异色瓢虫对与本土蚜虫共存的外来扶桑绵粉蚧的搜寻和捕食行为

【目的】外来入侵物种作为猎物可能影响本土广谱捕食者的搜寻和捕食行为。本研究旨在揭示异色瓢虫Harmonia axyridis对与本土豌豆修尾蚜Megoura japonica混合发生的外来入侵扶桑绵粉蚧Phenacoccus solenopsis的搜寻和捕食行为。【方法】试验前对异色瓢虫设两个饲喂猎物种类处理：用扶桑绵粉蚧连续饲养3代以上(前期饲喂粉蚧的瓢虫)和用豌豆修尾蚜连续饲养3代以上(前期饲喂蚜虫的瓢虫)。在盆栽蚕豆Vicia faba苗上随机选一片叶接扶桑绵粉蚧3龄若虫和3或4日龄豌豆修尾蚜若蚜,在总猎物数量20-30头(具体数量随机确定)范围内随机组配两种猎物数量使粉蚧占比从5.6%至83.3%不等,待猎物在叶片上稳定后接入1头饥饿24 h的异色瓢虫4龄幼虫,连续观察2 h,统计异色瓢虫首次捕食是否选择粉蚧、捕食的粉蚧数量占总捕食猎物数量的比例、搜索用时占总搜捕用时的比例以及处理粉蚧用时占总搜捕用时的比例;以扶桑绵粉蚧在猎物斑块中的比例和饲喂猎物种类处理为自变量因素,用回归模型拟合其对异色瓢虫搜寻和捕食行为等观测变量的影响。【结果】异色瓢虫4龄幼虫首次捕食选择粉蚧概率随粉蚧比例增大而增大,粉蚧比例每增大10%,首次捕食粉蚧概率增大77.2%,而且此概率不受此前饲喂猎物种类的影响。捕食的粉蚧数量占比与粉蚧比例的关系受饲喂猎物种类的影响：粉蚧比例每增加10%,前期饲喂粉蚧的瓢虫捕食的粉蚧数量占比增大137%,而前期饲喂蚜虫的瓢虫捕食的粉蚧数量占比增大60%。异色瓢虫搜索用时比例受粉蚧比例的影响,但不受饲喂猎物种类的影响：粉蚧比例每增加10%,搜索用时比例增大13%;前期饲喂粉蚧的瓢虫搜索用时比例略低于前期饲喂蚜虫的瓢虫(降低7%)。异色瓢虫处理粉蚧用时比例受粉蚧比例的影响,但不受饲喂猎物种类的影响：粉蚧比例每增加10%,处理粉蚧用时比例增大41%。【结论】本研究结果说明在遭遇外来入侵扶桑绵粉蚧与本土蚜虫共存的猎物斑块时,异色瓢虫对粉蚧的捕食选择依赖于其相对比例,依赖程度因此前取食粉蚧而增强。     

吡虫啉对异色瓢虫种群控害功能的影响

【目的】杀虫剂对天敌的非致死效应是杀虫剂安全性评估的重要内容。【方法】本研究以吡虫啉亚致死浓度处理的大豆蚜Aphis glycines饲喂异色瓢虫Harmonia axyridis,测定了异色瓢虫的发育历期、存活率、蛹重和捕食功能反应。【结果】异色瓢虫G0代不论从哪个龄期开始饲喂毒蚜,LC25(W)处理各龄期其发育均显著延长,且未成熟期(1龄至成虫)显著延长,蛹重和存活率显著降低;异色瓢虫G0代从1龄、3龄和4龄开始饲喂毒蚜,显著延长G1代的3龄龄期,显著缩短G1代的4龄龄期;G0代从4龄开始饲喂毒蚜,显著延长G1代1-3龄的发育历期;G0代不论从哪个龄期开始饲喂毒蚜,G1代蛹重都显著降低,G1代幼虫存活率无显著的变化;异色瓢虫对LC25处理的2龄、3龄和4龄幼虫的最大捕食量显著降低,其余组无显著变化。【结论】吡虫啉亚致死浓度对异色瓢虫G0代和G1代的生长发育均产生影响,且影响异色瓢虫的捕食能力,从而影响异色瓢虫种群的控害功能,这种杀虫剂对非靶标天敌昆虫的非致死效应需要在杀虫剂的安全性评估中予以考虑。     

温度和光周期对两种瓢虫捕食习性和发育的影响（英文）

【目的】在农业上,气候变化影响作物产量、蚜虫动态以及捕食性瓢虫对蚜虫的调节作用。一些瓢虫为广布种,而另一些瓢虫种类却只在特定地理范围内分布,而有关气候因子如何影响瓢虫分布了解甚少。【方法】评价不同温度(15℃,20℃,25℃,30℃和35℃)和光周期(8L∶16D,12L∶12D和16L∶8D)对两种瓢虫[七星瓢虫Coccinella septempunctata(Linnaeus)(一种广布种)和狭臀瓢虫Coccinella transversalis Fabricius(一种东方/南亚瓢虫)]幼虫取食和利用豌豆蚜Acyrthosiphon pisum(Harris)的影响。【结果】尽管两种瓢虫的捕食作用和发育速率均在25℃时最高,但是随着日长的增加(即光周期从8L∶16D增加到16L∶8D)捕食作用进一步增强。与狭臀瓢虫相比,在所有温度和光周期下,七星瓢虫幼虫的取食量更高,生长和发育速率更快,其新羽化的成虫体重更重。非线性回归模型显示,七星瓢虫和狭臀瓢虫的最低发育温度分别为11℃和10.5℃左右,最高发育温度分别为41℃和43℃左右。狭臀瓢虫的幼虫捕食和发育速率对气候因子的依赖性强于七星瓢虫。【结论】本研究表明,广布种瓢虫对气候因子的敏感性比土著种瓢虫弱,因而可以广泛分布于不同的地理区域。因此,与土著种瓢虫相比,广布种瓢虫更适于作为生防因子。     

捕食性瓢虫的体型大小影响其偏好捕食防御性强的猎物吗?（英文）

【目的】尽管瓢虫表现出种间和种内特异性体型大小的变异,但是瓢虫体型大小的变异是否会改变其选择捕食防御性强(即表现出各种防御反应,包括积极躲避捕食、挣脱捕食者或频繁利用防御性化学物质)的猎物,这一问题尚不清楚。本研究中,我们假设不论体型大小,捕食性瓢虫七星瓢虫Coccinella septempunctata(L.)和六斑月瓢虫Menochilus sexmaculatus(Fab.)都将增加其对猎物萝卜蚜Lipaphis erysimi(Kaltenbach)的捕食,只要猎物处于防御性强的龄期,原因是处于防御性强的龄期的猎物体型大且更有活力。【方法】我们将萝卜蚜4龄若虫期作为防御性强的龄期,将2龄若虫期作为防御性弱的龄期,评价七星瓢虫和六斑月瓢虫这两种瓢虫的大型和小型变异体对萝卜蚜的偏好性。【结果】结果表明,六斑月瓢虫的大型和小型雌性变异体更多地捕食防御性弱的萝卜蚜,而七星瓢虫的大型和小型雌性变异体分别对防御性强和防御性弱的萝卜蚜捕食较多。在混合饲料上,七星瓢虫雌性变异体对两类蚜虫的捕食百分比相似,而六斑月瓢虫变异体对防御性弱的萝卜蚜的捕食百分比较高。尽管随着七星瓢虫雌虫体型的增大而对两类猎物的捕食增多,但随着六斑月瓢虫雌虫体型的增大,只对防御性强的蚜虫的捕食量增加。【结论】本研究结果与我们的假设相反,并证明了:(1)小型瓢虫更多地只是捕食防御性弱的猎物,而大型瓢虫选择性地捕食防御性强的猎物;(2)在瓢虫种内和种间,随着捕食者体型的增大,对防御性强的猎物的偏好性增加。可将这些结果用于瓢虫的室内大规模饲养,以提高对萝卜蚜的生物防治。     

五个不同抗病品种小麦对麦长管蚜生长发育的影响

【目的】麦长管蚜Sitobion avenae (Fabricius)是我国麦区常发性的一种害虫,其寄主范围广、繁殖力强,适应机制多样,每年都对我国的小麦产量造成重大损失。【方法】为选育优良抗性品种小麦,比较不同品种小麦对麦长管蚜生长发育的影响,本实验在室内选取了5种抗蚜性未知的不同小麦品种,观察并统计麦长管蚜在不同品种小麦上的发育历期及成蚜体重和繁殖力。【结果】不同品种小麦对麦长管蚜若蚜的生长发育影响不同,其中,用绵阳31号饲养的麦长管蚜若蚜平均发育历期最长为180.86 h,用棉农4号饲养的若蚜平均发育历期最短172.92h,且差异显著。川麦55号上的麦长管蚜的成虫平均发育历期最高为20.93 d,棉麦1403上的麦长管蚜的成虫平均发育历期最低为15.57 d,差异显著。棉农4号上的麦长管蚜成蚜平均体重最大为0.70 mg,荣麦4号上的成蚜平均体重最小为0.50 mg,其余3个处理间差异不显著。川麦55号上的麦长管蚜的平均产蚜量最高为23.1只,显著高于其他4个处理,而其余4个品种小麦上的麦长管蚜繁殖力差异不显著。【结论】麦长管蚜取食棉农4号后缩短了其若蚜的发育历期,其种群增长速率可能加快从而加重对小麦的危害;而取食绵阳31号的若蚜发育历期延长,种群增长延缓,为害减弱。就繁殖力和成虫发育历期来说,麦长管蚜在川麦55的适合度更高,为害更重。     

七星瓢虫对两种麦蚜控制作用的模拟研究

应用二次回归旋转组合设计方法研究了七星瓢虫成虫、幼虫与两种麦蚜共存系统中瓢虫对麦长管蚜和禾谷缢管蚜的捕食量模型.结果表明七星瓢虫对两种麦蚜的捕食量随着瓢虫密度的增加而减少,随着该种麦蚜密度的增加而增加,且七星瓢虫无选择性.七星瓢虫不同个体间的干扰作用对其捕食麦长管蚜数量有显著影响,两种麦蚜数交互作用对七星瓢虫捕食禾谷缢管蚜数量影响显著.该模型可用来预测田间蚜虫的变化,指导麦田蚜虫防治.     

亚致死剂量杀虫剂对两种蚜虫翅型、发育和生殖的影响

【目的】研究亚致死剂量杀虫剂对桃蚜Myzuspersicae(Sulzer)和萝卜蚜Lipaphiserysimi(Kaltenbach)翅型、发育和生殖的影响。【方法】采用叶片浸渍法测定了7种杀虫剂对两种蚜虫的毒力,并计算了实验所需的亚致死浓度LC10;采用微虫笼法测定了7种杀虫剂对桃蚜和萝卜蚜翅型分化、发育和生殖的影响。【结果】在20℃下,烯啶虫胺延长了桃蚜的发育历期;噻虫啉显著增加了桃蚜的产仔数量。在25℃,噻虫啉显著降低萝卜蚜有翅蚜比例;噻虫啉、吡虫啉、阿维菌素和烯啶虫胺延长了萝卜蚜发育历期;噻虫啉、阿维菌素、烯啶虫胺、啶虫脒和噻虫嗪显著降低了萝卜蚜产仔数量。【结论】亚致死剂量的杀虫剂对桃蚜和萝卜蚜的发育历期及产仔数量均有影响,但仅对萝卜蚜的翅型比例产生影响,对桃蚜的翅型分化比例无显著影响。     

播期对大豆蚜及其天敌种群动态的影响

【目的】研究大豆播期对大豆蚜Aphis glycines Matsumura及其天敌的影响。【方法】试验在2012年、2013年进行,设置了3个大豆播期处理。每周调查播期处理田大豆蚜种群及天敌种类和数量,分析大豆蚜种群数量、种群增长率的时序动态、大豆蚜和天敌的关联度。【结果】不同播期条件下大豆蚜有翅蚜及无翅蚜的种群动态趋势基本一致,有翅蚜蚜量高峰期要早于无翅蚜1周。处理间的大豆蚜田间始见期与终见期随着播期推后而延迟,大豆蚜在田间扩散和消退的时期也随着大豆播期延后。晚播的两个处理高峰期蚜量多于或等于正常播期处理的蚜量。大豆蚜与天敌关联度随着播期的推后而变高。在调查的7种天敌中大豆蚜与异色瓢虫的关联度最高,草蛉、小花蝽和蚜茧蜂也表现较高的关联度。【结论】播期会显著影响大豆蚜的田间始见期和终见期,随着播期的推迟大豆蚜种群高峰期蚜量以及大豆蚜与天敌的关联度都会提高。     

作物多样性对大豆蚜的控蚜效应

【目的】研究大豆蚜发生为害及大豆与多种作物间邻作种植对大豆蚜的控制作用,为大豆蚜的可持续综合治理提供理论依据。【方法】采用系统调查的方法,研究大豆蚜和天敌田间种群动态;通过田间罩笼、人工接蚜和释放天敌的方法,研究捕食性天敌对大豆蚜种群的控制作用;在佳木斯地区进行大豆与早熟马铃薯间作,牡丹江地区进行黄瓜-大豆-玉米、甜葫芦-大豆-玉米、烟草-大豆-香瓜、甜菜-大豆-玉米等多作物带状穿插种植模式,以单作大豆田为对照,对不同种植模式的大豆田大豆蚜与天敌进行调查,研究作物多样性对大豆蚜的控制作用。【结果】2009年6月中下旬大豆蚜开始侵入大豆田,3~5周后田间有蚜株率达到100%,大豆蚜种群发生高峰期在7月下旬至8月上旬,9月上旬在田间逐渐消失。草蛉、瓢虫和寄生蜂等为蚜虫天敌优势种;按大豆蚜与天敌数量之比700︰1,释放异色瓢虫和叶色草蛉成虫7 d后,蚜虫种群减退率分别为54.78%和78.79%;大豆与早熟马铃薯间作,在大豆蚜种群迅速增长期早熟马铃薯收获(7月20日)后第5天,豆田蚜虫天敌总数是收获前的2.6倍,与同期单作大豆田相比,间作田大豆蚜种群数量降低了51.3%。大豆与甜葫芦、香瓜、烟草和玉米等作物进行多样性间作种植,在大豆蚜田间发生高峰期,单作豆田益害比为1︰65.2,多样性种植区的大豆田益害比为1︰26~1︰42,与单作大豆田相比,间作田大豆蚜种群数量降低40.7%~83.5%。【结论】2009年大豆蚜的种群高峰期为8月3日,田间的天敌优势种类为草蛉、瓢虫和寄生蜂。早熟马铃薯与大豆间作,在大豆蚜种群迅速增长期间收获早熟马铃薯,大量蚜虫天敌转移至间作的大豆田,从而形成对大豆蚜的控制。大豆与其它经济作物间邻作,大豆田天敌昆虫与蚜虫的益害比明显提高,表明利用农田作物多样性能充分发挥自然天敌的生物控害作用。     

高温胁迫六斑月瓢虫对其生物学特性及其捕食作用的影响

【目的】为明确高温胁迫下对六斑月瓢虫Menochilussexmaculates的生物学特性及其捕食作用的影响。【方法】在35℃高温处理不同时长(3、6、9 h)的胁迫下,探究六斑月瓢虫的生长发育、存活、繁殖力和虫态特征的变化规律,同时评估了其对豆蚜Aphis craccivora的捕食功能与寻找效应。【结果】与25℃饲喂相比,高温胁迫下六斑月瓢虫的幼期历期和雌雄虫寿命随着胁迫时长的增加而缩短,且高温胁迫不同程度降低了六斑月瓢虫的产卵量、卵孵化率和幼期存活率,而对六斑月瓢虫4龄幼虫、成虫的体长和虫重无影响。通过研究捕食作用,与常温25℃相比,35℃高温胁迫在一定程度上促进了六斑月瓢虫对蚜虫的捕食效能,其中在高温胁迫9 h后,其捕食能力(a'/Th)和寻找效应(S)均高于3 h和6 h的。【结论】高温对六斑月瓢虫的生物学特性产生负面的影响,而对其捕食活动具有正面的影响。研究结果为六斑月瓢虫的生物防治提供了科学依据,同时为全球气候变暖下天敌昆虫的保护与利用奠定了基础数据。     

The interplay between density- and trait-mediated effects in predator-prey interactions: a case study in aphid wing polymorphism

Natural enemies not only influence prey density but they can also cause the modification of traits in their victims. While such non-lethal effects can be very important for the dynamic and structure of prey populations, little is known about their interaction with the density-mediated effects of natural enemies. We investigated the relationship between predation rate, prey density and trait modification in two aphid-aphid predator interactions. Pea aphids (Acyrthosiphon pisum, Harris) have been shown to produce winged dispersal morphs in response to the presence of ladybirds or parasitoid natural enemies. This trait modification influences the ability of aphids to disperse and to colonise new habitats, and hence has a bearing on the population dynamics of the prey. In two experiments we examined wing induction in pea aphids as a function of the rate of predation when hoverfly larvae (Episyrphus balteatus) and lacewing larvae (Chrysoperla carnea) were allowed to forage in pea aphid colonies. Both hoverfly and lacewing larvae caused a significant increase in the percentage of winged morphs among offspring compared to control treatments, emphasising that wing induction in the presence of natural enemies is a general response in pea aphids. The percentage of winged offspring was, however, dependent on the rate of predation, with a small effect of predation on aphid wing induction at very high and very low predation rates, and a strong response of aphids at medium predation rates. Aphid wing induction was influenced by the interplay between predation rate and the resultant prey density. Our results suggests that density-mediated and trait-mediated effects of natural enemies are closely connected to each other and jointly determine the effect of natural enemies on prey population dynamics.     

Potential for intraguild predation and competition among predatory Coccinellidae and Chrysopidae

In a laboratory study two coccinellid species, Coleomegilla maculata (DeGeer) and Harmonia axyridis Pallas, completed preimaginal development on lacewing eggs, Chrysoperla carnea Stephens or pea aphids, Acyrthosiphon pisum (Harris) in similar times. Preimaginal survival on C. carnea eggs was similar to survival on A. pisum for all stages of C. maculata and H. axyridis. Coccinellid adults that developed on C. carnea eggs were smaller than adults reared on A. pisum. Coccinella septempunctata L. did not complete preimaginal development on C. carnea eggs. Chrysoperla carnea preimaginal developmental time was approximately 20 days when fed either C. maculata eggs or A. pisum. Chrysoperla carnea fed C. maculata eggs developed into smaller adults, compared to adults reared as larvae on A. pisum, Ostrinia nubilalis (Hübner) eggs, or A. pisum alternated daily with O. nubilalis eggs. C. carnea did not complete preimaginal development on H. axyridis eggs. Cannibalism occurred more frequently between C. carnea third instars than between C. maculata fourth instars. When a C. carnea third instar was paired with a C. maculata fourth instar, more C. maculata were preyed upon by C. carnea, regardless of the herbivorous prey density. In the field these two predator species may negatively affect each other and reduce their suppression of pest densities.     

Effect of spatial heterogeneity on the role of Coccinella septempunctata as an intra-guild predator of the aphid pathogen Pandora neoaphidis

The foraging behavior of starved and non-starved adult and larval Coccinella septempunctata on groups of plants in the presence of Pandora neoaphidis-infected Acyrthosiphon pisum, uninfected aphids or a mixture of these two prey types was compared. In general results of these studies confirmed the results of previous work comparing foraging behavior on a smaller spatial scale in Petri dishes. However, behaviors were modified in response to spatial complexity, prey quality, and the host plant. Starved C. septempunctata adults and larvae fed for longer and consumed more aphids than non-starved coccinellids. Both larvae and adults fed on infected aphids and in some cases entirely consumed them. This was thought to be due to the ease of capture of infected (dead) aphids and the feeding stimuli provided by the presence of the host plant and, where there was a choice of prey, uninfected aphids in the environment. Both larvae and adults spent the majority of the time foraging in the upper regions of plants and visited more plants when they were not starved or when they were in the presence of less suitable, infected aphid prey.     

Effect of plant nutrition on aphid size,prey consumption,and life history characteristics of green lacewing

Plant quality can directly and indirectly affect the third trophic level. The predation by all the instars of green lacewing, Chrysoperla carnea （S.） （Neuroptera： Chrysopidae） on the cereal aphids, Rhopalosiphum padi （L.）, and Sitobion avenae （F.） at varying nitrogen fertilizer levels was calculated under laboratory conditions. Wheat plants were grown on four nitrogen fertilizer levels and aphids were fed on these plants and subsequently offered as food to the C. carnea. Aphid densities of 10, 30, and 90 were offered to first, second, and third instar larvae of green lacewing. Increased nitrogen application improved nitrogen contents of the plants and also the body weight of cereal aphids feeding on them. Aphid consumption by green lacewings was reduced with the increase in nitrogen content in the host plants of aphids. Predation of both aphid species by first, second, and third instars larvae of C. carnea was highest on aphids reared on plants with the lowest rate of fertilization, suggesting a compensatory consumption to overcome reduced biomass （lower aphid size）. Total biomass devoured by C. carnea on all nitrogen fertilizer treatments was not statistically different. Additionally, the heavier host prey influenced by the plant nutrition had an effect on the life history characteristics of green lacewings. The larval duration, pupal weight, pupal duration, fecundity, and male and female longevity were significantly affected by the level of nitrogen fertilization to the aphid＇s host plants, except for pupal duration when fed on S. avenae. This study showed that quantity of prey supplied to the larvae affects the prey consumption and thereafter the life history characteristics of green lacewings.     

The use of honeydew in foraging for aphids by larvae of the ladybird beetle, Coccinella septempunctata L. (Coleoptera: Coccinellidae)

Abstract.  1. To clarify the use of honeydew in foraging for aphids by larvae of the ladybird beetle, Coccinella septempunctata L., searching behaviour of ladybird larvae for Aphis craccivora Koch and Acyrthosiphon pisum Harris and the abundance of honeydew under aphid colonies were examined in laboratory experiments.
2. More larvae responded by climbing the plants with aphids than responded to plants without aphids. When the plants were replaced with sticks, in order to exclude visual and olfactory cues from plants and aphids, more larvae of C. septempunctata climbed sticks above the area that contained honeydew than climbed sticks above the area that did not contain honeydew. Then, ladybird larvae use honeydew as a contact kairomone when foraging for aphids.
3.  Aphis craccivora deposited a larger number of honeydew droplets beneath the plants than did similar numbers of A. pisum. Thus, C. septempunctata larvae licked more frequently the honeydew of A. craccivora than that of A. pisum and spent longer searching on the area containing honeydew of A. craccivora than that of A. pisum . Consequently, a larger number of larvae climbed a stick above honeydew of A. craccivora than that of A. pisum.
4. It may be also considered that C. septempunctata larvae can distinguish honeydew of the two aphid species and respond more strongly to A. craccivora than A. pisum.     

Using food for different purposes: female responses to prey in the predator Coccinella septempunctata L. (Coleoptera: Coccinellidae)

Abstract.  1. Although predatory insects often feed on diverse prey, their reproductive activity may be linked most strongly to a more restricted range of prey. The propensity of adult females of the ladybird beetle, Coccinella septempunctata L., to attack two natural prey species, pea aphids [ Acyrthosiphon pisum (Harris)] and alfalfa weevil larvae [ Hypera postica (Gyllenhal)], was compared, and the degree to which ladybird egg production depends on consumption of aphids vs. weevils was assessed.
2. Coccinella septempunctata females more readily attacked aphids than weevil larvae. This was true regardless of whether females had fed previously on aphids or on weevil larvae.
3. When females were provided with few to many aphids daily, or few aphids plus an excess number of weevil larvae, their rates of egg production depended primarily on the number of aphids consumed.
4. Addition of weevil larvae to diets of limited numbers of aphids increased egg production, but only modestly. Thus, consumption of weevil larvae may have served mostly for self-maintenance, thereby enabling females to use for egg production more of the nutrients and energy obtained from limited consumption of aphids.
5. The females' linkage of egg production primarily to aphid rather than weevil consumption may be adaptive, as their offspring are much less able as larvae to survive and mature on a diet of weevils rather than aphids.     

The importance of honeydew as food for larvae of Chrysoperla carnea in the presence of aphids

Larvae of the common green lacewing Chrysoperla carnea are predacious and feed on a wide range of small, soft‐bodied arthropods. In addition to their feeding on prey arthropods to cover their nutritional requirements for growth and development, the consumption of non‐prey foods such as honeydew has been reported. It is commonly believed that these food supplements are primarily exploited by the larvae when prey is scarce or of low nutritional quality. Here, we assess whether C. carnea larvae also use honeydew when high‐quality aphid prey are readily available. In a choice experiment, the feeding behaviour of C. carnea larvae was observed in the presence of both aphids and honeydew. The larvae were starved, aphid‐fed, or honeydew‐fed prior to the experiment. The time spent feeding on honeydew compared with feeding on aphids was highest for starved larvae and lowest for honeydew‐fed larvae. Among the three treatments, the aphid‐fed larvae spent the most time resting and the least time searching. In an additional experiment food intake was assessed in terms of weight change when larvae were provided with an ad libitum supply of either aphids or honeydew. Larvae yielded a significant lower relative weight increase on honeydew compared with aphids. The reduced weight increase on honeydew was compensated when larvae were subsequently provided with aphids, but not when honeydew was provided again. This study showed that (i) prior honeydew feeding reduces overall aphid consumption, and (ii) larvae do consume honeydew even after they have been given ad libitum access to aphids. The fact that larvae of C. carnea still use honeydew as a food source in the presence of suitable prey underlines the importance of carbohydrates as foods.     

Ontogenetic change of prey preference in the generalist predator Zelus renardii and its influence on predator–predator interactions

1. Two field experiments were conducted to test the hypothesis that the intensity of predation by a generalist predator on two species of prey changes with the developmental stage of the predator. The generalist predator studied was Zelus renardii Kolenati (Hemiptera: Reduviidae) and the prey were the lacewing larva, Chrysoperla carnea Stephens, and the cotton aphid, Aphis gossypii Glover.
2. Zelus renardii and lacewings feed on aphids, thereby acting as potential competitors. In addition, Z. renardii feeds on lacewings. Thus, Z. renardii is an intraguild predator of lacewings.
3. Zelus renardii exhibited changes in prey preferences across developmental stages. The older stages of Z. renardii exerted greater mortality on lacewings and fed on larger lacewing larvae than did the younger stages.
4. Lacewings suppressed aphid population growth strongly. In contrast, none of the stages of Z. renardii was an effective control agent of the cotton aphid.
5. The addition of Z. renardii frequently disrupted the effective control of aphids generated by lacewings. In one of the two replicates of the experiment, the disruption increased with the developmental stage of Z. renardii , paralleling the increase in lacewing mortality.
6. Although the developmental stage of Z. renardii can influence the prevalence of intraguild predation and the intensity of the disruption of the aphid biological control, these experiments have demonstrated that even the youngest instars of Z. renardii can cause substantial lacewing mortality and release aphid populations from regulation.     

Selection of aphid prey by a generalist predator: do prey chemical defences matter?

1. For predators, prey selection should maximise nutrition and minimise fitness costs. In the present study, it was investigated whether a generalist predator [Chrysoperla carnea (Stephens) lacewing larvae] rejected harmful, chemically‐defended prey [Brevicoryne brassicae (Linnaeus) aphids] when non‐defended prey [Myzus persicae (Sulzer) aphids] were available. 2. It was tested: (i) whether consuming different prey species affects predator mortality; (ii) whether naïve predators reject chemically‐defended prey while foraging when non‐defended prey are available; (iii) whether the relative abundance of each prey affects the predator's prey choice; and (iv) whether predators learn to avoid consuming chemically‐defended prey after exposure to both prey species. 3. Consumption of B. brassicae yielded greater C. carnea mortality than M. persicae consumption, but naïve C. carnea did not reject B. brassicae in favour of M. persicae during foraging. When presented at unequal abundances, naïve predators generally consumed each aphid species according to their initial relative abundance, although, predation of non‐defended prey was less than expected when defended prey were initially more abundant, indicating a high consumption of B. brassicae impeded M. persicae consumption. With experience, C. carnea maintained predation of both aphid species but consumed more M. persicae than B. brassicae, indicating a change in behaviour. 4. Although prey choice by C. carnea may change with experience of available prey, prey chemical defences do not appear to influence prey choice by naïve predators. This inability to avoid harmful prey could facilitate wider, indirect interactions. Myzus persicae may benefit where high consumption of B. brassicae hinders predators in the short term, and in the long term, increases predator mortality.     

Cannibalism and interspecific predation in two predatory ladybirds in relation to prey abundance in the field

Life tables for two predatory ladybirds,Coccinella septempunctata andHarmonia axyridis, were constructed in two years in which prey abundance differed. The prey aphid,Aphis gossypii, was abundant on its primary host from late May to late June. Females ofH. axyridis andC. septempumctata laid their eggs during the increase and peak in aphid abundance. The oviposition period ofC. septempunctata started before and was shorter than that ofH. axyridis. In both species, intraguild predation and/or cannibalism of the egg and fourth instar stages, but rarely of other developmental stages, were observed. Fourth instar larvae ofH. axyridis had to complete their development when aphids were scarce more frequently than those ofC. septempunctata. The highest frequency of intra- and interspecific predation was of fourth instarH. axyridis larvae. In terms of intraguild predation, the larvae ofH. axyridis preyed on larvae ofC. septempunctata, but the reverse was not observed. Percentage survival from egg to adult inH. axyridis was higher than inC. septempunctata in both years, and least in both species in the year of low aphid abundance. These results suggest that prey abundance influenced the frequency of cannibalism and intraguild predation, which were important in structuring this guild of ladybirds.