Effects of sub-lethal and lethal doses of lambda-cyhalothrin on oviposition experience and host-searching behaviour of a parasitic wasp, Aphidius ervi

In many parasitoid species, the recognition of chemical signals is essential to find specific hosts. This function is often impaired by exposure to insecticides that are usually neurotoxic. The behaviour of the Hymenopterous parasitoid Aphidius ervi (Haliday) (Hymenoptera: Aphidiinae) after surviving low doses of the pyrethroid lambda-cyhalothrin was examined in laboratory conditions. The host aphid was Myzus persicae (Sulzer) (Homoptera: Aphididae) on oilseed rape. Parasitoid females were exposed by contact with dry residues of the active ingredient at a lethal dose, LD20, and a sub-lethal dose, LD0.1. In a four-armed olfactometer, untreated and inexperienced females were attracted by the odour of M. persicae-infested plants and previous oviposition experience increased the duration of the attraction response. The response of inexperienced females decreased after an exposure to LD0.1 but not to LD20. No effect was observed when females had an oviposition experience prior to the olfactometer test. The oviposition activity was significantly decreased in the LD20-treated group but not in the LD0.1-treated one. All effects disappeared within 24h. Our work shows that orientation and oviposition behaviours may be impaired by low doses of lambda-cyhalothrin, depending on the dose, the parasitoid experience and the type of behaviour.     

Sub-lethal effects of deltamethrin on walking behaviour and response to host kairomone of the egg parasitoid Trissolcus basalis

The lethal doses of the pyrethroid deltamethrin were estimated for the egg parasitoid Trissolcus basalis (Wollaston) (Hymenoptera: Scelionidae), and the sub-lethal effects of an LD25 on female walking behaviour were evaluated. Linear speed of treated parasitoids was reduced compared with that of untreated ones for a period of up to 24 h. The sub-lethal effects of deltamethrin on parasitoid response to patches contaminated by a contact kairomone from its host, Nezara viridula L (Heteroptera: Pentatomidae), was also evaluated. Both treated and untreated parasitoids responded to host-contaminated patches by increasing residence time and decreasing linear speed. However, treated females showed a significantly lower residence time compared with untreated females. Both treated and untreated females showed a similar decrease over time in the proportion of time spent in the host-contaminated patch. Hence, we hypothesise that the sub-lethal effect of deltamethrin on host foraging may decrease T basalis efficacy in controlling N viridula.     

Odour and feeding preference of noctuid moth larvae conditioned to vanillin diet and non-vanillin diet

It is largely accepted that larval experience influence host-plant preference of larvae. In general, larval experience with a host plant induces both an odour and feeding preference for that plant. In a previous study, exposure of three noctuid stem borer species, i.e. Sesamia nonagrioides, Busseola fusca and B. nairobica, to a vanillin-enriched medium induced an olfactory preference for the odours of this medium in the larvae of these species. Here, we checked if the exposure to a vanillin-enriched medium also induced a feeding preference for this diet. Different life stages (i.e. neonate larvae to adults) of the three species were conditioned to an artificial diet enriched with vanillin over two generations. Thereafter, two-choice tests on third-generation larvae were done using a Y-tube olfactometer for odour preferences and diet choice experiments. Larvae of all three-species conditioned to the vanillin diet oriented significantly towards the odour of this diet, whereas the non-conditioned larvae did not. Still, apart for B. fusca, the conditioned larvae did not exhibit a feeding preference for this diet, thus odour preference did not match the feeding choice of the conditioned larvae. The implication of this result on insect’s adaptability to a new host plant in a changing environment is discussed.     

多杀菌素对菜蛾绒茧蜂的致死和亚致死效应

以对多杀菌素高抗的小菜蛾纯合子品系作寄主饲养菜蛾绒茧蜂,用多杀菌素田间推荐使用浓度(25 mg/L)分别处理处于卵期、幼虫期和蛹期的绒茧蜂,其中卵期和幼虫期通过处理寄主幼虫间接处理,并测定该药剂对成虫的毒力,系统观察该杀虫剂对绒茧蜂各虫期的致死和亚致死作用。与对照相比,绒茧蜂卵期或幼虫期其寄主受药后,可导致蜂幼虫死于寄主体内或啮出寄主的过程中,使结茧化蛹率下降43% ~56%,成虫羽化率下降19% ~33%,成蜂雌性比下降11% ~25%,而成虫大小、寿命和寄生力未受显著影响;在蛹期受药使成虫羽化率下降10%,成蜂寿命缩短,但对成虫寄生力无显著影响;对成虫24 h的LC99为4.31 mg/L。结果表明,多杀菌素可进入寄主作用于其体内的蜂卵和幼虫,或直接作用于蜂蛹和成虫,从而对绒茧蜂各个虫态产生显著的致死和亚致死效应,尤以对成虫高毒。     

斑痣悬茧蜂对受药寄主幼虫的选择性及其后代表现

为探究受到杀虫剂亚致死影响的寄主幼虫对寄生蜂的寄主选择及其子代蜂的影响,以容性寄生蜂斑痣悬茧蜂Meteorus pulchricornis为研究对象,以氯氰菊酯亚致死浓度处理的甜菜夜蛾Spodoptera exigua4龄幼虫为寄主幼虫,进行非选择性和选择性试验。非选择性试验表明,斑痣悬茧蜂成功寄生（完成化蛹）的概率随受药寄主的体重增大而提高,而且受药寄主有效存活的概率亦随其体重增大而提高;与对照寄主相比,寄生蜂对受药寄主的寄生率降低60.2%、子代蜂发育历期显著延长、子代蜂体型（用后足胫节长度表示）显著增大。与来自对照寄主的子代蜂相比,来自受药寄主的子代蜂的寄生能力（用寄生率表示）未受影响,但其后代的结茧率降低10%、发育历期显著缩短、体型显著增大,说明羽化蜂的发育适合度得到了提高。选择性试验结果得出不一致的结论,根据对寄生蜂攻击次数的分析,未发现其在对照与受药寄主之间存在显著偏好;但根据第2次攻击的寄主识别期变量进行的风险分析,受药寄主被寄生风险显著低于对照寄主（低59.7%）,说明寄生蜂偏好攻击对照寄主幼虫。研究结果说明,斑痣悬茧蜂通过偏好体型较大的寄主幼虫,而减轻了受到杀虫剂亚致死效应的间接不良影响。结果表明该寄生蜂具有鉴别出接受亚致死杀虫剂不久的寄主幼虫的能力。     

豌豆潜蝇姬小蜂对美洲斑潜蝇幼虫的产卵寄生和取食寄主行为描述

在实验室条件下,以秒表配合解剖镜的观察方法,比较了豌豆潜蝇姬小蜂Diglyphus isaea对美洲斑潜蝇Liriomyza sativae的产卵寄生和取食寄主的2种寄主处理行为。结果显示：2种处理行为的发生流程存在差异。雌蜂产卵寄生的行为流程为：搜索、刺探、梳理、产卵器插入（产卵）和休息;而雌蜂取食寄主的行为流程为：搜索、刺探、梳理、产卵器插入（不产卵）、取食寄主和休息。雌蜂用于产卵寄生的总处理时间（342.2±33.6s）显著低于用于取食寄主的总处理时间（1327.8±134.2s）;其中2种寄主处理行为中对应的产卵器插入行为时间分别为85.9±7.4s和483.2±43.5s;产卵寄生的雌蜂不取食,而取食寄主的雌蜂的平均单次取食时间为233.8±17.3s。研究结果表明,潜蝇姬小蜂的取食寄主方式属于为非同时发生-致死型。     

两种肿腿蜂对锈色粒肩天牛虫粪及其寄主植物气味的学习行为

经研究,白蜡吉丁肿腿蜂Sclerodermus pupariae Yang et Yao与哈氏肿腿蜂Sclerodermus harmandi (Buysson)均可寄生锈色粒肩天牛Apriona swainsoni(Hope)的低龄幼虫,可用于该害虫的生物防治。为了探讨其学习行为,采用Y-型嗅觉仪、培养皿两种方法,测定了锈色粒肩天牛虫粪及其寄主植物——国槐韧皮部的气味刺激对交配后的白蜡吉丁肿腿蜂和哈氏肿腿蜂的雌蜂嗅觉记忆的影响。结果表明,这两种肿腿蜂在羽化后经过对上述两种气味源48h接触后,有学习经历的雌蜂对两种气味源的选择性比没有学习经历的雌蜂对气味源的选择性相比显著提高。在对气味源的搜寻判断上,有学习经历的雌蜂所用时间显著少于没有学习经历的雌蜂。培养皿试验表明,有学习经历的雌蜂对锈色粒肩天牛虫粪及国槐树枝韧皮部水提物或正丁烷提取物的趋向率要高于没有学习经历的雌蜂,但二者差异不显著。两种寄生蜂的嗅觉记忆具有一定的稳定性和持久性,当其脱离学习环境一定时间后,对气味源仍有较强的趋向性。     

Bt棉对斑痣悬茧蜂寄主选择及其子代发育的影响*

［目的］ 评价转Bt基因棉通过非靶标寄主斜纹夜蛾和甜菜夜蛾幼虫对寄生蜂的影响。［方法］ 分别采用选择性试验和非选择性方法,观察斑痣悬茧蜂对取食Bt棉叶和常规棉叶的斜纹夜蛾和甜菜夜蛾幼虫的产卵选择偏好,并观察子代蜂在不同处理幼虫体内的发育表现。［结果］ 取食Bt棉叶的斜纹夜蛾幼虫体重与取食常规棉叶的没有显著差异,而取食Bt棉叶的甜菜夜蛾幼虫体重显著小于取食常规棉叶。对斜纹夜蛾幼虫的选择性试验表明,斑痣悬茧蜂未表现出对取食Bt棉寄主幼虫的偏好。［结论］ 斑痣悬茧蜂子代的历期、存活以及羽化成蜂的体型大小等发育适应度特征,不受寄主幼虫所取食的食料植物的影响。     

Impact of sub-lethal residues of azinphos-methyl on the pheromone-communication systems of insecticide-susceptible and insecticide-resistant obliquebanded leafrollers Choristoneura rosaceana (Lepidoptera: Tortricidae)

The effects of sub-lethal residues of azinphos-methyl on pheromone production, calling, female attractiveness and the ability of males to locate sources of natural and synthetic pheromone were compared in azinphos-methyl-susceptible (susceptible) and azinphos-methyl-resistant (resistant) obliquebanded leafrollers, Choristoneura rosaceana (Harris). The amount of pheromone in susceptible females was reduced by 29-33% after exposure to azinphos-methyl; this treatment did not affect the pheromone content of resistant females. Azinphos-methyl-treated resistant females contained 39-43% less pheromone than azinphos-methyl-treated susceptible females. Resistant females that were not treated with azinphos-methyl contained 35-56% less pheromone than susceptible females that were not treated with insecticide. The incidence of calling was reduced by 67-100% in azinphos-methyl-treated susceptible females; the incidence of calling by resistant females was not affected by exposure to azinphos-methyl. The incidence of calling by azinphos-methyl-treated susceptible females was 58-100% lower than that of azinphos-methyl-treated resistant females. There was no difference in the incidence of calling between susceptible and resistant females that had not been treated with insecticide. In a flight tunnel, treatment with insecticide reduced the attractiveness of susceptible females by 38%; treatment with insecticide did not affect the attractiveness of resistant females. There was no difference in the proportion of males attracted to susceptible and resistant females that had, or had not been treated with insecticide. In an apple orchard, the attractiveness of susceptible and resistant females treated with azinphos-methyl was reduced by 84 and 12%, respectively. The proportion of males attracted to azinphos-methyl-treated susceptible females was 58% lower than the proportion attracted to azinphos-methyl-treated resistant females, whereas, if females were not treated with insecticide, the proportion attracted to resistant females was 57% lower than the proportion attracted to susceptible females. In a flight tunnel, azinphos-methyl did not affect the ability of susceptible or resistant males to locate a source of pheromone gland extract. Likewise, in an apple orchard, the insecticide treatment had no effect on the ability of susceptible or resistant males to locate a source of synthetic pheromone. In a flight tunnel, there was no difference in the proportion of azinphos-methyl-treated susceptible and resistant males locating a source of pheromone gland extract; however, in the orchard, 39% fewer azinphos-methyl-treated resistant males located a source of synthetic pheromone than azinphos-methyl-treated susceptible males. A similar proportion of susceptible and resistant males that had not been treated with insecticide located a source of pheromone gland extract in the flight tunnel, but in the orchard, the proportion of resistant males not treated with azinphos-methyl that located the source of synthetic pheromone was 32% lower than the proportion of susceptible males not treated with this insecticide. The implications of the differences in the effect of sub-lethal residues of azinphos-methyl on the pheromone communication system of susceptible and resistant moths are discussed in relation to the theory of the development of insecticide resistance, the detection of resistance in feral populations of moths using sex pheromone-baited traps, and the control of moths using sex pheromone-mediated mating disruption.     

合理施用选择性杀虫剂促进瓜绢螟天敌的控害作用

田间小区药效试验表明，乐斯本、氰戊菊酯、抑太保、Bt对葫芦科作物主要害虫瓜绢螟低龄幼虫都有很高的毒杀效果，其中抑太保、Bt效果较为缓慢。室内生测表明，乐斯本对寄生于瓜绢螟卵的赤眼蜂高毒，Bt则无毒。在秋黄瓜作物生长前中期连续施用乐斯本或Bt防治瓜绢螟，施药期间瓜绢螟均可得到较好的控制；但随着季节推移，在施用乐斯本的地块，瓜绢螟卵被寄生率很低，而在使用Bt的地块持续上升，高达70％以上；在停止使用杀虫剂12d后，施用乐斯本的地块瓜绢螟为害严重，而使用Bt的地块虫害被有效控制。结果表明，合理使用选择性农药可对天敌起到显著的保护和促增作用，并使瓜绢螟得到有效控制。     

Residual sprays for the control of the crazy ant Anoplolepis longipes (Jerd.) in the seychelles

Attempts to find suitable quick-acting toxic sprays, for the control of Anoplolepis longipes (Jerd.) in buildings, involved investigations of the toxicity and weathering properties of several insecticide formulations. Their mammalian toxicity was also considered and, particularly for indoor applications, their odour and non-staining properties. Bendiocarb, gamma-HCH and chlorpyrifos were particularly effective, killing ants rapidly after minimal contact with spray deposits, but gamma-HCH and chlorpyrifos weathered better than bendiocarb and were therefore more suitable for outdoor applications.     

稻纵卷叶螟颗粒体病毒亚致死作用对宿主生长、繁殖和生理生化的影响

稻纵卷叶螟颗粒体病毒(CnmeGV)是感染稻纵卷叶螟的专性杆状病毒。明确CnmeGV亚致死作用对稻纵卷叶螟生长发育、繁殖能力和生理生化的影响,为应用CnmeGV防治稻纵卷叶螟提供依据。CnmeGV 1×10⁵ OB/g浓度处理3龄稻纵卷叶螟幼虫10 d后存活幼虫虫体内仍普遍检测到CnmeGV的存在,从而产生亚致死作用。亚致死CnmeGV处理对稻纵卷叶螟的生长发育产生明显影响,主要表现在变态发育的化蛹、羽化和产卵过程,存活个体蛹重减轻了15.95%,羽化率下降了24.81%,产卵量减少41.5%,差异显著。同时雌雄性比从1.11下降到0.82。CnmeGV亚致死处理诱导幼虫能量代谢增强,中肠消化酶中淀粉酶、脂肪酶活性显著提高,而解毒酶中羧酸酯酶活性显著下降,谷胱甘肽转移酶活性显著提高。CnmeGV亚致死作用影响到虫体激素分泌,幼虫体内蜕皮激素、保幼激素水平较对照分别下降了4.59和5.62倍。CnmeGV亚致死处理雌成虫卵黄蛋白含量下降了40.63%,可能是导致产卵量降低的主要因素。     

Reproductive potential of the parasitic wasp Microplitis rufiventris Kok. (Hym.: Braconidae), reared in hosts treated with chitin synthesis inhibitors

Different developmental stages of Microplitis rufiventris Kok. larvae were each exposed to a sublethal dosage (0.4ppm) of Lefenuron [N-{2,5-dichloro-4-(1,1,2,3,3,3-hexafluoropropoxy)-phenylaminocarbonyl}-2, 6-difluorobenzamide] or Lefenuron/Deltanet [O-n-butylO-(2.2-dimethyl-2, 3-dihydrobenzofuran-7-y1)-N, N'-dimethyl-N-N'-thiodicarbamate] by feeding treated artificial diets to parasitized Spodoptera littoralis (Boisd.) larvae to evaluate their effects on the reproductive potential of resulting parasitoids. Lefenuron treatments caused a great reduction in the reproductive ability of either the host insect or its parasitoid. Ovaries of parasitoid females (1 day old) emerged from Lefenuron/Deltanet treatments contained more ova than those from either Lefenuron or controls. Experienced females from Lefenuron/Deltanet treatments deposited significantly more eggs and contained at death more remaining mature oocytes in their calyx and egg-reservoirs. The combination of carbamate insecticide (Deltanet) and chitin-inhibiting growth regulator (Lefenuron) may enhance the reproductive ability of insect parasitoid and may provide a potential means for developing more effective biological control methods against insect pests.     

Reproductive potential of the parasitic wasp Microplitis rufiventris Kok. (Hym.: Braconidae), reared in hosts treated with chitin synthesis inhibitors

Different developmental stages of Microplitis rufiventris Kok. larvae were each exposed to a sublethal dosage (0.4ppm) of Lefenuron [N-{2,5-dichloro-4-(1,1,2,3,3,3-hexafluoropropoxy)-phenylaminocarbonyl}-2, 6-difluorobenzamide] or Lefenuron/Deltanet [O-n-butylO-(2.2-dimethyl-2, 3-dihydrobenzofuran-7-y1)-N, N'-dimethyl-N-N'-thiodicarbamate] by feeding treated artificial diets to parasitized Spodoptera littoralis (Boisd.) larvae to evaluate their effects on the reproductive potential of resulting parasitoids. Lefenuron treatments caused a great reduction in the reproductive ability of either the host insect or its parasitoid. Ovaries of parasitoid females (1 day old) emerged from Lefenuron/Deltanet treatments contained more ova than those from either Lefenuron or controls. Experienced females from Lefenuron/Deltanet treatments deposited significantly more eggs and contained at death more remaining mature oocytes in their calyx and egg-reservoirs. The combination of carbamate insecticide (Deltanet) and chitin-inhibiting growth regulator (Lefenuron) may enhance the reproductive ability of insect parasitoid and may provide a potential means for developing more effective biological control methods against insect pests.     

Response to the insecticide chlorpyrifos by arthropods on maize canopy

We assessed the response of maize canopy arthropods to the insecticide chlorpyrifos. Four 0.3 ha (18 2 180 m) plots were divided into two subplots, a control and a treated area. During tasseling of the plants, the treated area was sprayed twice, with an interval of 3 days. Ten plants were sampled: 1 day before spraying, and 7, 14, 21 and 28 days after spraying. The insecticide had no effect on insect herbivores: a high density of Spodoptera frugiperda larvae was present in the treated plots. A few predator arthropod species were negatively affected by the insecticide, but their numbers or activity increased 2 weeks after the treatment of the plots. A canonical variate analysis showed no pronounced effect of the insecticide on arthropod communities; the largest variations on species abundance were related to sampling occasion. These results can be explained by the combination of the short period of chlorpyrifos residual activity on the plant surface and the great potential for recolonization of the areas by most of the monitored arthropods.     

Integrated Management for Carrot Weevil

The carrot weevil, Listronotus oregonensis (LeConte) (Coleoptera: Curculionidae) is a major pest of carrots in northeastern North America. The females oviposit in the leaf petiole and the developing larvae make tunnels in the carrot roots. Exclusive reliance on chemical control and the poor control obtained, prompted, in the early 1980s, research on the ecology and physiology of the pest and its natural enemies. Carrot weevil females start their oviposition by 147±9DD_7°C but they oviposit only in carrots past the 4 true-leaf-stage. As a result, oviposition is delayed, and damage reduced, in late-sown carrots. Monitoring carrot weevil adults in the spring with either carrot root sections or wooden plate traps enables growers to apply control treatments only if the population density justifies it. Egg parasitoids of the genus Anaphes (Hymenoptera: Mymaridae) are the most important natural enemies and they account, in untreated plots, for up to 80% mortality. Their effectiveness could be improved by managing field borders to establish secondary host species. An IPM programme was developed in the 1980s based on the research results obtained and, through regular monitoring, has achieved a substantial decrease in pesticide use.     

Sub-lethal influences of different insecticides on oviposition preference of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) on cotton in relation to altered plant morphology

We investigated the sub-lethal influences of spinosad, chlorpyriphos, endosulfan, acephate and cypermethrin on the oviposition responses of Helicoverpa armigera (Hübner) to cotton plants, under cage and laboratory conditions. The rank order of toxicity (LC₅₀ values as a per cent) of test insecticides against third instar larvae using the leaf disc method was: spinosad > chlorpyriphos > endosulfan > acephate > cypermethrin. On whole plants, females laid more eggs on acephate LC₅₀-, acephate LC₃₀- and cypermethrin LC₅₀-treated cotton plants than on the control. The chlorpyriphos-treated plants were least preferred for oviposition. When excised cotton leaves from different treatments were used in a multiple-choice test, cypermethrin LC₅₀- and endosulfan LC₃₀-treated leaves received more eggs than the control. The repeated application of sub-lethal concentrations of different insecticides reduced plant height in the case of acephate LC₃₀ and cypermethrin LC₅₀, while plant spread and upper canopy leaf area were reduced in both treatments of acephate and cypermethrin. Reduced plant spread, upper canopy leaf area followed by plant height were found associated with oviposition preference by H. armigera females.     

杀虫剂对韭菜迟眼蕈蚊毒力与药效相关性研究

韭菜迟眼蕈蚊Bradysia odoriphaga 以幼虫蛀食韭菜根茎造成危害,为使毒力测定方法与田间幼虫受药方式具有较高程度的一致性,建立了胃毒触杀联合毒力测定法,利用该方法测定了分属三个类别的4种杀虫剂即毒死蜱、辛硫磷、丙硫克百威、吡虫啉对韭菜迟眼蕈蚊3龄幼虫的毒力,以辛硫磷为标准药剂,毒死蜱、吡虫啉和丙硫克百威的相对毒力倍数分别为10.36、2.61和2.30。田间达到50%防效所需药剂浓度以辛硫磷为最高,毒死蜱、吡虫啉和丙硫克百威对辛硫磷的防效比值分别为9.58、1.88和2.05。胃毒触杀联合毒力法测得的药剂毒力高低排序及相对毒力倍数与田间小区试验结果基本一致,与常规的单一触杀法比较,该法测定结果的重现性好,并且与田间药效试验结果相关性高。同时讨论了不同操作方法对室内毒力测定结果的影响。     

Insecticide susceptibility of surviving Cotesia plutellae (Hym: Braconidae) and Diaeretiella rapae (M'Intosh) (Hym: Aphidiidae) as affected by sublethal insecticide dosages on host insects

The effects of sublethal dosages of insecticides applied to Plutella xylostella L. (Lepidoptera: Yponomeutidae) and Lipaphis erysimi Kaltenbach (Homoptera: Aphidiidae) on the insecticide susceptibility of the surviving endoparasitoids, Cotesia plutellae Kurdjumov (Hymenoptera: Braconidae) and Diaeretiella rapae (M'Intosh) (Hymenoptera: Aphidiidae), were studied in Shangjie, Minhou, China. The susceptibility to methamidophos and the sensitivity of acetylcholinesterase (AChE) to methamidophos and dichlorvos in the adults of host insects were substantially lower than those in the two parasitoids. The host insects were treated with sublethal dosages of methamidophos in P. xylostella and of methamidophos and avermectin in L. erysimi. The cocoon formation in the two parasitoids decreased significantly, from 35.0% (control) to 13.0% (with methamidophos treatment) for C. plutellae; from 20.6% (control) to 9.0% (with methamidophos treatment) and from 24.3% (control) to 16.7% (with avermectin treatment) for D. rapae. The susceptibility to methamidophos of the resultant emerging adults of the two parasitoids was found to be significantly lower than that of the control when the parasitoids were left in contact with the same dosages of methamidophos. The average AChE activity inhibition by methamidophos and dichlorvos in 34-60 adults of the two parasitoids that emerged from the treatments (15.1% and 31.8% respectively for C. plutellae, and 21.1% and 26.9% for D. rapae) was also significantly lower than those of the controls (55.4% and 48.3% respectively for C. plutellae, and 42.9% and 51.7% for D. rapae). The bimolecular rate constant (k(i)) values of AChE to methamidophos and dichlorvos in the adults of parasitoids without the insecticide treatment were 1.78 and 1.56 times as high as those that emerged from the host insects treated with methamidophos for C. plutellae, and 1.91 and 1.66 times as high as those in the case of D. rapae. It is suggested that there is a difference in AChE sensitivity to insecticides between the resultant emerging parasitoids with and without insecticide pretreatment. Furthermore, the introduction of the insecticides to the host insects could be an important factor in the insecticide resistance development of the endoparasitoids. The natural selectivity would favour the parasitoids that had developed an insensitivity to the insecticide(s).     

Plant phylogeny determines host selection and acceptance of the oligophagous leaf beetle Cassida rubiginosa

BACKGROUND

Predicting the host range of biocontrol agents is important for the safe and effective implementation of biocontrol of weeds. In this study, we examined the phylogenetic pattern of host selection and acceptance by the biocontrol beetle, Cassida rubiginosa. The beetle was released in New Zealand for control of Cirsium arvense, its primary host plant, but has potential to attack many Cardueae (thistles and knapweeds) species. We conducted a series of no-choice and choice experiments and modelled the responses of Cassida rubiginosa in relation to phylogenetic distance from Cirsium arvense.

RESULTS

The olfactory recognition (single odour) and preference (two odours) of the beetle showed a significant phylogenetic relationship. These relationships showed a high degree of correlation with 66.9% of the variation in olfactory recognition and 82.8% of the variation in olfactory preference explained by phylogeny. Where the beetle could contact plants, under no-choice conditions there was no phylogenetic pattern to host plant acceptance. However, under choice conditions, phylogenetic distance was a strong predictor of feeding and oviposition preference. These relationships showed a high degree of correlation, with 63.4% of the variation in feeding preference, and 89.0% of the variation in oviposition preference, explained by phylogeny.

CONCLUSIONS

As far as we are aware, this is the first demonstration of an herbivorous insect that exhibits a phylogenetic pattern to olfactory host plant selection. Host plant utilisation by Cassida rubiginosa in New Zealand will be mostly restricted to Cirsium and Carduus species, with minimal potential for impact on other Cardueae weeds. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.