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南太平洋海域調査研究報告
OCCASIONAL PAPERS

No.58（2017 年 3 月）
No.58（March 2017）

A Newly Invasive Long-Horned Beetle from Mainland
Kyushu Attacks Citrus Trees in the Amami Islands
SAKAMAKI Yositaka, TSUDA Katsuo and MIYAKE Masataka
Faculty of Agriculture, Kagoshima University

Abstract
In the Amami Islands many kinds of citrus have been introduced from continental China and Taiwan.
As there are few indigenous insect pests, introduced citrus species have been well-kept and have diversified
in Kikaijima, Tokunoshima and Okinoerabujima islands. As a result, we can now find a plentiful variety ofcitruses in home yards in these areas. About 2008, however, many of the trees appeared to weaken and thendied over the course of one or two years. The problem spread rapidly. For example, in one village in Kikai
Island the total number of citrus trees drastically decreased from 2,800 to 2,000 over a period of four years.
These dead trees had many distinct 2cm-circular exit holes of long-horned beetle at ground level. Theislands have long been home to a type of long-horned beetle, Anoplophora oshimana, that had neverattacked citrus trees. From 2011, we started to simultaneously examine the species of long-horned beetlesin the citrus orchards and to conduct new control strategy against the beetles. The new strategy involves awide-area application of biopesticide band, Beauveria bassiana, Bio-Lisa®, conducted in theabovementioned village. It took three years to decrease long-horned beetle numbers by 90%. DNA analysis
revealed that the long-horned beetle in the orchards was hybrid population between A. oshimana and A.
malasiaca. Anoplophora malasiaca is a notorious pest of citrus trees in main island Japan. We estimate thatthe latter long-horned beetle established itself in the islands before 2008 and hybridized with the endemic
long-horned beetle.
Keywords: Anoplophora malasiaca, A. oshimana, biopesticide band, DNA analysis, hybrid population

Introduction
The history of citrus cultivation on the Amami Islands, which include Amami-Oshima I.,
Kikaijima I., Okinoerabujima I., Tokunoshima I. and Yoron I., is ancient. The people living onthese islands have cultivated many types of citrus trees from China and mainland Japan, butsports and natural hybrids of these citrus trees have been cultivated and handed down within
individual homes for centuries. Consequently, each farmer has unique cultivars of citrus in hisorchard or residential yard, which can be considered valuable genetic resources (YAMAMOTOet al. 2006). For example, in two local citrus cultivars on Kikaijima I. (Citrus keraji and C.
keraji var. kabuchii), the polymethoxy flavone content of the juice is four-fold higher than78
SAKAMAKI Yositaka, TSUDA Katsuo and MIYAKE Masataka

that of satsuma mandarin (Citrus unshu), and these local citruses are considered to be a goodsource of phytonutrients (YAMATOMO et al. 2008). Few studies have examined thephytonutrients in local citruses from the Amami Islands or examined the cultivars from theislands in detail. YAMAMOTO et al. (2006) reported that severe citrus damage caused by thecitrus long-horned beetle on Kikaijima and Tokunoshima islands is worsening and becoming
a serious threat to local citrus cultivation. In this report, we interviewed people living on theislands who have experienced citrus damage caused by the long-horned beetle to confirm
YAMAMOTO’s report. Second, we assessed the damage status in 2011 and began to control thelong-horned beetle in an experimental model village in Kikaijima in 2012. Here, we provide
an interim report of these actions to protect local citruses against long-horned beetle damage
and discuss the future of these control methods to conserve local citrus populations.
The citrus long-horned beetle, Anoplophora malasiaca, is one of the well-known
wood-boring species of the family Cerambycidae that is distributed across mainland Japan.
This species usually attack many types of hardwood trees, as well as citrus trees, willow,
poplar, walnut, ficus, sycamore, rose, pear, peach and winter hazel (HAYASHI 1984,MAKIHARA 2007). The closely related species Anoplophora oshimana, which is distributed
across Amami-Oshima, Okinoerabujima, Tokunoshima, Okinawajima, Ishigakijima andIriomotejima islands, is also known to have a broad spectrum of host plants (HAYASHI 1984,MAKIHARA 2007), but it is thought to prefer winter hazel over citrus; thus, A. oshimana is notcommonly regarded as an insect pest for citrus cultivation on these islands.
We tried to interview a number of citrus farmers and local government officials from
Kikaijima I. regarding citrus damage caused by the long-horned beetle in 2011–2012. They
stated that a severe outbreak of the beetle started about 10 years ago and that the damage wasobvious from 2006–2008. Another farmer that observed damage more than 10 years ago
answered that the beetle rarely attacked citrus trees, but did observe damage to winter hazel
trees used as a windbreak in orchards. In the area one official had been aware a phenomenon
where white spots pattern on back of the long-horned beetle changed from yellowish tobluish-white was reported on Amami-Oshima I. (MAKIHARA 2007), which suggests that thenative A. oshimana, which has yellowish white spots, was replaced by A. malasiaca, which
has bluish white spots, originating from mainland Japan, Kyushu, Shikoku and Honshu
islands.

Example of Decreased Citrus Trees in a Village on Kikaijima I.
Oasato-Nishime is a small village (approximately 25 ha) in the center of Kikaijima I.
There are fewer than 100 houses in the village, and half of the houses are empty. In the village,a tree suffering from citrus greening disease (Citrus Huang-Long-Bin) was first observed in
December 2003. Since this was the first record of the disease on the island and some
additional trees suffering from the disease were found in the village, all citrus trees cultivatedand present (about 2,800 trees in total) were counted, identified, numbered and mapped using

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A Newly Invasive Long-Horned Beetle from Mainland Kyushu Attacks Citrus Trees in the Amami Islands

a GIS system by the local government of Kikai Town in 2005 as part of a citrus greening
disease eradication program. Using this map, a mortality survey of all citrus trees in thevillage was traceable. Thus, we traced the change in number of citrus trees in the village using
the map and numbering system. Additionally, fewer than ten trees were felled by citrus
greening disease after 2005.
The change in number of citrus trees in the village during 2006–2008, which decreasedslightly but was generally stable, was about 2,800. The number of trees then decreased to2,600 by the end of 2006 and to 2,500 by 2010. Only 1,600 trees were thicker than about 2 cmin diameter, meaning we could use a microbial insecticide containing Beauveria brongniartii(Biolisa Kamikiri Slim®; Idemitsu Kosan Co. Ltd., Tokyo, Japan). When we establishedcontrol of the long-horned beetle using this microbial insecticide, we excluded trees narrower
than 2 cm in diameter to reduce the use of the expensive insecticide and the labor required to
set the control measures. In addition, we did not count the number of narrow trees. If weassume that the trees we excluded accounted for approximately 20% of the citrus trees in thevillage, the total number of citrus trees would be decreased to about 2,000 (Fig. 1). In thiscase, the village lost 1/3rd of the trees over four years.

Choice of a Suitable Control Method
We avoided using chemical insecticides to control the long-horned beetle because thevillage has a water well that many people living in adjacent villages use, and we had toconserve the village’s insect fauna, which was damaged by a chemical insecticide used tocontrol an insect vector of citrus greening disease during 2004–2008.

Total number of citrus trees

3000

2500

2000

Ohasato-Nishimevillage
1500

2006

20072008

2009

2010

2011

2012

Fig. 1. Change of the number of citrus trees in Oasato-Nishime Village of Kikai Town, 2006–2008. The
Oasato-Nishime Village lost 1/3rd of citrus trees from 2008 to 2011.

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SAKAMAKI Yositaka, TSUDA Katsuo and MIYAKE Masataka

Alternatively, we chose a microbial insecticide (Biolisa Kamikiri Slim®), which consistsof a non-woven fiber band impregnated with a fungus (B. brongniartii) to control the beetleon citrus trees. The reason we chose this particular microbial insecticide is that the fungal
strain originated from Japan, ensuring that the fungus would die in the local environment.
Thus, the use of microbial agents to control the long-horned beetle is one form ofenvironmental load-reducing control.
However, the microbial band takes 10 days to kill an adult beetle, so the female beetle
can still lay a portion of her eggs. Since the longevity of an adult female is typically 2–3months, the fungus can reduce the beetle longevity time to 1/9th to 1/6th if the fungus infects
just after emergence.
Since the female beetle typically has 200–300 eggs in her ovary and the preoviposition
period of the beetle is 7–15 days, a female exposed to the insecticide just after emergence will
lay few eggs. The fungal infection rate using the microbial band is approximately 1 month.
Therefore, an effective technique for setting the microbial band is to fasten it to an infectedtree at about 40 cm above the ground during the onset of the adult emergence season.
An efficacy report on the microbial band from Okinawajima I. (KYUSHU AGRICULTURE
PROMOTION COUNCIL 1994) stated that 50–100% of adult beetles captured in experimentalorchards (about 11–15 ha) containing the microbial band were infected by B. brongniartii, but
the larvae boring into the citrus tree did not decrease during the later season. Consequently,
the report concluded that control by the band was limited on Okinawajima I. because thesubtropical island has more essential host tree species adjacent to the forest than mainlandJapan. The report estimated that many non-infected females invaded from surrounding forestsand deposited eggs within the experimental orchard (Fig. 2). The report did not perform a trialof the band on the other islands in the Okinawa Islands and their adjacent Amami Islands, andpeople living in the isolated island area have abandoned use of the band. Since Kikaijima I.
belongs to the Amami Islands, whose climate is subtropical and similar to that on
Okinawajima I., a similar phenomenon may occur if we set the band in some citrus orchards.
To avoid similar failures, we set a microbial band on all citrus trees in the village (about 25ha). Using this widespread approach, we hoped to determine the actual efficacy of themicrobial band (at least in the central area of the village). It may be possible to identify
invader females at the edge of the setting village to decrease the likelihood of invader females
reaching the central area of the village.

An Effect of Wide-Area Control by an Entomopathogenic Fungal Pesticide
During our first visit, we observed that many residents were unaware of the correlationbetween citrus tree damage and the citrus long-horned beetle. We first distributed a leaflet to
all residents of Kikaijima I. to discuss the correlation between citrus damage and thelong-horned beetle, the life cycle of the long-horned beetle, the morphology of the beetle at all
developmental stages (egg, larva, pupa and adult) and control methods. Simultaneously, we

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A Newly Invasive Long-Horned Beetle from Mainland Kyushu Attacks Citrus Trees in the Amami IslandsFig. 2. Schematic comparison of environmental conditions for setting the microbial band between mainland
Japan and subtropical isolated islands (Okinawa, Amami).

held a meeting to explain the long-horned beetle control method using the microbial band andwe identified participants to set bands the next day in the Oasato-Nishime. These actions
increased the residents’ awareness of control of the citrus long-horned beetle.
When we set the microbial bands in May 2012 and in May and June 2013, more than ten
residents participated. Since they knew the position of every citrus tree, setting the bands on
more than 1,500 trees only took half a day. The infection rate of B. brongniartii in the wild
beetle at 2 weeks after setting the bands was more than 70% in May and June 2013 (MIYAKEet al. unpublished data). This indicated that most of the female beetles that emerged in thevillage could lay few or no eggs and died. In autumn, when the damage caused by larvae
became visible, we searched for freshly damaged trees and counted the number of damage
signs by larvae, which exhausted frass like sawdust. The larval density, which was calculated
based on the number of damage signs, was 1.3 larvae/citrus tree before setting the bands in
2011, but was 0.11 larvae/tree at 2 years after setting the bands (in 2013; MIYAKE et al.
unpublished data). Thus, we were able to achieve high efficacy for the control of long-horned
beetle larvae. This control efficacy was completely different from that on Okinawajima I.
(KYUSHU AGRICULTURE PROMOTION COUNCIL 1994). This may be because we set themicrobial bands in a larger area than on Okinawajima I. (i.e., broader effect).
These results suggest that microbial band control can be extremely useful in isolatedisland areas if people use this approach with considering a broader effect. Unfortunately,
during our 2-year survey 30% of the fixed observation trees (n=108) died. To protect thecitrus trees throughout Kikaijima I., we need to rapidly expand the treatment area.

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SAKAMAKI Yositaka, TSUDA Katsuo and MIYAKE Masataka

DNA Analyses of the Citrus Long-Horned Beetle in Kikaijima I.
We conducted DNA analyses of Mitochondrial COI region (about 800 bp) and nuclear
ITS2 region (about 500 bp) of the long-horned beetle from Kikaijima I. The COI sequences ofthose samples were similar to the sequence of Anoprophora oshimana, but the ITS2 sequence
were intermediate status between A. malasiaca and A. oshimana. These results must explain
as introgressive hybridization of the citrus long-horned beetle inhabit in Kikaijima I. by A.
malasiaca’s gene.

References
HAYASHI, M. 1984. Cerambycidae. In: The Coleoptera of Japan in Color, Vol. 4 (Eds.
HAYASHI, M., MORIMOTO, K. and KIMOTO, S.), 1–146, Hoikusha Pub. Co. Ltd., Osaka,Japan (in Japanese).
KYUSHU AGRICULTURE PROMOTION COUNCIL 1994. Establishment of Biological Control ofLonghorned Beetles on Endemically Special Fruit Trees by Entomopathogenic Fungi.
Study Report of Important New Techniques in Kyushu District Series No. 22, 97 pp.,
Kagoshima Fruit Tree Experimental Station, Tarumizu City, Japan (in Japanese).
MAKIHARA, H. 2007. Lamiini. In: Longicorn Beetle of Japan (Eds. OHBAYASHI, N. andNIISATO, T.), 576–605, Tokai University Press, Hadano, Kanagawa, Japan (in Japanese).
YAMAMOTO, M., MATSUMOTO, R., UECHI, Y., IJICHI, T., KUBO, T. and TOMINAGA, S. 2008.
The Polymethoxy Flavones Content of Local Citrus Accessions on the Island ofKikaijima in Kagoshima Prefecture, Japan. Bulletin of the Faculty of Agriculture,Kagoshima University, 58: 1–7 (in Japanese with English Summary).
YAMAMOTO, M., MATSUSHIMA, K., IJICHI, T., UECHI, Y., KAWAGUCHI, S., NAKANO, H.,NOMURA, T., TANIMURA, O., KUBO, T. and TOMINAGA, S. 2006. Exploration andPreservation of Local Citrus Germplasms in the Amami Archipelago. Bulletin of theExperimental Farm, Faculty of Agriculture, Kagoshima University, 29: 5–11 (in Japanesewith English Summary).