J. Sci. Dev. 2009, 7 (Eng.Iss.1): 17 - 21 HA NOI UNIVERSITY OF AGRICULTURE 17 Interactions between the predatory mites Amblyseius cucumeris (Oudermans) and minute pirate bug Orius sauteri (Poppius) in prey patches of thrips Thrip palmi (Karny) Tương tác sinh học giữa nhện bắt mồi Amblyseius cucumeris (Oudermans) và bọ xít bắt mồi Orius sauteri (Poppius) trong môi trườngcó vật mồi bọ trĩ Thrip palmi (Karny) Vu Quoc Ngu 1 , Arnold Van Huis 1 and Nguyen Van Dinh 2 1 Laboratory of Entomology- Wageningen University- The Netherlands 2 Laboratory of Entomology- Hanoi Agricultural University TÓM TẮT Trong điều kiện phòng thí nghiệm (độ ẩm 50 - 70%, nhiệt độ 25 ± 2 o C, 16 h ánh sáng) nghiên cứu theo dõi tương tác sinh học giữa nhện bắt mồi Amblyseius cucumeris (Oudermans) và bọ xít bắt mồi Orius sauteri (Poppius) trong môi trường có nhiều vật mồi bọ trĩ Thrips palmi (Karny). Trong hộp olfactometer, nhện bắt mồi không thể hiện sự ưa thích nửa hộp nào giữa 2 nửa hộp, một nửa có lá đậu với bọ trĩ còn nửa hộp kia có lá đậu với bọ trĩ và cả bọ xít bắt mồi. Bọ xít bắt mồi cũng có phản ứng tương tự. Khi hai động vật bắt mồi được đưa vào cùng một hộp petri, chúng không tấn công lẫn nhau, kể cả trong trường hợp không có vật chủ bọ trĩ. Từ những kết quả trên có thể đưa ra kết luận rằng sẽ không có ảnh hưởng xấu lẫn nhau khi hai động vật được thả cùng trong một khoảng không gian nhằm kiểm soát vật hại rau T. palmi. Từ khoá: Amblyseius cucumeris, olfactometer, Orius sauteri, Thrips palmi, tương tác sinh học. SUMMARY In the laboratory, under conditions of 25 ± 2 o , 50 - 70% RH and 16 h light, the research investigated biointeraction between predatory mite Amblyseius cucumeris (Oudermans) and minute pirat bug Orius sauteri (Poppius) in their prey patches of thrips Thrips palmi (Karny). In the glass petri dishes-olfactometer, A. cucumeris did not show preference between the olfactometer side of bean leaf with thrips and another olfactometer side of bean leaf with thrips and heteroconspecific predator O. sauteri. The other predator O. sauteri also showed the same strength. When put them together in a bean leaf, O. sauteri and A. cucumeris did not attack each another even in the absence of their shared prey. From these results the conclusion can be made that there is no negative effect when both predator A. cucumeris and O. sauteri are released in same field to control pests like the phytophagus thrips T. palmi. Key words: Amblyseius cucumeris, biointeraction, olfactometer, Orius sauteri, Thrips palmi. Interactions between the predatory mites Amblyseius cucumeris 18 1. INTRODUCTION Thrips, together with phytophagous mites and aphids are the most dangerous pests of many vegetables and ornamental crops in Vietnam (Dinh, 2002). Thrips palmi (Karny) is native to the tropics and was first found on the islands of Indonesia. It is now established throughout the tropics and subtropical zones. It cannot overwinter in temperate zones, but may manage to complete two to three life cycles if introduced. Thrips palmi is a polyphagous species, but is best known as a pest of Cucurbitaceae and Solanaceae plants. Among vegetables injured are bean, cabbage, cantaloupe, chili, Chinese cabbage, cowpea, cucumber, bean, eggplant, lettuce, melon, okra, onion, pea, pepper, potato, pumpkin, squash, and watermelon. In Vietnam, it was suggested that T. palmi attacked 12 species of commercial crops (Loi, 2001, cited by Yorn and Hung, 2005). Groundnut and cucumber were considerably damaged compared to others. Potato is also a primary host of T. palmi, as it occurs from early spring to the end of summer; in the field it can be highly infested at the end of spring (Hung, 2002). Vuong (1998, cited by Yorn and Hung, 2005) studied the composition of thrips species on groundnut and she found four species: Scirthothrips dorsalis Hood, Frankliniella schutzei (Trybom), T. palmi and Megalurothrips usitatus Bagnall). An (1999, cited by Yorn. and Hung, 2005) reported that T. palmi was a serious pest on watermelon in Camau province. Other studies indicated that T. palmi is a serious harmful insect on bean, eggplant and cucumber; damage sometimes being recorded up to 60% (Yorn. and Hung, 2005). This study was focused on interactions between the predatory mite Amblyseius cucumeris, the minute pirate bug Orius sauteri (Poppius) and their shared prey the thrips species Thrips palmi (Karny). Both A. cucumeris and O. sauteri are predators of the thrips T. palmi. Both species are reared and innundatively released in fields to protect vegetables from harmful thrips. Researchers from the Entomology laboratory (Hanoi University) did a lot of work to produce and release both predators to control phytophagus mites and thrips in vegetable crops. There is a question whether one natural enemy affects the performance of the other. The interactions between two predators were also investigated under laboratorial conditions. It was tested the hypothesis that A. cucumeris and O. sauteri discriminate between patches with prey only and patches with prey and the other predator. Response of A. cucumeris and O. sauteri are studied in the laboratory, using petridishes. Furthermore it was investigated the intraguild predation of A. cucumeris and O. sauteri on the other predators on bean leaves in absence or in presence of their shared prey T. palmi. 2. MATERIALS AND METHODS Thrips T. palmi were reared on bean plants Phaseolus vulgaris in a climatic-controlled room (25 ± 2 o C, 50 - 70% RH, 16 h light). Clean plant were grown in a climatic room (same regime) until they were 10-days old. They were then placed in three separated closed cages: one cage for rearing thrips, one cage for rearing the predator A. cucumeris, and the other for rearing the minute pirate bug O. sauteri. When the thrips populations developed well on bean plants, the predator A. cucumeris or O. sauteri were released (all stages were used to get enough numbers in a short time). Predator A. cucumeris culture, T. palmi and Orius sauteri were from the continuous rearing in the Entomology laboratory After another four weeks, the populations were well developed and their numbers enough for being used in the experiments. 2.1. Olfactometer experiment Glass Petri dishes of 10 cm diameter are used to study the response of adult female predators to volatiles. The glass is divided into two parts with a border. When the lid is closed, these two parts are isolated from each other. In the center of the border is a bridge, closed during incubation period and open during the experiment (Fig. 1). Bean leaf discs (diameter 2.5 cm) are placed on wet cotton wool in a plastic container and infested each with 25 larvae and 25 adults of the prey T. palmi. Primary leaves of two plants are used to make the odour sources as equal as possible. The next day, 5 predators are added to one of the two leaf discs. The leaf discs are used as odour source the next day, hence they are infested with thrips for 2 days, and one of the leaf discs has predators for 1 day. Vu Quoc Ngu, Arnold Van Huis and Nguyen Van Dinh 19 Fig. 1. Set-up with glass petridish diameter 10 cm. In the centre is a border with bridge, closed during incubation period and opened during experiment Adult female predators are starved for 1-3 h prior to the experiments. This is done to motivate the predators to seek for the prey (Ibrahim et al., 2006). Two bean leaf discs are placed opposite in a glass Petri-dish. An adult female predator is released in the center of the petri dish (also a center of bridge). Each individual is observed until she reaches one of the two leaf discs during a maximum time of 5 min, and is subsequently removed. In this way, each predator is tested separately. 2.2. Intraguild predation It was measured the rates of intraguild predation of adult females on heteroconspecific larvae or adult females in the absence of the shared prey. Bean leaf discs (=2.5 cm) are placed on wet cotton wool in a plastic container. Twenty five larvae or five adults of the female predator of one species are added to clean leaf discs. Five adult females of the other species are added the same day. One day later, live and killed individuals are counted. Experiments are done in a climate room ((25 ± 2 0 C; 16 h light). The experiment is replicated forty times. 3. RESULTS AND DISCUSSION It is known that plants under insect attack emit specific volatiles (Dicke et al., 1990; Turling et al., 1990; Vet and Dicke, 1992; Takabayashi and Dicke, 1996 - cited by Jetske and Dicke 2005). Herbivore-induced plant volatiles are used as foraging cues by a diverse range of arthropod carnivore species, including parasitoid wasps, and predatory bugs and mites (Jeske and Dicke, 2005) so it was expected that under attack of thrips T. palmi bean plants (in the experiment bean leaves) will emit a specific blend of chemicals to attract predators such as A. cucumeris and O. sauteri. It is also knows that insects often release specific chemicals or excretes for marking territories to prevent other insects from coming in their occupied Interactions between the predatory mites Amblyseius cucumeris 20 territories so expectation was that the chemicals emitted from bean leaf with prey patches (with T. palmi only) are different from the chemicals emitted from bean leaf with prey patches and predator (A. cucumeris or O. sauteri). The goal of the olfactometer experiment was to check how A. cucumeris and O. sauteri responded to these two groups of chemicals. In the first experiment, in 19 of total 40 replicates the predator A. cucumeris went to the bean leaf with prey T. palmi and predator O. sauteri and in 21 replicates A. cucumeris went to the bean leaf with T. palmi only. The result showed that the predator A. cucumeris has no preference in the choice of two bean leaves: the bean leaf with or without the heteroconspecific predator O. sauteri (P = 0.874, non - parametric binomial test). When O. sauteri was given a choice between the bean leaf with T. palmi and A. cucumeris and the bean leaf with T. palmi only, O. sauteri also did not discriminate between the two sides. In 22 of 40 replicates O. sauteri went to the bean leaf with T. palmi and A. cucumeris and in 18 replicates O. sauteri went to the side with T. palmi only on the bean leaf. There is no significance as P = 0.635, non-parametric binomial test (see the figure 02 for detail). In experiments in 1997 - 1999, Janssen and her staff found that Phytoseiulus persimilis avoids plants with the two-spotted spider mites and conspecifics, whereas it does not avoid plants with two-spotted spider mites and Neoseiulus californicus. Ibrahim et al. (2006) also found that P. persimilis did not avoid the volatiles emanating from bean leaves with spider mites and the heteroconspecific predator N. californicus. In my experiment the result showed the same trend for A. cucumeris and O. sauteri as they did not show any preference in the choice between bean leaves with prey only and bean leaves with prey and the other heteroconspecific predators. The answer for that maybe that both predators do not recognize the volatiles emitted from the other predator or they recognize these volatiles but do not recognize the other predators as a threat. In fact, they are not biologically closely related species: A. cucumeris attacks only immature larvae thrips and consume one larva during 24 hours while O. sauteri can kill much more (hundreds) and all stages of thrips, so A. cucumeris is not a food competitor for O. sauteri. Proportion of predators on both sides of the olfactometer Fig. 2. The response of A. cucumeris (bar 2) when offered a choice between odours from leaves with thrips and leaves with thrips and the other predator O. sauteri in an olfactometer and the response of O. sauteri when offered a choice between odours from leaves with thrips and leaves with thrips and the other predator A. cucumeris (bar 1) 0.55 0.475 0.45 0.525 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1 2 To prey patches with heterospecific predators To prey patches with no heterospecific predators Vu Quoc Ngu, Arnold Van Huis and Nguyen Van Dinh 21 The second reason for the non - significant preference maybe the set-up of the experiment: not enough time for incubation (only 2 days for prey and one day more for the predator). The third reason may be that the experimental device was not good enough: the volatiles from the two parts could have been mixed during the period when putting the predator in the releasing point. It may have been better to use an Y-tube olfactometer to study the response of insects to chemicals emitted by plants or animals. However, these were not available in the laboratory and there was not enough time to acquire one. In the second experiment, 25 larvae of O. sauteri and 05 adult A. cucumeris were released together in one bean leaf in 40 replicates and after one day it was found that in all replicates the numbers of two predators remained the same. There were no mortalities and no escapes. The result indicates that there is no predation between two predator species and it makes no sense to test the intraguild predation between two predators in the presence of their shared prey T. palmi as planned in the beginning. The minute pirate bug O. sauteri is very big compared to the predatory mite A. cucumeris, and A. cucumeris is very fast so it is understandable that one is not a prey of the other even in the absence of their shared prey. The result from the second experiment is in agreement with the first, indicates that each predator does not recognize the other as a threat of predation or food competition. 4. CONCLUSION There is no negative effect when both predators A. cucumeris and O. sauteri are released in the field to control pests like the phytophagus thrips T. palmi. When one predator does not discriminate prey patches with or without the other predator, the predator will establish itself in the fields regardless of the presence of the other predator. Both predators can be released together in one field to control pests such as T. palmi because there is no predation between two predators in the case that the populations of the prey are low. Amblyseius cucumeris or O. sauteri does not affect the performance of the other in finding and killing harmful thrips in crops. Acknowledgements First of all, I wish to thank Prof. Dr. Arnold Van Huis and Prof. Dr. Nguyen Van Dinh for supervising my research project at the Entomology department, Hanoi Agricultural University and for correcting this report. Many thanks to Assoc. Prof. Dr. Nguyen Thi Kim Oanh, Prof. Dr. Ha Quang Hung. I would like to thank the Vietnamese Government, Ministry of Training and Education; and Project 322 for financially supporting my MSc. Programme. REFERENCES Hung H. Q. and Huong B. T. (2002). Biological characteristics of Orius sauteri (Hemiptera- Anthocoridae) rearing on Thrips palmi and eggs of Corcyra cephalonica. National conference on insects Hanoi: 210-214. Hung H. Q. Yorn T. and Huong B. T. (2005). Thrips on crops and their control. Vietnamese Agricultural press: 58. Ibrahim C., Janssen A. and Sabelis M.W., (2006). Intraguild interaction between the predatory mites Neoseiulus californicus and Phytoseiulus persimilis. Experimental and Applied Ecology 38: 33-46. Janssen A., Bruin J., Jacobs G., Schraag R. and Sabelis M.W. (1997). Predators use volatiles to avoid prey patches with conspecifics. J. anim. Ecol. 66: 223-232. Janssen A., Pallini A., Venzon M. and Sabelis M.W. (1998). Behaviour and indirect interactions in food webs of plant-inhabiting arthropods. Exp. Appl. Acarol. 22: 497-521. Janssen A. (1999). Plants with spider-prey attract more predatory mites than clean plants under greenhouse conditions. Entomol. Exp. Appl. 90: 191-198. Janssen A., Pallini A., Venzon M. and Sabelis M.W. (1999). Absence of odour-mediated avoidance of heterospecific competitors by the predatory mite Phytoseiulus persimilis. Entomol. Exp.Appl. 92: 73-82. . research investigated biointeraction between predatory mite Amblyseius cucumeris (Oudermans) and minute pirat bug Orius sauteri (Poppius) in their prey patches of thrips Thrips palmi (Karny). In the. 17 Interactions between the predatory mites Amblyseius cucumeris (Oudermans) and minute pirate bug Orius sauteri (Poppius) in prey patches of thrips Thrip palmi (Karny) Tương tác sinh học. their shared prey the thrips species Thrips palmi (Karny). Both A. cucumeris and O. sauteri are predators of the thrips T. palmi. Both species are reared and innundatively released in fields