The Bovicola ovis Schrank (1781) (Pediculus ovis Schrank, 1781; Trichodectus sphaerocephalus Nitsch, 1818; Trichodectus ovis Neveu-Lemaire, 1912; Bovicola ovis Ewing, 1929) is cosmopolitan chewing louse of sheep spread all over the world. Bovicola ovis belongs to family Bovicolidae of Ischnocera suborder, Phthiraptera order (Lyal, 1985). Bovicola spp. is susceptible to high temperature but it is also intolerant to moisture. In a damp fleece, with a relative humidity of more than 90%, it will die in six hours and when covered by water it will drown in an hour (Urquhart et al., 1978).
Balochistan is an arid zone with dry climate, rate of rainfall is very low and temperature is variable in different parts of the province. The sheep population is 38 %. This scarce population is additionally facing B. ovis, which has greatly infested. In Pakistan studies on the species related chewing lice incidence in sheep have never been made, neither reports of presence of Bovicola ovis species in Pakistan are available, while, the same species has been reported from India (Kumar, 2000). The main objective of the current study is to describe the morphological and taxonomic features of Bovicola ovis encountered in sheep of Balochistan, Pakistan with confirmation of their presence.
Materials and Methods
Specimens were collected randomly from five districts of Balochistan i.e. Quetta, Mastung, Sibi, Bolan and Pashin. Collection was carried out from January to December 2001. Chewing lice were extracted from sheep by standard procedures (Dunn, 1932), using delousing chamber containing chloroform vapour. Sixty nine sites on sheep were inspected for lice as suggested by James (1998) and Stanley (2000).
A total of 237 adult B. ovis were extracted. However, only 161 adult lice were suitable for analysis. Only well preserved lice (with all required characters) were used. Slides were mounted permanently by Canada balsam. Measurements were made using a binocular microscope fitted with an eye piece micrometer scale.
Fourteen characters were measured for the study of size. These characters were based on those used by Eveleigh and Amano, (1977) and were chosen for the reproducibility of measurement and overall morphological representation.
Family Bovicolidae Keler,
Genus Bovicola Ewing.
The body of the insect was pale yellow colored, with elongated and oval shape of 1.79 mm (Fig. 1). Morphological variation with fourteen biometrical parameters were also studied (Tables 1 and 2).
Head: Width bigger than length, anterolateral margin of the head smoothly rounded, dorsum of the head with setae of short length of greater abundance anteriorly than posteriorly. Two long setae at the temple margin. Ventrally setae present in fewer amounts, greater abundance anterolaterally of long size, few setae also found posterolaterally.
Antenna filiform, three segmented hidden in the grooves of the head. First segment of antenna has less number of short setae, ventrally one setae found at the base, few present at the tip near the base of second segment, in males it is much swollen. Second segment longer and narrower than first, with large number of setae, a long seta found ventrally.
Third segment was crowded with setae of moderate and long size, tip has large number of short setae crossing each other.
Eyes are degenerate or absent.
Thorax: Thorax with dorsal and lateral setae of moderate length. Two setae present at the margin of prothorax, few setae present along lateral margins and posteriorly (dorsally) on the prothorax and pterothorax; posterior setal row of prothorax submarginal median gap present; posterior setal row of pterothorax submarginal, with median gap absent (Fig. 2); row incorporating two very long setae between posterolateral and posteromedian angles.
|Table 1:||Biometrical parameters in individuals from female Bovicola ovis Shrank (1781) species of 139 specimens measured
|Table 2:||Biometrical parameters in individuals from male Bovicola ovis Shrank, 1781 species of 22 specimens
|Fig. 1a:||Bovicola ovis (Male 1.52 mm)
|Fig. 1b:||Bovicola ovis (Male 1.52 mm)
Ventrally few setae of medium and long size were scattered. Two long setae were present mid posteriorly. Row of short was setae without median gap.
Foreleg shorter than others, femur broader with few setae, tibia longer with two long setae, tarsus two segmented with many bristles at the base of claw.
|Fig. 2:||Rows of setae on prothorax and pterothorax
|Fig. 3:||Posterior row of setae on abdominal tergites.
Mid leg long, femur much broader having long bristles near the base (Fig. 4) and few short bristles, tibia has medium to large sized bristles, one very long at the base of tarsus; tarsus two segmented, few large sized bristles at the tip only, second has few bristles, one very long at the base of the claw.
|Fig. 4:||Femur of foreleg and mid leg.
|Fig. 5:||Gonoapophysis of female showing internal lobe.
Hind leg long, femur broad and long medium to long sized setae regular, the base is narrow, tibia long, base is narrow while tip is broad consisting of medium to large sized setae, tarsus two segmented short, with few hair at the tip, pointed curved claw.
Abdomen: Abdomen was segmented having eight segments (Fig. 1), elongated and oval shaped with six pairs of spiracles; long, short or medium sized setae were present. Tergites and sternites consist of a row of setae posteriorly (Fig. 3). Each segment laterally bears spot densely crowded with a number of setae; 4-8 segments have a long hair on lateral sides. The last segment in males rounded with short and female with long hair. Gonoapophysis of female with large internal lobe, inner margin consist of long hair (Fig. 5). Cerci absent.
The widest measured part of the head was the temporal corner. The head width (HW) of the female ranged from 0.4 to 0.58 mm with a mean of 0.49 mm. HW of the male ranged from 0.30 to 0.54 mm with a mean of 0.42 mm while the head length (HL) of the female ranged from 0.31 to 0.59 mm with a mean of 0.45 mm and in the male HL was 0.33 to 0.43 with mean 0.38 mm. In both the genders mean HW was greater than HL, while, in males the HL was also found greater than HW. Thorax width (TW) was greater than thorax length (TL) and the values of total body length (TBL) was greater in females than that of males. The bigger TBL in females (average 1.79 mm vs 1.52 mm in male) was probably due to bigger abdominal length.
Most authors consider the total body length as principal metric parameter in the morphological description of the species. According to our data (Tables 1 and 2) the TBL of Bovicola ovis varied from 1.64 to 1.94 mm in females and between 1.42 to 1.63 mm in males. These values are similar to those of Werneck (1936) but are different from Neveu-Lemaire (1938) who found both the sexes of same body length (1.0 mm).
The primary morphological characters, TBL, HL/HW, TL/TW, AL/AW, the smoothly curved anterolateral margin, the shape of the basal antennal segment, the thorax and the abdomen with row of hair posteriorly, lateral spots of abdomen having bundle of hair, abdomen with six pairs of spiracles and gonoapophysis with internal lobe (Furman and Catts, 1982), setae restricted to lobe only could be used in differentiation of species.
The species is closely related to B. ovis of cattle (Neveu-Lemaire, 1938), but could be separated by primary morphological characters mentioned above, while the head of B. ovis is quadrangular, narrowing anteriorly and setae on inner margin of gonoapophysis not restricted to lobe. This study confirms the presence of B. ovis in Balochistan, Pakistan.
Thanks are due to Ricardo L. Palma, Museum of New Zealand; Dr. P.N. Prelesov, Trakia University, Bulgaria; Peter J. James, Senior Research Scientist SARDI Australia, for their guidance and valuable literature they provided.