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Host Preference of Anisopteromalus Calandrae (howard) (hymenoptera : Pteromalidae)

Md. Abdul Hannan
Department of Zoology, University of Dhaka. Dhaka-1000, Bangladesh.

Anwara Kabir
Department of Zoology, University of Dhaka. Dhaka-1000, Bangladesh.

Abstract/ Executive Summary:

The pteromaJid wasp. Anisopteromalus calandrae (Howard) was released to three host Insects Silophllus oryzae (Linn.). Rizopertha domtnica (Fab.) and Callosobruchus chinensts (Linn.) under various time limit exposures for determination of host preference. It was found that the parasitoid preferred S. oryzae followed by C. chinensis and R. dominlca.. The difference between S. oryzae and C. chinensts however was not significant. Under all the experimental conditions. R. domtnica found to be the least preferred host.

Keywords: Host preference, Pteromalid, Anisopteromalus calandrae

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End Date:

Program Area: Pest Management

Commodity: Insects

Objectives:

To determine the preference of A. calandrae under different time limit exposures providing Sitophilus oryzae (Linn.). Rhizopertha dominica (Fab.) and Callosobruchus chinensis (Linn.) as hosts.

Methodology:

The host insects S. oryzae, R. dominica and C. chinensis were cultured in the laboratory using appropriate grain media. The parasitoid, A. calandrae was also reared separately using all the three host species. The appropriate host stage (3rd and 4th instars) for the experimentation was determined through a series of tests and dissections under a stereo microscope. Since the hosts' developing stages remain within the grain kernels those were marked with different colourations. The experiments were carried out in glass petridishes (8.5 cm dia). At the bottom of each petridish was placed a piece of circular white paper on which the marked seeds of each type containing the 3rd and 4th instar host larvae were placed in a random manner. In each petridish one newly emerged male and two virgin female parasitoids were introduced. In each set of experiment 30 host containing seeds of each type (total 90) were placed. The right stage of the host larvae were confirmed by dissecting some grains before setting up of the experiments. The petridishes were arranged in six sets each having five replications. The parasitoids were allowed to oviposit for 24. 48. 72, 96, 120 and 240 hr respectively in sets I to VI. They had open choice to select the host they preferred. The experiments were carried out under the laboratory temperature and relative humidity conditions (29 ± 2°C, 75±5% rh). The data were analysed statistically.

Source of Information: Journal of the Asiatic Sociaty of Bangladesh Science 22(1): 43-47. 1996, ISSN 1016-6974

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Achievement/Findings:

The results is seen that the parasitoid, A. calandrae selected its host for oviposition according to its choice and preference. From the total experimental analysis it is evident that the parasitoid preferred the hosts in the following orders : S. oryzae > C. chinensis > R. dominica. The mean number of total progeny emerging from S. oryzae at the end of 240 hr was 13.06 ± 4.14, from R. dominica 4.46 ± 2.64, and from C. chinensis 11.66 ± 5.67. When different treatments with the three host species are compared it is seen that maximum total number of offsprings (18.8 ± 4.60) of the parasitoid emerged from S. oryzae at 120 hr exposure. followed by C. chinensis (19 ± 6.44) at 48 hr and R. dominica (7.2 ± 3.42) at 240 hr. Evidence of preference for a particular host type may be shown by the deviation of the proportion of the host type attacked from the proportion available in the environment. This indicates that the total or innate preference underlying this phenomenon. is a complex searching behavior of the parasitoids. Most parasitoids are usually not host specific but they have choice of their host food.The most important factor in determining host selection is ecological. Vinson showed that host specificity is regulated by a chain of chemical cues and that both genetic and laming components are involved. A. calandrae is a parasitoid of many different hosts. In the present experiments. of the three hosts tested, preference was shown towards S. oryzae followed by C. chinensis. R. dominica found to be least preferred. It is most likely that the female parasitoid could discriminate inter and intraspecific size differences. R. dominica larvae being smallest of the three host types, it was mostly avoided as ovipositional site. Although marked difference was observed in case of s oryzae and C. chinensis as hosts, the difference was not significant statistically. R. dominica however. was least preferred by A. calandrae for its progency production

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