Insect and mite pests of pepino (Solanum muricatum Ait.) in Japan

Abstract To further increase the basic knowledge regarding the establishment of pest control for pepino (Solanum muricatum Ait.), we conducted surveys of pepino pests in Japan. Thirty-four insect and four mite species were recognized as pests of pepino plants in the present study. Including the results of previous studies, a total of 41 species of insects and mites have been reported as pests of pepino plants in Japan. Three species, namely onion thrips (Thrips tabaci), two-spotted spider mites (Tetranychus urticae), and cotton whiteflies (Bemisia tabaci), are likely the most important insect and mite pests of pepino plants, because they were collected from more than half of the study sites and were much more abundant on pepino plants than the other pest species.


Introduction
Pepino (Solanum muricatum Ait., the Spanish name for sweet cucumber) is a solanaceous plant cultivated as a fruit crop and native to the Andes. To date, 22 insect and three mite species have been recorded as pests of pepino worldwide (excluding Japan). Seven of them, inclusive of the two-spotted spider mite Tetranychus urticae Koch, 1836, are regarded to be the most important among the pests of pepino (Larraín 2002;Galbreath and Clearwater 1983;Akyazi 2012). In 2016, our research team began a research project aimed at producing high quality and flavorsome pepino fruits, whose soluble solids content was rather low in the Japanese fruits (Sakata 2011). In order to establish solid pest control in its commercial cultivation and to produce high quality and stable pepino fruits, our research team has tried to comprehensively elucidate the pests of pepino in the project.
To date, 13 insect and mite species have been recorded in Japan as pests of pepino (Kim et al. 2017). However, few studies have been conducted on pests of pepino plants in Japan. The reason for this may be that the number of pests of pepino plants recognized in Japan is rather low compared to those of other popular solanaceous crops such as tomato (S. lycopersicum), eggplant (S. melongena), potato (S. tuberosum), and green pepper (Capsicum annuum) (The Japanese Society of Applied Entomology and Zoology 2006). This low number of pests is attributable to the small area in which studies have been conducted on pepino, which has a radius of 250 m at most (Kim et al. 2017). In order to develop an accurate understanding of pests of pepino plants, it is necessary to conduct research across an extensive area of Japan.
In order to expand the basic knowledge required for the establishment of pest control for pepino plants, we conducted investigations of pepino pests in Japan in the experimental fields of our university, Tokyo University of Agriculture, as well as on farms and in garden centers in Japan. This study was conducted under a project for regional development titled 'Launching of Nodai-branded Pepino Crop' conducted by the Faculty of Agriculture, Tokyo University of Agriculture (Kim et al. 2017). This paper documents the results of our field surveys of pests of pepino plants in Japan after the latest report by Kim et al. (2017), with a brief discussion on pests of importance to the cultivation of pepino in Japan.

Study sites
This study was conducted at 11 sites in Japan (Fig. 1). Of these, sites 1-7 are in a warmtemperate climate zone, and sites 8-11, on Okinawa Island, are in a subtropical climate zone. The sites are as follows: Site 1 (Fig. 2a)   Study sites 1-6. Insect and mite pests of pepino (Solanum muricatum Ait.) in Japan

Sampling methods
All specimens were collected by looking at or beating the leaves, branches and fruits of pepino plants. A total of more than 80 collections were performed in the 11 study sites (once at sites 1, 6, 7, 10, and 11; three times at site 4; four times at sites 8 and 9; nine times at site 5; 24 times at site 3; and more than 30 times at site 2) from February 24th, 2017 to March 14th, 2019. Our sampling period followed that of Kim et al. (2017), with two exceptions, as unidentified specimens collected on October 26th and November 23rd, 2016 represented the species not found in this main survey. Each of the collections was conducted for a maximum of three hours during the daytime by one or two persons. The collected insects and mites were killed immediately after capture, using ethyl acetate. Aphids, lepidopteran larvae, and mites were fixed in plastic bottles filled with 70-80% ethanol. All specimens, which were killed with ethyl acetate and fixed with ethanol, were prepared as dry mounted, slide-mounded, or ethanol preserved for morphological examination. Slide-mounted specimens were prepared with the following procedure: specimens were macerated in a hot 5-7% KOH solution for 5 minutes; macerated specimens were washed in distilled water for a few minutes; washed specimens were moved from distilled water onto a drop of Neo-Sigaral (balsam-like liquid for easy preparation method; Shiga-Konchu-Fukyusha, Tokyo, Japan) on the middle of a glass slide, and then covered gently with a 12 mm (15 mm for larger specimen) cover glass.

Identification methods
Identification of insect and mite specimens was performed using stereoscopic microscopes (Olympus SZ60 and Olympus SZX16, Tokyo, Japan) and optical microscopes (Olympus BH-2 and Olympus BX41, Tokyo, Japan) by Tadashi Ishikawa, Yoshihiro Yamada, and Naoki Kaneko according to the following studies: Kawai (1980), Dworakowska (1982), Moritsu (1983), Kimoto and Takizawa (1994) Collected specimens were regarded as pests only in this paper if these were insects or mites that directly damaged pepino plants, were known as pests of pepino plants in the native range and introduced regions of pepino plants other than Japan (Galbreath and Clearwater 1983;Larraín 2002;Grinberg et al. 2005;Akyazi 2012), or were known as pests of major solanaceous crops such as tomato, eggplant, potato, and green pepper, in Japan, with reference to studies such as Umeya and Okada (2003) and The Japanese Society of Applied Entomology and Zoology (2006). All examined specimens are preserved in the Insect Collection (IC) at the Laboratory of Entomology, Tokyo University of Agriculture, Atsugi-shi, Kanagawa, Japan (LETUA).

Results
In this study, 701 individual insects and mites belonging to 38 species were recognized as pests of pepino plants (Suppl. material 1). They consisted of 34 hexapod species belonging to 17 families in seven orders (which are classified into two classes, the Entognatha and the Insecta) and four mite species in one family and one order (Table 1). Of these 38 species, 35 have been known as pests of solanaceous crops such as tomato, eggplant, potato, and green pepper in Japan (Yasunaga et al. 1993;Yasunaga et al. 2001
Mites feeding on pepino.
1918), Campylomma plant bugs (Campylomma livida Reuter, 1885), tobacco flea beetles (Epitrix hirtipennis (Melsheimer, 1847)), vegetable leafminer (Liriomyza sativae Blanchard, 1938), potato tuberworms (Phthorimaea operculella (Zeller, 1873)), tobacco cutworms (Spodoptera litura (Fabricius, 1775)), cabbage loopers ( Trichoplusia ni (Hübner, 1803)), broad mites (Polyphagotarsonemus latus (Banks, 1904)), and two-spotted spider mites (Tetranychus urticae Koch, 1836). In the present study, our surveys conducted in different locations in Japan revealed the presence of 38 species of insect and mite pests on pepino plants, as mentioned above (Table 1). Ten pest species were frequently recorded in the previous studies (Furusato 1984;Takagi 1985;Takahashi 1985;Kita 1986;Odagiri et al. 1986;Ozawa 1986;Kim et al. 2017) as well as in the present study. In addition, three species, namely solanum mealybugs, potato tuberworms, and broad mites, were not found in our surveys.  Furusato (1984), Takahashi (1985), Takagi (1985), Kita (1986), Odagiri et al. (1986), Ozawa (1986)  Including the results of the present study, a total of 41 species of insects and mites have been recorded as pests of pepino plants in Japan (Table 2). Therefore, 28 species are newly recorded as pepino pests in Japan. This increase in the number of pest species is likely the result of not only the longer sampling period in this study, but also the fact that more study sites were sampled in the present study than in the study by Kim et al. (2017), who undertook surveys for approximately one and a half years in three sites located within a radius of 250 m in Kanagawa Prefecture (sites 3, 4, and 5 in this study correspond to plots A, B, and C in Kim et al. (2017), respectively). In particular, the inclusion of study sites on Okinawa Island (sites 8-11), which has a subtropical climate, may be one of the major factors behind the increase in the number of pest species recorded, since Okinawa has insect species unique to the region, such as spotted grasshoppers, tussock caterpillars, Chinese thrips (Haplothrips chinensis Priesner, 1933), and Prolygus plant bugs (Prolygus bakeri (Poppius, 1915)).
Among the 38 species detected in the present study, onion thrips (Thrips tabaci Lindeman, 1889), two-spotted spider mites, and cotton whiteflies were collected from more than half of the study sites, that is, from 8 sites, 7 sites, and 6 sites, respectively. Moreover, these three species, on an empirical basis, were much more abundant on pepino plants than the other pest species, and from several hundred to thousands of individuals of these three species were found on each pepino plant (Fig. 15). In Japan, these three species may be considered the most important insect and mite pests of pepino plants.
In the world, 25 species of insects and mites are known as pests of pepino plants and seven species of them are considered as important pests (Larraín 2002;Galbreath and Clearwater 1983;Akyazi 2012). Of these seven, four species, namely two-spotted spider mites, green peach aphids, solenopsis mealybugs ( Phenacoccus solenopsis Tinsley, 1898), and broad mites, are distributed in Japan. The former two species are common to Japan and the world as pests of pepino plants. The latter two species have not been found so far from pepino plants in Japan, but attention should be paid to future trends. On the other hand, onion thrips and tobacco whiteflies, which are considered to be likely the most important pests in Japan in the present study, are not important in other countries to date; however, these two species might be important pests because they are distributed worldwide.
Although most of the Japanese pest species of pepino plants are leaf-feeders, two lepidopteran species, tussock caterpillars and tobacco budworms (Helicoverpa armigera (Hübner, 1808)), were observed feeding on the fruits of pepino plants in the current study (Fig. 16). This results in holes in the fruits, which may negatively affect the commercial value of pepino. Pest management will be important for the cultivation of pepino plants, because no pesticides applicable to these plants have been registered in Japan to date. Therefore, biological control will have to be used for the commercial cultivation of pepino at the moment. Insect pests feeding on the fruits of pepino.