India is endowed with a rich wealth of medicinal plant. Isabgol (Plantago ovata Forsk.)is one of the most important medicinal plants in the Unani and Ayurvedic system of medicine. It belongs to order Plantaginates which consist of only a single family Plantaginacae. This family consists of three genera and about 200 species. These species either are annual or perennial herbs. All of these species except four belong to the genus Plantago. About 10 species of Plantago are recorded in India.

P. ovata is only the cultivated species of the country because of its bold seed. Indian P. ovata is preferred over European Plantago psyllium and Plantago indica (Trease and Evans, 1978). P. ovata is known to be grown as wild in warmer and drier part of the Mediterranean region of India. It is one of the important medicinal crop traditionally cultivated in North Gujarat, Saurashtra and Kachchh region of Gujarat. South Western Rajasthan, Haryana, Madhya Pradesh and Punjab are also produced small quantity of isabgol. In Gujarat, it occupies about 26 641 ha of area, producing about 32 864 M.T. seed and productivity 1.23 M.T. per hectare which is highest in terms of area and production in the world (Anon, 2007; 2008).

1 Result and Discussion    
1.1 Nymph
The nymphs were found to pass through four different nymphal instars when reared on isabgol. Earlier, Passlow and Roubieck (1967), Nayar et al (1981) also recorded four nymphal instars of this pest on various host plants.

1.2 First instar
Freshly borned first instar nymphs were oval in shape, dorsally convex, greenish brown or yellowish-brown in colour with three pairs of legs. Antennae were six segmented, short, filliform and light black in colour. A pair of tube like structure (siphunculi/cornicles) was observed dorsally on the posterior region of abdomen.

Duration (Table 1) of first instar nymph was found minimum of 1 and maximum of 3 days with an average of (2.04±0.16) days.
 

Table 1 Duration of different nymphal instars of A. gossypii

The body length of first instar nymphs measured from 0.44 to 0.56 mm with an average of (0.510±0.007) mm and breadth 0.34 to 0.44 mm with an average of (0.380±0.005) mm (Table 2).

Table 2 Measurement of different stages of A. gossypii

1.3 Second instar

Freshly moulted second instar nymphs were oval in shape and greenish brown to willow green in colour. They were similar to the first instar nymphs in their general appearance and morphological characters, except in body size. In freshly moulted nymph, the exuvium of the preceding instar was seen near the posterior end of the abdomen.

Duration of the second instar was observed minimum of 1 and maximum of 4 days with an average of (1.68±0.16) days (Table 1). The measurement of second instar nymphs indicated that each nymph varied from 0.66 to 0.96 mm with an average of (0.47±0.01) mm in length and 0.38 mm to 0.56 mm with an a average of (0.470±0.010) mm in breadth (Table 2).

1.4 Third instar

Newly moulted third instar nymphs were spinach in colour and oval in shape. Third instar nymphs were distinguishable in general appearance from that of previous nymphal instars. They possessed three pairs of well developed legs latro-ventrally on three thoracic segments, which become more conspicuous. The antennae were well developed and black in colour.

Duration of the third instar nymphs (Table 1) revealed minimum of 1 and maximum of 4 days with an average of (2.00±0.17) days. Measurement of the third instar nymphs revealed that the nymph varied from 1.00 to 24 mm with an average of (1.140±0.012) mm in length and 0.52 to 0.64 mm with an average of (0.540±0.006) mm in breadth.

1.5 Fourth instar

Fourth instar nymphs were emerald green in colour and similar to that of the third instar nymphs in their general appearance and morphological characteristics except in body size.

The duration of fourth instar nymphs (Table 1) was ranged from 1 and 3 days with an average of (1.64±0.12) days. Measurement values for fourth instar nymphs showed that it varied from 1.28 to 1.52 mm with an average of (1.39±0.13) mm in length and 0.64 to 0.76 mm with an average of (0.71±0.008) mm in breadth (Table 2).

1.6 Total nymphal period

Total nymphal period was considered from birth of first instar nymph to the end of fourth instar. It ranged from 7 to 9 days with an average of (8.46±0.20) days (Table 1). 

As the nymph grows, its colour was changed from greenish brown to willow green, spinach and finally emerald green.

The average duration of first, second, third and fourth instar nymphs was (2.04±0.16), (1.68±0.16), (2.00± 0.17) and (1.64±0.13) days, respectively. However, Ullah (1982), Jamwal et al (1988), have recorded slightly higher (9.42 to 11.48 days) nymphal duration of A. gossypii. The variation might be due to the effect of host plants and climatic conditions.

1.7 Adult

The adults were oval in shape and bottle green to dark green in colour. They were larger in body size than the nymphal stages and possessed a pair of well developed conspicuous black coloured cornicles at posterior region of abdomen. Wings when present were in two pairs and transparent with black veins. The black coloured antennae were much larger in size than the nymph stages.

The longevity of adult (Table 3) was recorded minimum of 11 and maximum of 21 days with an average of (16.36±0.54) days. However, In contrast to above, Kersting et al (1999) showed 12.6 (at 30/35℃) to 39.7 days (15℃) longevity of A. gossypii at different temperatures.

Table 3 Longevity and reproduction parameters of A. gossypii reared on isabgol

Ullah K., 1982, Biological study of cotton aphid A. gossypii Pakistan,J. Agril. Res., 1(2): 135-138