Apanteles Machaeralis Wilkinson (Hymenoptera: Braconidae) to Determine Its Biology When Diaphania Indica (Lepidoptera: Pyralidae) Is Its Host
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Proc. Indian Acad. Sci. (Anim. Sci.), Vol. 99, No.5, September 1990, pp. 353-362. © Printed in India. Biology of ApanteJes machaeralis Wilki~on (Hymenoptera: Braconidae) a parasite of Disphsni« indica (Saunders) (Lepidoptera: Pyralidae) CLEMENT PETER and B V DAVID Fredrick Institute of Plant Protection and Toxicology, Padappai 601301, India MS received 11 December 1989;revised 16 June 1990 Abstract. Studies were conducted on the endoparasite Apanteles machaeralis Wilkinson (Hymenoptera: Braconidae) to determine its biology when Diaphania indica (Lepidoptera: Pyralidae) is its host. Eggs were deposited in host larvae and increased greatly in size before hatching. The first instar larva was very active with functional mandibles, whereas the second stage larva was quiescent. The third instar larva spins its cocoon outside the body of the dead host. Mean development time from egg to adult was 12·63 days at 29·25± 1·82°e and 59-{j6% RH. There is no preoviposition period. The sex ratio was 1: 1·22(males/females). Mean adult longevity was not significantly different for males (9,31 days) and females (11,68 days). Keywords. Apanteles machaeralis; biological control; biology. 1. Introduction The pumpkin caterpillar, Diaphania indica (Saunders) has been reported from several parts of India and other regions of the world causing damage to various cucurbitaceous plants. Patel and Kulkamy (1956) have conducted detailed studies on the biology of this insect on Coccinia grandis (L.) Voight in Gujarat. However literature on the natural enemies of D. indica is very meagre. During the course of the studies on the natural biological control of this insect pest a solitary endoparasite, Apanteles machaeralis Wilkinson was reared as a major parasite of D. indica from Padappai. Previously, Bhatnagar (1948) reported A. machaeralis as a parasite of D. indica from Bihar. The present study was carried out since there is no information available on the biology of A. machaeralis as a parasite of D. indica. 2. Materials and methods 2.1 Rearing method and maintenance ofstock culture The adults which emerged from field collected parasite cocoons were fed with 20% honey solution. After 24 h the females were separated out. Twenty-five first instar larvae were released on Coccinia leaves inserted into a glass vial (6 x 1·5em) placed inside a plastic jar (12 x 10 em) and 3 mated females were released into each jar. The larvae were exposed to the parasite for 12 h. At the end of this period the parasites were removed from the jar and the larvae allowed to feed on the leaves. The leaves were changed periodically until the parasite larvae completed their development inside the host larvae and the parasite cocoons were formed. These cocoons were Part of a Ph.D thesis submitted to the University of Madras by the"" author. 353 354 Clement Peter and B V David collected from the rearing jars and placed in specimen tubes until the adults emerged. These adults were fed with 20% honey solution and used again for further rearing. The laboratory culture of this parasite was frequently rejuvenated by mixing with field collected material. 2.2 Life history and morphology of immature stages To study the life history of the parasite one-day old females were selected from the stock culture. They were placed in specimen tubes measuring 15x 2 COl. A first instar larva was taken on a fine camel hair brush and placed close to the female in the tube. After oviposition by the parasite the larva was placed in a plastic jar with Coccinia leaves. This procedure was repeated until the female refused to show any interest in the larva offered to it. Larvae were exposed to 10 females daily and those exposed to the same female on a particular day were placed together in plastic jar and the date recorded on it. To determine the incubation period the larvae were dissected at periodic intervals of 6 h and the development of the eggs was followed until hatching was observed. When the egg was fully developed, observation period was narrowed to 3 h. Parasite eggs were removed from the host larvae at periodic intervals and measured with a calibrated ocular micrometer using a compound microscope. To establish the larval period the parasitized host larvae were dissected at periodic intervals of 12 h using a Carl Zeiss Zoom Citoval-2-stereo-microscope. The parasite larvae were measured with a calibrated ocular micrometer and drawn using a camera lucida attached to a Carl Zeiss Laboval 4 compound microscope. Magnification used for drawing the larval stages ranged from X32 to X640. This arrangement for measuring and drawing of the various stages was made use for all the biology studies carried out in the present investigation. The drawings formed only an outline of the various immature stages and do not represent the accurate morphological features as indicated in the text. The constant movement of the live specimens rendered the drawing process very difficult The larval stages were determined by studying the shape and size of mandibles at different stages. To determine the shape and size of the larval mandibles the larvae were boiled in a 100/0 KOH .solution for 45 s for clearing but not completely removing the host tissues. After being washed in distilled water they were mounted in Hoyer's medium on microscope slides. The head. capsules and mandibles were also measured. The cocoons were dissected using a microscissor at 12 h intervals to record the prepupal and pupal periods. Both stages were measured. In order to determine the fecundity, 25 host larvae were exposed for 24 h to a single mated female in a plastic jar. The larvae were reared on Coccinia leaves. Three- replications were maintained. After 24 h the host larvae were dissected and the number of eggs present in each larva was counted. This procedure was repeated until all females died. From this data the total number of eggs laid by each female was estimated. Field collected cocoons were observed for emergence of adults which were sexed to assess the sex-ratio. Biology of A. machaeralis 355 To study the host stage preference for oviposition, larvae of D. indica of the following age groups were selected: 1-2,2-3,3-4,4-5, 5-{), 6-7, 7-8, 8-9 and 9-10 day old larvae. Twenty-five larvae belonging to each age group were released on Coccinia leaves and placed in a jar with wire mesh fitted lid. A single mated female was released into each jar. Three replications were maintained for each stage exposed. The number of cocoons formed for each stage was recorded at the completion of the larval development of the parasite. The pre-oviposition and oviposition periods were determined by exposing D. indica larvae to the parasite females at regular intervals of 24 h beginning with the day of emergence. The larvae were dissected after each exposure and those having parasite eggs were determined. Host larvae were exposed continuously until the female died. Five replications were maintained for this study. The adult specimens were initially preserved in 70% alcohol. These specimens were then mounted on slides using the following methodology. The specimen was treated in 10"10 KOH for 10-12 h for clearing the tissues and then transferred to glacial acetic acid to dissolve the organic matter, if any. It was passed through carboxylol. The processed specimens were dissected in clove oil and the different parts were mounted on slides in DPX mounting medium. Slide mounts of complete specimen were also prepared. The various parts of the adult were measured. 3. Results and disamion 3.1 Immature stages 3.1a Egg: The egg immediately after deposition is elongate with a long thin pedicel. The chorion is thin, transparent and devoid of any sculpturing. The egg develops rapidly after deposition and changes greatly in size and shape. When freshly laid it measures Q-043 mm long from tip to the end of the pedicel and 0'056 mm wide. After 6 h the length increases to (}O48 mm and in width to (}o 1 mm. At the end of 12 h after deposition, the egg measures (}O532 mm long and (}o102 mm wide at the broad end. After 20 b, the fully developed embryo is clearly seen inside the chorion. The full grown egg just before hatching measures (}O62 mm long and (}o 12 mm wide at the broad end (figure lA-D). Thus within 24 h after oviposition there is an increase of 1·45 times in size compared to the freshly laid egg. The width of the egg also increases to 2·4 times the original size. This increase is more pronounced in the transverse direction. The general shape and size of the egg of A. machaeralis is similar to several other species of solitary Apanteles studied. The rapid increase in the size of the egg after oviposition has been reported for other species too. In A. solitarius Ratzeburg an increase of 1·96 times in length and 1·5 times in width was reported at the time of hatching (Parker 1935). A 4-fold increase in width and 1·25 times increase in length has been reported for A. angaleti Muesebeck (Narayanan et al 1956). Allen (1958) recorded an increase of 1·58 times in length and 2·88 times in width for A. medicaginis Muesebeck. Cardona and Oatman (1971) reported an increase of 1'37 times in length and 2'4 times in width for A..dignus Muesebeck. In certain Euphorinae and Meteroinae the increase is even greater (Balduf 1926). 356 Clement Peter and B V David ~..