Performance of Lymantria xylina (Lepidoptera: Lymantriidae) on Artificial and Host Plant Diets

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1 ECOLOGY AND BEHAVIOR Performance of Lymantria xylina (Lepidoptera: Lymantriidae) on Artificial and Host Plant Diets TSE-CHI SHEN, CHIH-MING TSENG, LI-CHING GUAN, AND SHAW-YHI HWANG 1 Department of Entomology, National Chung Hsing University, Taichung, Taiwan 402 J. Econ. Entomol. 99(3): 714Ð721 (2006) ABSTRACT Lymantria xylina Swinhoe (Lepidoptera: Lymantriidae) is a serious defoliator of hardwood and fruit trees in Taiwan. The larvae of L. xylina feed on 63 species of host plants, belonging to 29 families. Because a large number of larvae are needed for the production of nucleopolyhedrosis virus (NPV) or other related studies, the development of a suitable artiþcial diet is very important for the mass rearing of this moth in the laboratory. In this study, eight artiþcial diets, modiþed from different formulas, and one host plant, Liquidambar formosana Hance, were used to feed L. xylina caterpillars. Through various bioassays (Þrst instar survival trial and long- and short-term feeding trials), the most suitable diet for the L. xylina was selected by performance comparisons with L. formosana. After the Þrst instar survival trial, two of the diets were discarded, because no larva survived on these diets. The results of the long-term feeding trial indicated that the larvae grew successfully on only three kinds of artiþcial diet. Finally, results of the short-term feeding trial revealed that a diet (diet A), modiþed from the gypsy moth, Lymantria dispar (L.), formula diet, was the most appropriate for the L. xylina. Larvae fed on diet A had better survival rate, pupal weight, adult size, efþciency of conversion, and relative growth rate than larvae fed on other diets; they did not grow as well as those fed on L. formosana, however, except for pupal and adult weight, and approximate digestibility. In summary, diet A was found to be the best of the artiþcial diets for the L. xylina and is suitable for mass rearing of this moth in the laboratory. KEY WORDS Lymantria xylina, Liquidambar formosana, artiþcial diet, feeding trial Lymantria xylina (Lepidoptera: Lymantriidae) is a major pest of casuarina, Casuarina equisetifolia L., and acacia, Acacia confusa Merr., forests, natural areas, and fruit tree orchards in Taiwan, Japan, India, and the eastern coast of mainland China (Chao et al. 1996). L. xylina is closely related to the gypsy moth, Lymantria dispar (L.), which is an extremely serious forest pest in North America. Similar to the gypsy moth, L. xylina is univoltine. Shortly, after emergence and mating in summer, females lay a single, hair-covered egg mass, consisting of 100Ð1000 eggs (Shen et al. 2003). Like L. dispar, eggs of the L. xylina undergo diapause as pharate Þrst instars, before the complete consumption of the extra embryonic yolk (Gray et al. 2001, Hwang et al. 2004). The larvae hatch in April of the following year, after an 8Ð9-mo dormancy (Hwang et al. 2004). Larval stages last 1.5Ð2 mo, having Þve to eight instars (Chang and Weng 1985, Chao et al. 1996). The pupal stage lasts 2 wk. Adult males emerge Þrst, followed several days later by adult females. L. xylina is a polyphagous herbivore, and the number of recorded host plants for this moth includes and most likely exceeds 69 species of trees and shrubs, belonging to 29 families (Chang and Weng 1985, Chao 1 Corresponding author, oleander@dragon.nchu.edu.tw. et al. 1996). Outbreaks of L. xylina infestations have only been found in casuarina plantations; however, serious defoliation on fruit trees also has occurred in several areas of central Taiwan (Chao et al. 1996). Current infestations of fruit trees and other hardwoods by L. xylina indicate the real threat posed by this moth. Although a potentially serious pest of hardwood and fruit trees in Taiwan, little is known about L. xylina (Chao et al. 1996, Gries et al. 1999, Shen et al. 2003). For management purposes, more studies must be undertaken to understand its population dynamics, the relationship with its host plants, and potential controlling agencies. To study this moth, mass production in the laboratory is necessary. Generally, the food sources used to rear herbivorous insects in the laboratory can be divided into natural hosts and artiþcial diets (Kao 1995). Past studies have indicated that the larvae of some insect species performed better on natural host plants than on artiþcial diets (Hirai 1976, Hou and Hsiao 1986, Dosdall and Ulmer 2004). However, for research purposes, problems can arise when rearing caterpillars on natural host plants. First, plants are a suboptimal food for insect herbivores, because of inadequate nutrient ratios and the occurrence of allelochemicals (e.g., tannins and alkaloids) that need to /06/0714Ð0721$04.00/ Entomological Society of America

2 June 2006 SHEN ET AL.: L. xylina ON DIFFERENT DIETS 715 Table 1. Composition of artificial diets for rearing of L. xylina ArtiÞcial diet Component I a II b III c IV d A B C D E F G H Wheat germ 23 g 20 g 18 g 15 g 18 g 15 g 12 g 9 g Formosan sweet gum leaf powder 3 g 3 g 3 g 3 g Soybean powder 6 g 6 g 5 g 5 g Kidney bean powder 5 g 5 g Corn powder 14.5 g 14.5 g Yeast powder 5 g 5 g 3 g 3 g 3.6 g 3.6 g Casein 5 g 5 g Cholesterol 1 g 1 g 1 g 1 g 1 g 1 g 1 g 1 g WessonÕs salt mix. 1.6 g 1.6 g 0.5 g 0.5 g 0.5 g 0.5 g Ascorbic acid 0.5 g 0.5 g 0.5 g 0.5 g 0.5 g 0.5 g 0.5 g 0.5 g Vitamin mix. 1.5 g 1.5 g 1.5 g 1.5 g 0.5 g 0.5 g L-Cysteine 0.1 g 0.1 g Methyl-p-hydroxybenzoate 0.4 g 0.4 g 0.3 g 0.3 g 0.3 g 0.3 g Chloramphenicol 0.05 g 0.05 g 0.05 g 0.05 g 0.05 g 0.05 g Sorbic acid 0.4 g 0.4 g 0.05 g 0.05 g 0.05 g 0.05 g 0.05 g 0.05 g Agar 3 g 3 g 3 g 3 g 3 g 3 g 3 g 3 g Distilled water 180 ml 180 ml 180 ml 180 ml 180 ml 180 ml 180 ml 180 ml a ModiÞed from ODell et al. (1985). b ModiÞed from Tang (unpublished). c ModiÞed from Tang (unpublished). d ModiÞed from Kao (1995). be detoxiþed (Bailey 1976, Schoonhoven et al. 1998, Cohen 2004). Second, plant material is difþcult to standardize, because individual plants and plant parts may greatly vary with season, developmental stage, and so on. However, artiþcial diet formulations allow for precise management of nutritional factors, and they have been developed for many insect species, beginning in the 1950s (Schoonhoven et al. 1998). Especially for L. xylina, mass rearing is a requisite in the production of the microbial insecticide nucleopolyhedrosis virus (NPV) or can provide individuals for other research. No artiþcial diet, however, has yet been developed for this moth. Thus, the objective of this study was to assess the effects of some of the artiþcial diets of common lepidopteran pests on the performance of L. xylina, in the hope of Þnding a suitable artiþcial diet for this moth. In addition, we also compared the performance of L. xylina on artiþcial diets and on one of its natural host plants, Liquidambar formosana Hance. Materials and Methods Source and Treatment of Egg Masses. In late May 2003, L. xylina egg masses were collected from two heavily overrun areas in central Taiwan, according to Shen et al. (2003). These areas were located at Mingchien, Nantoa ( N, E) and Erhshui, Changhua ( N, E). Approximately 200 egg masses were collected from each site. In the laboratory, the egg masses were surfacesterilized, by soaking in 0.1% sodium hypochlorite with 1% Tween 80 solution for 10 min., and rinsing under running tap water for 5 min. Then, the egg masses were air-dried. To obtain individual eggs, the egg masses were broken up and the hairs removed, by rubbing against sticky tape. The dehaired eggs, from different egg masses, were mixed and placed into petri dishes ( 500 eggs/dish). These dishes were then moved to a Percival growth chamber (Percival, Perry, IA) to expose them to chilled conditions (10 C), to terminate diapause (Hwang et al. 2004). After 120 d of chilling, the eggs were sterilized again and placed in the Percival growth chamber at 28 C:25 C (L:D) with a photoperiod of 12:12 (L:D) h. The larvae, used in the feeding bioassays, had hatched after 4Ð7 d; the larvae were reared in this environmental chamber, during all feeding trials. Composition and Preparation of Diets. In this study, eight artiþcial diets, in four diet categories (diets AÐH), and foliage (diet I) from the host plant L. formosana were used to feed L. xylina larvae. The compositions of all artiþcial diets used in this study are listed in Table 1. Diets A and B were modiþed from the gypsy moth high wheat germ diet (ODell et al. 1985), with the primary component being wheat germ. The main composition of diets C and D was wheat germ and soybean powder, the formulations of these two diets being modiþed from the Spodoptera exigua (Hübner) diet (L. C. Tang, unpublished). Diets E and F were modiþed from the S. litura diet (L. C. Tang, unpublished), with the basic components being wheat germ, soybean powder, and kidney bean powder. Finally, wheat germ and corn starch made up the principal ingredients of diets G and H, which also had been modiþed from the S. litura diet (Kao 1995). In addition, to test the necessary of adding feeding stimulant, L. formosana, leaf powder was added to the artiþcial diets B, D, F, and H. To prepare diets A and B, agar was added into 150 ml of distilled water in a 1-liter beaker, covered with foil, and autoclaved (121 C; 15 min).

3 716 JOURNAL OF ECONOMIC ENTOMOLOGY Vol. 99, no. 3 Cholesterol was then dissolved in ethyl ether and blended with the main component wheat germ. On the side, we mixed the other ingredients with 30 ml of distilled water as the mingling solution. After autoclaving, the agar was poured into the mixer and stirred with the wheat germ (and leaf powder for diets B, D, F, and H). The mingling solution was added into the mixture as the agar was chilled to 50 C. Then, we distributed the still soft diet mixture into plastic rearing cups (3 cm in diameter by 2.5 cm in height); each cup contained food up to 0.3 cm in height (to feed the Þrst, second, and third instars). Alternatively, we also poured the soften diet mixture into petri dishes (14.5 cm in diameter by 1.5 cm in height to feed fourth and older instars). The diet mixture was allowed to solidify at room temperature and was kept in the refrigerator until needed. The preparation procedures for the other diet categories were similar to those of diets A and B. However, for diets C and D, cholesterol was blended with wheat germ and soybean powder; for diets E and F, cholesterol was blended with wheat germ, soybean powder, and kidney bean powder; and cholesterol was blended with wheat germ and corn starch for diets G and H. The mingling solution combinations were also slightly different. Feeding Trials of L. xylina. To evaluate the quality of different artiþcial diets, as well as that of the host plant, we conducted three types of insect bioassays: a Þrst instar survival trial, and a long- and a short-term feeding trial. First instar survival trials were conducted to assess diet quality on the survivorship of L. xylina larvae. In this bioassay, 10 newly hatched larvae were placed into each plastic rearing cup, containing arti- Þcial diet. Nine diets (eight artiþcial diets [diet AÐH] and one host plant [diet I]) were used in this trial, with six replicates (10 larvae per replicate) for each diet. After the larvae had been placed in each rearing cup, containing one of the artiþcial diets, it was covered with a lid, inverted, and placed into the Percival chamber (ODell and Rollinson 1966, ODell et al. 1985). For the foliage treatment, we placed the larvae into petri dishes (9 cm in diameter by 1.5 cm in height) containing an excised L. formosana leaf. The leaf petiole was wrapped with wet cotton, to maintain leaf turgor, and leaves were changed every 1 to 2 d. After the larvae had molted to the second instar, we recorded the survival rates for each treatment. The long-term feeding trial was conducted to assess the effects of diets on insect development and growth over the entire larval feeding, pupal, and adult stages. In this bioassay, we only used the diets in which the Þrst instars had survival rates of 60% from the Þrst instar survival trial (diets AÐF and I). One hundred larvae were tested on each diet. Each assay consisted of one newly hatched and weighed larva, placed into a plastic rearing cup, with either artiþcial diet or foliage. To facilitate feeding, larvae were grouped (10) in a cup and were individually fed when they reached the third instar (ODell et al. 1985). The cup was covered with a lid and then inverted in the Percival chamber. Because of increased body size, we transferred fourth instars into petri dishes (5.5 cm in diameter by 1.2 cm in height) and Þfth instars into even larger petri dishes (9 cm in diameter by 1.5 cm in height). To separate feces from diets, a suitably sized piece of the artiþcial diet was segmented and stuck onto the inner side of the lid. The feeding methods for diet I (foliage of L. formosana) were similar to the procedures used in the Þrst instar survival trial. All larvae were fed with corresponding diets until pupation and eclosion. We recorded both male and female data on larval period, pupal period, pupal weight, and adult weight. In addition, we also recorded larvae survival rates and calculated the growth rate, based on data from this trial. The growth rate formula, giving a relative growth rate, and representing the mean weight gain per day was growth rate [ln(pupal weight) ln(hatching weight)] (larval period) (Nylin et al. 1993, Gotthard et al. 1994, Fischer and Fiedler 2000). The short-term feeding trial was conducted to evaluate the effects of diet quality on growth rates, food consumption rates, and food processing efþciencies of fourth instars. In this bioassay, only the diets with which larvae could successfully pupate, in the longterm feeding trial, were used (diets A, E, and F, and I). A group of larvae was reared on the gypsy moth wheat germ diet (Cat. no , ICN Biomedicals Inc., OH) from hatching until molting to the fourth instar. Each assay consisted of a newly molted and weighed fourth instar placed into a petri dish (5.5 cm in diameter by 1.2 cm in height) containing a suitably sized artiþcial diet disk. For diet I (foliage of L. formosana), the larvae were placed into the larger petri dishes, similar to those used in the Þrst instar survival trial, with the leaves being added to each dish. One larva was used for each replicate, with 30 replicates for each diet. We changed the food every 1 to 2 d, or as necessary, during the bioassay. Upon molting to the Þfth instar, the survival rate and fourth instar duration were recorded; then, the larvae were frozen, ovendried at 40 C for 1 wk, and reweighed. Frass and uneaten diet material also were collected, dried at 40 C for 1 wk, and weighed. Nutritional indices were calculated to evaluate insect growth, consumption, and food utilization efþciency (Haynes and Millar 1998, Schoonhoven et al. 1998). These indices were calculated from standard formulas for approximate digestibility (AD), efþciency of conversion of digested food (ECD), efþciency of conversion of ingested food (ECI), and total consumption (TC), as described by Waldbauer (1968) and Haynes and Millar (1998). We used the initial, rather than the average weights of larvae, to calculate relative growth rate (RGR) and relative consumption rate (RCR) (Farrar et al. 1989). Initial dry weights were estimated, based on a wet-to-dry weight conversion factor, and determined from 10 newly molted fourth instars. Likewise, the initial dry weight of the diets fed to larvae were estimated by dry weight conversion, by using the suitable-sized piece, segmented from each artiþcial diet (diets A, E, and F) or the foliage collected from the host plant (diet I), and dried at the time of the bio-

4 June 2006 SHEN ET AL.: L. xylina ON DIFFERENT DIETS 717 Fig. 1. Survival rate of Þrst instars of L. xylina reared with different diets (mean SE) (TukeyÕs studentized range test). AÐH, artiþcial diets; I, host plant leaves of L. formosana. * Survival rate values are transformed to arcsine values when analyzed by ANOVA. assay. During the bioassay, a few larvae died because of a virus infection. Because infected larvae were easily distinguished from the others, they were excluded from our analyses. Chemistry of Diets in Short-Term Feeding Trial. To reveal the chemical components of the diets, we measured water and nitrogen content (nutrient manifestations) from diets used in the short-term feeding trial (diets A, E, and F, and I) because water and nitrogen were the primary components provided for the caterpillars (Zalucki et al. 2002). Concurrent with the feeding trials, Þve pieces of each artiþcial diet were randomly segmented (in diet I, Þve pieces of foliage of L. formosana were collected), weighed, oven-dried at 40 C for 1 wk, reweighed, ground, and stored in a freezer ( 20 C). Water content and total nitrogen content were quantiþed for each diet sample. We determined water content by weight difference between the wet and dry weights of the diet samples. Diet nitrogen content was veriþed by standard micro- Kjeldahl assays. Diet samples were digested in acid (Parkinson and Allen 1975), and nitrogen content was quantiþed by the micro-nesslerization technique (Lang 1958). Glycine p-toluene-sulfonic acid (5.665% N) served as a nitrogen standard. Statistical Analyses. In all trials, means and standard errors of testing values were calculated by descriptive statistics (PROC UNIVARIATE, SAS Institute 1999). For the Þrst instar survival trial, survival rates were analyzed by analysis of variance (ANOVA) (PROC ANOVA, SAS Institute 1999), followed by comparisons of means using TukeyÕs studentized range (honestly signiþcant difference) test. We analyzed the testing values in long- and short-term feeding trials, and the chemistry of the diets, by ANOVA (PROC GLM, SAS Institute 1999), followed by comparisons of means by using least-signiþcant difference (least signiþcant difference) test. Results First Instar Survival Trial. Results of this trial indicated that the Þrst instar survival rate of L. xylina varied signiþcantly among insects reared with different diets (Fig. 1). Except for diets G and H, Þrst instars survived well ( 60%) on most diets. Caterpillars fed on diets E and F had the highest survival rate (100%); no caterpillar survived beyond Þrst instar on diets G and H, which were modiþed from the S. litura diet (Kao 1995). Long-Term Feeding Trial. Because all Þrst instars died when fed on diets G and H, these two diets were excluded from the long-term feeding trial. All caterpillars, fed on diets B, C, and D died during the trial, so these data were excluded from the analysis. The result of the long-term feeding trial revealed that,

5 718 JOURNAL OF ECONOMIC ENTOMOLOGY Vol. 99, no. 3 Table 2. Performances of L. xylina reared with different diets in long-term feeding trails (mean SE) (28 C:25 C; photoperiod of 12:12 L:D ) Larval period (d) Pupal period (d) Pupal wt (mg) Adult wt (mg) Growth rate Male Female Male Female Male Female Male Female (%/d) Diet a Survival rate (%) A a a a 2, a a a c B 0 C 0 D 0 E a b d 1, b b b d F b b c 1, b a b b I c b b 1, b a b a F b df 3, 67 3, 62 3, 61 3, 60 3, 67 3, 62 3, 58 3, 60 3, 130 P Within a column, means bearing the same letter are not signiþcantly different (P 0.05). a AÐF, artiþcial diets; I, host plant L. formosana. b Growth rate values are transformed to arcsine values when analyzed by ANOVA. overall, caterpillars grew better on their host plant than on artiþcial diets. The survival rate and growth rate of L. xylina were signiþcantly higher on the host plant than on the artiþcial diets (Table 2). Caterpillars fed on the host plant (diet I) had the shortest larval period and the highest growth rate (Table 2). The results also indicated that, except for the pupal period, larvae performance varied signiþcantly among the different diets (P 0.001) (Table 2). Pupal and adult weights varied by 1.5- and 3-fold, respectively, among the different diets (Table 2). In summary, larvae grew well on the foliage of L. formosana (diet I), with the highest survival and growth rates. Moreover, caterpillars fed on diet A had the longest larval period and the highest pupal and adult weights. Short-Term Feeding Trial. In this bioassay, we only tested those diets, with which the larvae could pupate and eclose well, during the long-term feeding trial (diets A, E, and F, and I). Results of the short-term feeding trial revealed that performance (duration, growth rate, and food processing efþciency) of fourth instars of L. xylina varied substantially among the different diets (Table 3). L. xylina larvae had RGR and RCR values but a shorter duration on the host plant diet (diet I) than on artiþcial diets (diets A, E, and F). In contrast, the digestibility (AD) and conversion ef- Þciencies (ECD and ECI) were higher for larvae fed on artiþcial diets. Of the three artiþcial diets, A, E, and F, larvae fed on diet A had the best performance, with the highest approximate digestibility (AD) and efþciency of conversion of ingested food (ECI). Additionally, the survivorship of fourth instars of L. xylina was 75% in all diets tested. In general, the performance of L. xylina, in this short-term study, paralleled that of insects in the long-term study, with faster growth and higher consumption on host plant foliage. Diets and Host Plant Chemistry in Short-Term Feeding Trial. Water (P 0.001) and nitrogen (P ) content of diets varied signiþcantly (Table 4). All artiþcial diets had higher water (1.4-fold) and nitrogen ( 2.4-fold) content than found in the host plant. There was no signiþcant difference in water and nitrogen content among the artiþcial diets. Discussion In this study, it was clearly demonstrated that the performance of L. xylina varied signiþcantly among different diets. Caterpillars fed on diets in which the principal ingredient is corn starch cannot survive. In addition, our results also indicated that the necessity of adding feeding stimulant (L. formosana powder) on artiþcial diets is still unclear. The current literature indicates that some herbivorous insects, such as Leucania separate Walker, Plutella xylostella (L.), and Mamestra configurata Walker, survived and grew better on host plants, than on artiþcial diets (Hirai 1976, Hou and Hsiao 1986, Dosdall and Ulmer 2004). The results of our study revealed a similar pattern with survival rates and growth rates increasing by 60 and 30%, respectively, in the host plant. Because this was the Þrst generation of the L.

6 June 2006 SHEN ET AL.: L. xylina ON DIFFERENT DIETS 719 Table 3. Performances of L. xylina reared with different diets in short-term feeding trails (mean SE) (28 C:25 C; photoperiod of 12:12 L:D ) Diet a Survival rate (%) DUR (d) AD (%) ECD (%) ECI (%) TC (mg) RGR (mg/mg/d) RCR (mg/mg/d) A b a a c b b E a bc b b c b F b b b b b b I c c c a a a F b df 3, 61 3, 61 3, 61 3, 61 3, 61 3, 61 3, 61 P AD, approximate digestibility; DUR, duration; ECD, efþciency of conversion of digested food; ECI, efþciency of conversion of ingested food; RCR, relative consumption rate; RGR, relative growth rate; TC, total consumption. Within a column, means bearing the same letter are not signiþcantly different (P 0.05). a A, E, and F, artiþcial diets; I, host plant L. formosana. b AD, ECD, and ECI values are transformed to arcsine values when analyzed by ANOVA. xylina to feed on artiþcial diets, the insects may need more time to adapt to the artiþcial diets (Kao 1995). According to Schoonhoven et al. (1998), plants are suboptimal food, because of the diluted nutrients in a medium of indigestible compounds. In response to low-quality foods, herbivorous insects may have compensatory reactions, such as increased food consumption and nutrient utilization efþciency (Timmins et al. 1988, Wheeler and Halpern 1999, Awmack and Leather 2002, Chen et al. 2004), that result in a Þnal biomass equivalent to larvae fed on high-quality food (Slansky and Feeny 1977). The foliar nitrogen content of L. formosana was lowest for all diets tested, and the caterpillars consumed signiþcantly more L. formosana biomass, than that consumed in the other diets. Thus, our results suggest that compensatory feeding may occur in L. xylina, in response to poor-quality host plant foliage. Comparisons of the performance of L. xylina, among the various artiþcial diets, revealed differences in their ability to effectively use the diets. Because different insect species often vary to some extent in their speciþc nutritional requirements, small changes in diet composition may have drastic effects on insect performance (Schoonhoven et al. 1998). The larvae of L. xylina did not feed well on diet G, which was modiþed from the S. litura diet (Kao 1995). In contrast, Table 4. SE) Water and nitrogen content in different diets (mean Diet a Water content (%) Nitrogen content (%) A a a E a a F a a I b b F b df 3, 19 3, 19 P Within a column, means bearing the same letter are not signiþcantly different (P 0.05). a A, E, and F, artiþcial diets; I, host plant L. formosana. b Water and nitrogen content values are transformed to arcsine values when analyzed by ANOVA. caterpillars grew very well on another diet, which had also been modiþed from the S. litura diet (diet E) (L. C. Tang, unpublished). The composition of these two diets was very similar and the cause of the signiþcant difference is unknown. Our results also revealed that caterpillars fed on diet C, which was modiþed from the S. exigua diet (L. C. Tang, unpublished) could not successfully pupate. The reason for this is also unclear, but diet composition may play an important role. The main protein source in diet C was wheat germ; past studies have revealed that the protein source is a critical factor inßuencing insect growth (Schoonhoven et al. 1998, Cohen 2004). It also has been found that S. exigua and Helicoverpa zea (Boddie) reared on a synthetic diet containing animal protein (casein) had superior growth compared with those fed on diets containing vegetable protein (soybean powder) (Duffey et al. 1986). Our results showed that the caterpillars grew best on diet A, which also contained casein as the main protein source except from wheat germ. Concerning the necessity of adding feeding stimulant, we added leaf powder of L. formosana on several diets. The results revealed that where adding leaf powder makes the diet better is still questionable. Caterpillars of L. xylina performed no worse or somewhat better on diets with leaf powder added. Larvae used in this study were from Þeld-collected eggs, and they had no experience on artiþcial diets. Therefore, these caterpillars may have difþculty to adapt the artiþcial diets. Our long-term feeding trial indicated that the overall survival rates were signiþcantly low on all the artiþcial diets. This low survival may mask the effects of leaf powder. In addition, the water and nitrogen content in the diets of herbivores have been considered as important factors affecting their performance (Schoonhoven et al. 1998). Schoonhoven et al. (1998) revealed that in caterpillars, the developmental period was longer when higher nutrient food was provided; the caterpillars seemed need more time to digest and absorb the nutrient, and the Þnal pupal weight was heavier than those fed on poor nutrient diet. Timmins et al. (1988)

7 720 JOURNAL OF ECONOMIC ENTOMOLOGY Vol. 99, no. 3 also indicated that the feeding time for caterpillars was longer on diets having an elevated water content than on normal water content diets. Our results were similar to those of others in that diet (diet A), which contained higher water and nitrogen, was the more nutritious diet. Moreover, concerning the unit price of the artiþcial diets, we found that the unit price of diet A (1.78 NT$/g dry material) was less than that of diet E (2.04 NT$/g dry material) or F (2.03 NT$/g dry material). Combining this information, with the results of the feeding performances, it was determined that diet A could be the best diet of those we tested for artiþcial rearing of L. xylina caterpillars. In summary, this research has indicated that diet composition has a signiþcant effect on L. xylina performance and that the diet, modiþed from the gypsy moth diet, was the most suitable for L. xylina. In addition, larvae reared on the host plant grew faster than those reared on artiþcial diets. We also found that size of laboratory-reared adults was signiþcantly larger than Þeld-captured adults and these laboratory-reared adults can successfully reproduce in laboratory (S.- Y.H., unpublished data). However, this study is only a Þrst step. For future mass rearing purposes, the diet composition and ratios may require Þne-tuning to improve insect survive and performance. Acknowledgments We thank L. C. Tang for valuable suggestions in preparing artiþcial diets and rearing methods and R. Haesevoets for comments on the manuscript. Two anonymous reviewers provided helpful comments. This research was supported by Grant 92AS BQ-B2 from the Bureau of Animal and Plant Health Inspection and Quarantine, Council of Agriculture, Taiwan (to S.-Y.H.). References Cited Awmack, C. S., and S. R. Leather Host plant quality and fecundity in herbivorous insects. Annu. Rev. Entomol. 47: 817Ð844. 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