三种寄主植物叶片提取物对美洲斑潜蝇雌成虫嗅觉记忆的影响

先提供气味刺激,再提供含不同寄主植物叶片提取物的蜜糖刺激,采用Y型嗅觉仪测定了3种寄主植物（丝瓜、番茄和菜豆）叶片表面非挥发性次生化合物刺激对美洲斑潜蝇Liriomyza sativae雌成虫嗅觉记忆的影响。结果表明：菜豆叶片沸水提取物能促进雌成虫对芳樟醇的嗅觉记忆,而丝瓜和番茄叶片沸水提取物则能提高雌成虫对正己烷的记忆能力。因此,不同寄主植物叶片提取物影响了美洲斑潜蝇雌成虫对不同气味的嗅觉记忆。     

寄主挥发物、叶色和表皮毛在美洲斑潜蝇寄主选择中的作用

在室内条件下 ,初步研究了寄主挥发物、叶色和表皮毛在美洲斑潜蝇寄主选择中的作用。在嗅觉仪试验中 ,寄主叶片挥发物对美洲斑潜蝇雌成虫没有明显的引诱作用 ;在叶色反应试验中 ,美洲斑潜蝇雌成虫在叶子圆片上停留的时间明显大于在滤纸圆片上停留的时间 (p<0 .0 1) ,其在有叶片区域分布的数量明显多于空白对照 (p <0 .0 1) ;在表皮毛试验中 ,美洲斑潜蝇在无毛叶片上的产卵量明显大于在有毛叶片上的产卵量 (p <0 .0 1)。上述结果表明 ,在对寄主的定向和定位过程中 ,美洲斑潜蝇的视觉起着重要的作用 ,而嗅觉不起作用 ;叶片表皮毛有抑制产卵的作用     

美洲斑潜蝇蛹期化学环境对成虫嗅觉定向的影响

将美洲斑潜蝇Liriomyzasativae Blanchard蛹分别暴露于3种植物挥发物-芳 樟醇、β-子丁香烯和3- 己烯-1-醇,羽化后用Y形嗅觉仪测定雌成虫对相应挥发物的定向反 应。蛹期暴露于3-己烯-1-醇后羽化的雌成虫趋向该化合物的比率（37.7%）和平均反应时 间（21.5 s）,与对照组（30.4%,35.0 s）差异不显著;β-子丁香烯处理组雌成虫选择 该化合物的比率（46.2%）与对照组（42.0%）差异不显著,但平均反应时间（21.0 s）却显著短于对照组（41.5 s）。蛹期经芳樟醇处理后雌成虫选择该化合物的比率（52.9%）显著 高于对照组（28.4%）,平均反应时间（19.5 s）也显著短于对照组（34.5 s）。以芳樟醇为处理化合物的进一步研究表明,蛹发育早期是诱导成虫产生定向反应的敏感时期。将1、3、5 、7 日龄蛹分别暴露于芳樟醇48 h后,只有1日龄组蛹羽化的雌成虫趋向芳樟醇的比率（54%） 显著高于对照组（26%）;但1、3、5 日龄组蛹羽化的雌成虫对芳樟醇的平均反应时间均显著 短于对照组。此外,蛹期暴露于芳樟醇的持续时间也影响雌成虫对该化合物的定向反应,2日龄 蛹分别暴露于芳樟醇24、48、72、96和120 h后,只有处理时间大于72 h的雌成虫选择该化合物 的比率才显著高于对照组;但所有处理组羽化雌成虫的平均反应时间均显著低于对照组。由此 推断,美洲斑潜蝇蛹期经历的化学环境会影响成虫的嗅觉定向反应。     

6种寄主果实对南瓜实蝇和瓜实蝇产卵选择及其子代发育的影响

为探讨南瓜实蝇和瓜实蝇对不同寄主的产卵选择性及其与子代生长发育的关联度,采用生态测定方法,研究2种实蝇对南瓜、黄瓜、姜柄瓜、西葫芦、丝瓜和苦瓜6种寄主果实的产卵选择以及幼虫取食6种寄主后对其生长发育的影响。在产卵选择性试验中,2种实蝇对6种寄主的产卵选择性较为一致,均偏向于在丝瓜和黄瓜上产卵。在非产卵选择性试验中,南瓜实蝇在黄瓜和姜柄瓜上的产卵量较多;瓜实蝇在丝瓜和姜柄瓜上的产卵量较多;2种实蝇都对姜柄瓜有一定的偏好。在气味诱导的产卵选择性试验中,南瓜实蝇在姜柄瓜和黄瓜上的产卵量较多;瓜实蝇在黄瓜和丝瓜上的产卵量较多;2种实蝇都对黄瓜气味有一定的偏好;且南瓜实蝇和瓜实蝇都不偏好在苦瓜上产卵。南瓜实蝇分别取食黄瓜、苦瓜时,其幼虫期、蛹期较短;取食姜柄瓜时,蛹重最大;分别取食南瓜和黄瓜时的化蛹率、羽化率最高。瓜实蝇取食西葫芦时,幼虫期较短;取食丝瓜时,蛹期较短,且蛹重最大;分别取食黄瓜和南瓜时的化蛹率、羽化率最高。南瓜实蝇和瓜实蝇对不同寄主果实的产卵选择性均存在明显差异,寄主外部物理性状对实蝇的产卵选择有显著影响,2种实蝇对6种寄主果实产卵选择性和幼虫生长发育适应性的相关性不显著。     

美洲斑潜蝇成虫的卵巢结构观察及营养影响卵子发生的试验

卵育型(Synovigenic)植食性昆虫的雌成虫需要取食寄主植物组织或非寄主食物(如花蜜、花粉等)以延长寿命和促进产卵。为了明确寄主食物和非寄主食物对美洲斑潜蝇Liriomyza sativae卵子发生的功能差异,本实验在明确美洲斑潜蝇成虫卵巢发育动态和结构的基础上,比较了清水(饥饿,对照)、菜豆叶片、20%葡萄糖溶液、菜豆叶片+20%葡萄糖溶液四种处理下的雌成虫卵子发生动态。结果显示:美洲斑潜蝇为强卵育型昆虫,初羽化成虫体内无卵子;两侧卵巢管数之和为11-18根,大多数情况下,左右两侧卵巢管数目不等。成虫在饥饿条件下,几乎不能形成成熟卵子;继续取食寄主叶片、20%葡萄糖溶液和寄主叶片+20%葡萄糖溶液,均可显著促进卵子发生和卵成熟,但补充葡萄糖溶液起到极显著促进作用;成虫不具备卵子重吸收功能。本文重点从卵育型角度,对美洲斑潜蝇取食寄主食物和非寄主食物的营养功能进行了讨论。研究结果为美洲斑潜蝇以及该类植食性害虫的室内饲养和田间生态调控提供了依据。     

美洲斑潜蝇寄生峰——黄腹潜蝇茧蜂成虫的生物学特性

黄腹潜蝇茧蜂Opius caricivorae Fischer是美洲斑潜蝇Liriomyza sativae Blandchard幼虫 蛹期的一种重要内寄生蜂。在实验室条件下,用菜豆Phaseolus vulgaris L.上的美洲斑潜蝇作为寄主,对其成蜂的生物学特性做了初步研究。成虫主要在白天羽化,羽化高峰期在8:00～10:00,且多数（91%）当日交尾,羽化出的成蜂性比明显偏雌性（雌∶雄=1.51∶1）。在17℃～33℃温度下,提供蜂蜜液时,黄腹潜蝇茧蜂雌蜂和雄峰的寿命随着温度的升高而缩短,雌蜂的寿命明显长于雄峰的寿命,分别从17℃时81天和47天降到33℃时的14天和13天。雌蜂羽化后1～2天即可产卵,在21℃～29℃温度下,产卵高峰期在2～7日龄,平均产卵量随温度变化的方程为=-0.057x^{2+2.728x-20.601（r2=0.934）。而且成蜂取食能够致死寄主。另外,本文对雌蜂的寄主搜索、产卵和寄主取食行为做了详细描述。}     

非嗜食植物次生化合物与生态措施对美洲斑潜蝇种群控制作用的评价

应用种群动态控制的状态空间分析法,通过生命表参数模拟美洲斑潜蝇种群数量动态,通过输入不同的控制措施(施用非嗜食植物次生化合物即马缨丹乙醇提取物、施用机油乳剂和释放美洲斑潜蝇寄生性天敌)对美洲斑潜蝇种群动态控制的作用,研究这些控制措施的组合对美洲斑潜蝇种群动态的控制,模拟结果表明,在美洲斑潜蝇成虫产卵高峰期施用马缨丹乙醇提取物(1g·100ml^-1和机油乳剂(300X),在幼虫高峰期释放寄生蜂(2000头·100m^-2),可以达到控制美洲斑潜蝇种群增长的效果,起到保护菜豆免害的作用。     

南美斑潜蝇寄主选择性与植物营养物质及叶绿素含量的关系

采用非自由选择法,在室内研究了南美斑潜蝇寄主选择性及其与植物叶片营养物质和叶绿素含量的关系.结果表明,南美斑潜蝇成虫对不同供试植物的选择性存在显著差异,选择性最强的为菜豆、茼蒿和西葫芦,最差的为番茄和甘蓝.相关分析表明,南美斑潜蝇成虫寄主选择性与叶片可溶性糖含量存在显著的正相关关系(R＝0.5014,P=0.0174,F＝6.717),而与叶片可溶性蛋白和叶绿素含量相关关系不显著.     

六种植物叶片中葫芦素B对美洲斑潜蝇寄主选择性的影响

在网室条件下 ,测定了美洲斑潜蝇对豇豆、苦瓜、黄瓜、白瓜、节瓜和丝瓜的寄主选择性。结果表明 ,美洲斑潜蝇在 6种不同植物叶片上的幼虫数、虫道数和为害程度具有明显的差异。从幼虫数和为害程度综合分析 ,美洲斑潜蝇在豇豆和丝瓜上的幼虫数、为害程度最高 ,分别是 0 .183头 / cm2 ,13.4 7%和 0 .0 99头 / cm2 ,2 3.4 2 % ,表明该虫对豇豆和丝瓜的选择性最强。在苦瓜上没有美洲斑潜蝇的幼虫寄生及取食虫道。该虫对其它 3种植物的选择性依次为节瓜、白瓜和黄瓜。在此基础上 ,进一步研究了不同植物叶片甲醇提取物中葫芦素 B的含量与美洲斑潜蝇寄主选择性的关系。经高效液相色谱 (HPL C)测定 ,苦瓜中的葫芦素 B含量最高 (2 3.8μg/ ml) ,其次是黄瓜 (9.6 μg/ ml)、白瓜 (4 .3μg/ ml)、豇豆 (2 .7μg/ ml)和节瓜 (2 .5 μg/ m l) ,丝瓜中含量最少 ,仅为1.3μg/ ml。分析结果证实不同植物叶中的葫芦素 B含量与其幼虫数呈负相关 (r1 =- 0 .82 0 6 ,r0 .0 5=0 .811) ;将不同植物叶中的葫芦素 B含量和美洲斑潜蝇的为害程度分别转换成对数后进行相关性分析 ,二者之间的相关性呈极显著的负相关(r2 =- 0 .980 4 ,r0 .0 1 =0 .917)。说明随着寄主植物叶片中葫芦素 B含量的增加 ,美洲斑潜蝇的幼虫数及为害程度明显     

冷藏对美洲斑潜蝇蛹期发育和生存的影响

【目的】美洲斑潜蝇Liriomyza sativae Blanchard自20世纪90年代入侵我国后已经成为蔬菜和观赏植物的重要害虫。然而,近些年该昆虫已经逐渐成为研究植物和昆虫、昆虫抗寒性和寄主适应性等热点课题的模式种类。因此,为了实验室条件下更好保藏该虫的种群,本文研究了冷藏(世代发育起点温度8℃)对该斑潜蝇蛹发育和生存的影响。【方法】以化蛹后第3天的蛹为实验对象,8℃低温冷藏,并以冷藏时间(0、7、14、21、28和35 d)为参试因子研究了冷藏时间对美洲斑潜蝇蛹羽化率的影响;化蛹后每24 h解剖观察一次蛹并对蛹期发育阶段进行划分;根据划分的蛹期阶段,对处理中未羽化的蛹进行解剖比对,得到对低温最敏感的蛹期。【结果】随着冷藏时间的增长,美洲斑潜蝇的蛹羽化率逐渐降低。超过14 d后,羽化率明显下降。冷藏至35 d时羽化率为零。解剖正常发育的美洲斑潜蝇的蛹,将蛹期分为预蛹期、隐头蛹期、显头蛹初期、半透明眼期、浅黄色到琥珀色眼期、红褐色眼期、鬃毛蛹期。不同冷藏时间条件下,未羽化的蛹死亡时间主要为鬃毛蛹期,且鬃毛蛹期死亡的蛹的数量与贮藏时间呈正比例关系。【结论】在室内冷藏美洲斑潜蝇时,3日龄蛹8℃贮藏少于14 d为宜;鬃毛蛹期(10~11日龄蛹)对低温比较敏感,冷藏过程中,应避免鬃毛蛹期的蛹。     

普通丝瓜叶片成分和物理结构对黄足黑守瓜取食和定位的影响

黄足黑守瓜是普通丝瓜生长过程中危害叶片的主要害虫.本文对普通丝瓜不同部位叶片挥发性成分、营养成分和物理结构对黄足黑守瓜取食和定位的影响进行了系统研究.本实验采用顶空固相微萃取-气相色谱-质谱法分析了普通丝瓜不同部位叶片挥发性成分,研究结果表明,嫩叶主要挥发性成分有(Z)-3-己烯-1-醇(27.65%)和植醇(45.77%),成熟叶挥发性成分主要有(Z)-3-己烯-1-醇(49.34%),老叶挥发性成分主要有植醇(63.25%),且挥发性成分对黄足黑守瓜远距离定位起到了引导作用.同时,本研究还采用5点取样法、3,5-二硝基水杨酸法和考马斯亮蓝法分别研究了普通丝瓜不同部位叶片营养成分含量与黄足黑守瓜取食之间的关系,实验结果表明,黄足黑守瓜喜食植物叶片嫩叶部位,喜食部位叶片的总糖与还原糖含量、蛋白质含量都最高,且总糖含量与蛋白质含量比值最高.叶片物理结构调查采用石蜡切片法,发现叶片的物理结构对于黄足黑守瓜取食很少造成影响.通过研究,使我们充分地了解影响黄足黑守瓜取食不同部位叶片的因素,便于今后的育种和栽培过程中加强不利于黄足黑守瓜取食的因素,以达到安全、环保地进行农业生产的目的.     

南亚果实蝇对六种果实的趋性和产卵选择性

南亚果实蝇Bactroceratau(Walker)是危害黄瓜、南瓜、冬瓜、丝瓜和苦瓜等果蔬作物的一种重要检疫性害虫。趋性反应和产卵选择性实验结果表明,该虫对不同的果实切片具有不同的趋性和产卵选择性。在黄瓜、南瓜和丝瓜上,成虫的落虫数量分别占落虫总量的23.68%,19.94%和21.18%,产卵量分别占产卵总量的21.57%,18.93%和22.74%,均高于其它3种果实冬瓜、苦瓜和柑橘上落虫数和产卵量。幼虫在黄瓜、南瓜和丝瓜上取食的数量亦较高,分别占幼虫总量的23.33%,31.44%和21.67%;而在柑橘上仅占幼虫总量的2.22%。成虫和幼虫均对受害与未受害果实的趋性和选择性表现出一定的差异,总体上在受害果实上的虫口数量较多,而在未受害果实上的数量较少。因此,在这6种寄主植物中,南亚果实蝇喜好在黄瓜、南瓜和丝瓜以及受害的果实上获得补充营养或产卵。     

Adult experience modifies attraction of the leafminer parasitoidOpius dissitus (Hymenoptera: Braconidae) to volatile semiochemicals

Oviposition-experienced females of Opius dissitus Muesebeck, a braconid parasitoid of Liriomyza sativaeBlanchard, preferentially landed on leafminer-infested rather than uninfested lima bean (Phaseolus lunatus L.) plants in a flight tunnel assay. Both naive and oviposition-experiencedparasitoids responded strongly to odors of infested lima bean plants in a four-arm olfactometer in comparison with odors of uninfested plants, suggesting that volatile semiochemicals are used in host location. Parasitoids with an oviposition experience on lima bean (lima-experienced) spent significantly more time in the infested odor than naive individuals, however, eggplant-experienced wasps did not spend significantly more time in the infested odor field than naive wasps. When parasitoids reared on leafminers in lima bean were provided a choice between the odor of infested lima bean and the odor of infested eggplant or cotton, naive and lima-experienced wasps preferred infested lima odor. An oviposition experience on the other plant species resulted in a dramatic shift in preference. It was concluded that the experience effect was due, at least in part, to associative learning, as has been reported for other parasitoids. The parasitoids may perceive unconditioned stimuli during host contact and oviposition on an infested leaf and may associate those stimuli with volatile semiochemicals emanating from the leaf or host. Subsequently, the volatiles associated with the presence of hosts are used in directing the search for hosts.     

Effects of hexane extract of Lantana camara leaves on reproductive bioactivities of Dysdercus koenigii Fabricius (Heteroptera: Pyrrhocoreidae)

Effects of hexane extract of Lantana camara leaves were investigated on reproductive bioactivities of Dysdercus koenigii by assessing mating behavior, oviposition behavior and fertility of the adults emerged from treated fifth instar nymphs. Leaves of L. camara were extracted in hexane by ‘cold extraction method’. The fifth instar nymphs were treated with the extract by ‘dry film residual method’ for 24 h and the adults emerged from these nymphs were used for the experiments. The results indicated that treated males showed altered courtship behaviour, lesser number of mounting attempts and took relatively more time to mate than the normal males. The treated females, very often, exhibited mating refusal and non-receptive behaviour towards the courting males. This led to decrease in percent successful mating. Also, the mating in the treated insects frequently got disrupted and terminated prior to insemination. The treatment of the females with the extract resulted in alteration of their oviposition behaviour. Consequently, the treated females laid lesser number of egg batches and total number of eggs in their life span. Although the eggs laid by the treated females were fertile, the percent hatchability was lesser than normal. The results signify that hexane leaf extract of L. camara possesses phytochemicals, which adversely impaired the reproductive bioactivities of D. koenigii. Therefore, some of these compounds individually or synergistically can be employed in integrated pest management of D. koenigii by hampering its reproductive potential.     

Olfactory responses of the leafminer Liriomyza sativae (Dipt., Agromyzidae) to the odours of host and non-host plants

Abstract: Electroantennogram (EAG) responses of male and female leafminer Liriomyza sativae Blanchard to 15 species of host and non-host plant odours were recorded. The most distinct EAG responses of both sexes were obtained in the host plants bean and tomato. EAG responses to other host plants, such as cucumber, celery, chrysanthemum, towel gourd and cotton were reduced. Odours of non-host plants, such as Chinese rose, tobacco and morning glory elicited minimal EAG responses. In a behavioural study, both sexes of L. sativae were more attracted by the odours of host plants than of non-host plants. Thus, olfactory cues are important for host plant location by L. sativae . In addition, the combination of strong EAG and behavioural responses for both males and females to specific plant odours suggests that host plant volatiles can be important as aggregation cues for both sexes.     

Continuous exposure to the deterrents cis‐jasmone and methyl jasmonate does not alter the behavioural responses of Frankliniella occidentalis

Behavioural responses of Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), a generalist, cell sap‐feeding insect species with piercing‐sucking mouthparts, after continuous exposure to two deterrent secondary plant compounds are investigated. We compared in choice assays on bean leaf discs, the settling, feeding, and oviposition preferences of F. occidentalis females that had no experience with the two fatty acid derivatives methyl jasmonate and cis‐jasmone before testing (naïve thrips) vs. females that had been exposed to the deterrent compounds before testing (experienced thrips). The thrips were exposed to the deterrents at low or high concentrations for varied time periods and subsequently tested on bean leaf discs treated with the respective deterrent at either a low or a high concentration. Frankliniella occidentalis females avoided settling on the deterrent‐treated bean leaf discs for an observation period of 6 h, independent of their previous experience. Our results demonstrate that feeding and oviposition deterrence of the jasmonates to the thrips were not altered by continuous exposure of the thrips to the jasmonates. Habituation was not induced, neither by exposure to the low concentration of the deterrents nor by exposure to the high concentration. These results indicate that the risk of habituation to two volatile deterrent compounds after repeated exposure is not evident in F. occidentalis. This makes the two compounds potential candidates to be integrated in pest management strategies.     

Development and Leaf Consumption by Spodoptera cosmioides (Walker) (Lepidoptera: Noctuidae) Reared on Leaves of Agroenergy Crops

Spodoptera cosmioides (Walker) (Lepidoptera: Noctuidae) is a polyphagous pest that threatens more than 24 species of crop plants including those used for biodiesel production such as Ricinus communis (castor bean), Jatropha curcas (Barbados nut), and Aleurites fordii (tung oil tree). The development and leaf consumption by S. cosmioides reared on leaves of these three species were studied under controlled laboratory conditions. The egg-to-adult development time of S. cosmioides was shortest when reared on castor bean leaves and longest when reared on tung oil tree leaves. Larvae reared on castor bean and Barbados nut leaves had seven instars, whereas those reared on tung oil tree leaves had eight. Females originating from larvae reared on castor bean and Barbados nut leaves showed greater fecundity than did females originating from larvae reared on tung oil tree leaves. Insects fed on castor bean leaves had shorter life spans than those fed on tung oil tree and Barbados nut leaves although the oviposition period did not differ significantly. The intrinsic and finite rates of increase were highest for females reared on castor bean leaves. Total leaf consumption was highest for larvae reared on tung oil tree leaves and lowest for those reared on Barbados nut leaves. We conclude that castor bean is a more appropriate host plant for the development of S. cosmioides than are Barbados nut and tung oil tree.     

Experience with methyl salicylate affects behavioural responses of a predatory mite to blends of herbivore-induced plant volatiles

Many natural enemies of herbivorous arthropods use herbivore‐induced plant volatiles to locate their prey. These foraging cues consist of mixtures of compounds that show a considerable variation within and among plant–herbivore combinations, a situation that favours a flexible approach in the foraging behaviour of the natural enemies. In this paper, we address the flexibility in behavioural responses of the predatory mite Phytoseiulus persimilis Athias‐Henriot (Acari: Phytoseiidae) to herbivore‐induced plant volatiles. In particular, we investigated the effect of experience with one component of a herbivore‐induced volatile blend: methyl salicylate (MeSA). We compared the responses of three groups of predatory mites: (1) those reared from egg to adult on Tetranychus urticae Koch (Acari: Tetranychidae) on lima bean plants (Phaseolus lunatus L. that produces MeSA), (2) those reared on T. urticae on cucumber (Cucumus sativus L. that does not produce MeSA), and (3) those reared on T. urticae on cucumber in the presence of synthetic MeSA. Exposure to MeSA during the rearing period (groups 1 and 3) resulted in an attraction to the single compound MeSA in a Y‐tube olfactometer. Moreover, exposure to MeSA affected the choice of predatory mites between two volatile blends that were similar, except for the presence of MeSA. Predators reared on lima bean plants preferred the volatile blend from T. urticae‐induced lima bean (including MeSA) to the volatile blend from jasmonic‐acid induced lima bean (lacking MeSA), but predators reared on cucumber preferred the volatile blend from the latter. Predatory mites reared on cucumber in the presence of synthetic MeSA did not discriminate between these two blends. Exposure to MeSA for 3 days in the adult phase, after rearing on cucumber, also resulted in attraction to the single compound MeSA. We conclude that a minor difference in the composition of the volatile blend to which a predatory mite is exposed can explain its preferences between two odour sources.     

The interaction between host and host plant influences the oviposition and performance of a generalist ectoparasitoid

The successful development of parasitoids of herbivores depends on the quality of their host, which is often affected by the host plant. Therefore, a parasitoid’s oviposition decisions will directly depend on the host, but also on plant quality. Here, we investigated the direct effects of host species and the indirect effects of the host’s food plant on the oviposition decisions and performance of the gregarious ectoparasitoid Euplectrus platyhypenae Howard (Hymenoptera: Eulophidae). With a series of no‐choice experiments, we determined the oviposition and performance of the parasitoid on: (1) two caterpillar species, fall armyworm, Spodoptera frugiperda JE Smith (Lepidoptera: Noctuidae), and velvet armyworm, Spodoptera latifascia Walker, reared on maize (Zea mays L., Poaceae), (2) the same caterpillars reared on maize, bean (Phaseolus vulgaris L., Fabaceae), or squash (Cucurbita pepo L., Cucurbitaceae) leaves, and (3) S. latifascia caterpillars reared on leaves of wild and cultivated lima bean, Phaseolus lunatus L. All these insects and plants originate from Mesoamerica where they have coexisted for thousands of years in the traditional agricultural system known as Milpa in which maize, beans, and squash are planted together. We found that the preferred and best combination of host and host plant for parasitoid performance was S. frugiperda on maize. Parasitoids laid larger clutches, had higher survival, and more females and larger adults emerged from S. frugiperda reared on maize. However, when both caterpillar species were reared on squash, S. latifascia was the better host. Contrary to the literature, S. frugiperda was not able to develop on bean plants. Results from the lima bean experiment showed that parasitoid performance was best when S. latifascia was reared on leaves of cultivated compared to wild lima bean. These findings are discussed in the context of mixed cropping in which the ability of generalist parasitoids to switch among hosts and host plant species could be advantageous for pest management.     

Response of predatory mites with different rearing histories to volatiles of uninfested plants

The behavioural response of the predatory mite Phytoseiulus persimilis to volatiles from several host plants of its prey, spider mites in the genus Tetranychus, was investigated in a Y-tube olfactometer. A positive response to volatiles from tomato leaves and Lima bean leaves was recorded, whereas no response was observed to volatiles from cucumber leaves, or leaves of Solanum luteum and Solanum dulcamara.Different results were obtained for predators that differed in rearing history. Predators that were reared on spider mites (Tetranychus urticae) on Lima bean leaves did respond to volatiles from Lima bean leaves, while predators that had been reared on the same spider mite species but with cucumber as host plant did not respond to Lima bean leaf volatiles. This effect is compared with the effect of rearing history on the response of P. persimilis to volatile allelochemicals of prey-infested plant leaves.