蚜虫对设施辣椒产量和品质的影响

【目的】探讨不同蚜害等级危害对设施辣椒产量和品质的影响,为设施蔬菜的科学防控、按质定价及制定蚜虫经济阈值提供参考。【方法】通过田间蚜虫量调查,进行蚜害分级,并测定不同蚜害等级下辣椒叶片和果实的SPAD值,采收后记录单株果数,称重,计算座果率及单株果重等产量指标;同时测定不同蚜害等级下辣椒果实可溶性蛋白、可溶性糖、维生素C含量等品质指标。【结果】当蚜害等级达Ⅲ级及以上时,即可导致设施辣椒产量和品质相关指标明显下降,且随着蚜害等级增加,下降越显著。当蚜害等级达Ⅴ时,辣椒叶片和果实的SPAD值比对照分别下降了38.29%和29.49%,辣椒座果率比对照下降了21.28%,单株果重比对照下降了40.09%,且1、2级果数量明显减少;辣椒可溶性糖、维生素C含量比对照分别下降了35.66%、39.29%,可溶性蛋白含量略有下降,但与对照无显著差异。【结论】当蚜害等级为Ⅲ级以上,即株虫量为50头以上时,辣椒产量、品质出现明显下降,因此,当辣椒整株虫量达50头以上时要及时进行蚜虫防治。     

麦长管蚜的序贯二项式分类抽样设计与管理决策优化：样本单位虫口数阈的重要性

依据１９８８～１９９１年间对麦长管蚜（Ｓｉｔｏｂｉｏｎａｖｅｎａｅ）种群的抽样数据和新的抽样理论而设计了用样本单位（分蘖株）虫口数阈Ｔ（每株不超过Ｔ头蚜虫,Ｔ≥０）进行样本分类的序贯二项式分类抽样方案,用于蚜害的管理决策。负载不超过Ｔ头蚜虫的植株比例（ＰＴ）与种群密度（ｍ,头／株）的关系通过拟合经验式ｌｎ［－ｌｎ（ＰＴ）］＝ａ＋ｂｌｎ（ｍ）和负二项分布的概率模型而建立。一系列Ｔ值（０～２５）和３个干扰阈限即经济危害水平（２．５和１０头／株）用于抽样方案的设计和比较,以优化麦作不同生育期控制蚜害的决定。抽样设计的可靠程度和经济性状分别由运行特征（ＯＣ）函数和平均样本数（ＡＳＮ）函数判别。结果显示,各干扰阈限的抽样设计随Ｔ值的增大而愈趋合理。传统的０－ｌ抽样（Ｔ＝０）被证明错误决策的风险很大,所需样本数最多,应当摒弃。考虑到Ｔ过大会增加处理单位样本的时间,作者建议使用略高于干扰阈限的Ｔ值进行麦蚜的分类抽样和田间管理决策。     

豆柄瘤蚜茧峰的嗅觉定向反应(英文)

豆柄瘤蚜茧蜂Lysiphlebusfabarum对能寄生于包括大豆蚜Aphisglycines和豆蚜A.craccivora的多种蚜虫中。本实验研究了豆柄瘤蚜茧蜂在风洞中对以下气味源的嗅觉走向反应：未受损伤的寄主食料植株（UD）、机械损伤的寄主食料植株（MD）、蚜害植株（AD ,带蚜虫;AD～,不带蚜虫）、以及致害蚜虫。发现以豆蚜为寄主的豆柄瘤好茧蜂对AD 和AD~的正走向率高于对UD和MD的正走向率,以大豆蚜为寄主的豆柄瘤蚜虽峰对AD 的趋性高于对UD和大豆蚜。同时,豆柄瘤蚜茧蜂对UD、MD和致害蚜虫的定向反应率没有显著差异。这说明植食性昆虫的取食活动能诱导被害植株提高自身对害虫天敌的吸引力。此外还发现大豆是否受蚜害并不直接影响大豆蚜进行寄主定位。     

球孢白僵菌对烟蚜茧蜂生命参数及控害效果的影响

在室内评价了球孢白僵菌对烟蚜茧蜂生命参数及控害效果的影响。分别在烟蚜茧蜂寄生桃蚜后不同时间进行高剂量（1900孢子/mm^{2）接菌,检测蚜虫感病率和寄生蜂形成的僵蚜率及僵蚜出蜂率。结果表明,球孢白僵菌对僵蚜率和僵蚜出蜂率的影响随接菌时间不同而变化。在烟蚜茧蜂寄生前1d、寄生当天和寄生后3d接菌,蚜虫感病率分别为59.6%、56.2%和34.8%;与对照相比,僵蚜率分别下降94%、59%和47%,僵蚜出蜂率分别减少83%、54%和49%。在寄生后5d或7d接菌,僵蚜率和僵蚜出蜂率不受明显影响,但蚜虫感病率降低到8.2%以下。对蚜尸内白僵菌菌体含量检测表明,随着烟蚜茧蜂寄生后接菌时间的推移,菌体数量迅速下降。寄生蜂寄生后5d或7d接菌,蚜尸内几乎检测不到菌体。直接喷雾接菌烟蚜茧蜂,成蜂寿命缩短4d左右,且81.8%的蜂尸受白僵菌感染。接菌后的寄生蜂对蚜虫寄生率几乎无影响,但寄生蜂在蚜虫体内的存活时间缩短了27.8%。}     

毒砂防治高粱蚜虫效果好

随着两杂作物的推广,杂交高梁的种植面积不断扩大,高粱蚜虫发生危害,已成为生产上的一个突出问题。由于蚜虫吸食高梁的汁液,严重影响高梁的生长发育,轻者叶子变红,重者不能抽穗,严重地块颗粒无收。一般减产40—60%。全大队发生面积曾达600多亩。我们根据蚜虫的消长规律,采取边防治边试验,发现乐果毒砂(土)冶蚜效果高,药效长,而且简便易行。 一、高梁蚜虫发生情况 高粱蚜虫于6月初发现,6月21日调查,蚜虫主要在植株的下部叶片,7月份以后由于气温较高,蚜虫繁殖快,由7月7日的蚜株率11%,百株蚜量50头,7月25日的蚜株率增到100%,百株蚜量为2,100多头,发生严重的“窝子蜜”地块普遍出现流油株,百株蚜量为12万余头。蚜虫由底部叶片逐渐向中上部叶片蔓延,随着蚜虫不断增殖,天敌数量逐渐增多,因此8月间蚜虫数量逐渐下降。     

蓝光对设施黄瓜蚜虫种群的控制作用

利用灯光控制害虫是蔬菜绿色防控的重要手段之一。本文以黄瓜为供试材料,研究蓝光照射对设施黄瓜蚜虫种群数量的影响。结果表明,蓝光照射对设施黄瓜上有翅蚜和无翅蚜均有较强的驱避作用,蓝光照射2 d后,有翅蚜和无翅蚜种群数量分别下降了65.91%和45.26%,校正虫口减退率分别达到了54.22%和52.83%。随着照射时间的延长,蚜虫种群数量持续下降,校正虫口减退率不断上升,照射14 d后,有翅蚜和无翅蚜种群数量分别下降了78.18%和96.40%,校正虫口减退率分别达到了76.67%和96.40%。蓝光照射可以增加黄板对蚜虫的诱集虫量,蓝光照射3 d后,处理区黄板上蚜虫的数量较对照区黄板增加65.08%。研究发现,蓝光照射对黄瓜蚜虫具有直接的驱避作用,同时还可以增加黄板对蚜虫诱集作用。     

烟蚜为害的经济损失研究

陕西渭北烟草种植区迁飞到烟田的蚜虫有6种,但只有桃蚜Myzus persicae(Sulzer)能够建立种群,造成为害。从烟草旺长开始,按烟株上蚜量和蚜虫分泌蜜露,引起霉菌滋生,污染叶面积的比例分为0、I、II、III、IV级。以未受蚜害的0级为对照,受蚜害的I、II、III、IV级的中上等烟下降分别为6.93%、13.05%、28.51%和30.94%,经济损失率分别为9.86%、23.81%、36.12%和39.59%。化学成分分析表明：I、II、III和IV级烟叶的烟碱含量分别降低10.61%、19.29%、10.61%和25.40%,还原糖分别降低15.04%、19.23%、40.98%和44.86%,蛋白质含量分别提高16.17%、31.99%、37.02%和38.72%。这就表明桃蚜为害既影响烤烟的外观质量、又影响内在品质。1头蚜虫经济损失率＝0.0695%。     

球孢白僵菌对烟蚜茧蜂生命参数及控害效果的影响

在室内评价了球孢白僵菌对烟蚜茧蜂生命参数及控害效果的影响。分别在烟蚜茧蜂寄生桃蚜后不同时间进行高剂量(1900孢子/mm2)接菌,检测蚜虫感病率和寄生蜂形成的僵蚜率及僵蚜出蜂率。结果表明,球孢白僵菌对僵蚜率和僵蚜出蜂率的影响随接菌时间不同而变化。在烟蚜茧蜂寄生前1d、寄生当天和寄生后3d接菌,蚜虫感病率分别为59.6%、56.2%和34.8%;与对照相比,僵蚜率分别下降94%、59%和47%,僵蚜出蜂率分别减少83%、54%和49%。在寄生后5d或7d接菌,僵蚜率和僵蚜出蜂率不受明显影响,但蚜虫感病率降低到8.2%以下。对蚜尸内白僵菌菌体含量检测表明,随着烟蚜茧蜂寄生后接菌时间的推移,菌体数量迅速下降。寄生蜂寄生后5d或7d接菌,蚜尸内几乎检测不到菌体。直接喷雾接菌烟蚜茧蜂,成蜂寿命缩短4d左右,且81.8%的蜂尸受白僵菌感染。接菌后的寄生蜂对蚜虫寄生率几乎无影响,但寄生蜂在蚜虫体内的存活时间缩短了27.8%。     

性信息素和香根草在盐碱地稻二化螟绿色防控中的应用

[目的] 探索滨海盐碱地水稻生态种植模式下,利用性诱剂和香根草对水稻二化螟的综合防治效果。[方法] 在0.3%~0.6%的土壤盐分下,种植中粳中晚熟南粳9108水稻品种,设置4种绿色防控措施,每15~20 d调查诱捕螟虫量、虫害穴率、虫害株率、防治效果,并比较水稻的食味品质、生长和产量指标。[结果] 综合利用性诱剂和香根草对水稻螟虫的综合防治技术,可以降低虫害穴率7.10%,降低虫害株率5.72%,防治效果达87.31%,可以显著的提高水稻结实率22.80%,稻谷产量为6810.45 kg·hm^-2,提高了22.35%,显著提高了稻米的外观品质,食味值提高了4.29%。[结论] 性诱剂与香根草配合进行水稻螟虫的绿色防控,可以作为滨海盐碱地水稻生态种植模式的主要防控措施。     

脱共生作用对黑豆蚜氨基酸代谢的影响(英文)

为了解共生菌对黑豆蚜蛋白质、氨基酸代谢的影响 ,用利福平处理黑豆蚜以除去其细胞内共生细菌 ,产生脱共生蚜虫。结果表明 ,被脱去共生菌的蚜虫与未经抗生素处理的正常蚜虫相比 ,7日龄时 ,脱共生蚜虫每毫克鲜重的总蛋白含量降低了 2 9% ,每毫克鲜重的游离氨基酸含量提高了 17%。对黑豆蚜取食的蚕豆苗韧皮部组织中必需氨基酸所占的比例进行分析后发现 ,蚕豆苗韧皮部组织中的必需氨基酸含量仅占 2 0 % ,而有共生菌的黑豆蚜组织中必需氨基酸已达到 4 4% ,脱共生后降低到 37% ,这些结果证明了黑豆蚜的胞内共生菌为其寄主提供了部分必需氨基酸。通过对游离氨基酸组成的分析发现 ,在测定的 17种氨基酸中 ,必需氨基酸中的苏氨酸在共生蚜虫中所占的比例为 2 1 6 % ,在脱共生蚜虫中仅为 16 7%。同样 ,非必需氨基酸中的酪氨酸和丝氨酸 ,在共生蚜虫中分别占总游离氨基酸的 8 9%和 5 6 % ,而在脱共生蚜虫中却分别升高到 2 1 1%和 13 6 %。这些结果表明 ,各种氨基酸比例的失调 ,造成了脱共生蚜虫蛋白质合成受阻和部分游离氨基酸的积累 ,并因此导致蚜虫发育和繁殖的失调。     

Effect of temperature on development, growth and feeding of Coccinella septempunctata and Hippodamia convergens reared on the tobacco aphid, Myzus persicae nicotianae

Preimaginal development, mortality, aphid consumption rate, and size and weight upon reaching the adult stage of the aphidophagous coccinellids Hippodamia convergens Guérin-Méneville and Coccinella septempunctata L. collected from Karditsa, central Greece, were examined at four constant temperatures (14, 17, 20 and 23 °C) and L16:D8. The coccinellids fed on the tobacco aphid, Myzus persicae nicotianae Blackman. Egg, larval and pupal mortality was highest at 14 °C reaching 85.0, 73.8 and 29.4% in H. convergens and 49.3, 75.4 and 58.8% in C. septempunctata, respectively. Total preimaginal development ranged from 57.2 to 70.4 days at 14 °C, and to 16.9 and 22.1 days at 23 °C in H. convergens and C. septempunctata, respectively. Heavier and larger adults of H. convergens were obtained at 17 and 20 ° C. In C. septempunctata temperature did not affect adult weight while the lowest size was observed at 14 and 17 °C. Day-degrees requirements for preimaginal development in H. corvengens were 212.9 above a developmental threshold of 11.0 °C. The corresponding values for C. septempunctata were 281.5 and 10.7 °C. In H. convergens total and daily aphid consumption ranged from 46.8 aphids at 14 °C to 85.0 aphids at 23 °C and from 1.5 aphids at 14 °C to 9.2 aphids at 23 °C, respectively. The corresponding values for C. septempunctata were 112.0 and 2.7 at 14 °C and 157.7 and 12.4 at 23 °C. The results show the high potential of both predators as biological control agents against the tobacco aphid. The knowledge obtained could be essential for their appropriate use and for the improvement of mass rearing systems.     

Evaluation of Lecanicillium longisporum, Vertalec for simultaneous suppression of cotton aphid, Aphis gossypii, and cucumber powdery mildew, Sphaerotheca fuliginea, on potted cucumbers

The commercial preparation of Lecanicillium longisporum, Vertalec^® was evaluated for simultaneous suppression of cotton aphid and cucumber powdery mildew on potted cucumber plants. Vertalec was applied onto cucumber plants that had been infested with either cotton aphid, spores of Sphaerotheca fuliginea or both. Irradiation-inactivated Vertalec (II Vertalec) was also applied to an identical series of cucumber plants as a control. The Vertalec was highly pathogenic against adult aphids with an LT₅₀ of 6.9 days. II Vertalec did not affect aphid survival. Application of either active or II Vertalec significantly suppressed spore production of S. fuliginea compared to the water control. For dual control assays, Vertalec applications were made one day after infestation of both aphid and S. fuliginea onto potted cucumbers. Fifteen days after the Vertalec treatments, the numbers of surviving aphids and the production of powdery mildew spores were significantly reduced compared with the water control. The presence of aphids also suppressed S. fuliginea spore production. Our results suggest the potential of a dual role for Vertalec as a microbial control agent of aphids and powdery mildew in cucumber.     

Aphelinus albipodus(Hymenoptera: Aphelinidae) andDiaeretiella rapae(Hymenoptera: Braconidae) Parasitism onDiuraphis noxia(Homoptera: Aphididae) Infesting Barley Plants Differing in Plant Resistance to Aphids

Russian wheat aphid,Diuraphis noxia(Mordvilko), as a pest of small grains, has prompted research into biological control and host plant resistance. In the presence of Russian wheat aphid, leaves of a susceptible barley (Morex) are curled and chlorotic and sustain large densities of this aphid, while leaves of a resistant barley (STARS-9301B) remain flat and green and sustain fewer aphids. Might parasitism of Russian wheat aphid byAphelinus albipodusHayat & Fatima andDiaeretiella rapaeMcIntosh be affected differently by these plant types? When presented the plants separately and based on parasitism rate relative to aphid density, the largerD. rapaewas more effective in parasitizing relatively high densities of aphids within curled leaves of Morex than relatively low densities of aphids on uncurled leaves of STARS-9301B. Parasitism byA. albipodusdid not significantly differ among the plants. When given a choice of plants, approximately equal rates of parasitism occurred on the two plant lines for both parasitoid species, and parasitism byD. rapaewas greater thanA. albipodus.These data indicate that using parasitoid size as an indicator of success in a physically restricted environment may be misleading, when considered in a plant environment responsive in several manners to aphids (chlorosis, curling, and ability to sustain Russian wheat aphid). We expect that use of resistant barley will result in decreased parasitoid abundance as aphid densities decrease. However, parasitism rates are expected to be approximately equal on resistant and susceptible barley. In this system, plant resistance and biocontrol are compatible management strategies.     

入侵植物香丝草水浸提液对蚕豆和玉米根尖染色体行为的影响

以采自农田中自然生长的植物群落中的香丝草为供体,以典型的双子叶植物蚕豆和典型的单子叶植物玉米的幼苗为受体,运用根尖微核试验和染色体畸变试验,研究了香丝草的根、茎、叶和幼果4种器官水浸提液对受体的遗传毒性。结果表明:(1)在香丝草不同器官水浸提液作用下,蚕豆和玉米根尖细胞的有丝分裂各时期均受到明显影响,细胞中出现了微核、染色体桥、染色体断片、染色体环、染色体粘连及染色体滞后等多种染色体畸变。(2)香丝草各器官水浸提液对蚕豆幼苗根尖细胞分裂的抑制作用明显大于玉米。(3)香丝草各器官水浸提液对蚕豆和玉米幼苗根尖的染色体畸变诱导存在显著的浓度效应,即水浸提液浓度越高,受体的微核率和畸变率越高,相应的有丝分裂指数越低,水浸提液的诱导作用与浓度呈正相关关系,但不是简单的加和作用。(4)香丝草各器官水浸提液均具有较强的遗传毒性,但整体化感效应表现为叶＞幼果＞茎＞根,即叶片产生的化感作用最强。因此,香丝草分泌的化感物质可能通过对受体植物生长点的细胞有丝分裂和细胞形态产生影响,造成受体植物染色体的多种畸变和不可逆的遗传损伤,从而成功入侵新的栖息地。     

Aphid-host plant interactions: does aphid honeydew exactly reflect the host plant amino acid composition?

Plants provide aphids with unbalanced and low concentrations of amino acids. Likely, intracellular symbionts improve the aphid nutrition by participating to the synthesis of essential amino acids. To compare the aphid amino acid uptakes from the host plant and the aphids amino acid excretion into the honeydew, host plant exudates (phloem + xylem) from infested and uninfested Vicia faba L. plants were compared to the honeydew produced by two aphid species (Acyrthosiphon pisum Harris and Megoura viciae Buckton) feeding on V. faba. Our results show that an aphid infestation modifies the amino acid composition of the infested broad bean plant since the global concentration of amino acids significantly increased in the host plant in response to aphid infestations. Specifically, the concentrations of the two amino acids glutamine and asparagine were strongly enhanced. The amino acid profiles from honeydews were similar for the two aphid species, but the concentrations found in the honeydews were generally lower than those measured in the exudates of infested plants (aphids uptakes). This work also highlights that aphids take large amounts of amino acids from the host plant, especially glutamine and asparagine, which are converted into glutamic and aspartic acids but also into other essential amino acids. The amino acid profiles differed between the host plant exudates and the aphid excretion product. Finally, this study highlights that the pea aphid, a “specialist” for the V. faba host plant, induced more important modifications into the host plant amino acid composition than the “generalist” aphid M. viciae.     

Xylem ingestion by winged aphids

When aphids and their host plant are incorporated in a DC electrical circuit, phloem and xylem ingestion register as separate waveforms of the electrical penetration graph (EPG) signal. Aphids are primarily phloem feeders; xylem ingestion is seldom reported but can be induced experimentally by fasting the insects in desiccating conditions. In experiments with the black bean aphid, Aphis fabae Scop., young winged (alate) and unwinged (apterous) virginoparous adults were collected from their natal host plants (broad bean, Vicia faba L.) and allowed 3-h continuous EPG-recorded access to V. faba seedlings. Several aphids (47% of both morphs) showed ingestion from phloem sieve elements. Alate aphids also showed frequent xylem ingestion (60% of individuals), but no apterous aphids exhibited this activity. The EPG technique involves attachment of a fine gold wire electrode to each insect, a process that may affect normal behaviour at the plant surface. However, when the technique was modified to monitor the stylet activities of freely-settled aphids, high levels of xylem ingestion by alates were also recorded. The results suggest that the developmental physiology of winged aphids somehow predisposes them to xylem ingestion, possibly as a result of dehydration during the teneral period. Alate aphids may reduce their weight by fasting before take-off, giving aerodynamic benefits, but making rehydration, via xylem uptake, a priority following plant contact.     

TheTy1-copia group retrotransposons inVicia species: copy number, sequence heterogeneity and chromosomal localisation

We present an in-depth study of theTy1-copia group of retrotransposons within the plant genusVicia, which contains species with widely differing genome sizes. We have compared the numbers and sequence heterogeneities of these genetic elements in three diploidVicia species chosen to represent large (V. faba, 1C=13.3 pg), medium (V. melanops, 1C=11.5 pg) and small (V. sativa, 1C=2.3 pg) genomes within the genus. The copy numbers of the retrotransposons are all high but vary greatly, withV. faba containing approximately 10⁶ copies,V. melanops about 1000 copies andV. sativa 5000 copies. The degree of sequence heterogeneity ofTy1-copia group elements correlates with their copy number within each genome, but neither heterogeneity nor copy number are related to the genome size of the host. In situ hybridization to metaphase chromosomes shows that the retrotransposons inV. faba are distributed throughout all chromosomes but are much less abundant in certain heterochromatic regions. These results are discussed in the context of plant retrotransposon evolution.     

The role of natural enemy guilds in Aphis glycines suppression

Generalist natural enemy guilds are increasingly recognized as important sources of mortality for invasive agricultural pests. However, the net contribution of different species to pest suppression is conditioned by their biology and interspecific interactions. The soybean aphid, Aphis glycines (Hemiptera: Aphididae), is widely attacked by generalist predators, but the relative impacts of different natural enemy guilds remains poorly understood. Moreover, low levels of A. glycines parasitism suggest that resident parasitoids may be limited through intraguild predation. During 2004 and 2005, we conducted field experiments to test the impact of different guilds of natural enemies on A. glycines. We contrasted aphid abundance on field cages with ambient levels of small predators (primarily Orius insidiosus) and parasitoids (primarily Braconidae), sham cages and open controls exposed to large predators (primarily coccinellids), and cages excluding all natural enemies. We observed strong aphid suppression (86- to 36-fold reduction) in treatments exposed to coccinellids, but only minor reduction due to small predators and parasitoids, with aphids reaching rapidly economic injury levels when coccinellids were excluded. Three species of resident parasitoids were found attacking A. glycines at very low levels (<1% parasitism), with no evidence that intraguild predation by coccinellids attenuated parasitoid impacts. At the plant level, coccinellid impacts resulted in a trophic cascade that restored soybean biomass and yield, whereas small natural enemies provided only minor protection against yield loss. Our results indicate that within the assemblage of A. glycines natural enemies in Michigan, coccinellids are critical to maintain aphids below economic injury levels.     

Population level effects of cadmium and the insecticide imidacloprid to the parasitoid, Aphidius ervi after exposure through its host, the pea aphid, Acyrthosiphon pisum (Harris)

The objective of this study was to assess the influence of toxic substances with different modes of action on a two-species system: an aphid-specific parasitoid, Aphidius ervi Haliday, feeding on the pea aphid, Acyrthosiphon pisum (Harris). The instantaneous rate of population increase (r_i) was used as a measure of population level toxic effect in this study. The toxicants evaluated were imidacloprid, a nonpersistent neurotoxic insecticide, and cadmium, a chronic pollutant with a tendency to accumulate. We evaluated the effects of cadmium and imidacloprid on A. pisum and A. ervi because both toxicants can occur together in polluted areas where crops are grown. Cadmium (200 or 400 mg kg⁻¹ dry weight soil) and imidacloprid (4 or 40 g a.i. ha⁻¹) were applied to soil contained in plastic pots in which broad bean plants, Vicia faba L., were grown. Results of this study indicated that cadmium at the concentrations tested, reduced population growth rate of the pea aphid. Imidacloprid also reduced aphid growth rate, but only at the highest concentration tested (40 g a.i. ha⁻¹). Combinations of cadmium and imidacloprid had the greatest impact on aphid growth rate. Imidacloprid alone had no effect on population growth rate of the parasitoid. However, cadmium alone or in combination with imidacloprid had a negative impact on A. ervi by reducing population growth rate 77%. These results indicate that negative impacts on parasitoids may occur in areas where cadmium contamination is present and imidacloprid is used to control aphids.     

Genetic variation in the effect of a facultative symbiont on host-plant use by pea aphids

Ecological specialisation on different host plants occurs frequently among phytophagous insects and is normally assumed to have a genetic basis. However, insects often carry microbial symbionts, which may play a role in the evolution of specialisation. The bacterium Regiella insecticola is a facultative symbiont of pea aphids (Acyrthosiphon pisum) where it is found most frequently in aphid clones feeding on Trifolium giving rise to the hypothesis that it may improve aphid performance on this plant. A study in which R. insecticola was eliminated from a single naturally infected aphid clone supported the hypothesis, but a second involving two aphid clones did not find the same effect. We created a series of new pea aphid–R. insecticola associations by injecting different strains of bacteria into five aphid clones uninfected by symbionts. For all aphid clones, the bacteria decreased the rate at which aphids accepted Vicia faba as a food plant and reduced performance on this plant. Their effect on aphids given Trifolium pratense was more complex: R. insecticola negatively affected acceptance by all aphid clones, had no effect on the performance of four aphid clones, but increased performance of a fifth, thus demonstrating genetic variation in the effect of R. insecticola on pea aphid host use. We discuss how these results may explain the distribution and frequency of this symbiont across different aphid populations. Julia Ferrari and Claire L. Scarborough contributed equally to the work.