Some developmental differences inEpinotia granitalis (Lepidoptera: Tortricidae) between two host tree species

To detect developmental differences inEpinotia granitalis in two host tree speciesCryptomeria japonica andChamaecyparis obtusa, the fourth or fifth instar larvae were collected daily from the two species located on the grounds of the National Forest Tree Breeding Center, from April 19 to May 9 in 1994 and April 18 to May 10 in 1995. Larvae ofE. granitalis collected fromC. obtusa had heavier body weight, developed to larger adults than those collected fromC. japonica, and mortality from the fourth or fifth instar larval stage to adults onC. obtusa was lower than that onC. japonica. All these facts suggest that larval performance onC. obtusa was higher than that onC. japonica.     

Protective effect of floor cover against soil erosion on steep slopes forested with <Emphasis Type="Italic">Chamaecyparis obtusa</Emphasis> (hinoki) and other species

 We evaluated the protective effects of floor cover against soil erosion in three types of forest located on steep slopes under a humid climate: 22- and 34-year-old Chamaecyparis obtusa (hinoki), 34-year-old Cryptomeria japonica (sugi), and 62-year-old Pinus densiflora (red pine) stands. We measured sediment transport rates (sediment mass passing through one meter of contour width per millimeter of rainfall), using sediment traps, before and after removing floor cover. Raindrop splash erosion was dominant in the experimental stands. Floor cover percentage (FCP) during the preremoval stage varied from 50% to 100% among the four stands, and sediment transport rates ranged from 0.0079 to 1.7 g m⁻¹ mm⁻¹. The rates increased to 1.5–5.6 g m⁻¹ mm⁻¹ immediately after removing floor cover, and remained high throughout the experiment. The presence of physical cover near the ground has a crucial effect on sediment transport on forested slopes. The protective effect ratio (the ratio of the sediment transport rate in a control plot to that in the removal plot) in a young hinoki stand, in which the FCP decreased markedly, was 0.3 at most, which is close to the rate for bare ground. The protective effect ratio in the red pine stand was ≤0.003. We concluded that the protective effect of floor cover in undisturbed forests in Japan differs by over two orders of magnitude, based on comparisons with previous studies. Received: March 11, 2002 / Accepted: August 16, 2002 Present address: Department of Forest Site Environment, Forestry and Forest Products Research Institute, Ibaraki 305-8687 Japan Tel. +81-298-73-3211; Fax +81-298-74-3720 e-mail: miura@affrc.go.jp Present address: Department of Forest Site Environment, Forestry and Forest Products Research Institute, Ibaraki 305-8687 Japan Tel. +81-298-73-3211; Fax +81-298-74-3720 e-mail: miura@affrc.go.jp Acknowledgments This study was supported by the Research Council of the Ministry of Agriculture, Forestry, and Fisheries, of Japan. We thank H. Ujihara, S. Ujihara, and M. Ogasawara in Otoyo, Kochi, who provided the experimental stands used in this study. We also thank K. Hirai, S. Kuramoto, E. Kodani, and the rest of the staff at the Shikoku Research Center, Forestry and Forest Products Research Institute, for their help in conducting the experiments. Correspondence to:S. Miura     

Factors enabling Epinotia granitalis (Lepidoptera: Tortricidae) overwintered larvae to escape from oleoresin mortality in Cryptomeria japonica trees in comparison with Semanotus japonicus (Coleoptera: Cerambycidae)

The factors involved in the successful escape of overwintered larvae of Epinotia granitalis from host oleoresin in the phloem of Cryptomeria japonica were studied. The mortality, period, and body weight of E. granitalis overwintered larvae while feeding on the phloem of C. japonica were compared with the same parameters for Semanotus japonicus larvae. The seasonal fluctuation in the ability of C. japonica to form traumatic resin canals in the phloem was also assessed. The oleoresin mortality of E. granitalis was low compared with that of S. japonicus. Although both species started feeding on approximately the same date in spring, the feeding period of E. granitalis was only about 24 days, showing that E. granitalis faced the danger of host oleoresin for a shorter period than S. japonicus. The larval weight of E. granitalis was consistently greater than that of S. japonicus through the phloem-feeding period of E. granitalis, and the growth rate was also higher in E. granitalis, suggesting that E. granitalis had a better ability to avoid host oleoresin. These results demonstrated that not only the feeding habits, that is, the tendency of a single larva to feed at several sites, but also the shorter feeding period and larger body size were probably the important factors facilitating escape of E. granitalis from host oleoresin mortality. Furthermore, the ability of C. japonica to form traumatic resin canals increased after the starting date of larval feeding in spring. Because E. granitalis finished feeding before the culmination of the ability of C. japonica to form traumatic resin canals, it was likely that the shorter feeding period was the most important factor in enabling E. granitalis to escape from mortality by host oleoresin.     

Structural characteristics of cell walls of kenaf (<Emphasis Type="Italic">Hibiscus cannabinus </Emphasis>L.) and fixation of carbon dioxide

 Kenaf (Hibiscus cannabinus) plants are widely known for their contribution to the global and regional environment because of their ability to fix CO₂. On the other hand, some scientists have doubts about CO₂ fixation by kenaf and have misgivings about the effect of kenaf on the ecosystem. We have characterized the structural characteristics of cell walls of bast fibers, cores, roots, and leaves of kenaf during the maturation of plants and investigated the rate of photosynthesis. During maturation of the kenaf plant the cellulose (bast fiber 52–59%, core 44–46%) and lignin (bast fiber 9.3–13.2%, core 18.3–23.2%) contents increased significantly. The aromatic composition of the lignin of bast fiber was significantly different from that of the core lignin and of other plants. The lignin of bast fiber appears similar to pure syringyl lignin. Fixation of CO₂ by kenaf plants and their contribution to the global environment are discussed. A significatly high rate of photosynthesis of kenaf plants was observed compared to that of woody plants in Japan, but the amount of CO₂ fixation depends on the characteristics of the plantation. If the kenaf was planted in high density, about twice as much CO₂ was fixed as was fixed by trees in a tropical rain forest. Received: April 22, 2002 / Accepted: July 24, 2002 Acknowledgments This project was supported by the Science and Technology Agency (STA) fellowship of the Japan International Science and Technology Exchange Center (JISTEC), which has been successfully applied by Dr. Shuji Hosoya, Forestry and Forest Products Research Institute. We thank Dr. Toshio Sumizono and Mr. Masao Sakurai, Forestry and Forest Products Research Institute, for their kind help in determining the rate of photosynthesis and cultivating the kenaf plants, respectively. We also express our appreciation to Dr. Quang Hung Le, College of Agriculture and Forestry, Ho Chi Minh City, Vietnam for offering information about the cultivation of kenaf at Thu Duc District, Ho Chi Minh City.     

中国林业科学研究院林产化学工业研究所

中国林业科学研究院林产化学工业研究所(简称林化所)成立于1960年,为副司局级单位,是专业从事木质和非木质林产品化学加工与利用,集基础研究、应用研究、产品开发及工程设计为一体的综合性国家科研院所。拥有中国工程院院士、国际木材科学院院士等一批国内外专家。有博士、硕士培养点和博士后流动站。以我所为依托,建立了生物质化学利用国家工程实验室、国家林产化学工程技术研究中心、林业生物质高效转化利用国际科技合作基地、产业技术创新类国家引才引智示范基地、国家油茶科学中心-加工利用实验室、国家林业和草原局林产化学工程重点实验室、国家林业和草原局生物质能源工程技术研究中心、国家林业和草原局活性炭工程技术研究中心、国家林业和草原局生物质能源研究所、国家林业和草原局林产化工中试基地、国家林业和草原局林化产品质量检验检测中心(南京)、江苏省生物质能源与材料重点实验室等研发平台,为开展生物质领域的研究、科技成果转化、技术集成与孵化提供了良好的条件。     

中国林业科学研究院林产化学工业研究所

中国林业科学研究院林产化学工业研究所(简称林化所)成立于1960年,为副司局级单位,是专业从事木质和非木质林产品化学加工与利用,集基础研究、应用研究、产品开发及工程设计为一体的综合性国家科研院所。拥有中国工程院院士、国际木材科学院院士等一批国内外专家。有博士、硕士培养点和博士后流动站。     

Effects of differences in forest floor and canopy vegetation on ectomycorrhizas ofBetula platyphylla var.japonica: A test using seedlings planted into soils taken from various sites

Effects of different forest floor vegetation types in secondary forest and of conversion to plantation on the quality and quantity of ectomycorrhizas are mostly unknown.Betula platyphylla var.japonica seedlings were used for bioassays of ectomycorrhizal fungal inoculum using soils from four 50-year-oldB. platyphylla var.japonica forests that had different types of forest floor vegetation: two with shrub types, one with aSasa type, and one with a grass type. Seedlings were also grown in soil from a nearby monospecific plantation ofChamaecyparis obtusa. Ectomycorrhizas formed 13 to 26% of root length of seedlings grown in soil from the five different sites. The maximum percentage of ectomycorrhizal formation was obtained from the grass-type forest. The dominant type of ectomycorrhiza in the two shrub-type forest soils was the same as that in theSasa-type forest soil. The dominant types of ectomycorrhizas in the grass-type forest soil and in theC. obtusa plantation soil were different from that in the two shrub-type forest soils and in theSasa-type forest soil. The results of this investigation suggest that the type of forest floor vegetation, accompanied with changes in thickness of the A₀ horizon, might affect the ectomycorrhizal fungi in the soils ofB. platyphylla var.japonica forests. Establishment of artificial plantations ofC. obtusa might change the ectomycorrhizal fungi that could associate withB. platyphylla var.japonica seedlings in soil.     

三芳胺基D-A结构化合物的溶致变色行为研究

研究了3个系列D-A结构化合物在5种不同极性溶剂中的荧光发射光谱及紫外吸收光谱,探讨了化合物的溶致变色规律,结果表明:3个系列化合物在不同极性溶剂中的荧光发射波长发生明显位移,在甲醇中发射波长最大,在环己烷中最小,但在二氧六环、四氢呋喃、二氯甲烷中,随着溶剂极性逐渐减小,发射波长发生红移;在不同极性溶剂中的荧光强度也各不相同,其中,在环己烷中最大,在甲醇中最小。化合物的紫外吸收波长受溶剂极性的影响,均在甲醇中有最小吸收波长,在不同极性溶剂中化合物的吸光度也不相同,在甲醇及环己烷中的吸光度较大。3个系列化合物均具备作为荧光分子探针探测外部环境极性大小的潜能。     

寄主树木、寄主和环境因子对松褐天牛深沟茧蜂寄生率的影响研究

[目的]松材线虫病是我国对森林危害和威胁最严重的病害,控制其传播媒介昆虫松褐天牛是防治松材线虫病的主要手段。作者发现的松褐天牛深沟茧蜂(Iphiaulax monochamusi Yang)是寄生松褐天牛中老龄幼虫的重要天敌。为明确松褐天牛深沟茧蜂的寄生率与寄主树木、寄主和环境因子的关系,开展了本研究。[方法]通过解剖46株松褐天牛危害致死的马尾松,调查了松褐天牛深沟茧蜂寄生率与马尾松、松褐天牛和环境因子之间的关系。[结果]调查研究表明:寄主树木的高度、胸径和树龄对松褐天牛深沟茧蜂寄生率没有显著影响,松褐天牛的数量对松褐天牛深沟茧蜂寄生率亦没有显著影响,而松褐天牛幼虫龄期和松褐天牛幼虫在树干上的位置显著影响松褐天牛深沟茧蜂寄生率。松褐天牛深沟茧蜂寄生率与松褐天牛龄期呈显著正相关,其偏好寄生3~5龄幼虫;就天牛在其危害寄主树木上的位置而言,松褐天牛深沟茧蜂偏好寄生马尾松主干上部和在韧皮部危害的松褐天牛幼虫,其对位于马尾松树干上部的寄主幼虫寄生率最高,达27.38%,对在韧皮部生活、危害的寄主幼虫寄生率为20.18%,显著高于位于木质部生活的寄主幼虫寄生率(5.46%)。逐步回归分析表明:影响松褐天牛深沟茧蜂寄生率的关键环境因子是寄主树木的坡位和其它天敌寄生率,其中,坡位与松褐天牛深沟茧蜂呈显著正相关,其它天敌寄生率与松褐天牛深沟茧蜂寄生率呈显著负相关。[结论]以上研究初步明确了松褐天牛深沟茧蜂的寄生率与寄主树木、寄主害虫和天敌之间的关系,为今后利用该重要天敌控制松褐天牛打下了基础。     

异海松酸糠醛类酰腙化合物的合成及生物活性研究

以异海松酸为原料,采用先酰氯化后与水合肼反应的方法,制备得到异海松酸酰肼,然后再与不同取代基的糠醛发生反应,制备得到5种异海松酸糠醛类酰腙化合物:异海松酸基(糠醛)酰腙(4a)、异海松酸基(5-甲基糠醛)酰腙(4b)、异海松酸基(5-羟甲基糠醛)酰腙(4c)、异海松酸基(5-溴-2-糠醛)酰腙(4d)和异海松酸基(5-(4-溴苯基)糠醛)酰腙(4e),并采用FT-IR、1 H NMR、13 C NMR和MS对产物结构进行了确证。生物活性测定结果表明:目标化合物对肺炎链球菌、肺炎克雷伯氏菌、大肠杆菌、表皮葡萄球菌和金黄色葡萄球菌这5种菌种均具有一定的抑制活性,其中4a对肺炎克雷伯氏菌具有很好的抑菌活性,最低抑菌浓度为1.95 mg/L,化合物4c对肺炎链球菌具有非常好的抑菌活性,最低抑菌浓度仅为0.98 mg/L。当异海松酸糠醛类酰腙化合物的浓度为100μmol/L时,化合物4d对人体肝癌(Hep G2)、乳腺癌(MDA-MB-231)、前列腺癌(PC-3)和宫颈癌(Hela)这4种人体肿瘤细胞均具有较高的抑制率,其抑制率分别为75.17%、82.33%、78.52%和80.97%;化合物4e对人体肝癌(Hep G2)的抑制率高达93.68%,说明其对人体肝癌细胞具有很强的抑制活性。     

Study on the parasitoids ofPissodes nitidus Roel

A systematic observation and intensive study on the parasitoids ofPissodes nitidus were made in Langxiang and Xin'qing Forestry Bureau in Xiaoing'an Mountain area in 1996–1999, including the diagnosis, life history, biological characteristics ofEurytoma sp. and parasitoid complex ofPissodes nitidus. There were about 70 species of parasitoids onPissodes nitidus, including Eurytomidae, Ichneumonidae and Braconidae etc. Among them,Eurytoma sp. is a dominant species and a braconid,Ipobracon sp. is a subdominant species, and they play an important role in controlling the pest. Biography: HU Chun-xiang (1955-), male, Associate professor in Forest Resources and Environment Collage of Northeast Forestry University, Harbin 150040, P. R. China Responsible editor: Chai Ruihai     

Potential host ranges of three Asian larval parasitoids of Drosophila suzukii

Asobara japonica (Hymenoptera: Braconidae), Ganaspis brasiliensis and Leptopilina japonica (Hymenoptera: Figitidae) are Asian larval parasitoids of spotted wing drosophila, Drosophila suzukii (Diptera: Drosophilidae). This study evaluated these parasitoids’ capacity to attack and develop from 24 non-target drosophilid species. Results showed that all three parasitoids were able to parasitize host larvae of multiple non-target species in artificial diet; A. japonica developed from 19 tested host species, regardless of the phylogenetic position of the host species, L. japonica developed from 11 tested species; and G. brasiliensis developed from only four of the exposed species. Success rate of parasitism (i.e., the probability that an adult wasp successfully emerged from a parasitized host) by the two figitid parasitoids was low in hosts other than the three species in the melanogaster group (D. melanogaster, D. simulans, and D. suzukii). The failure of the figitids to develop in most of the tested host species appears to correspond with more frequent encapsulation of the parasitoids by the hosts. The results indicate that G. brasiliensis is the most host specific to D. suzukii, L. japonica attacks mainly species in the melanogaster group and A. japonica is a generalist, at least physiologically. Overall, the developmental time of the parasitoids increased with the host’s developmental time. The body size of female A. japonica (as a model species) was positively related to host size, and mature egg load of female wasps increased with female body size. We discuss the use of these parasitoids for classical biological control of D. suzukii.

     

Evaluation of efficiency of <Emphasis Type="Italic">Trichogramma evanescens</Emphasis> reared on different factitious hosts to control <Emphasis Type="Italic">Helicoverpa armigera</Emphasis>

The release of mass propagated egg parasitoids could be one option to control the lepidopteran pests. The efficiency of the parasitoid Trichogramma evanescens (Westwood) reared on eggs of three different factitious hosts; Sitotroga cerealella, Ephestia kuehniella and Galleria mellonella was studied for controlling bollworm Helicoverpa armigera. Efficiency of Trichogramma was studied by measuring parasitism rates, emergence rates, longevity and sex ratio. Wasps reared from each source were tested on the source host and on the target host, H. armigera under laboratory conditions. Rates of parasitism on H. armigera eggs, emergence rates of parasitoids and their longevity were the highest for wasps reared on H. armigera. Wasps reared on S. cerealella gave comparable rates. However, wasps from E. kuehniella gave the lower rates and G. mellonella gave the lowest ones. Parasitized eggs of H. armigera and S. cerealella produced more parasitoid females than eggs of E. kuehniella and G. mellonella. Results are discussed for magnifying efficiency of the parasitoid in controlling H. armigera in the field.     

Experimental release of a parasitoid, Doryctes yogoi Watanabe (Hymenoptera: Braconidae), onto Semanotus japonicus Lacordaire (Coleoptera: Cerambycidae) inoculated into live Japanese cedar trees (Cryptomeria japonica D.DON)

Release experiments of Doryctes yogoi Watanabe onto Semanotus japonicus Lacordaire larvae inoculated into Japanese cedar, Cryptomeria japonica D. Don, were conducted to clarify the role of the parasitoids in the mortality of S. japonicus and the efficiency of the parasitoid as a natural enemy of the beetle. S. japonicus larvae were inoculated into three types of samples: live trees, girdled trees, and logs, each of which was treated in three ways: D. yogoi was released into the sample, the sample was screened (excluding natural enemies), or the sample was used as a control. In live trees, more than 90% of the larvae were killed by resin flow, and the percentage of parasitism by D. yogoi was less than 6%. In girdled trees, most of the larvae were dead due to the resin in the trees, having survived inoculation as well as in live trees, but many larvae were parasitized by D. yogoi in dead trees like logs. The present study revealed three negative effects of resin flow on parasitism by D. yogoi in the live trees. First, most of the host larvae died before reaching a size suitable for parasitism. Second, parasitoid larvae were caught in the resin with their hosts and died. Third, the host-searching and oviposition of female D. yogoi were obstructed by resin flow on the surface of the trunk. The efficiency of D. yogoi as a natural enemy of S. japonicus is discussed.     

Comparative virulence of blue-stain fungi isolated from Japanese red pine

 We made inoculations to determine the comparative virulence of blue-stain fungi isolated from Japanese red pine (Pinus densiflora Sieb. & Zucc.). Based on the symptoms caused by each fungus, the most virulent fungus was Leptographium wingfieldii. Also, Ophiostoma minus was relatively virulent while lesions induced by some species did not differ from those in the control treatment. Based on the results, we concluded that the pathogenicity of the blue-stain fungi varied widely, and thus their impact on the host most likely varies too. Received: June 7, 2002 / Accepted: October 4, 2002 Present address: JST Domestic Research Fellow, Forest Pathology Laboratory, Tohoku Research Center, Forestry and Forest Products Research Institute, 92-25 Nabeyashiki, Shimo-Kuriyagawa, Morioka 020-0123, Japan Tel +81-19-648-3961; Fax +81-19-641-6747 e-mail: H_masu@hotmail.com Acknowledgments We thank Drs. Ohtaka and Usuki, Plant Pathology and Mycology Laboratory, Institute of Agriculture and Forestry, University of Tsukuba, for technical assistance. Contribution No. 174, Plant Pathology and Mycology Laboratory, Institute of Agriculture and Forestry, University of Tsukuba. Correspondence to:H. Masuya     

林业生物质基果蔬涂膜保鲜剂的研究进展

由于果蔬极易腐烂、保质期短,如果贮藏不当容易造成巨大的经济损失,因此对果蔬进行保鲜显得尤为重要。目前,常用的保鲜方法是低温贮藏和保鲜剂处理,其中涂膜保鲜技术因其成本较低、保鲜效果良好而备受关注。但常用的化学保鲜剂如二溴四氯乙烷、三唑类等对人体健康有一定的危害。林业生物质具有来源广泛、绿色环保、可持续性等特点,在果蔬涂膜保鲜剂领域得到广泛的研究与应用。主要介绍了多糖、紫胶、松香及其衍生物等林业生物质资源作为涂膜保鲜材料在果蔬保鲜中的应用,着重探讨其涂膜保鲜的效果,分析了目前林业生物质基果蔬保鲜剂存在的问题,并对林业生物质基涂膜保鲜剂的未来发展进行了展望。     

萜类植物源除草活性物开发及应用研究进展

综述了近年来国内外萜类化合物及其衍生物在除草应用领域的研究进展,从天然萜类精油、萜类化合物单组分以及萜类衍生物(包括席夫碱衍生物、硫脲衍生物、酰胺衍生物、含氧衍生物及其他)除草应用的角度出发,对近年来萜类植物源除草剂的开发和应用进行了系统的归纳和总结,着重介绍了松节油单萜衍生物的合成及其除草应用的研究现状及成果,展望了萜类植物源除草剂的发展方向及应用前景。     

补充营养对白蜡吉丁肿腿蜂寄生效率和发育进程的影响

[目的]为了探明补充营养是否对白蜡吉丁肿腿蜂雌蜂的寄生效率、生殖能力和寿命有显著影响。[方法]本文通过在白蜡吉丁肿腿蜂搜寻到寄主前期为其提供寄主血淋巴和蜂蜜补充营养,调查有前期补充营养经历的肿腿蜂对寄主麻天牛的寄生率、母蜂生殖能力和子代蜂发育进程的变化。同时,给予刚羽化的肿腿蜂雌蜂短期的补充营养的过程,调查其寿命长短的变化情况。[结果]研究结果表明,寄主血淋巴和糖类物质均可以作为供肿腿蜂补充营养的潜在食物源。寄生前期取食寄主血淋巴和蜂蜜的肿腿蜂寄生率显著高于前期仅补充蒸馏水的个体。补充营养后可促使寄生蜂卵的成熟,可以使肿腿蜂更快的开始产卵进程。前期取食寄主血淋巴的肿腿蜂生殖能力显著高于寄生前期仅补充蒸馏水的个体,取食蜂蜜的肿腿蜂产卵量较前2组均无显著差异。寄生蜂母蜂是否补充营养对其子代的发育过程和性比无显著影响。此外,生存分析结果表明,刚羽化的肿腿蜂补充营养后,其寿命显著延长。取食寄主血淋巴或蜂蜜的寄生蜂寿命均约为羽化后无营养补充经历雌蜂个体的2倍。[结论]以上结果表明,白蜡吉丁肿腿蜂在寄生过程开始前期的补充营养过程可以显著的增强其对寄主害虫的控制作用和延长其寿命。取食蜂蜜或寄主血淋巴对肿腿蜂生殖和寿命的增强作用相近。建议在害虫的生物防治中,可以通过在天敌释放区周边配植一定的蜜源植物以此实现对天敌昆虫资源更有效的利用和保护。     

Transport rates of surface materials on steep forested slopes induced by raindrop splash erosion

We used small (25 cm) sediment traps to evaluate the properties of surface material transport on steep slopes under humid temperate conditions in the Shikoku district of Japan. We sampled ten stands ofChamaecyparis obtusa (hinoki),Cryptomeria japonica (sugi),Pinus densiflora (red pine), and deciduous hardwood forest. Transport rates were estimated by dividing the amount of mass transported by the mass of rainfall during a given period. These rates varied widely among the ten stands: 0.0065–0.31 g m⁻¹ mm⁻¹ (a difference of two orders of magnitude) for fine earth, 0.00017–0.97 (four orders) for gravel, and 0.020–0.24 (one order) for litter. The transport rates in young hinoki stands with a low floor cover percentage (FCP) showed no seasonal changes. The transport rates changed by one or two orders of magnitude in hardwood forests with clear seasonal changes in FCP, as well as in juvenile and middle-aged hinoki and sugi stands, where understory floor cover increased and decreased seasonally. Rainfall intensity, however, showed no positive effects on transport rates, even in stands that had changing transport rates. The rates were mostly determined by forest type. We demonstrate that transport rate is an inherent property of a forest that reflects floor cover conditions and indicates the potential of surface material transport. This study was supported by the Research Council in the Ministry of Agricuture, Forestry and Fisheries, Japan.     

Performance of four <Emphasis Type="Italic">Trichogramma</Emphasis> species (Hymenoptera: Trichogrammatidae) as biocontrol agents of <Emphasis Type="Italic">Heliothis virescens</Emphasis> (Lepidoptera: Noctuidae) under various temperature regimes

Trichogramma spp. are major parasitoids of lepidopteran pest eggs, but there is large variation in efficacy toward a given pest among the numerous described Trichogramma species. It is important to select the Trichogramma species that most effectively parasitize and develop in target pest eggs for biological control. In this context, Trichogramma pretiosum, T. exiguum, T. atopovirilia and T. acacioi were studied in Heliothis virescens eggs under different thermal conditions. The parasitoids were reared at constant temperatures of 20, 25 and 30°C and tested at these respective temperatures, while parasitoids reared at 25°C were also tested at 20 and 30°C, for a total of 20 species–temperature combinations. About 30 H. virescens eggs were offered to the parasitoids for 24 h. Among the four species, parasitism rate by T. atopovirilia was highest at all temperature conditions, whereas T. acacioi had the lowest rates of parasitism at 25°C and 25/30°C. Parasitism ranged from 13.8 to 43.8% among all species–temperature combinations. Viability (emerged parasitoids) ranged from 80.8 to 98.4%, and was deemed satisfactory. The emergence rates of T. exiguum and T. acacioi were affected by temperature. Temperature also affected the sex ratio of T. exiguum at 25/30°C, whereas T. pretiosum and T. acacioi produced females predominantly independent of temperature. Overall, the parasitoid T. atopovirilia was the most efficient in parasitizing H. virescens eggs, though the levels of parasitism obtained might not ensure its successful use in biological control programs. The temperature-related differences in biological traits observed in the four Trichogramma species tested hint at the importance of making careful choices regarding climatic conditions where the parasitoid is going to be used when selecting a species for biological control programs.