Rearing of Ostrinia Palustralis (Lepidoptera: Crambidae) Larvae with a Switchover of Two Kinds of Artificial Diets
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Appl. Entomol. Zool. 39 (3): 363–366 (2004) http://odokon.ac.affrc.go.jp/ Rearing of Ostrinia palustralis (Lepidoptera: Crambidae) larvae with a switchover of two kinds of artificial diets Mai FUKUZAWA,* Sadahiro TATSUKI and Yukio ISHIKAWA Laboratory of Applied Entomology, Graduate School of Agricultural and Life Sciences, The University of Tokyo; Tokyo 113–8657, Japan (Received 17 September 2003; Accepted 11 February 2004) Abstract A method was established to rear the entire larval stage of Ostrinia palustralis, an oligophagous species that feeds on dock plants Rumex spp., on artificial diets. Silkmate L4M (an artificial diet for the “polyphagous” silkworm mutants) supplemented with 20% R. japonicus dried leaf powder was initially provided to the neonate larvae, and the diet was switched to Silkmate 2M (a standard diet for silkworms) 14 days post-inoculation. These diets supported larval growth with a pupation rate of about 70%. This rate was comparable to that for conventional rearing using fresh host plant leaves. Although the larval period was significantly extended as compared with the conventional rearing, no dif- ference in the pupal weight was found between the two groups. The number of eggs laid by the resultant adult females and the hatchability of the eggs were also comparable. Utilization of the two kinds of artificial diets enabled rearing of this species throughout the year with much reduced labor. Key words: Ostrinia palustralis; artificial diet; Silkmate 2M; Silkmate L4M; Rumex the second instar, because the 1st and 2nd instar INTRODUCTION larvae have not been successfully reared on any of Ostrinia palustralis (Lepidoptera: Crambidae) is the artificial diets tested to date. Host plant leaves one of eight Ostrinia species currently found in must be collected from the field every 3–4 days be- Japan, which include agriculturally important pests cause the leaves given to the O. palustralis larvae such as the Asian corn borer O. furnacalis, and deteriorate rapidly due to bacterial or fungal con- adzuki bean borer O. scapulalis (Mutuura and tamination, which often causes septicemia in the Munroe, 1970; Ohno, 2003). O. palustralis is an larvae. Moreover, due to the unavailability of fresh oligophagous insect that feeds on dock plants such host plants during the winter, one could not main- as Rumex japonicus, R. obtusifolius, and R. crispus tain the insects throughout the year. (Polygonaceae) (Hattori and Mutuura, 1987). Al- In our laboratory, all Ostrinia species found in though O. palustralis feeds only on weeds and does Japan except O. palustralis are routinely reared on not have any economic significance, it is an impor- a commercial diet for the silkworm, Silkmate 2M tant species for clarifying the evolutionary history (e.g., Kageyama et al., 1998). As stated above, 1st of host plant diversification and species differentia- and 2nd instar larvae of O. palustralis cannot be tion in Ostrinia (Ishikawa et al., 1999). reared on Silkmate 2M. However, we have long Studies on O. palustralis have been hindered by known that larvae in the 3rd and later instars can be difficulties in collecting this insect from the field reared on this diet (Huang et al., 1998). This sug- and mass rearing in the laboratory. The rearing of gests that newly hatched larvae of O. palustralis O. palustralis is a very laborious process. First of die because they do not feed on the artificial diet, all, the larvae have to be reared individually in rather than because of a deficiency of nutrients in plastic tubes to avoid cannibalism. Second, they the diet. We suspected either that Silkmate 2M have to be fed fresh leaves from the host plant until lacks feeding stimulant(s) for O. palustralis, or the *To whom correspondence should be addressed at: E-mail: [email protected] DOI: 10.1303/aez.2004.363 363 364 M. FUKUZAWA et al. mulberry leaf powder contained in Silkmate 2M steamed for 40 min. During cooling, 2.5 ml of 19% deters feeding of O. palustralis larvae. Since a formaldehyde solution was added, and the diet was commercial diet for “polyphagous” mutant silk- mixed thoroughly and then kept in a refrigerator worms, Silkmate L4M, which contains a much until use. lower percentage of mulberry leaf powder, is com- Rearing experiments. Newly hatched larvae mercially available, we tested this diet with and obtained from eight females were used for the rear- without the powdered leaves of the host plants of ing experiments. Columns of diet (12 mm O. palustralis. We considered it possible to stimu- diam.ϫ35 mm) were prepared using a cork borer, late feeding by O. palustralis through the addition and a small hole was made on top using a tooth- of the host plant powder to the diet. In the present pick to facilitate burrowing and feeding by the study, we tested three kinds of artificial diets for newly hatched larvae. A rolled host plant (R. rearing the earlier instars of O. palustralis with the japonicus) leaf was used for conventional rearing aim of rearing this insect without using fresh host (Huang et al., 1998). Using a small soft brush, plant leaves throughout the larval stage. hatching larvae were placed in the hole of the col- umn or on the host plant leaf in plastic tubes (18 mm diam.ϫ95 mm). The host plant leaf was MATERIALS AND METHODS changed every 4 days. O. palustralis larvae were Insects. Adult females of O. palustralis were reared on one of four diets for 14 days, and there- collected with a sweep net at Iruma, Japan in May after, columns of Silkmate 2M were added weekly, 2003, and maintained in individual plastic cups regardless of the initial diet. Pupae formed inside (430 ml) with a cotton pad soaked with a 3% su- the column were taken out and sexed based on the crose solution. A cut leaf of the host plant (R. morphology of the abdominal tips, and maintained japonicus) was included in the cup to stimulate in a plastic cup (40 ml) individually. oviposition. After allowing oviposition for a few Mating and oviposition experiments. Two days, the leaf was removed, and the neonates from pairs of 1- or 2-day-old adults were allowed to the eggs laid on the surface of the plastic cup were mate in a screen cage (25 cmϫ25 cmϫ25 cm) for 2 used for the experiments. The insects were reared days, and then female moths were individually in an environmental chamber maintained at 23°C, housed in plastic cups (430 ml) with a cotton pad with 60% R.H. and a 16 h light: 8 h dark photocy- soaked with a 3% sucrose solution to allow them to cle. lay eggs. Three days later, the number of eggs laid Artificial diets. Silkmate 2M (a diet for the silk- on the surface of the cup was counted. worm, dry formula, mulberry leaf powder content: 26% on dry weight basis) and Silkmate L4M (a RESULTS diet for “polyphagous” mutants of the silkworm, mulberry powder content: 4%) were purchased Rearing experiments from Nihon Nosan Co. (Yokohama, Japan). Host We reared 305 neonate larvae of O. palustralis plant powder was prepared in our laboratory; on four kinds of diets (Table 1). About 70% of the leaves of R. japonicus were collected from the larvae succeeded in pupating when Silkmate L4M field, dried naturally, and powdered using an elec- supplemented with 20% Rumex powder was used tronic blender. We made every effort to collect only as the initial diet, while few larvae reached the the leaves of R. japonicus, but R. obtusifolius and pupal stage when they were given either Silkmate R. crispus might be included because the three 2M or Silkmate L4M alone (Table 1). The pupation Rumex species are similar. Larvae of O. palustralis rate for conventional rearing, i.e., host plant leaf can be reared on any of the three Rumex species for 14 days and then a switch to Silkmate 2M, was (unpublished data). about 80%. More than 80% of larvae raised on In a stainless steel container (14 cmϫ20 cmϫ Silkmate 2M and Silkmate L4M alone died during 7.5 cm), 250 g of Silkmate 2M, 250 g of Silkmate the first 14 days, suggesting that they did not feed L4M, or 200 g of Silkmate L4M plus 50 g of host on these diets. Although the larval period of O. plant powder were weighed. After addition of palustralis reared on Silkmate L4M with Rumex 750 ml of water and thorough mixing, the diet was powder was significantly extended as compared Table1.Effect of initial diet on the growth of Ostrinia palustralis larvae No. No. of pupae Mortality (%) Pupation Larval period (d)b,d Pupal period (d)b,d Pupal weight (mg)b,d,e Emergence Initial dieta of during 14 ratec (%) larvae Male Female daysc (%) Male Female Male Female Male Female Host plant 80 34 28 16 a 79 b 95 25.9Ϯ3.6 a 26.1Ϯ2.7 a 10.7Ϯ0.7 a 10.7Ϯ0.8 a 133Ϯ16 a 140Ϯ20 a Silkmate 2M 70 4 5 83 b 17 a 89 42.8Ϯ3.3 b 41.0Ϯ3.5 b 9.75Ϯ1.0 a 10.0Ϯ1.4 a 134Ϯ30 a 142Ϯ23 a Silkmate L4M 70 2 4 91 b 9 a 100 38.5 b 37.3Ϯ3.3 b 9.5 a 10.3Ϯ0.6 a 147 a 149Ϯ15 a (34, 43) (11, 8) (149, 144) L4Mϩ20% host 85 30 28 31 a 69 b 86 36.5Ϯ7.9 b 34.8Ϯ6.0 b 10.3Ϯ0.8 a 9.67Ϯ0.7 a 141Ϯ17 a 147Ϯ14 a plant powder a A column of artificial diet, Silkmate 2M, was supplied 14 days post-inoculation to every experimental group.