Population dynamics
The present study confirmed the occurrence of 1301 specimens of ladybird beetle which belongs to 12 genera of 5 tribes and 2 sub-families and 13 species were collected throughout the sampling period (Fig 2; Fig 3). Of these 320, 246, 224, 187,124 and 200 ladybird specimens were collected from six respective sites Haringhata, Chakdah, Ranaghat, Santipur, Chapra, Tehatta (Table 3).
Shannon Wiener index (H) was 2.36, 2.21, 2.22, 1.97, 2.13, and 2.04 for the Haringhata, Chakdah, Ranaghat, Santipur, Chapra and Tehatta, respectively (Table 1). The maximum Shannon Wiener index was estimated to be 2.36 in Haringhata indicating the maximum species diversity of the predatory coccinellids.
Simpson’s index is used to measure the dominance of individual species in the sampling unit or sampling area. This index could be understood by deciphering the values from 0 to 1, as 0 indicates low dominance and 1 means high dominance. This shows precisely that dominance of a particular ladybird species influences the dominance of other species in a community. The calculated values of Simpson’s diversity index (D) of ladybird species were 0.8925, 0.8662, 0.8713, 0.8028, 0.8621 and 0.8466 for Haringhata, Chakdah, Ranaghat, Santipur, Chapra and Tehatta respectively (Table 1). The high values of this index in the current study revealed that Haringhata had the high dominance of coccinellids.
Pielou’s evenness index is a measure of equitability which suggests how evenly the individuals are distributed among different species. The values of this index were 0.9207, 0.8632, 0.8689, 0.7702, 0.8305 and 0.7986 for the six respective sites of the present study. C. nigrita was the maximally observed species (23.36 %) followed by N. pumilus (13.45%) and A. cardoni (12.99%) (Table 2; Figure 4). Figure 5 indicated location wise variation in lady bird count in the study region. Haringhata indicated highest lady bird (median count-20) incidence whereas lowest incidence was recorded in Chapra (median count-15). All the other locations indicated similar kind of ladybird incidence. Similarly, there was seasonal variation in lady bird incidence (Figure 7). The seasonal incidence of lady bird in the region can be summarised as Winter (~40) >Summer (~30) >Post Monsoon (~20) >Monsoon (~10) which indicates that the presence of lady bird is highly influenced by rainfall. Drier months are the golden period for ladybirds. From this figure we can deduce that except B. suturalis, C. circumdatus and M. dilatata all the species were present in winter season. C. circumdatus was the least abundant species with 0.61% frequency percentage. Majorly noticed three coccinellid predators are illustrated here with diagnostic notes to facilitate their identification and remain others are provided with short description.
Family Coccinellidae
Subfamily Coccinellinae
Tribe Noviini
Novius pumilus Kapur
(Figures 3 m1-m4, 8, 9, 10, 11)
Rodolia pumila Weise, 1892: 26.
Rodolia okinawensis Miyatake, 1959: 127.-Nakane 1963: 207.-Sasaji 1971: 239.
Novius pumilus: Pang et al. 2020: 20.
Diagnosis: Form is subrounded, with a moderately convex dorsum and a distal half which constricts substantially towards the apex (Figure 9 a). Head and pronotum with brownish red or orange in colour without any markings in clypeaus and frons (Figure 9 b, d). Eyes small, oval shaped, moderately separated, interocular distance about 1.25-1.5x as wide as an eye (Figure 9 d). Ventral side of the body orange in colour (Figure 9 c). Antennae 9 segmented, broadly clubbed and terminal antennomere U-shaped (Figure 9 e; 11 b). Elytra completely orange in colour (Figure 9 f). Elytral epipleuron broad and thick (Figure 9 g; 11 c) Mouthparts (maxilla, labium, labrum and mandible) as illustrated (Figure 9 h-k) Abdominal postcoxal line complete with semicircular shape (Figure 9 l; 11 a).
Male genitalia (Figure 10 a-e) as illustrated, tegmen stout, penis guide in dorsal view and ventral view as long as parameres, paramere gently curved on basal portion in latero-ventral view and strongly curved on basal portion in dorsal view with dense seate inner on the inner side and distal end; penis guide in dorsal view mostly wider at base, gradually narrowed towards apex and form a little stem; penis guide in lateral view as same as dorsal view only the little stem slightly curved on the apex (Figure 10 a, b; 11 d, e). Penis stout (Figure 10 c, d; 11 f), greatly curved with a well-defined penis capsule, penis capsule slightly curved outer arm and typical looking inner arm, penis apex (Figure 10 e; 11 g) not modified gradually narrowed towards tip and form a thread like structure at the end.
Immature stages: Larvae (Figure 8 c, d) pinkish red in colour. Pupae (Figure 8 e) reddish orange in colour. Reflex bleeding can be seen from eclosing adult most in case (Figure 8 f).
Tribe Chilocorini
Chilocorus nigrita Fabricius
(Figures 2 c1-c4, 12, 13, 14, 15)
Coccinella nigrita Fabricius, 1798: 79.
Chilocorus nigritus: Mulsant 1850: 463; Crotch, 1874: 184; Korschefsky 1932: 240; Greathead & Pope 1977: 264.
Chilocorus nigrita: Bielawski 1957: 86; Samways 1989: 345; Booth et al. 1990: 90; Booth 1998: 362; Poorani 2002: 312; Kovář 2007: 593; Li et al. 2018: 9.
Diagnosis: Body nearly hemispherical, strongly convex, shiny and glabrous (Figure 12 d; 13 a). Head dull orange to brownish in colour (Figure 13 d). Pronotum blackish in middle, slightly light tone in the sides and brownish-yellow colour on the frontal-lateral side (Figure 13 b). Eyes approximately oval, moderately separated, interocular distance 1.5x as wide as an eye (Figure 13 d). Ventral side of the body brownish-yellow in colour (Figure 13 c). Antennae 8 segmented, stout and terminal antennomere U-shaped (Figure 13 e; 15 b). Dorsal side of the elytra black in colour (Figure 13 f). Elytral epipleuron greatly broad, thick, inner half of elytral epipleuron neutral-yellow in colour and outer margin brownish to black in colour (Figure 13 g; 15 c). Mouthparts (maxilla, mandible, labrum, labium) as illustrated (Figure 13 h-k). Abdominal postcoxal lines incomplete, reaching posterior margin of abdominal ventrite 1 and running along posterior margin, then almost reaching lateral margin (Figure 13 l).
Male genitalia (Figure 14 a-e) as illustrated, tegmen stout and bulky (Figure 14 a-c; 15 d, e), Penis guide in dorsal view and ventral view longer than pararmeres, parameres in dorsal view strongly tapering at base then gradually broadened up with a dense short setae on the inner sides and distal end and in lateral view parameres slightly curved at basal ½ then widen with a group of long setae; penis guide in dorsal view slightly narrow at base, gradually broadened up to basal ½, narrowing from apical ¼ to apex and form a needle like shape; penis guide in lateral view mostly wider at base, slightly narrow at basal ½ then broadened up apical ¼ and gradually tapering towards apex to form a sharp Knife-like structure . Penis slender (Figure 14 d; 15 f), penis capsule with long outer and short inner arm, apex of penis (Figure 14 e; 5 g) truncate with membranous appendages.
Immature stages: Larvae (Figure 12 a) have a nearly cylindrical body with the dorsal and lateral surfaces covered with spine like projections. Pupae (Figure 12 b, c, e) are exarate and enclosed in longitudinally and medially split open larval exuvium.
Tribe Coccinellini
Anegleis cardoni Weise
(Figures 2 d1-d4, 16, 17, 18, 19)
Verania cardoni Weise, 1892: 19 (Holotype, ZMB; Type locality: ‘Chota-Nagpore’-Mandar).
Coelophora cardoni: Gorham 1894a: 202; 1894b: 209.
Micraspis cardoni: Timberlake 1943: 27.
Anegleis cardoni: Iablokoff-Khnzorian 1982: 295; Poorani 2002a: 321
Diagnosis: Form round and strongly convex (Figure 16 e, f; 17 a). Head oyster yellow colour, posteriorly blackish (Figure 17 d). Pronotum creamy yellow colour with a pair of triangular dots (sometimes fused with each other) in the middle and a pair of triangular markings on the posterior margin (Figure 17 b). Eyes semicircular, fairly separated, interocular distance 2x wide as an eye (Figure 17 d). Ventral portion of body brown to yellowish-orange in colour (Figure 17 c). Antennae long, 11 segmented, densely clubbed and terminal antennomere U shaped (Figure 17 e; 19 b). Elytra creamy yellow in colour, each elytron has two thin black stripes: an inner stripe that is curved posteriorly towards the lateral border and an outer stripe that is bent anteriorly towards the suture, a tiny round spot close to the apex (Figure 17 f). Medial black suture line present (Figure 17 a). Elytral epipleura broad and thick (Figure 17 g; Figure 19 c). Mouthparts (labium, labrum, mandible and maxilla) as illustrated (Figure 17 h-k). Abdominal postcoxal lines incomplete, reaching posterior margin of abdominal ventrite 1 and running along posterior margin (Figure 17 l; 19 a).
Male genitalia (Figure 18 a-e) as illustrated, tegmen stout (Figure 18 a-c; 19 d-f) penis guide dorsally or ventrally almost same as long as parameres, parameres in dorsal view thick, strongly tapering at base then gradually broadened up with a dense short setae on inner side and distal end and in lateral view parameres slightly curved at base; penis guide in dorsal view extremely narrow at base, gradually broadened towards apex and form a distinct inverted Y-shaped structure; penis guide in lateral view immensely narrower at base, greatly wider at basal ½, then tapering towards apex and form a curved tweezer shape. Penis stout (Figure 18 d, e; 19 g, h) moderately curved with well-defined penis capsule, penis capsule with moderately long outer and short inner arm, inner arm forms a hooklike shape, apex of penis (Figure 18 e; 19 h) distinct and wrench shaped.
Immature stages: Larva purplish brown to dark brown with creamy white to light yellow in colour (Figure 16 a, b, c). Pupa reddish brown with light shade of pink colour (Figure 16 d).
Species account
Illeis confusa Timberlake(Figure 2 a1-a4)
Description: Body is elongated oval with a glabrous, mildly convex dorsum. Elytra yellow in colour, head and pronotum creamy white colour. Pronotum always with a pair of black dots.
Chilocorus circumdatus Gyllenhal (Figure 2 b1- b4)
Description:Body is broadly oval to nearly circular, with a hemispherical, highly convex, and smooth dorsal surface. The elytra are reddish-brown with a narrow black border along the lateral edges, approximately 1/10th of the elytral width.
Micraspis discolor Fabricius (Figure 2 e1-e4)
Description: Body is semicircular to oval with moderately convex dorsum. Elytra reddish brown in colour.
Cheilomenes sexmaculata Fabricius (Figure 2 f1-f4)
Description:Form oval to subrounded. Dorsal side of the body mostly convex, glabrous and shiny. Ground colour is orange or yellowish orange. Pronotum with T shaped median marking. Elytra have two zigzag black lines, a posterior subapical black spot and black suture line.
Jauravia pallidula Motschulsky (Figure 3 g1-g4)
Description:The shape is generally semicircular, with a moderately convex back that is densely covered in silvery white hairs, and the colour is orange to reddish brown.
Coccinella transversalis Fabricius(Figure 3 h1-h4)
Description: The body is elongated, oval, and convex. The head is black with two creamy yellow, subtriangular spots near the inner edges of the eyes. The pronotum is black with light cream at the anterolateral corners. The scutellar shield is black. The elytra are bright orange featuring an oval spot near the scutellum, a large trilobed spot on the humeral region, a transverse band at the apical third that doesn’t reach the lateral margin, and three smaller apical spots—one sutural and two lateral, often fused into a transverse marking.
Propylea dissecta Mulsant(Figure 3 i1-i4)
Description: The body is oval with moderately convex dorsum. Anchor-shaped black markings are present on each elytron on the humeral region. A transverse band with circular endings like a dumbbell shape formation present on the apical third. Black suture line is present. Pronotum with large transverse black marking.
Brumoides suturalis (Fabricius)(Figure 3 j1-j4)
Description: The body is oval with a convex dorsum. The head and pronotum are orange. The elytra are gleaming white, featuring three black stripes: one on each elytron in a mid-dorsal position that doesn’t reach the apex, and one sutural stripe that also doesn’t extend to the apex.
Ortalia vietnamica Hoang(Figure 3 k1-k4)
Description: Body is elongated oval with convex dorsum. Elytra orange in colour with densely covered silvery white hairs. Pronotum and head is creamy yellow in colour.
Megalocaria dilatata (Fabricius)(Figure 3 l1-l4)
Description: Body is round with greatly convex dorsum and glabrous. Elytra reddish brown in colour, five black spots on each elytron arranged in 1-2-2 pattern. Pronotum with two black oval spots on the posterior margin.