Biological Control 37 (2006)

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1 Biological Control 37 (2006) control as an alternative control method has attracted much attention recently. Anthocorid bugs and phytoseiid mites are already used for successfully controlling thrips in greenhouses (Chambers et al., 1993; Gillespie, 1989; Kawai, 1995; Ramakers et al., 1989; Riudavets and Castane, 1998). Also, in Japan, a predatory thrips, Franklinothrips vespiformis (Crawford), has been established as a biological control agent for Thrips palmi Karny and Frankliniella occidentalis (Pergande) (Arakaki and Okajima, 1998; Ohishi and Yasuda, 2002). However, more species should be added to the list of availwww.elsevier.com/locate/ybcon Potential of Haplothrips brevitubus (Karny) (Thysanoptera: Phlaeothripidae) as a predator of mulberry thrips Pseudodendrothrips mori (Niwa) (Thysanoptera: Thripidae) K. Kakimoto a, *, H. Inoue a, N. Hinomoto b, T. Noda b, K. Hirano c, T. Kashio d, K. Kusigemati e, S. Okajima f a Kagoshima Prefectural Sericultural Experiment Station, Higashi-ichiki, Kagoshima , Japan b National Institute of Agrobiological Sciences, Tsukuba, Ibaraki , Japan c Central Research Institute, Ishihara Sangyo Kaisha, Ltd., Nishi-shibukawa, Shiga , Japan d National Agricultural Research Center for Kyushu Okinawa Region, Kurume, Fukuoka , Japan e Faculty of Agriculture, Kagoshima University, Korimoto, Kagoshima , Japan f Laboratory of Entomology, Tokyo University of Agriculture, Atsugi, Kanagawa , Japan Received 8 August 2005; accepted 26 January 2006 Available online 7 March 2006 Abstract The predation potential of Haplothrips brevitubus (Karny) for thrips was evaluated in the laboratory. When second stage larvae of Pseudodendrothrips mori (Niwa) were presented to an adult H. brevitubus at densities of 10, 20, 30, and 40 larvae per cage at 25 C over 24 h, the number of larvae consumed per day increased with an increasing density up to 30. Predation of H. brevitubus exhibited the type II functional response. The mean development time of the egg, larva, and pupa of H. brevitubus were 4.5, 9.6, and 4.8 days, respectively, at 25 C. The survival rate from egg to adult emergence was 94.7%. One H. brevitubus larva consumed 41.6 P. mori larvae on average during the total larval period. Adult longevity was 35.2 days in females and 34.6 days in males. The pre-oviposition period was 2.7 days and the oviposition period was 31.5 days. The lifetime fecundity was eggs and the mean daily oviposition rate was 3.6 eggs. Calculated mean generation time (T) was 29.5 days, intrinsic rate of natural increase (r m ) was 0.162, and net reproductive rate (R 0 ) was The r m value of H. brevitubus was higher than that of Thrips palmi Karny and almost equal to that of Frankliniella occidentalis (Pergande). These results indicate that H. brevitubus has good potential as a predator of P. mori and is likely to be useful for controlling thrips. Ó 2006 Elsevier Inc. All rights reserved. Keywords: Predatory thrips; Haplothrips brevitubus; Biological control; Natural enemy; Thrips; Functional response 1. Introduction Thrips are one of the most important crop pests in the fields and in greenhouses because of their high level of resistance to insecticides and their cryptic habit that result in reducing the effects of insecticide application (Brødsgaard, 1994; Immaraju et al., 1992). Therefore, biological * Corresponding author. Fax: address: k-kakimoto@po.minc.ne.jp (K. Kakimoto) /$ - see front matter Ó 2006 Elsevier Inc. All rights reserved. doi: /j.biocontrol

2 K. Kakimoto et al. / Biological Control 37 (2006) able biological control agents for thrips; the predators that are currently being used do not possess optimal characteristics. They have, for example, low reproduction and predation under low-temperature conditions (Nagai and Yano, 1999, 2000; Tommasini and Benuzzi, 1996), variable effectiveness on different crops (Riudavets, 1995), low establishment rate, and high production costs. Members of the genus Haplothrips Amyot & Serville are mostly herbivorous (Miyazaki and Kudo, 1988). For example, Haplothrips chinensis Priesner has been recorded as a pest of rose and Hibiscus in Taiwan (Wang and Hsu, 1996; Wang, 1997). Yet some Haplothrips species are known to prey on thrips (Riudavets, 1995). For example, H. victoriensis Bagnall has been reported to be a natural enemy for the two-spotted spider mite, Tetranychus urticae Koch (Bailey and Caon, 1986). In a mulberry field in Kagoshima, Japan, we observed H. brevitubus (Karny) adults and larvae preying on the mulberry thrips, Pseudodendrothrips mori (Niwa) (Fig. 1). H. brevitubus is a common species widely distributed in the temperate region of Japan (Okajima, unpublished data). However, the biology of H. brevitubus has not been studied. Clarification of its feeding habits is important for the determination of its pestiferous status. Moreover, if we could ascertain that H. brevitubus is an effective thrips predator, we may be able to exploit it as a biological control agent. To evaluate the predation potential of H. brevitubus, we conducted experiments on its functional responses and life history parameters, using P. mori as prey in the laboratory. We demonstrate here that H. brevitubus is a predator of thrips and a potentially useful biological control agent. 2. Materials and methods 2.1. Insect and its rearing Pseudodendrothrips mori was collected from mulberry fields at the Kagoshima Sericultural Experiment Station, Higashi-ichiki, Kagoshima, Japan ( N, E), in September They were reared in a 9 cm diameter 12 cm depth plastic boxes with mulberry leaves at 25 C and a 16:8 h light:dark (L:D) cycle. Haplothrips brevitubus adults were collected from the same mulberry fields mentioned above and identified using male genitalia. To maintain the H. brevitubus culture, sufficient numbers of P. mori larvae were provided with a piece of mulberry leaf (7 7 cm) in each plastic box and reared at 25 C under 16:8 (L:D). A sheet of filter paper (9 cm diameter) was laid on the bottom of the rearing box to control the humidity. Offspring produced by rearing for two or three generations were used for the following experiments Predation by adult H. brevitubus on second stage larvae of P. mori We examined the functional response of adult H. brevitubus to second stage larvae of P. mori. Female adults were starved for 24 h before the experiment by being confined singly in 3.5 cm diameter 7.5 cm depth glass vials at 25 C and 16:8 (L:D). These females were placed singly with second stage larvae of P. mori at densities of 10, 20, 30, or 40 per vial with a piece of mulberry leaf (2 2 cm) and a piece of filter paper (2 2 cm) at 25 C and 16:8 (L:D). After 24 h, the number of P. mori larvae killed by the adult H. brevitubus was counted. The number of replication was from 10 to 12 at each prey density. To estimate the mortality rate of P. mori larvae under conditions without predators, 40 second stage larvae of P. mori were confined in a glass vial with a piece of mulberry leaf (2 2cm) at 25 C and 16:8 (L:D). After 24 h, the number of dead P. mori larvae was counted Development, survival, and reproduction of H. brevitubus Fig. 1. Predation by Haplothrips brevitubus adult (A) and larva (B) on Pseudodendrothrips mori larva. Development time of the egg, larva, and pupa of H. brevitubus fed on second stage P. mori larvae were examined at 25 C and 16:8 (L:D). To obtain eggs of H. brevitubus, 30 H. brevitubus female adults were placed in the plastic box (9 cm diameter 12 cm depth) with a piece of mulberry leaf (7 7 cm) and sufficient amount of P. mori larvae for 24 h. Mulberry leaf pieces ( cm) with H. brevitubus eggs

3 316 K. Kakimoto et al. / Biological Control 37 (2006) on them were singly placed in plastic tubes (1 5 cm) with a piece of filter paper (1 1 cm). A piece of moist cotton wool was put in each tube to provide humidity. Newly hatched H. brevitubus larvae were singly transferred to 3.5 cm diameter 7 cm depth polystyrene bottles with more than 20 second stage larvae of P. mori on a piece of mulberry leaf (2 2 cm) and a piece of filter paper (2 2 cm) and were reared at 25 C and 16:8 (L:D). The number of P. mori larvae killed by H. brevitubus was counted daily and new prey larvae were supplied every day. Second stage pupae of H. brevitubus were singly transferred to plastic tubes (1 5 cm) with a piece of moist cotton wool and a piece of filter paper (1 1 cm) and kept until adults emergence. To examine lifetime fecundity and longevity, a pair of H. brevitubus adults captured within 24 h after emergence was reared in the polystyrene bottle (3.5 cm diameter 7 cm depth). A mulberry leaf chip (2 2 cm) containing a sufficient number of P. mori larvae, as well as a piece of moist cotton wool and a piece of filter paper (2 2 cm) were placed in the rearing bottle. If the male died before oviposition by the coupled female, another newly emerged male was supplied. The leaf chip containing P. mori larvae was renewed every 24 h and the number of eggs laid on the leaf chip was counted under a binocular microscope at 50 magnification. Oviposition rates and survival of adults were observed until the female died Data analysis Data obtained from the functional response experiment were fitted to the Holling disc equation (Holling, 1959): N a P ¼ ant 1 þ at h N ; where N a is the number of successful attacks per predator during a specific time period (T) (=1 day in this study); N is the initial density of the prey, and a and T h are the rate of successful attack and the time required to handle the prey, respectively. Parameters were estimated using Mathematica 3.0 software (Wolfram Research Inc., 1996). The intrinsic rate of natural increase (r m ) was calculated from the survival rate (l x ) of immature and adult stages and the age-specific fecundity schedule (m x ) by using an iterative technique after substituting trial values (Birch, 1948): X 1 l x m x expð r m xþ ¼1; where x is the age in days. The female sex ratio was assumed to be 0.5. The net reproductive rate (R 0 ) and the mean generation time (T) were calculated from Birch (1948) and Laughlin (1965): R 0 ¼ X1 l x m x ;, T ¼ X1 X 1 x l x m x l x m x. The differences of predation rates of H. brevitubus adults on second stage P. mori larvae were subjected to analysis of variance (ANOVA) for different prey densities and different larval ages, and means were separated by Tukey Kramer HSD (p = 0.05) test. All analyses were carried out using the StatView software (SAS Institute Inc., 1998). 3. Results 3.1. Functional response of H. brevitubus on second stage larvae of P. mori Because the mortality of P. mori under conditions without a predator was 0%, all deaths of P. mori larvae were counted as due to predation by H. brevitubus. The number of P. mori larvae consumed by H. brevitubus adults increased with an increasing density up to 30 larvae and was saturated at 40 (Fig. 2). Predation of H. brevitubus on P. mori larvae exhibited the type II functional response (Holling, 1959). Parameters a (=rate of successful attack) and T h (=handling time) were and 0.043, respectively. The number of prey consumed per day at the densities from 20 to 40 was significantly higher than that at a density of 10 (Fig. 2). The mean maximum number of prey consumed per day was 12.4 on average at a prey density of Development, survival, and reproduction The development time of egg, larva, and pupa are shown in Table 1. Individual developmental rates in the same stage were nearly equal. The survival rate from egg to adult emergence was 94.7%. Only one individual of the initial 20 insects died at the pre-pupal stage. The numbers of prey consumed each day during the larval stages are shown in Fig. 3. The numbers of prey consumed by a first stage H. brevitubus larvae were per day, and there were no significant differences among ages within the same stage. The number of prey consumed Fig. 2. Functional response of Haplothrips brevitubus female adults on Pseudodendrothrips mori second stage larvae. Data indicate the means ± SD. Different small letters indicate significant differences among predation rates (Tukey Kramer test, p < 0.05). Curves are lines of best fit as predicted by the Holling disc equation and non-linear regression, y = 0.762x/( x).

4 K. Kakimoto et al. / Biological Control 37 (2006) Table 1 Development time and survival rates of Haplothrips brevitubus fed on Pseudodendrothrips mori larvae at 25 C Stage Development time (mean ± SE, days) Survival rate (%) Egg 4.5 ± First stage larva 3.1 ± Second stage larva 6.5 ± Pre-pupa 1.0 ± First stage pupa 1.0 ± Second stage pupa 2.8 ± From egg to adult emergence 18.9 ± Number of replication Fig. 3. Larval consumption of Haplothrips brevitubus on Pseudodendrothrips mori second stage larvae. Numbers examined are shown in parentheses. Different small letters indicate significant differences among ages (Tukey Kramer test, p < 0.05). by a second stage H. brevitubus larvae was per day; this was significantly larger than the numbers consumed by a first stage larva, with the exception of the first stage on day 3. Consequently, one H. brevitubus larva consumed 41.6 P. mori larvae on average to complete their pre-imaginal development. Oviposition and survivorship curves of female adult H. brevitubus are shown in Fig. 4. Oviposition started 2 Fig. 4. Oviposition (open circle) and survivorship (closed circle) curves of Haplothrips brevitubus female adults. days after emergence and continued intermittently until the female died. Female and male longevities were 35.2 and 34.6 days, respectively. The mean oviposition rate per female per day was 3.6 eggs, and the total lifetime fecundity per female was eggs. Calculated mean generation time (T, in days) was 29.5 days, the net reproductive rate (R 0 ) was 56.5, and the intrinsic rate of natural increase (r m,day 1 ) was , respectively. 4. Discussion The genus Haplothrips includes more than 230 species worldwide, mostly feeding in flowers (Mound and Zapater, 2003). However, feeding habit of H. brevitubus has not been unknown. It is known that some Haplothrips species are carnivorous (Riudavets, 1995). Ours is the first report of H. brevitubus as a predator of thrips. Aeolothrips intermedius Bagnall, a predatory thrips, consumes about 25 Thrips tabaci Lindeman larvae during its larval stage (Bournier et al., 1979). On the other hand, A. intermedius and Franklinothrips vespiformis female adults respectively consume 2.3 and 4.7 of Frankliniella occidentalis larvae each day (Zegula et al., 2003). The quantity of P. mori larvae (41.6 larvae) consumed by H. brevitubus during the larval stage was larger than that of A. intermedius. H. brevitubus female adults each consumed about 12 P. mori larvae. This consumption is higher than those of A. intermedius and Franklinothrips vespiformis. Further, the mean daily oviposition rate of H. brevitubus (3.6 eggs) fed on P. mori larvae was larger than that of Franklinothrips vespiformis fed on Frankliniella occidentalis (0.67 eggs) (Zegula et al., 2003). Thus, H. brevitubus seems to have higher predatory and reproductive ability as a natural enemy of thrips than do other predatory thrips such as A. intermedius and Franklinothrips vespiformis. The intrinsic rate of natural increase (r m ) of pests thrips reared at 25 C were in Thrips palmi (Kawai, 1985), (Katayama, 1997) and (Van Rijn et al., 1995) in Frankliniella occidentalis, and 0.17 in T. tabaci (Murai, 2000), respectively. The r m value of H. brevitubus in this present study was higher than the r m value of T. palmi and nearly equal to that of Frankliniella occidentalis, and lower than that of T. tabaci. Comparison of the r m value between natural enemies and pests can be used for pre-selecting of natural enemies in augmentative use of natural enemies (Van Lenteren and Manzaroli, 1999). Thus, the high r m value of H. brevitubus suggests that H. brevitubus is a promising natural enemy for pests thrips. The r m value of phytoseiid mites when provided with Frankliniella occidentalis or T. tabaci were from 0.14 to 0.18 in Amblyseius cucumeris (Oudemans) (Castagnoli and Simoni, 1990; Van Rijn and Van Houten, 1991) and 0.22 in A. barkeri (Hughes) (Van Rijn and Van Houten, 1991) at 25 C. And at 25 C, A. cucumeris female adult consumes 6.6 Frankliniella occidentalis larvae and 3.6 T. tabaci larvae daily (Castagnoli et al., 1990), A. barkeri female adult consumes 3.0 T. tabaci larvae daily (Bonde,

5 318 K. Kakimoto et al. / Biological Control 37 (2006) ). It seems that while H. brevitubus have lower reproductive ability, H. brevitubus have higher predatory ability than phytoseiid mites. On the other hand, r m value of anthocorid bugs Orius species about at 25 C is in O. insidiosus (Say) (Tommasini and Nicoli, 1993), in O. laevigatus (Fieber) (Coccuza et al., 1997), in O. sauteri (Poppius) (Nagai and Yano, 1999). O. insidiosus female adult consumes about 40 Sericothrips variabilis (Beach) adults daily (Isenhour and Yeargan, 1981) and O. sauteri female adult consumes about 40 T. palmi larvae daily (Nagai and Yano, 2000), respectively when provided with sufficient amount of prey. Consequently, H. brevitubus seems to have medium potential as natural enemy of thrips between phytoseiid mites and anthocorid bugs. However, here we studied the biology of H. brevitubus provided only with P. mori larvae. We need to investigate the performance when provided with other thrips such as T. palmi, Frankliniella occidentalis, andt. tabaci. Furthermore, we need to clarify the feeding habits of H. brevitubus including flower and pollen. For example, it is known that the development time of H. victoriensis, a predator of T. urticae, larvae became shorter when provided with seed lucerne crops flower than provided with T. urticae eggs (Bailey and Caon, 1986). The role of H. brevitubus as a biological control agent against thrips in greenhouses also needs further study, in regard to mass rearing protocols, diapause incidence under short-day conditions, and estimation of effectiveness in the fields. Acknowledgments We thank M. Akimine of the Kagoshima Prefectural Experiment station for her technical support, S. Urano of the National Agricultural Research Center for Kyusyu Okinawa Region for his invaluable comments for data analysis, and three reviewers for their helpful comments on the manuscript. 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