肠道细菌弗氏柠檬酸杆菌和产酸克雷伯氏菌对斑翅果蝇生长发育和物质代谢的影响

【目的】明确弗氏柠檬酸杆菌Citrobacter freundi和产酸克雷伯氏菌Klebsiella oxytoca两种肠道共生细菌对斑翅果蝇Drosophila suzukii生长发育和物质代谢的影响。【方法】以正常饲养条件下的斑翅果蝇、构建的斑翅果蝇无菌品系以及弗氏柠檬酸杆菌和产酸克雷伯氏菌单一共生菌感染的斑翅果蝇品系为材料,检测不同品系间斑翅果蝇的卵孵化率、3龄幼虫体重和化蛹率;测定不同斑翅果蝇品系3龄幼虫体内蛋白质、氨基酸、糖原和游离脂肪酸等代谢物的含量及超氧化物歧化酶(SOD)、过氧化氢酶(CAT)和过氧化物酶(POD)的活力。【结果】正常饲养条件下的斑翅果蝇卵孵化率、3龄幼虫体重、化蛹率及3龄幼虫体内蛋白质的含量均高于其他斑翅果蝇品系,且无菌品系中的最低。弗氏柠檬酸杆菌和产酸克雷伯氏菌感染的斑翅果蝇品系3龄幼虫中的氨基酸和糖原含量均低于斑翅果蝇无菌品系和正常品系。弗氏柠檬酸杆菌感染斑翅果蝇品系3龄幼虫体内游离脂肪酸的含量较其他品系的也降到最低。弗氏柠檬酸杆菌和产酸克雷伯氏菌感染斑翅果蝇品系3龄幼虫体内POD活力显著高于无菌品系和正常品系,而CAT活力显著低于无菌品系。【结论】斑翅果蝇肠道中无肠道共生细菌时生长发育迟缓,在食物中分别添加弗氏柠檬酸杆菌和产酸克雷伯氏菌后可一定程度上促进斑翅果蝇的发育,这与添加肠道共生菌后斑翅果蝇体内代谢物的变化密切相关。     

云南省斑翅果蝇寄生性天敌昆虫种类调查

斑翅果蝇作为危害蓝莓、杨梅、葡萄、樱桃等软皮水果的重要害虫之一,已经引起国内外广泛关注,明确斑翅果蝇寄生性天敌昆虫的种类、分布和自然寄生状况,可以为斑翅果蝇天敌的保护利用提供科学依据。本文通过在云南省斑翅果蝇适生区采集斑翅果蝇的栽培寄主和野生浆果果实,带回实验室培养5~8d,解剖果实并挑出斑翅果蝇蛹,收集其中羽化的斑翅果蝇寄生性天敌昆虫,并记录其种类和数量,计算寄生率。本研究共采集调查了45种植物果实,有15种植物果实可被斑翅果蝇危害,其中杨梅中的斑翅果蝇种群数量最大,达到96.03头/百果;共收集到5种斑翅果蝇的寄生蜂,其中幼虫寄生蜂有丽盾瘿蜂Ganaspis brasiliensis、细毛瘿蜂Leptopilina japonica和反颚茧蜂Asobara sp.,蛹寄生蜂有果蝇锤角细蜂Trichopria drosophilae和蝇蛹金小蜂Pachycrepoideus vindemmiae,寄生蜂的自然寄生率最高可达27.81%。结果表明,丽盾瘿蜂的虫口数量最多,分布最广,为斑翅果蝇的田间优势种寄生蜂。斑翅果蝇的寄生性天敌昆虫在斑翅果蝇化蛹后的1~2周达到羽化高峰期,对斑翅果蝇具有较好的自然控制作用。     

斑翅果蝇自然种群生命表的初步研究

【目的】为了探究在自然环境中影响斑翅果蝇Drosophila suzukii种群的关键因子。【方法】本研究于2015年7—9月,应用生命表技术,采用室内分段饲养和田间观察相结合的方法进行调查统计,组建了斑翅果蝇自然种群生命表。【结果】室外斑翅果蝇各发育阶段的历期为:卵期(22.50±2.78)h、1龄幼虫期(23.14±2.27)h、2龄幼虫期(48.86±4.14)h、3龄幼虫期(79.00±11.01)h、蛹期(99.00±6.00)h;斑翅果蝇为A型存活曲线;在果园,斑翅果蝇7月世代的关键虫期为卵期,8月、9月世代的关键虫期为1~2龄幼虫期;在杉树林,斑翅果蝇8月、9月世代的关键虫期均为卵期;卵期的关键致死因子为自然死亡,1~2龄幼虫的关键致死因子为竞争。【结论】影响斑翅果蝇自然种群的关键致死因子为自然死亡和竞争。其存活曲线为A型,不同的生态环境的关键致死因子不同,不同发育阶段的关键致死因子也不同。     

日本细毛环腹瘿蜂生物学特性研究

日本细毛环腹瘿蜂为斑翅果蝇幼虫优势寄生性天敌之一,对斑翅果蝇具有较大的控制潜能.本研究以斑翅果蝇为寄主,在实验室条件下,通过饲养与观察,研究了日本细毛环腹瘿蜂的寿命、行为节律、寄主选择、生长发育及繁殖.结果显示:不同营养条件下,寄生蜂寿命长短依次为20％蜂蜜水＞10％蜂蜜水＞清水＞对照.寄生蜂羽化期为8d,第4天为羽化高峰期,羽化期每日10:00-12:00为羽化高峰期,16:00-18:00为产卵活动高峰期.寄生不同龄期的斑翅果蝇幼虫对寄生蜂幼虫存活率没有影响,对蛹存活率、后代性比、总发育历期有显著影响,寄生2龄幼虫对寄生蜂有更好的适合度,也对寄主2龄幼虫有选择偏好.日本细毛环腹瘿蜂在3日龄达到产卵高峰为13.38头,平均每雌产卵147.50个.日本细毛环腹瘿蜂卵、幼虫、雄蜂蛹、雌蜂蛹历期分别为1.30 d、8.67 d、8.86 d、10.27 d,雄蜂的羽化时间比雌蜂平均提前1.41 d.综上结果,日本细毛环腹瘿蜂可作为斑翅果蝇生物防治的重要材料加以应用.     

食物中添加葡萄糖对斑翅果蝇发育与肠道细菌群落结构的影响

【目的】明确食物中添加葡萄糖对斑翅果蝇Drosophila suzukii发育及肠道细菌结构的影响,并筛选与斑翅果蝇糖代谢相关的肠道细菌种类。【方法】将添加不同浓度葡萄糖(0, 5%和10%)的食物饲喂斑翅果蝇的常规饲养品系和去除肠道微生物后的无菌品系,观察其生长发育情况以及体内葡萄糖含量的变化,并利用PacBio测序平台对各处理斑翅果蝇常规饲养品系成虫的肠道细菌进行多样性分析。【结果】与对照组相比,5%葡萄糖处理组斑翅果蝇常规饲养品系幼虫存活率和成虫羽化率分别提高60.44%和123.79%, 10%葡萄糖处理组幼虫存活率提高87.87%,但添加葡萄糖对斑翅果蝇无菌品系的发育无显著影响。无菌斑翅果蝇成虫无法利用葡萄糖,其体内葡萄糖含量明显高于常规饲养品系成虫体内的。肠道细菌多样性分析表明,斑翅果蝇常规饲养品系成虫肠道优势菌属主要为葡萄杆菌属Gluconobacter和醋杆菌属Acetobacter,食物中添加葡萄糖显著增加了肠道菌群多样性指数,醋杆菌属、普罗维登斯菌属Providencia和摩根氏菌属Morganella的丰度明显增加。斑翅果蝇常规饲养品系成虫肠道优势种为乳酸乳球菌L...     

斑翅果蝇对四种非寄主果实的产卵选择适应性

[目的]针对斑翅果蝇(Spotted wing Drosophila,SWD,Drosophila suzukii Matsumura)常见寄主果实期较短,评估4种非寄主果实(香蕉、紫心火龙果、芒果、红提)对斑翅果蝇种群的适合度,筛选最佳饲养水果。[方法]测定了人工饲料饲养的斑翅果蝇对4种水果气味的选择反应及其产卵选择性,比较了分别用4种水果饲养的斑翅果蝇的生物学特性(产卵量、卵历期、孵化率、幼虫历期、化蛹率、蛹历期、羽化率、成活率、雌雄比)。[结果]斑翅果蝇对4种非寄主果实气味喜好为:香蕉芒果红提紫心火龙果,产卵选择喜好表现为:香蕉紫心火龙果芒果红提,且香蕉饲养的斑翅果蝇后代成活率最高,各虫态历期最低。[结论]在4种非寄主果实中,香蕉既能引诱斑翅果蝇,也能刺激其产卵,且后代成活率显著最高,宜作为长期饲料进行实验室种群扩增。     

斑翅果蝇Drosophila suzukii Matsumura生物防治研究进展

本文简要概述了近年来国内外在斑翅果蝇Drosophila suzukii Matsumura生物防治研究方面取得的主要进展,内容包括自然天敌寄生蜂、捕食性天敌和病原微生物的研究与利用。目前,国内外对斑翅果蝇生物防治的研究,集中在寄生蜂资源调查和实验室内防治效果的研究,目前发现与斑翅果蝇相关的寄生蜂种类最多的是开臂反颚茧蜂Asobara。而对于捕食性天敌和病原微生物的研究还停留在实验室测试阶段,尚未深入田间应用。本文还讨论了今后斑翅果蝇生物防治的研究方向,以期为斑翅果蝇可持续控制提供生物防治方面的参考。     

斑翅果蝇田间发生与为害特性观察

【目的】明确斑翅果蝇Drosophila suzukii在杨梅园的发生为害特性,为斑翅果蝇的综合防治提供科学依据。【方法】2016年4月至7月在红河州石屏县采用糖醋酒溶液诱捕斑翅果蝇成虫,调查斑翅果蝇的田间种群动态;从果园采集鲜果及落果带回室内观察虫果率;从土壤中取样以调查土壤中斑翅果蝇蛹量;通过定期清除落果评价果园清洁对斑翅果蝇种群的影响。【结果】斑翅果蝇在4月下旬至7月中旬在杨梅园均有发生,其发生高峰期在在6月底至7月初。在斑翅果蝇发生高峰期,杨梅果实的被害率可达100%。新鲜虫害果及落果中既有斑翅果蝇也有其它果蝇。这表明多种果蝇可同时为害杨梅果实。斑翅果蝇除了可在果实中化蛹外,也有少量入土化蛹。清理地上落果会显著降低果园中斑翅果蝇的种群数量。【结论】斑翅果蝇与其它种类果蝇混合发生、为害杨梅鲜果。及时清除地上落果能显著降低果园斑翅果蝇种群数量。     

杨梅果实成熟度及挥发物对斑翅果蝇定向行为的影响

【目的】杨梅Myrica rubra作为中国特有的水果,是斑翅果蝇Drosophila suzukii Matsumura的主要寄主之一,且受其危害严重。通过室内测定不同成熟度杨梅果实及其挥发物对斑翅果蝇定向行为的影响,明确不同成熟度杨梅果实及其挥发物在斑翅果蝇寄主定向中的作用。【方法】利用动态顶空吸附法提取不同成熟度的杨梅果实挥发物,并用Y-型嗅觉仪测定斑翅果蝇对不同成熟度杨梅果实及其挥发物的嗅觉反应。【结果】杨梅果实成熟度愈高,其p H值和糖度值愈高、酸度值愈低;成熟杨梅果实对斑翅果蝇已交配雌虫和未交配雌虫引诱效果极显著(P0.01),半熟杨梅和生杨梅果实对斑翅果蝇未交配雌虫引诱效果极显著(P0.01)、对已交配雌虫引诱效果显著(P0.05);3种成熟度杨梅果实对斑翅果蝇雌虫(已交配或未交配)引诱效果均表现为:成熟杨梅果实半熟杨梅果实生杨梅果实;成熟杨梅果实挥发物对斑翅果蝇已交配雌虫和未交配雌虫引诱效果显著(P0.05),半熟杨梅和生杨梅果实挥发物对斑翅果蝇未交配雌虫引诱效果显著(P0.05),但对已交配雌虫引诱效果不显著(P0.05)。【结论】不同成熟度杨梅果实及其挥发物对斑翅果蝇的定向行为有重要的影响。     

基于广义可加模型分析温湿度因子对斑翅果蝇田间种群动态的影响

探究温湿度因子对田间斑翅果蝇Drosophila suzukii Matsumura种群发生动态的影响,为进一步开展环境胁迫下斑翅果蝇适应性机制研究提供前期基础和参考.本文监测统计了 2016-2017年田间斑翅果蝇成虫种群动态数据,并利用广义可加模型(Generalized Additive Models,GAM)分析温湿度因子对成虫种群发生动态的影响.结果表明,通过模型检验和广义交叉验证值(Generalized Cross-Validation,GCV)对比,得出温湿度因子显著影响了2016-2017年斑翅果蝇田间成虫种群发生动态(P＜0.05),斑翅果蝇雌成虫、雄成虫、总种群数量的GAM模型参数α分别为2.21346、2.55606和3.08316;雌成虫、雄成虫、总种群数量与温湿度因子关联的GCV值分别为0.57299、0.74501、0.64611,因此雌成虫种群数量与温湿度因子拟合的模型最优;结合温湿度预测曲线分析,斑翅果蝇成虫种群发生动态与温湿度因子之间呈非线性相关,其中温度在23℃以下呈局部负相关,在23℃以上呈局部正相关;与湿度呈正相关,但影响程度较低,因此温度是影响斑翅果蝇成虫种群数量动态的关键生态因子.本文通过探究环境因子对田间斑翅果蝇种群消长规律的影响,为斑翅果蝇的种群发生机制提供了生态学理论基础.     

Association between olfactory sensitivity and behavioral responses of Drosophila suzukii to naturally occurring volatile compounds

Drosophila suzukii Matsumura (Diptera: Drosophilidae) is an invasive, destructive crop pest that originated in South East Asia. D. suzukii recently invaded Western countries and is threatening both European and American fruit industries. It is extremely attracted to otherwise undamaged, ripening fruits, unlike most other Drosophila species that attack only decaying or rotten fruits. Recent studies on different insect species showed that several naturally occurring compounds of easy market availability showing deterrent action may be used to supplement mass catches with food traps. Based on these considerations, the aim of the present work was to test the effects of some natural compounds (alone or in the mixture) on the olfactory system of the D. suzukii and the behavioral responses evoked. We measured by electroantennogram (EAG) recordings, the olfactory sensitivity of antennae to increasing concentrations of eugenol, vanillin, menthol, cis-jasmone; eugenol + vanillin, +menthol, +cis-jasmone; vanillin + menthol, +cis-jasmone. In addition, the behavioral responses to the same compounds and mixtures were evaluated. Our electrophysiological results show a dose-response relationship between the EAG amplitudes and the increasing concentrations of the olfactory compound. The behavioral results show that the number of laid eggs is significantly different between the standard diet and the standard diet + natural compound. These results underline a specificity in the olfactory sensitivity and in the ovipositing behavior of D. suzukii females; also, they could be valuable for the identification of key chemicals aimed at the future development of strategies in the management and control of this harmful insect for crops.     

Ecological, morphological and molecular studies on Ganaspis individuals (Hymenoptera: Figitidae) attacking Drosophila suzukii (Diptera: Drosophilidae)

Ganaspis individuals parasitizing Drosophila suzukii (Matsumura), a pest of fruit crops, were examined for host use and molecular and morphological differences from those attacking D. lutescens Okada and some other Drosophila species that breed on fermenting fruits. Wild cherry fruits were collected in the suburbs of Tokyo, and drosophilid pupae obtained from these fruits were examined for parasitism. Drosophila suzukii was the only drosophilid species infesting fresh wild cherry fruits, and Ganaspis individuals were the major parasitoids attacking D. suzukii in wild cherry fruits. In parasitism experiments, these Ganaspis individuals parasitized D. suzukii larvae in fresh cherry fruits, but did not parasitize those in Drosophila medium. In addition, they did not parasitize larvae of some other fruit-feeding Drosophila species even when these occurred in fresh cherry fruit. These Ganaspis individuals parasitizing D. suzukii were different from those parasitizing D. lutescens and some other drosophilids in nucleotide sequences of the COI gene, as well as in ITS1 and ITS2. They were also different in forewing and antenna morphology, although they showed some overlap in morphological traits. They are tentatively assigned as the suzukii- and lutescens-associated types of G. xanthopoda Ashmead. In the present field survey, Leptopilina japonica Novkovi? & Kimura and some Asobara species were also observed to attack D. suzukii larvae in wild cherry fruit.     

Chemical cues from competitors change the oviposition preference of Drosophila suzukii

Although Drosophila suzukii Matsumura (Diptera: Drosophilidae) infests fresh and ripening fruits, it is attracted to fermented fruits as well. Because fermented fruits attract other flies too, if D. suzukii utilizes fermented fruits as oviposition substrates, competition can be more intense on them. To avoid such competition, D. suzukii may change oviposition preference when particular species of competitor flies are present, but the effect of odor cues associated with competitors on the oviposition preference of D. suzukii is still unknown. To examine such an effect, we investigated the oviposition preference of D. suzukii in the presence of four competitor fly species – Drosophila melanogaster Meigen, Drosophila lutescens Malloch, Drosophila rufa Kikkawa & Peng, and Drosophila auraria Peng – and D. suzukii itself. We prepared artificial substrates with yeast treatment (Y⁺: yeast supplementation, Y⁻: control) and competitor fly treatment (F⁺: pre-inoculated with competitor fly odor, F⁻: control), and performed two-choice experiments using the substrates with various Y and F treatments. Our results showed that D. suzukii oviposited more eggs on Y⁺ substrates than on Y⁻ substrates when no competitor flies were present and the presence of competitor flies influenced D. suzukii’s oviposition preference for yeast-supplemented substrates and its effect changed depending on the competitor fly species. If the presence of competitors around fallen fruits on the ground suppresses D. suzukii’s oviposition on the fallen fruits and facilitates the oviposition on non-fermenting substrates in nature, it may drive D. suzukii to use ripening fruits on the tree. Such selective pressure may facilitate the evolution of morphological traits such as a serrated ovipositor in D. suzukii.     

A chitinase from Euphorbia characias latex is a novel and powerful plant‐based pesticide against Drosophila suzukii

Drosophila suzukii attacks on developing soft fruits have recently caused important economic losses in Europe. This study explores the effectiveness of a new control strategy against this insect pest that is based on a plant chitinase extracted from the latex of the Mediterranean spurge, Euphorbia characias. The ability of the purified Euphorbia latex chitinase (ELC) to degrade the chitin exoskeleton of D. suzukii was assessed using confocal laser scanning microscopy. ELC treatment caused reduced larval growth, higher mortality and notable degradation of external insect structures. Therefore, the chitinase may induce a double effect on the D. suzukii larvae, a direct injury on the larval bodies and an action as antifeedant. The effects of the ELC treatment were also tested on leaves of the insect's host plants, Fragaria × ananassa and Rubus idaeus, using physiological parameters (chlorophyll concentration, chlorophyll fluorescence, leaf gas exchange and water potential) and defence gene expression (FaPGIP, FaChi2_1 and FaChi2_2) as stress indicators. ELC at concentrations effective against D. suzukii did not damage the host plants. Only plant defence gene expression was somewhat enhanced during the early hours after ELC application. In conclusion, ELC, a natural product, proved to be an effective tool for use in the development of an environmentally friendly integrated management strategy against D. suzukii, a pest whose control by conventional chemical insecticides is problematic.     

Olfactory responses of Drosophila suzukii females to host plant volatiles

Drosophila suzukii Matsumura, an endemic pest in southeast Asia, has invaded Europe and the U.S.A. Unlike most of its closely related sibling species, the serrated ovipositor of D. suzukii permits ovipositing in undamaged fresh fruits. In the present study, volatiles are identified from host plants that are potentially involved in D. suzukii host recognition and oviposition behaviour. It is shown that mated females are attracted to volatiles emitted from intact fruits. The antennally‐active suite of compounds released from the fresh fruits is identified by gas chromatography coupled with electroantennographic detection, as well as gas chromatography‐mass spectrometry. In olfactometer bioassays, mated females are significantly attracted to an electroantennographically active volatile, isoamyl acetate, when tested at 10 µg of synthetic compound in a rubber septa, which has a release rate comparable to that of fresh fruits. In addition, a genomic survey shows that D. suzukii not only possesses the full repertoire of genes encoding odorant receptors activated by isoamyl acetate in D. melanogaster, but also that one of the genes, OR67a, is represented by five duplicated copies. These results indicate that D. suzukii uses olfactory cues to select oviposition sites. The identification of volatiles emitted by host fruits that attract D. suzukii may aid in the development of a selective and efficient synthetic lure for monitoring this pest. As a close relative of Drosophila melanogaster, D. suzukii provides a unique opportunity for understanding the physiological mechanisms involved in the shift of this species from use of rotten to ripe fruits for oviposition.     

Single and combined effects of Drosophila suzukii and Drosophila melanogaster on sour rot development in viticulture

Sour rot is a disease complex that causes serious damage in viticulture. The common vinegar fly Drosophila melanogaster (Diptera: Drosophilidae) is associated with sour rot in overripe or otherwise damaged grapes. Drosophila suzukii (Diptera: Drosophilidae) is an invasive species, which is suspected to induce sour rot in previously undamaged grapes due to the flies' ability to infest healthy, undamaged soft fruits with its serrated ovipositor. As a consequence, infection of healthy grapes by D. suzukii may facilitate the colonization by D. melanogaster. We investigated the single and combined effects of D. suzukii and D. melanogaster on sour rot development by measuring volatile acidity under near-natural conditions in the vineyard, along with laboratory experiments under controlled climate. In 2017, the combined field and laboratory experiments suggested that the presence of D. suzukii and D. melanogaster increased the volatile acidity levels at a similar rate. In 2018, the field experiments showed an only marginal increase in sour rot development in treatments with both Drosophila species. Under more favourable laboratory conditions, the presence of D. suzukii, but not D. melanogaster triggered sour rot emergence. A facilitating effect of D. suzukii infestation for D. melanogaster was not detectable. These findings suggest that D. suzukii does in fact have the potential to trigger sour rot, but will probably rarely do so under field conditions in the vineyard, at least in the studied region. Instead, our study showed that D. melanogaster can have a similar impact on sour rot development as D. suzukii, emphasizing the need of comparative studies.     

Functional stability of the aristaless gene in appendage tip formation during evolution

The appendages of an insect are subdivided into distinct segments or podomeres. Many genes responsible for the regionalization of the growing limb into subdomains have been isolated from Drosophila. So far, only one gene is known in the leg that is solely required for specifying the distal-most pattern element—the pretarsal claw. In Drosophila, the gene aristaless is expressed in the centre of the antennal and leg imaginal disc that represents the most distal position of appendages, and in a proximal region. When Drosophila aristaless function is impaired, antennae and legs develop without their distal-most structures—the arista and the claw. We describe here the analysis of aristaless in the beetle Tribolium—an insect that shows a different, more ancestral mode of appendage formation than Drosophila. In Tribolium, appendages grow out continuously during embryogenesis, and no imaginal discs are formed. Tribolium aristaless (Tc-al) expression starts midway during appendage elongation, and is seen in a distal and a proximal position of head and trunk appendages. At the end of embryogenesis, Tc-al is seen in four expression domains in the leg, in the dorsal epidermis, and ventrally in every segment in lateral groups of cells, presumably the histoblasts. Like in the Drosophila adult, Tc-al is required in the larva for the formation of the most distal structures of the leg and the antenna as revealed by RNAi experiments. We conclude that aristaless is evolutionarily robust, meaning that it has retained its expressional and functional characteristics, although a heterochronic change of the process of appendage elongation took place towards the evolution of the highly derived diptera.Edited by D. Tautz     

Oviposition preference for spherical surfaces is shared among multiple Drosophila species except D. melanogaster (Diptera: Drosophilidae)

Oviposition preference for spherical substrates has been reported in some insects but not in Drosophila species until the recent finding that Drosophila suzukii preferentially lays eggs on spherical surfaces with a smaller radius, whereas D. melanogaster does not. This finding raised two questions: (i) Was this trait specifically acquired in D. suzukii or lost in D. melanogaster? (ii) In the latter case, is it due to the long-term laboratory culture using oviposition substrates with flat surfaces? To answer these questions, we examined the oviposition preference of three Drosophila species using the stocks recently established from wild individuals. As with D. suzukii, D. simulans and D. takahashii showed significant preference for spherical surfaces with a smaller radius, suggesting that this trait is shared by multiple Drosophila species. In contrast, D. melanogaster did not show any preference for either smaller or larger radii, showing that the preference already has been lost in the natural population of D. melanogaster. It may be possible that the loss of oviposition preference for spherical surfaces is involved in the evolutionary process of D. melanogaster becoming a human commensal.     

Seasonal monitoring of Drosophila suzukii and its non-crop hosts in Wuhu,Eastern China

Drosophila suzukii (Matsumura) (Diptera: Drosophilidae) is a serious pest that prefers fresh fruits and is native to Southeast Asia. In our study, apple cider vinegar bait traps were used to capture and monitor the population dynamics of this native pest in Wuhu City, China, from May/June 2017 to May 2018. The research was conducted at 15 locations in two fruit orchards in Wuhu. Traps caught more adults in general in a Meiling blueberry orchard than in a Xicun mixed orchard, and the highest trap counts occurred near harvest time (October). Females had more mature eggs from September to November, and the number of mature eggs declined thereafter. We found several non-crop hosts, which can provide food and reproductive resources for D. suzukii and are common in forests and field margins. By comparing the number of captured adults in the Meiling and Xicun orchards, we found that blueberry was preferred by D. suzukii among the fruits in our search. Fruit ripening times differed among crops; therefore, fly populations moved between crop and non-crop habitats during the year or had varying population dynamics on different crops in different seasons. The D. suzukii population and the number of mature eggs decreased in summer and winter but increased in spring and autumn. Drosophila suzukii had higher survival rates with blueberry than those with other fruits, and D. suzukii could use four non-crop species growing around the orchards as host plants.     

Resistance of Drosophila suzukii to the larval parasitoids Leptopilina heterotoma and Asobara japonica is related to haemocyte load

Unlike other Drosophila species, the invasive Drosophila suzukii Matsumura (Diptera: Drosophilidae) shows a remarkable pest status. Among the physiological traits that may explain the high level of resistance to parasitoids of Drosophila larvae, the haemocyte load is shown repeatedly to play an important role. To determine whether haemocyte load can explain immunity resistance of D. suzukii to parasitoids, the haemocytes of parasitized and healthy larvae are quantified in two Japanese and three French populations of D. suzukii. Parasitization tests are conducted with two larval parasitoids: the paleartic Leptopilina heterotoma Thomson (Hymenoptera: Figitidae) and the Asian Asobara japonica Belokobylskij (Hymenoptera: Braconidae). Based on morphological and functional criteria, D. suzukii has classes of haemocytes similar to those described in Drosophila melanogaster. However, healthy larvae of the five populations tested possess particularly large numbers of haemocytes compared with D. melanogaster. Haemocyte load is also higher in larvae from the French populations than in the Japanese strains. The ability of D. suzukii larvae to encapsulate eggs of L. heterotoma is associated with a particularly high load of circulating haemocytes. However, it is notable that A. japonica induces a strong depression of the haemocyte population in this resistant host associated with an inability to encapsulate parasitoid eggs. The results show that the cellular immune system plays a major role in the failure of larval parasitoids to develop in most instances in larvae of D. suzukii, possibly contributing to the success of this species as an invader.