Parasitic Behaviour of Xanthopimpla pedator Fabricius (Hymenoptera: Ichneumonidae) on Tropical Tasar Silkworm, Antheraea mylitta Drury (Lepidoptera: Saturniidae) Reared on Seven Forestry Host Plants in Uttarakhand, India

Narendra Kumar Bhatia et al. Parasitic behaviour of X. pedator on A. mylitta 244 245 loss (Jolly et al., 1974; 1979). Parasitoids are known to attack the Saturniids, and 350 parasitoid species have been recorded from 175 Saturniid species (Peigler, 1994). Ichneumon fly, Xanthopimpla pedator Fabricius (Hymenoptera: Ichneumonidae) and Uzi fly, Blepharipa zebina Walker (Diptera: Tachinidae) are the important endoparasitoids (insects that develop inside another insect and killing it because of their development) of A. mylitta. X. pedator is an idiobiont (such a parasitoid, which prevents further development of its host) solitary larval-pupal endoparasitoid (egg is laid in the host larva, but adult parasitoid does not emerge until host pupates) of A. mylitta. Xanthopimpla Saussure 1892 is one of the largest genera of Ichneumonidae and the species of the genus are endoparasitoids Introduction Tropical tasar silkworm, Antheraea mylitta Drury (Lepidoptera: Saturniidae) is a polyphagous silk producing insect of commercial importance, widely distributed in moist deciduous, semi evergreen, dry deciduous and tropical dry deciduous forests in India (Rao, 2001). Poor people in forest fringe area commercially rear the larvae of this silk producing insect on different forest tree species for small household income. In nature, A. mylitta has opted forty-five forest tree species as primary, secondary and tertiary food plants (Srivastav and Thangavelu, 2005) and have built up sixty-four different forms of ecological populations called ecoraces (Rao et al., 2003). A. mylitta completes its life cycle twice or thrice in a year depending on the biotic and abiotic factors, and accordingly the race is recognised as bivoltine (BV) or trivoltine (TV). Daba (BV) and Sukinda (TV) are the most commercially exploited ecoraces of A. mylitta, which is a prerogative of India. In outdoor forest rearing, many pest and predators attack the larvae and pupae of A. mylitta causing 40-45% cocoon Fig. 1. a) emergence hole of Xanthopimpla predator; b) parasitized pupae; c) eaten out pupa by ichneumon larva; d) excreta of ichneumon larva; e) unemerged ichneumon fly; f) adult ichneumon fly. Fig. 2. a) seed of A. mylitta; b) 5 th instar larva of A. mylitta; c) spinning larva A. mylitta; d) cocoon hammock of A. mylitta; e) newly formed cocoon of A. mylitta; f) hardened cocoon of A. mylitta; g) male moth of A. mylitta; h) female moth of A. mylitta. Int. J. Indust. Entomol. Vol. 27, No. (2), pp. 243-264 (2013) 244 245 attractive of all the ichneumonid groups for biological study (Gauld, 1991). There are hundreds of published records on hostparasitoid associations between Saturniidae and Ichneumonidae, but studies on X. pedator are very rare and complete bio-ecology of X. pedator is still an enigma to sericulture scientists in India (Singh et al., 2010). According to meagre information available, X. pedator begins its life cycle in fifth instar spinning larva of A. mylitta by the time of hammock formation (Fig. 2d) to early cocooning stage (Fig. 2e) and uses its long ovipositor to drill through silky envelope of spinning larva and deposits single egg in the abdominal segment. In the course of development, silkworm transforms into pupa and after hatching, ichneumon of the Lepidopterans (Gomez et al., 2009) that belong to suborder Apocrita (Parasitica), which show greater degree of biological adaptations (Gauld and Bolton, 1988). After the revisionary works of Gauld (1991), the subfamily Pimplinae has become taxonomically one of the best-known ichneumonid taxa. Many Xanthopimpla species are very abundant in tropical forest areas of Uttarakhand state, India and it is common to see them flying in the forest vegetation. Xanthopimpla are easy to recognize, as they are lemon yellow in coloration and have very stout body (Fig. 1f). The ecological specialization coupled with wide ranges of hosts and biology, makes Xanthopimpla one of the most Fig. 3. Study area. Narendra Kumar Bhatia et al. Parasitic behaviour of X. pedator on A. mylitta 246 247 in the research block. Climate of the study site The climate of New forest, Dehradun is moderate due to its location at the foot of the Himalayas (Anonymous, 2011 b). Summer starts by March and lasts up to the mid of June, when the south-west monsoon sets in over Uttarakhand. Month of May and early part of June is hottest with mean temperatures of 36.2 o C with maximum temperature of 42 o C (Fig. 4a). Winter starts in November and continues up to February with mean daily maximum and minimum temperature of 19.1 o C and 6.1 o C, respectively. The average annual precipitation at the site was 2123.8 mm (Fig. 4b) and most of the rainfall was received during July to September (1937.60 mm). July and August are the wettest months, and in November and January, site received winter rainfall (67.6 mm). larva feeds the entire content of defenceless pupa (Fig.1c). Parasitoid’s larva pupates there and transforms into adult and pierces its way out by making a circular characteristic hole at the anterior region of the cocoon near peduncle (Fig. 1 a). In current study, effects of different forestry host plants, seasons of rearing and their interactions on parasitic behaviour of X. pedator were investigated, as the influence of these factors on biological success of this parasitoid was not known. In current study, seven forestry tree species were tested as food to rear A. mylitta, and parasitization rate of X. pedator in both the rearing seasons were recorded after completion of seed production process. Further, this was the first investigation to search for feasibility of tropical tasar silkworm rearing in tropical forests areas of Uttarakhand, a Himalayan state of India, where this commercial forest silkworm species has never been tried earlier in spite of huge availability of its forestry host plants. The broad objectives of this paper was: (1) to assess the effect of rearing season and host plants on sex wise parasitization of A. mylitta by X. pedator and; (2) to find out the most suitable forestry host plant for successful commercial rearing of A. mylitta in Uttarakhand. Findings of the study are analysed in respect of the following questions, which are still unanswered: (1) how female X. pedator does find and parasitize its host; (2) do forestry host plants influence the host selection behaviour of X. pedator; (3) reasons behind male specific parasitic behaviour of X. pedator; and (4) does size, shape or shell thickness of host cocoon influence the parasitic behaviour of X. pedator? Materials and Methods