266 مجلة وقايةلنبات ا العربية، مجلد29 ، عدد2 ) 2011 ( بح ــ وث) يات حيات: حيوية أعداء( Research Paper (Biology: Natural Enemies) Studies on Host Preference and Oviposition Behaviour of Trichogramma aurosum Sugonjaev and Sorokina Strains in Choice and Non-Choice Tests Rana Samara 1 , J.C. Monje 2 , T. Qubbaj 3 and C.P.W. Zebitz 4 (1) Palestine Technical University, Faculty of Agriculture, Palestine, Email: rana_samara@yahoo.com, (2) State Museum of Natural History, Germany; (3) Palestinian National Agricultural Research Center NARC, Palestine; (4) University of Hohenheim, Institute of Phytomedicine, Germany. Abstract Samara, R., J.C. Monje, T. Qubbaj and C.P.W. Zebitz. 2011. Studies on Host Preference and Oviposition Behaviour of Trichogramma aurosum Sugonjaev and Sorokina Strains in Choice and Non-Choice Tests. Arab Journal of Plant Protection, 29: 259-266. Oviposition behaviour and host selection of different German strains of the egg parasitoid Trichogramma aurosum Sugonjaev and Sorokina (Hymenoptera: Trichogrammatidae) were examined on eggs of five Lepidopteran hosts (Cydia pomonella (L.), Spodoptera littoralis (Boisd.), Helicoverpa armigera (Hübner), Agrotis segetum (Schiff.) and Lobesia botrana (Den. and Schiff.)). The parasitization behaviour of individual female wasps was examined in choice and non-choice tests. Single female wasps were observed for 90 min. using a rectangular grid. Results from the choice test revealed that 75–90% of C. Pomonella eggs attacked by T. aurosum strains were successfully parasitized. Values for L. Botrana and for A. segetum ranged between 40–80% and 40–70%, respectively. No significant preference was found between C. Pomonella eggs and host eggs of both L. botrana and A. segetum. Time needed by the female wasps to drill on eggs of L. Botrana was shorter than the time needed for drilling on C. Pomonella eggs. This could be due to differences in egg chorion thickness and, presumably, differences in chorion hardness. During direct observation of the parasitism behaviour it was noticed that all strains spent about 20% of the observation time for drilling on either C. Pomonella or L. Botrana eggs, 30–60% on resting, 4–15% on cleaning, < 4% on walking and < 1% on feeding. Results from the non-choice test showed that a significantly higher number of C. pomonella and L. botrana eggs were parasitized in comparison to the other hosts offered. The presence of hair-like structures deposited on eggs of S. littoralis and a thick egg chorion in H. armigera seems to represent a physical barrier that impedes successful parasitization. Keywords: Trichogramma aurosum, Cydia pomonella, Spodoptera littoralis, Helicoverpa armigera, Agrotis segetum, Lobesia botrana, host acceptance, host selection, parasitization behaviour. Introduction The codling moth, Cydia pomonella (L.), is a key pest of apple distributed world-wide, with exception of both Japan and China (16). Damage caused by this pest on apple trees could reach 95% when no control methods were applied (1). Insecticides are widely used to control this pest. Though, the increase of resistance has prompted interest in alternative control methods such as inundative biological control. Trichogramma spp. are egg parasitoids used worldwide for this control strategy against lepidopterous pests in forestry, orchards, and row crops (15, 23, 29). However, not only inoculative releases (classical biological control) but also inundative releases failed to reveal successful control of the target pest(s) (19, 30). In more than 10% of the reported cases, failing biocontrol could be traced back to selection of either the wrong species or inappropriate or unsuitable strains (31). Thus, biological control programmes require pre-introductory basic research on the performance of potential candidates (20, 21, 27, 28). One of the most important aspects of the parasitoid- host relationship is research done on host selection process (33). Selection process is usually based on Trichogramma biological characteristics, which includes fecundity, emergence rate, sex ratio, longevity, host preference for the target species, host searching activity and tolerance to local climatic conditions. According to Flanders (9); Gordh et al. (11) and Vinson (35), successful parasitism is divided into 5 steps: host habitat location, host location, host acceptance, host suitability and host regulation. The first three steps are referred to as aspects of the host selection process, which can be by selecting between hosts of different ages and or species (34). Host suitability is concerned with factors affecting the development of a parasitoid within potential hosts. Following the host finding and host selection process, host suitability is a final step in the host-parasitoid relationship toward successful parasitism (23), while host preference under controlled conditions is important in the risk assessment of biological control agents (14, 17). Host selection can be affected by environmental conditions or by host factors such as host chemical or physical cues, shape, size and host age. For biological control programs host preference tests were carried out on Trichogramma species/strains between its target pest and its factious host eggs (3, 4, 12, 13, 32, 33). This assessment of the host preference showed to be insufficient while various host eggs may not occur together in the field on the same crop and at the same time (32). Host preference tests should include a native Trichogramma species/strain found in the field with the target pest. These wasps may have adapted to the field conditions and synchronized with the presence of the pest. Since host preference tests are difficult to be carried out under field conditions, this study aimed at examining the host preference of five strains of T. aurosum for eggs of different lepidopterous host species in the laboratory. Van Dijken et al. (33) suggested that observation of the wasp behavioural performance using the rectangular grid is the most suitable method for determining host preference. Two experiments were designed for determining host preference: 1) choice tests, where female wasps have to choose between