (2010) in district Faisalabad. Aphid suppression was recorded which was due to the predatory action of beetles. Rana et al. (2012) also supported the suppression of S. graminum and D. noxia due to beetles. Relative abundance of insects and diversity over the sampling period was not consistent which was primarily because of increased application of chemicals that frequently alter the ratios of pest, predator and parasitoid in an agricultural system. This was also in line with the findings of Siddiqui et al. (2005). Insects were not present in the fields in January which was due to foggy weather and harsh environmental conditions. The variations were observed in the number of aphids (Homoptera) from March to April which was due to temporal fluctuations. Kutschbach-Brohl et al. (2010) reported the parallel temporal discrepancy in diversity and abundance of a variety of insect groups such as Hemiptera and Orthoptera. Abbas et al. (2014) also explained the seasonal fluctuations such as temperature as the cause of difference in the activity of different insect species.

4.2 Trophic guilds

Generally, it is assumed that predator-prey ratios obtained from abundance data of two species clearly indicates cyclic functioning of complex food web structure. Rana et al. (2012) also supported ecological agitation as a significant aspect for ecological collapse of fundamental group from an agricultural system.

4.3 Predator prey association

Omkar et al. (1997) found that many insect predators share the same prey species, but some prey species are preferred over other species. Similarly, in present study, C. septempunctata was significantly associated with all its preys, thus, acting as a general predator, but prefers D. noxia over S. graminum. Rana et al. (2012) also quoted the status of C. septempunctata as a general predator. In wheat, D. noxia and S. graminum was preferred prey species of most of the predators as compared to other prey species. C. septempunctata and C. hieroglyphica showed higher association with aphids (D. noxia). Different predator species showed significant feeding affinities towards single prey species that seemed to confirm the reduction of other prey species as a result of use of pesticides. Inayat et al. (2011) also reported the reduction of species due to the use of pesticides. This may be because of difference in handling of the prey species by the predators. Most of the predators-prey association trend observed in current study showed constant, significant relationship.

4.4 Shannon diversity index

Significant results regarding Diversity (H′ = 2.64), Evenness (E = 0.82) and Dominance (D = 0.08) of insect fauna sampled in 2017 was recorded (Table 8). These results were in line with the findings of Inayat et al. (2010) during her research in 2007–2008 in cropland of Faisalabad. Comparatively, faunal diversity of Faisalabad (2014) was higher than the diversity of Sialkot due to excessive use of insecticides in Sialkot. The pesticide application alters the pest and predator or parasitoid ratios in the agro-ecosystems causing more harm than good. Increased use of pesticides was also supported by Tariq et al. (2007) and Siddiqui et al. (2005).

4.5 Canonical correspondence analysis (CCA)

The CCA was performed on insects to check the effect of environmental factors like rainfall, wind speed, relative humidity and temperature. Most of the species showed strong association with temperature and rainfall. Maalik et al. (2013) and Mbapila et al. (2002) reported temperature as a primary factor for development and mortality of some insects (such as Lepidopterans).

Coccinellids and aphids are significantly related to each other. Ruby et al. (2010) also reported similar results related to the predatory action of Coccinellids (C. septempunctata, C. sexmaculata, Hippodamia convergens (Guerin-meneville) and Hippodamia variegate (Goeze)) on aphids in her study in Faisalabad. Therefore, selected Coccinellids can be introduced as biocontrol agents against aphids. Dixon, (2000) also highlighted the successful introduction of C. undecimpunctata for aphid biocontrol in New Zealand. These results are in conformance with the current findings. Thus, the current study will provide essential base line information of the insect fauna to agronomists in the area. They can take steps to sustain croplands in more efficient manner, which not only lead to increases in crop yield but also stabilize the food webs in the agro-ecosystems of Central Punjab.