Morphometrics and biological parameters of C. chinensis
The detailed bilogy and morphometrics of C. chinensis on two pigeonpea accessions ICPL 161(cultivar) and ICPW 68 (wild relative) are represented in the tabel 1.
Egg
Minimum incubation period of pulse beetle eggs was observed on ICPL 161, which ranged from four to five days. The maximum incubation period of eggs was 7–8 days on ICPW 68. The maximum number of eggs were deposited on the second day of oviposition, afterwards the number of eggs laid reduced gradually until the end of oviposition period. The highest total numbers of eggs were laid on ICPL 161 with an average of 42.35. While the lowest egg laying was recorded on ICPW 68 with an average of 24.68 eggs per female. The eggs were small, oval, white, smooth, laid singly and were glued on the pigeonpea grains surface by a secretion from the female beetles. The freshly laid eggs were translucent smooth and shining, which afterwards became yellowish white and were spectacular against the contrasting background of the grains. Many eggs were laid on a single grain.
The average length and breadth of the eggs were 0.56 ± 0.02 mm, 0.50 ± 0.03 mm and 0.31 ± 0.02 mm, 0.28 ± 0.02 mm on ICPL 161(Fig. 2) and ICPW 68 (Fig. 3) respectively. The egg hatching was determined by the change in colour of the eggs. The hatched eggs turned to creamish white colour due to the accumulation of frass inside the egg. The results are similar with Sathish et al., (2020) who reported mean incubation period of eggs ranging from 4.00 to 5.00 days on chickpea. The present findings are in agreement with the findings of Devi, et al., (2014) who reported the duration of egg from 6–7 days. The eggs measured 0.47 ± 0.08 mm in length and 0.12 ± 0.21 mm in breadth.
Table 1
Morphometrics and biological parameters of C.chinensis reared on pigeonpea genotypes (ICPL 161 and ICPW 68)
|
Stages
of bruchids
|
Length
(Mean ± SE) (mm)
|
Breadth
(Mean ± SE) (mm)
|
Duration
(Days)
|
|
ICPL 161
|
ICPW 68
|
ICPL 161
|
ICPW 68
|
ICPL 161
|
ICPW 68
|
|
Egg
|
0.56 ± 0.02
|
0.50.5 ± 0.03 ± 0.03
|
0.31 ± 0.02
|
0.280.28 ± 0.020.02
|
4–5
|
7–8
|
|
I
Instar
|
0.52 ± 0.01
|
0.48 ± 0.01
|
0.29 ± 0.04
|
0.29 ± 0.06
|
5–6
|
5–7
|
|
II
instar
|
1.4 5 ± .06
|
0.77 ± 0.10
|
0.81 ± 0.02
|
0.54 ± 0.03
|
5–6
|
5–6
|
|
III Instar
|
2.58 ± .10
|
1.2 ± 0.07
|
1.21 ± 0.03
|
0.8 ± 0.06
|
4–5
|
7–8
|
|
IV Instar
|
3.47 ± 0.08
|
2.28 ± 0.04
|
1.82 ± 0.08
|
1.26 ± 0.07
|
5–6
|
6–7
|
|
Pupae
|
3.6 ± 0.11
|
3.1 ± 0.02
|
2.1 ± 0.06
|
1.76 ± 0.04
|
6–7
|
7–8
|
|
Female
|
4.01 ± 0.02
|
3.65 ± 0.06
|
2.22 ± 0.03
|
2.09 ± 0.03
|
9–11
|
8–9
|
|
Male
|
3.73 ± .06
|
3.31 ± 0.01
|
1.99 ± 0.01
|
1.6 ± 0.04
|
8–9
|
7–8
|
First instar larva
After hatching, grubs bit through the base of the eggs shells and bored into the grains. The first instar larva was formed within the egg shell prior to penetrating the seed coat with a convenient visual marker signalling that embryonic development was almost completed. The first instar grub was small, opaque and creamish yellow in appearance. First instar grub exhibited longest average length of 0.52 ± 0.01 mm and an average breadth of 0.29 ± 0.04 mm on ICPL 161. While, the shortest length (0.48 ± 0.01 mm) and breadth (0.29 ± 0.06 mm) were recorded on ICPW 68. The head of grub was brown and body annulations were clearly visible. It was also characterised by a pair of pro-thoracic plates and the thoracic legs were represented by conical stumps. After the formation of the pigmented larval head capsule, they started to burrow from the egg through the seed coat and bored vertically for a short distance into the grains. The remaining eggshell became opaque white or mottled as it was filled with frass from the larva. The development period of first instar ranged from five to six days on ICPL 161 and five to seven days on ICPW 68.
Second instar larvae
After first moult the grub entered into second instar larval stage which was similar to the first instar except for its size and absence of pro-thoracic plates. Second instar grub measured an average of 1.45 ± 0.06 mm in length and 0.81 ± 0.02 mm in breadth on ICPL 161 compared to 0.77 ± 0.10 mm in length and breadth 0.54 ± 0.03 mm on ICPW 68. The body was stout and curved with the thoracic region characteristically larger than the posterior end. It was also recognized by the presence of casting of head capsule of the first instar. The brownish head was not distinct and was represented by the presence of mouthparts. The grub followed a horizontal path of boring to avoid getting deeper into the seed. The period of second instar grub ranged from five to six days both on ICPL 161 and ICPW 68.
Third instar larvae
The third instar grub was the most active stage and fed on grains endosperm voraciously. The average length of the third instar grub was 2.58 ± 0.10 mm and 1.21 ± 0.03 mm breadth on ICPL 161 while shortest length 1.20 ± 0.07 mm and breadth 0.80 ± 0.06 mm was recorded on ICPW 68. It was recognized based on the size and presence of castings of head capsules of the first and second moults, which were seen sandwiched by faecal pellets. The duration of third instar grub ranged from four to five days in ICPL 161 and seven to eight days in ICPW 68.
Fourth instar larva
The fourth instar grub was similar to third instar but varied in size and shape. The larva was white yellowish and slightly C-shaped with a small head. It was also distinguished based on the presence of three castings of head capsules seen sandwiched between the faecal pellets of the preceding and existing instars. The grub fed deeper into the grain extending upto the seed coat where it left a thin layer of testa appearing like a circular window. In this instar the larva appeared larger and fed on the entire endosperm voraciously. The larval duration ranged from five to six days on ICPL 161 and six to seven days on ICPW 68. The body length and breadth of the fourth instar larva were 3.47 ± 0.08 mm, 2.28 ± 0.04 mm and 1.82 ± 0.08 mm, 1.26 ± 0.07 mm in ICPL 161 and ICPW 68 respectively. The observations on larval instars indicated that the grubs moulted three times and the four instars were distinguished based on the size of larvae and castings of head capsule. The boring pattern of the grubs observed in the present investigation is comparable with those of Howe and Currie (1964) and Sibi (2003). The literature on the morphological and morphometric characters of grubs of C. chinensis is scanty. However, the findings of the present study are in confirmation with those of Sibi (2003), Ravindra (1998) and Vidyashree and Thirumalaraju (2015) who reported similar observations in C. analis, C. chinensis and C. maculatus.
Pupa
The pupa was creamy in colour, as the pupa aged its colour changed from creamy to dark brown. During the time of pupation, the larval structures were broken down and adult structures developed. The appendages were free but held close to the body. Maximum average pupa length 3.60 ± 0.11 mm and breadth 2.10 ± 0.06 mm were recorded on ICPL 161 and smallest average length (3.10 ± 0.02mm) and breadth (1.76 ± 0.04 mm) were recorded on ICPW 68. The pupa was exarate. The appendages were free but held close to the body. The mean lowest pupal duration was 6 to 7 days in ICPL 161 and highest mean pupal duration was recorded in ICPW 68 (seven to eight days). The structural development of the wings appeared on the first day, on second day appendages such as legs, antennae and proboscis developed freely and on third day eyes, mouthparts, forewing, hind wing and legs with cuticular hair developed. On fourth day almost all the parts developed but intersegmental region of the abdomen remained colourless and forewing was light green and on fifth day the forewings changed to dark brown with black patches. The present findings are in agreement with the findings of Devi, et al., (2014) who reported that the pupal development ranged from 6 to 8 days with an average of 6.80 ± 0.63 days which was in close agreement with the observations of Ahmad et al. (2016).
Adult
The adult emerged by chewing and removing a circular piece of the seed coat to form a round hole. The male antennae were pectinate with 4–10 segments conspicuously expanded anterolaterally, whereas the female antennae were serrate. The antennae of both sexes were with 4–11 segments and dark brown in colour. Pygidium of female was covered with white coloured setae. The adult males were 3.73 ± 0.06 mm, 3.31 ± 0.01 mm long and 1.99 ± 0.01 mm, 1.60 ± 0.04 mm in breadth, while females were 4.01 ± 0.02 mm, 3.65 ± 0.06 mm long and 2.22 ± 0.03 mm, 2.09 ± 0.03 mm in breadth on ICPL 161 and ICPW 68 respectively. The females of C. chinensis lived longer than the male beetles. The females lived for a period of 9 to 11 days, 7 to 9 days and the males lived for 8–9 days, 7 to 8 days on ICPL 161 and ICPW 68 grains. Adults were oval, chocolate or reddish brown, with long and erected antennae. The adult male was smaller and possessed a more round shape than the female whereas female adults had dark stripes on each side of the dorsal abdomen. The results are in confirmation with Venkate Gowda (1984) who reported that the male and female adult beetles of C. maculatus lived for 9.21 days and 9.89 days respectively on soybean. Similar observations were reported by Ravindra (1998) and Ramesh (1993). Varma and Anandhi (2010) reported that the adult longevity of C. chinensis was 11.0 days with a range of 9–12 days in green gram.