Simple SummaryFumigation is the most effective method for the control of Curculio sikkimensis in chestnuts. The effects of ethyl formate (EF) as a fumigant were investigated to evaluate its potential for practical use by farmers. A dose of 180.0 g/m3 and 12 h of fumigation resulted in 100% mortality on a small scale (2 m3). The results of these experiments indicate that EF could be conveniently used as a fumigant by farmers.Castanea crenata Siebold & Zucc. (Fagales: Fagaceae), a species of chestnut native to Korea and Japan, is distributed in Korea, Japan, and northeastern China, where chestnuts are a major economic agroforest product. Curculio spp. is among the main known pests of chestnuts around the world. In Korea, only phosphine (PH3) is permitted for the fumigation of C. sikkimensis larva-infested chestnuts. However, it is applied for large-scale fumigation, and its use is restricted. Moreover, it requires a long exposure time and an application device; thus, it cannot be used by small-scale farmers. In this study, the activity of ethyl formate (EF) as a fumigant against Curculio sikkimensis in chestnuts was investigated, and its potential for practical use by farmers was evaluated. The sorption of EF according to the filling ratio (FR) and fumigation time was tested, and the results revealed that 2.5% FR was the most effective. For C. sikkimensis in chestnuts, the mortality rate increased proportionately with the dose of EF. After exposure to 160 g/m3 of EF in a 12 L desiccator, the adult C. sikkimensis showed 100% mortality. According to the time–dose mortality data collected over 12 h of fumigation, the LCT90 and LCT99 values were estimated as 1052.0 and 1952.0 g·h/m3. The results revealed that immersion was not an effective method for controlling C. sikkimensis. According to the LCT values, a dose of 180.0 g/m3 and 12 h of fumigation resulted in 100% mortality on a small scale (2 m3). The results of this experiment indicate that EF could be conveniently used as a fumigant by farmers.

A correction to this paper has been published: https://doi.org/10.1007/s13355-021-00745-7

Curculio sikkimensis (Heller) (Coleoptera: Curculionidae) is a serious pest of the Japanese chestnut, Castanea crenata, because the larvae feed inside seeds. Chestnut seeds are usually harvested before the larvae leave them, meaning it is unlikely that the weevil is based in orchards. Instead, adults from neighboring woodlands likely invade orchards to oviposit. In this study, I examined host plant use and the course of development of Cu. sikkimensis in mixed oak and chestnut coppice stands to improve our understanding of weevil infestations in chestnut orchards. Females oviposited into seeds of three Quercus species and Ca. crenata, whose seed maturation times differed, over several months. The phenology of the weevil’s oviposition most closely tracked that of Quercus serrata seed maturation. Mature larvae left the seeds and burrowed into the soil, where they overwintered—in some cases for up to three winters because of prolonged diapause. Adults emerged over the course of 1 month and survived for about 2 months; such traits seem to enable this weevil to reproduce for several months. Thus, Cu. sikkimensis uses several host plants in coppice stands, and its oviposition phenology suggests that it is more dependent on Q. serrata than on Ca. crenata.

일부 밤 농사 및 가공 종사자의 밤바구미 훈증제 이황화탄소 사용실태 및 인식

Evidence for reversible change in intensity of prolonged diapause in the chestnut weevil Curculio sikkimensis

Many insects are ubiquitously associated with multiple endosymbionts, whose infection patterns often exhibit spatial and temporal variations. How such endosymbiont variations are relevant to local adaptation of the host organisms is of ecological interest. Here, we report a comprehensive survey of endosymbionts in natural populations of the chestnut weevil Curculio sikkimensis, whose larvae are notorious pests of cultivated chestnuts and also infest acorns of various wild oaks. From 968 insects representing 55 localities across the Japanese Archipelago and originating from 10 host plant species, we identified six distinct endosymbiont lineages, namely Curculioniphilus, Sodalis, Serratia, Wolbachia, Rickettsia and Spiroplasma, at different infection frequencies (96.7%, 12.8%, 82.3%, 82.5%, 28.2% and 6.8%, respectively) and with different geographical distribution patterns. Multiple endosymbiont infections were very common; 3.18±0.61 (ranging from 1.74 to 5.50) endosymbionts per insect on average in each of the local populations. Five pairs of endosymbionts (Curculioniphilus-Serratia, Curculioniphilus-Wolbachia, Sodalis-Rickettsia, Wolbachia-Rickettsia and Rickettsia-Spiroplasma) co-infected the same host individuals more frequently than expected, while infections with Serratia and Wolbachia were negatively correlated to each other. Infection frequencies of the endosymbionts were significantly correlated with climatic and ecological factors: for example, higher Sodalis, Wolbachia and Rickettsia infections at localities of higher temperature; lower Wolbachia and Rickettsia infections at localities of greater snowfall; and higher Curculioniphilus, Sodalis, Serratia, Wolbachia and Rickettsia infections on acorns than on chestnuts. These patterns are discussed in relation to potential host-endosymbiont co-evolution via local adaptation across geographical populations.

2003년부터 2006년까지 실내 및 실외에서 사육하여 얻어진 밤바구미의 발육단계별 형태측정을 하였다. 알의 크기는 0.8<TEX>${\pm}$</TEX>0.03 mm 이었다. 탈출유충은 평균 생체중이 98 mg, 체장은 10.65 mm, 체폭은 3.99 mm, 두폭은 1.70 mm이었다. 번데기의 크기는 암컷이 7.01 mm, 수컷이 6.53 mm으로 측정되었다. 암컷과 수컷 성충의 생체중, 체장, 체폭, 두폭, 주둥이 길이와 더듬이 길이를 조사하였다. 암컷의 생체중, 체장, 체폭과 두폭은 수컷보다 큰 것으로 유의성이 있으며, 암컷의 주둥이 길이와 더듬이 길이도 수컷보다 긴 것으로 유의성이 있었다. 암컷과 수컷 성충의 평균 생체중은 0.343과 0.268 g, 체장 7.76 과 7.14 mm, 체폭 3.38 과 3.01 mm, 두폭 1. 60과 1.37 mm, 주둥이 6.53과 3.56 mm, 더듬이 5.47과 4.63 mm로 각각 조사 되었다. 유충은 1~3 년까지 월동하면서 생체중, 체장, 체폭이 줄었다. 이러한 형태를 비교한 결과 주둥이 길이와 체장의 비율, 주둥이에 붙은 기절의 위치, 미부 생삭기의 모양으로 암수를 구분할 수 있었다. Measurements were made on morphology of each developmental stages of the chestnut weevil, Curculio sikkimensis, reared in the laboratory and field from 2003 to 2006. The size of egg was 0.8<TEX>${\pm}$</TEX>0.03 mm. The escaping larvae were measured, in average, as 98 mg in body weight, 10.65 and 3.99 mm in body length and width, and 1.70 mm in head width. Pupal size of female and male was 7.01 and 6.53 mm, respectively. The fresh weight (0.343 g), body length (7.76 mm) and width (3.38 mm), and head width (1.60 mm) of female adults were significantly bigger than those (0.268 g, 7.14 mm, 3.01 mm and 1.37 mm, respectively) of male adults. Proboscis length (6.53 mm) and antennal length (5.47 mm) of female was also significantly longer than those (3.56 and 4.63 mm, respectively) of male. The larvae of C. sikkimensis overwintered for 1~3 years and their body weight, body length, and body width were decreased. The ratio between proboscis length and body length, the basipodite position attached to the proboscis, and shape of the sex organ on the abdominal end could be used to discriminate sexes.

Thermal response and reversibility of prolonged larval diapause in the chestnut weevil, Curculio sikkimensis

Here we investigated the bacterial endosymbionts of weevils of the genus Curculio. From all four species of Curculio weevils examined, a novel group of bacterial gene sequences were consistently identified. Molecular phylogenetic analyses demonstrated that the sequences formed a distinct clade in the Gammaproteobacteria, which was not related to previously known groups of weevil endosymbionts such as Nardonella spp. and Sodalis-allied symbionts. In situ hybridization revealed that the bacterium was intracellularly harbored in a bacteriome associated with larval midgut. In adult females, the bacterium was localized in the germalia at the tip of each overiole, suggesting vertical transmission via ovarial passage. Diagnostic PCR surveys detected high prevalence of the bacterial infection in natural host populations. Electron microscopy identified the reduced cell wall of the bacterial cells, and the bacterial genes exhibited AT-biased nucleotide composition and accelerated molecular evolution, which are suggestive of a long-lasting endosymbiotic association. On the basis of these results, we conclude that the novel endocellular bacteria represent the primary symbiont of Curculio weevils and proposed the designation "Candidatus Curculioniphilus buchneri." In addition to "Ca. Curculioniphilus," we identified Sodalis-allied gammaproteobacterial endosymbionts from the chestnut weevil, Curculio sikkimensis, which exhibited partial infection frequencies in host insect populations and neither AT-biased nucleotide composition nor accelerated molecular evolution. We suggest that such Sodalis-allied secondary symbionts in weevils might provide a potential source for symbiont replacements, as has occurred in an ancestor of Sitophilus grain weevils.

밤 종실의 생산량과 재배 농가의 소득증대를 위한 친환경적 방제 기술을 보급하고자 밤의 주 생산지인 경상남도 밤나무 집단 재배지에서 몇 가지 친환경적인 방법으로 처리하였다. 그 결과, 복숭아명나방(Dichocrocis punctiferalis)의 피해율은 조생종(단택, 삼조생)의 경우, 웜스톱 처리구에서 피해율이 7.76%로 가장 낮았고, 웜스톱+목초액, 포충등 처리구 순으로 증가였다. 중생종(유마, 축파)의 피해율은 웜스톰 처리구에서 13.39%로 가장 낮았으며, 만생종(박미, 은기)은 피해율간 유의차가 있었다(p<0.05). 처리별 방제가는 조생종, 만생종 밤의 웜스톱 처리구에서 각각 40.49%, 41.89%로 가장 높았다. 밤바구미(Curculio sikkimensis)의 피해율은 조생종과 중생종 밤에서 낮았으며, 숙기별 처리간의 유의차가 없었다(p>0.05). 만생종 밤에서의 피해율은 웜스톱과 이미다클로프리드 처리구가 15.38%로 가장 피해율이 낮았으며, 항공방제, 웜스톱, 포충등 처리구 순이었다. 밤바구미(Curculio sikkimensis)에 대한 처리별 방제가는 조생종과 중생종에서는 낮았고, 만생종의 웜스톱과 이미다클로프리드, 항공방제 처리구에서 방제가는 각각 34.59%, 28.94%였다. This study was conducted to develop environmentally friendly control techniques to reduce chestnut insect pests. The study sites were selected in intensive chestnut orchards of Jinju city, Gyeongnam province. In early and middle-ripening cultivars of chestnut tree, the damage of chestnut fruits by Dichocrocis punctiferalis was significantly lower in wromstop than other treatment such as wromstop+wood vinegar, Capture-machine (p<0.05), While there was no significant difference among treatments in late-ripening cultivars. The hight control effect for D. punctiferalis was showed the highest in wromstop treanment with 40.49% and 41.89% in early and late-ripening cultivars. The control effects for Curculio sikkimensis in late-ripening cultivars of chestnut tree were 34.59% in wromstop imidacloprid treatment and 28.94% in air control treatment.

Beauveria bassiana strain HF338 had the highest pathogenicity among 77 isolates to larvae of the chestnut weevil, Curculio sikkimensis (Heller) (Coleoptera: Curculionidae). Its pathogenicity at 25°C was similar to that of Metarhizium anisopliae strain HF293. Its pathogenicity at 15°C remained high, whereas that of M. anisopliae HF293 was greatly reduced. Its pathogenicity to chestnut weevil adults and nut fruit moth, Cydia kurokoi (Amsel) (Lepidoptera: Tortricidae), was also higher than those of M. anisopliae HF293. In field tests, the survival rate of chestnut weevil larvae decreased to 2.9% when B. bassiana HF338 was applied at 1×1011 conidia/pot. The high pathogenicity of B. bassiana HF338 makes the strain a potential microbial agent for the control of chestnut pests.

BackgroundClimatic changes during glacial periods have had a major influence on the recent evolutionary history of living organisms, even in temperate forests on islands, where the land was not covered with ice sheets. We investigated the phylogeographical patterns of the weevil Curculio sikkimensis (Curculionidae), a generalist seed predator of Fagaceae plants living in both deciduous oak and evergreen forests of Japan. Its genetic structure was compared to that of another host-specific seed predator, C. hilgendorfi, inhabiting only evergreen forests.ResultsWe examined 921 bp of mitochondrial DNA for 115 individuals collected from 33 populations of C. sikkimensis from 11 plant species of three genera, Quercus, Lithocarpus, and Castanopsis. An analysis of molecular variance revealed that a large proportion (almost 50%, P < 0.001) of the total genetic variance could be explained by differences between two geographical regions, the southwestern and northeastern parts of the main islands of Japan. In contrast, no significant genetic differentiation of the weevil was observed among vegetation types of their utilized host plant species. The phylogeographical patterns of the generalist and the host-specific seed predator exhibited a congruent genetic boundary in the Chugoku-Shikoku region.ConclusionOur results suggest that geology and historical environment have contributed to shaping the present genetic structure of C. sikkimensis. The geographical patterns of genetic differentiation in the Chugoku-Shikoku region observed in the two types of Fagaceae-associated Curculio in this study have also been observed in several plant species growing in warm and cool temperate zones of Japan. The occurrence of this common pattern suggests that deciduous oak and evergreen forests of Japan survived together, or adjacent to each other, in small refugia during glacial ages, in the southwestern and northeastern parts of the main islands, although these two types of forests are presently distributed in cool and warm temperate zones of Japan, respectively.

This study was conducted to investigate the seasonal occurrence of chestnut weevil, Curculio sikkimensis. The chestnuts infected by the weevils were collected from Gongju, Buyeo, and Cheongyang in Chungnam Province, Republic of Korea. Investigation was focus on the escape period of chestnut weevil larvae from the fruits, invading time and vertical distribution in soil, survival rates of larvae during overwintering, emergence period, emergence rate, and sex ratio and longevity of adults. For precocious species, larvae escaped the chestnut from the mid-September to the early-October, middle species and slow species, were escaped from the late-September to the mid-October and from the early-October to the mid-November. After escaping from the chestnut fruits all of the larvae burrowed into the soil within 35 minutes. Overwintering larvae inhabited in the range of from the soil surface and highly distributed in the range of . The 74.1 % of wintering chamber were distributed within from the surface. Survival rates observed were 38.0% in 1st year, 16.0% in 2nd years, and 2% in 3rd years, respectively. Seasonal occurrence period of C. sikkimensis was from the early-Aug. to early-Oct. and the optimal occurrence period was the early and mid-Sept. Emergence rate decreased to 8.4% in 1st year, 3.6% in 2nd years, and 0.8% in 3rd years, respectively. Sex ratio was showed in the range of 0.51-0.55. It is female biased ratio. Longevity of adults was 9.9 days for female and 8.9 days for male.

Repeated cycles of chilling and warming effectively terminate prolonged larval diapause in the chestnut weevil, Curculio sikkimensis

ABSTRACT Nut weevil (Curculio sikkimensis) is one of the major constraints in natural regeneration of ban oak (Quercus leucotricho-phora) in the northwestern Himalayan regions of India. A study on the incidence of this pest in relation to site elevation, time and method of acorn collection and impact on germination after testing the feasibility of scarification for increased nursery production revealed that the acorn infestation ranged between 25.5 to 41.2% on the tree crowns and > 50% on the forest floor. On the basis of categorization of acorn predation by this pest, acorn damage scored as 1 gave better germination (72%) than healthy acorns (65%) under laboratory conditions. Scarification (seed cut + hot water treatment) to the healthy and insect damaged acorns (scored up to 2nd category) maximized germination. This treatment stimulated germination even in acorns damaged up to 3rd category. The seed cut and hot water treatment, as separate treatments also yielded better germination compared with referen...

Effect of temperature on the termination of prolonged larval diapause in the chestnut weevil Curculio sikkimensis (Coleoptera: Curculionidae)

Assessment of electron beam-induced DNA damage in larvae of chestnut weevil, Curculio sikkimensis (Heller) (Coleoptera: Curculionidae) using comet assay

Oak forests are dwindling in the Western Himalayan region. Curculio sikkimensis which is a pest of Oak acorns may be considered as one of the major causes which has resulted in decrease in natural regeneration. All the three instars of larvae were observed to feed on the endosperm tissue of the acorns. The third instar larvae usually ate away almost the whole endosperm and turned it into frass. The extent of damage was found to be higher in the pure forests (81.6%) than as compared to the scrub forests (48%). Infestation was found to be higher in case of the acorns collected from the tree crown than as compared to the acorns collected from the forest floor.

We investigated patterns of acorn growth in Quercus variabilis Blume and Quercus serrata Thunb., seasonal trends in emergence of seed insects found in the acorns, oviposition periods of the insects and falling periods of insect‐infested acorns. In Q. variabilis , two insect guilds were associated with acorn development: (i) the immature acorn feeding (IAF) guild [Curculionidae sp., Poecilips cardamomi (Schaufuss), and Characoma ruficirra (Hampson)]; and (ii) the mature acorn feeding (MAF) guild [ Curculio robustus (Roelofs), Curculio sikkimensis (Heller), and Cydia glandicolana (Danilevsky)]. In Q. serrata , there were three guilds: (i) the pistillate flower feeding (PFF) guild (cynipid wasp); (ii) the IAF guild [sap absorption by Mechoris ursulus (Roelofs)]; and (iii) the MAF guild ( M. ursulus , C. sikkimensis , Cydia danilevskyi (Kuznetzov), C. glandicolana and Autostichidae sp.). The succession of guilds during acorn development may be a consequence of the use by different species of the limited food resource. The lack of a PFF guild in Q. variabilis that was found in our field site would have a positive effect on IAF guilds in utilizing the acorns.

Ban oak (Quercus leucotricophora) is principal source of fuel and fodder in Western Himalayas. It multiplies through seeds only. There are many insect-pests feeding on oak seeds, but Oak acorn weevil Curculio sikkimensis Heller is most serious among them affecting the oak seeds (acorns) and interfering with its natural regeneration. Its detailed biology is being reported.