Oviposition Efficacy of Drosophila suzukii (Diptera: Drosophilidae) on Different Cultivars of Blueberry

Transcription

1 HORTICULTURAL ENTOMOLOGY Oviposition Efficacy of Drosophila suzukii (Diptera: Drosophilidae) on Different Cultivars of Blueberry HIROTOSHI KINJO, 1 YASUHISA KUNIMI, 1 TAKUYA BAN, 1 AND MADOKA NAKAI 1,2 J. Econ. Entomol. 106(4): 1767Ð1771 (2013); DOI: ABSTRACT Drosophila suzukii (Matsumura) is an important pest of thin-skinned fruits including blueberry, raspberry, strawberry, and cherry. Blueberry was introduced into Japan in the 1950s, and severe economic losses attributable to D. suzukii were Þrst reported in The objective of this study was to elucidate whether oviposition behavior varies among blueberry cultivars having different Þrmness of fruit. Fruit Þrmness in 12 cultivars of highbush blueberry (Vaccinium corymbosum L.) and rabbiteye blueberry (Vaccinium virgatum Aiton) was determined using a rheometer. More eggs tended to be laid in berries of cultivars possessing softer fruits than in those having Þrmer fruits. Choice tests, where one female was allowed to oviposit on blueberry fruits with different Þrmness, showed that softer fruits were more vulnerable to D. suzukii females than Þrmer fruits. KEY WORDS Drosophila suzukii, blueberry, cultivar, fruit Þrmness, oviposition 1 Graduate School of Agriculture, Tokyo University of Agriculture and Technology, Saiwai-cho, Fuchu, Tokyo , Japan. 2 Corresponding author, madoka@cc.tuat.ac.jp. Drosophila suzukii (Matsumura) is one of the most serious pests of thin-skinned fruits including blueberry, raspberry, cherry, grape, and strawberry (Kanzawa 1939; Sasaki and Sato 1995; Lee et al. 2011a,b; Walsh et al. 2011; Bellamy et al. 2013). D. suzukii females possess a serrated ovipositor and lay eggs into fresh fruits before harvest (Kanzawa 1939, Sasaki and Abe 1993, Walsh et al. 2011). This insect originated in eastern Asian countries, including Japan. It has invaded Europe and North America as a soft fruits pest since 2008, and the economic damage has been substantial, with estimated crop losses of up to 50% (Goodhue et al. 2011, Walsh et al. 2011, Cini et al. 2012). However, farmersõ losses can reach 100% if D. suzukii larvae are detected in the fruits, because in such a case the complete fruit load will be rejected by an inspector. Blueberry was introduced into Japan in the 1950s. Its cultivation has become widespread since the late 1990s, and severe economic losses attributable to D. suzukii were Þrst reported in 2002 (Shimizu 2006, Kawase et al. 2007). Highbush blueberry (HB; Vaccinium corymbosum L.) can receive signiþcant damage from D. suzukii, but rabbiteye blueberry (RE; Vaccinium virgatum Aiton) suffers little damage in Tokyo (J. Shimada, T. Shimizu, and T. Motobayashi, personal communication). However, the reasons for this difference in damage are not clear. The objective of this study was to elucidate whether female D. suzukii has a preference for oviposition in particular cultivars of blueberry. According to several previous studies, the Þrmness of the fruits may affect the efþcacy of oviposition by D. suzukii females (Kawase and Uchino 2005, Lee et al. 2011a). Seven HB cultivars and Þve RE cultivars were tested. In this study, the Þrmness of the fruits was measured using a rheometer, and the number of eggs laid by individual females was examined for each cultivar and correlated with fruit Þrmness. Finally, choice tests of different cultivars with different fruit Þrmness were performed to elucidate the factor(s) associated with oviposition preference of D. suzukii on blueberry fruits. Materials and Methods Insects and Fruits. A population of D. suzukii originally from Yamagata Prefecture was obtained from Tokyo Metropolitan University and reared at 25 C in glass tubes (25 mm in diameter by 90 mm in length) with artiþcial diet, as used for rearing Drosophila melanogaster (Meigen). The medium contains the following: glucose 100 g, cornmeal 90 g, yeast 40 g, agar 7 g, propionic acid 3 ml, and Bokinin solution 10 ml. Bokinin solution is 10% butyl 4-hydroxybenzoate in 70% ethanol. All insect rearing and experimentation was conducted under a photoperiod of 16:8 (L:D) h and 60% relative humidity (RH). HB and RE were collected from the farm in Tokyo University of Agriculture and Technology, Fuchu, Tokyo. Mature fruits were identiþed by the dark blue color of their skin and a dark blue ring along the stalk, according to the method of Ismail and Kender (1969). The HB cultivars used were ÔDarrow,Õ ÔMeader,Õ ÔCoville,Õ ÔBrigitta,Õ ÔDixi,Õ ÔHerbert,Õ ÔGeorgiagemÕ; RE included ÔTifblue,Õ ÔWoodard,Õ ÔDeliteÕ; and one cultivar was unassigned (B-26 strain). The fruits were harvested on 15 and 22 July, 3 August, and 1 September in /13/1767Ð1771$04.00/ Entomological Society of America

2 1768 JOURNAL OF ECONOMIC ENTOMOLOGY Vol. 106, no. 4 Table 1. Fruit firmness and estimated oviposition on different blueberry cultivars by D. suzukii Species Cultivar Date harvested Firmness of fruits (mg) a Estimated oviposition b Mean SE Mean SE HB Herbert 15 July Brigitta 15 July Meader 15 July Darrow 15 July Dixi 22 July Darrow 22 July Covil 15 July Georgiagem 22 July Darrow 3 Aug RE Unassigned (B-26 strain) 1 Sept Homebell 1 Sept Woodard 22 July Woodard 3 Aug Tifblue 22 July Tifblue 3 Aug Delite 1 Sept Delite 3 Aug a Mean Þrmness of fruits was examined using 10 fruits, except Dixi (6), Darrow (5), Georgiagem (6), and Woodard (7) on 22 July. b Number of eggs laid by a single female during 24 h is shown as estimated oviposition. Mean estimated oviposition was examined with six replications against each cultivar harvested each day, except Darrow on 22 July with Þve replications. Firmness of Blueberry Fruits in Different Cultivars. Firmness of blueberry fruits was determined using a rheometer (Fudoh Rheometer, RT-3005D, Rheotech, Tokyo, Japan) within 24 h of harvesting. Measurement was performed with a column plunger (diameter of 2 mm) at an insertion speed of 60 mm/ min. When the plunger was pushed into a fruit, the maximum resistance value occurred at the moment the plunger penetrated the fruit, and was deþned as the Þrmness of the fruit. Ten berries were examined for each cultivar. Preference of D. suzukii for Different Blueberry Cultivars. Oviposition by D. suzukii females on blueberry fruits was examined in the laboratory for berries harvested within the preceding 24 h, using different berries from the same harvested batches of fruits used for testing Þrmness as described above. Equivalent masses of fruits (5Ð6 g) were transferred to transparent plastic cups (4.5 cm in diameter by 3 cm in height), and then one 2- to 4-d-old female was placed in each cup to oviposit for 24 h at 25 C. Each cultivar was replicated six times, using females of the same age. The ßies were then removed and the fruits kept for 1Ð2 d at 25 C to allow the eggs to hatch. The fruits were soaked in carbonated water (soda water, Suntory Foods Ltd., Tokyo, Japan) at room temperature, and were shaken for 15Ð20 min and kept at 25 C for 24 h. Carbonated water allows live ßy larvae to emerge from the fruits (Shimizu 2006). The fruits were dissected under a dissecting microscope, and remaining unhatched eggs and dead larvae were counted. The total number of progeny (ßy larvae spontaneously emerging into the carbonated water, unhatched eggs, and dead larvae) per female ßy was recorded as estimated oviposition. Choice Test for Female Flies Between Firmer and Softer Fruits. Choice tests were conducted using three cultivarsñdarrow (HB), Herbert (HB), and Tifblue (RE). Darrow and Herbert fruits were harvested on 15 July and Tifblue on 22 July of Until the experiments were conducted on 22 July, fruits of Darrow and Herbert were kept at 4 C, and the Þrmness of fruits was examined just before the choice test. Combinations of 1) Herbert and Tifblue, and 2) Darrow and Tifblue fruits were placed in plastic cups (two fruits per cultivar in each cup, 4.5 cm in diameter by 3 cm in height) and exposed to a single female D. suzukii for 24 h. After removal of female ßies, the fruits were individually transferred to a half-ounce cup (4 cm in diameter by 2 cm in height) and incubated at 25 C for 1Ð2 d to allow hatching. The fruits were then treated with carbonated water, as described above, to count larvae and residual eggs. Six females were examined in each choice test. Data Analysis. Parameters recorded were analyzed with the statistical software JMP 10 (SAS Institute, Cary, NC). The results of fruit Þrmness were analyzed by one-way analysis of variance (ANOVA). For comparison of the Þrmness of fruits in two groups (different harvesting dates; HB vs RE; freshly harvested fruits vs 1 wk later), WelchÕs t-test was conducted. Estimated oviposition was analyzed by the KruskalÐ Wallis test, because the variables were not normally distributed. The correlation between Þrmness of fruits and log-transformed number of progeny was examined by PearsonÕs correlation analysis. The data for estimated oviposition between two cultivars (HB vs RE) were log-transformed and analyzed by WelchÕs t-test, because the data were normally distributed. Results Firmness of Blueberry Fruits in Different Cultivars. Firmness measurements for blueberry fruit cultivars are shown in Table 1. There were signiþcant differences in the Þrmness among all blueberry cultivars (F 20.7; df 16, 134; P ). Two RE cultivarsñdelite and TifblueÑwere signiþcantly

3 August 2013 KINJO ET AL.: OVIPOSITION BY Drosophila suzukii ON BLUEBERRY 1769 Estimated oviposition y = -0.04x R² = 0.32 HB RE Firmness of fruits (mg) Fig. 1. Correlation between Þrmness of blueberry fruits and estimated oviposition by D. suzukii females. Þrmer than most of the HB cultivars. However, the HB cultivar Herbert was signiþcantly softer than all other cultivars, both HB and RE, examined. Firmness of fruits was signiþcantly higher for RE than for HB examined (t 2.39; df 1, 12.5; P 0.03). The Þrmness of Darrow, Woodard, Delite, and Tifblue fruits, which were harvested on different dates, was examined, but the timing of harvesting did not significantly affect the Þrmness of fruits (F 3.48; df 2, 10.5; P for Darrow; t 0.89; df 1, 14.8; P 0.39 for Woodard; t 0.61, df 1, 17.5; P 0.55 for Delite) except Tifblue (t 2.69; df 1, 17.5; P 0.015). Preference of D. suzukii for Different Blueberry Cultivars. Estimated oviposition, as deþned above, is shown in Table 1. Delite, the Þrmest cultivar, received the fewest eggs, an average of 1.2Ð1.5 eggs oviposited per female. The KruskalÐWallis test indicated a signiþcant difference among the cultivars (H 34.2; df 16; P ). A linear regression plot of mean estimated oviposition by D. suzukii females on fruits of each cultivar and the Þrmness of the fruits is shown in Fig. 1. Among 12 different cultivars, estimated oviposition was negatively correlated with fruit Þrmness (r ; df 1, 15; P 0.018). Choice Tests for Female Flies Using RE and HB Fruits. Results from choice tests in which one female was presented with two cultivars having different fruit Þrmness are shown in Fig. 2. Fruits of Darrow (HB), with a Þrmness of 127 mg, received signiþcantly more oviposition by female D. suzukii than those of Tifblue (RE), with a Þrmness of 150 mg (t 3.1; df 1, 10; P 0.01). Similarly, fruits of Herbert (HB; Þrmness of 82 mg) received signiþcantly more oviposition by female D. suzukii than did Tifblue (RE) (t 4.2; df 1, 10; P 0.002). The Þrmness values of fruits for Herbert, Darrow, and Tifblue were , , and mg, respectively, and were significantly different from one another (F 34.9; df 2, 17; P 0.01). These results also indicated that more eggs were laid in softer fruits than in Þrmer fruits. In this experiment, Darrow and Herbert fruits harvested 1 wk previously were compared with Tifblue harvested on the experiment day. Although the harvest timing of fruits used in the choice test was different, the test needed to be performed on a single day. To determine whether preservation at 4 C for a week might affect the Þrmness of the fruits, Þrmness was measured again just before the choice tests were conducted. The Þrmness of Darrow fruits preserved for a week ( mg) was not signiþcantly different from that of fruits just harvested (t 1.35; df 1, 16.4; P 0.197). Similarly, Herbert fruits stored for a week ( mg) were not signiþcantly Fig. 2. Choice test for D. suzukii females on two species of blueberry fruits. (A) Herbert (HB) and Tifblue (RE), and (B) Darrow (HB) and Tifblue (RE), were available to D. suzukii females. Error bars show SEs. Average Þrmness of the fruits ( SE) is shown below the x-axis.

4 1770 JOURNAL OF ECONOMIC ENTOMOLOGY Vol. 106, no. 4 different from those just harvested (t 2.25; df 1, 8.2; P 0.053). Discussion Firmness of blueberry fruits varied signiþcantly among cultivars, but not between the two blueberry speciesñhb and REÑtested in this study (Table 1). The estimated oviposition by female D. suzukii during 24 h on fruits of different cultivars also varied, but was not signiþcantly different among cultivars. Large standard errors of estimated oviposition observed in this experiment may be attributable to various factors. For example, 2- to 4-d-old females were used in this experiment, but the variation in their ages may have affected their oviposition behavior. Kanzawa (1934) showed that female D. suzukii started to oviposit between 24 and 116 h, with an average of 47 h, after adult emergence. Estimated oviposition and fruit Þrmness were negatively correlated (Fig. 1). Female D. suzukii clearly tend to oviposit more eggs in softer fruits than in Þrmer fruits. Similarly, the level of D. suzukii infestation was weakly or moderately correlated with Þrmness of cultivars of HB blueberry from California and Oregon (Lee et al. 2011a), as well as with ph and Brix (sugar content). However, Lee et al. (2011a) measured the Þrmness of fruits using a different method from ours, namely as the force needed to squeeze the fruit by 1 mm. The squeezing force may be affected not only by skin Þrmness but also by other factors including the elasticity, intercellular space, water content, and size and shape of fruits. In the current study, unlike that of Lee et al. (2011a), Þrmness of fruits was measured by penetration of a plunger, and should thus correlate with the Þrmness of the fruitsõ skin. Using a procedure similar to ours, Hoshino et al. (2010) estimated the Þrmness of blueberry fruit skin from the difference between the Þrmness of the entire fruit and the Þrmness of the ßesh of the fruit (i.e., estimated Þrmness of skin Þrmness of [entire fruit ßesh of fruit]), and found that the Þrmness of an entire fruit is positively correlated with the Þrmness of the fruitõs skin. This suggests that Þrmer- or thicker-skinned fruits are attacked less by D. suzukii females than are thinnerskinned fruits. We also conducted choice tests between softer and Þrmer fruits using individual D. suzukii females (Fig. 2). In both experiments, the estimated oviposition was higher in softer fruits than in Þrmer fruits. Two choice tests in this study showed that the HB fruits were attacked more than RE by D. suzukii females: the ßies preferred Darrow (HB) to Tifblue (RE), whose fruits were signiþcantly Þrmer than those of Darrow. Herbert (HB) was more strongly preferred by D. suzukii females to Tifblue (RE), a pair in which fruit Þrmness was more markedly different. Lee et al. (2011a) suggested that the Þrmness of fruits is a factor in the oviposition preference displayed by D. suzukii females. Other factors including the sugar and acid content of the fruits, which may affect fruit odor, should also be examined to compare the vulnerability of RE and HB cultivars. Choice tests using HB cultivars from Oregon and California were also performed by Lee et al. (2011a), but the number of eggs laid did not differ among them. This inconsistency may be because RE and HB were used in this study whereas only HB cultivars, among which fruit Þrmness and other factors might vary to a lesser extent, were used by Lee et al. (2011a). Silva et al. (2005) examined the physicochemical, carbohydrate, and sensory characteristics of HB and RE blueberry cultivars, and reported that the Þrmness of the HB cultivars examined (Bluecrop and Jersey) was signiþcantly lower than that of the RE cultivars examined (Climax, Premier, and Tifblue). The Japanese name of D. suzukii is outou-shoujoubae, which is derived from sweet cherry (outou) and fruit ßy (shoujoubae). Initially, D. suzukii was an important pest of sweet cherry (Prunus avium L.) in Japan (Kanzawa 1934), but blueberry became an additional host plant of D. suzukii after it had spread in Japan, because blueberry is well suited to D. suzukii as a host plant. Sasaki and Sato (1995) found that the host plants of D. suzukii in Fukushima Prefecture were, in order of fruit ripening, cherry Prunus yedoensis Matsumura (late May to early June), sweet cherry (late May to early July), Elaeagnus multiflora Thunb. (late June), mulberry Morus bombycis Koidz. (late June to early July), blueberry (late June to October), blackberry and raspberry (middle July to October), Rubus parvifolius L. (early to late August), peach Prunus persica (L.) Batsch. (early August), Prunus buergeriana Miq. (middle to late September), and American pokeweed, Phytolacca americana L. (early October to late November). Thus, D. suzukii seems to switch among host plants when ripe fruits are available. The ßy population may build up after repeated occurrence on different host plants, because D. suzukii was estimated to undergo 10 generations per year in a laboratory study (Kanzawa 1939). Because all the host plants examined are sufþciently soft to allow D. suzukii females to attack, identifying potential host fruits that ripen before blueberry and controlling the population before blueberry is attacked may suppress outbreaks of this pest on fruit crops. Recently, blueberry breeding has been focusing on the Þrmness of the fruits (Proctor and Miesle 1991, Silva et al. 2005). Firmer fruits are preferred by fresh fruit consumers and are preserved longer than softerskinned fruits. Breeding of Þrmer fruits may also be beneþcial from the point of view of reducing damage by D. suzukii. Our data suggest that a Þrmness of 140 mg is the level that the fruit would need to attain for effective resistance against penetration by D. suzukii females, and this could be a target for fruit-breeding programs. Furthermore, laboratory studies indicate that cultivars or species producing Þrmer fruits are less vulnerable to D. suzukii females than those producing softer fruits (Lee et al. 2011a, Burrack et al. 2013, this study). Burrack et al. (2013) recently addressed host selection by D. suzukii in the Þeld and laboratory, and showed that fruit Þrmness may be one driver of this host selection. However, Þeld infestation was not sim-

5 August 2013 KINJO ET AL.: OVIPOSITION BY Drosophila suzukii ON BLUEBERRY 1771 ply correlated with the Þrmness of fruits. If softer fruits can act as a trap crop around more resistant crops, the preference trait of D. suzukii could be used to establish a cultural control strategy to manage D. suzukii in the Þeld, as mentioned by Burrack et al. (2013). To connect this laboratory observation and Þeld management, further practical Þeld studies are needed to establish a successful cultural control strategy against D. suzukii. Acknowledgments We sincerely thank Isao Ogiwara, Takashi Motobayashi, Hidenobu Tsujimura, Jun Shimada, Tomoe Shimizu, Satoshi Noma, and Mika Mashimo, all of Tokyo University of Agriculture and Technology; Koichiro Tamura of Tokyo Metropolitan University; and Ian Smith of Nara Institute of Science and Technology. This project was partially supported by a special research fund of MEXT, Japan: Research and development of security and safe crop production to reconstruct agricultural lands in Fukushima Prefecture based on novel techniques to remove radioactive compounds using advanced bio-fertilizer and plant protection strategies. References Cited Bellamy, D. E., M. S. Sisterson, and S. S. Walse Quantifying host potentials: indexing postharvest fresh fruits for spotted wing drosophila, Drosophila suzukii. PLoS ONE 8: e Burrack, H. J., G. E. Fernandez, T. Spivey, and D. A. Kraus Variation in selection and utilization of host crops in the Þeld and laboratory by Drosophila suzukii Matsumura (Diptera: Drosophilidae), an invasive frugivore. Pest Manag. Sci. (in press). Cini, A., C. Ioriatti, and G. Anfora A review of the invasion of Drosophila suzukii in Europe and a draft research agenda for integrated pest management. Bull. Insectol. 65: 149Ð160. Goodhue, R. E., M. Bolda, D. Farnsworth, J. C. Williams, and F. G. Zalom Spotted wing drosophila infestation of California strawberries and raspberries: economic analysis of potential revenue losses and control costs. Pest Manag. Sci 67: 1396Ð1402. Hoshino, H., K. Sya, M. Omura, S. Suzuki, N. Horiuchi, and I. Ogiwara Evaluations of joint strength between peduncle and fruit, fresh Þrmness and skin Þrmness in blueberries. Hortic. Res. (Japan) 9(Suppl. 2): 398. Ismail, A. A., and W. J. Kender Evidence of a respiratory climacteric in highbush and lowbush blueberry fruit. HortScience 4: 342Ð344. Kanzawa, T Studies on Drosophila suzukii (Preliminarly report). Yamanashi Kenritsu Nouji Shikenjo Gyomu Nenpo. Yamanashi Prefecture Agricultural Institute, Kofu, Japan. Kanzawa, T Studies on Drosophila suzukii. Yamanashi Kenritsu Nouji Shikenjo Gyomu Nenpo. Yamanashi Prefecture Agricultural Institute, Kofu, Japan. Kawase, S., and K. Uchino Inßuence of maturity and wounding on blueberry fruit injury by Drosophila suzukii. J. Jpn. Soc. Hortic. Sci. 74 (Suppl. 1): 281. Kawase, S., K. Uchino, and K. Takahashi Control of cherry Drosophila Drosophila suzukii injurious to blueberry. Shokubutu Boeki 61: 205Ð209. Lee, J. C., D. J. Bruck, H. Curry, D. Edwards, D. R. Haviland, R. A. Van Steenwyk, and B. M. Yorgey. 2011a. The susceptibility of small fruits and cherries to the spotted-wing drosophila, Drosophila suzukii. Pest Manag. Sci. 67: 1358Ð Lee, J. C., D. J. Bruck, A. J. Dreves, C. Ioriatti, H. Vogt, and P. Baufeld. 2011b. In Focus: Spotted wing drosophila, Drosophila suzukii, across perspectives. Pest Manag. Sci. 67: 1349Ð1351. Proctor, A., and T. J. Miesle Polygalacturonase and pectinmethylesterase activities in developing highbush blueberries. HortScience 26: 579Ð581. Sasaki, M., and N. Abe Occurrence of Drosophila in the cherry orchards (1) Species and the seasonal prevalence obtained by the bite trap. Ann. Rep. Plant Prot. North Jpn. 44:: 169Ð171. Sasaki, M., and R. Sato Bionomics of the cherry Drosophila, Drosophila suzukii Matsumura (Diptera: Drosophilidae) in Fukushima Prefecture, 3: Life cycle. Ann. Rep. Plant Prot. North Jpn. 46: 170Ð172. Shimizu, K Occurrence and control of the cherry Drosophila, Drosophila suzukii (Matsumura) in blue berry fruit. Shokubutu Boeki 60: 103Ð106. Silva, J. L., E. Marroquin, F. B. Matta, J. O. Garner, Jr., and J. Stojanovic Physicochemical, carbohydrate and sensory characteristics of highbush and rabbiteye blueberry cultivars. J. Sci. Food Agric. 85: 1815Ð1821. Walsh, D. B., M. P. Bolda, R. E. Goodhue, A. J. Dreves, J. Lee, D. J. Bruck, V. M. Walton, S. D. O Neal, and F. G. Zalom Drosophila suzukii (Diptera: Drosophilidae): invasive pest of ripening soft fruit expanding its geographic range and damage potential. J. Integr. Pest Manag. 2: 1Ð7. Received 17 December 2012; accepted 11 June 2013.