The role of host- and host-plant odours in the attraction of a parasitoid, Epidinocarsis lopezi, to the habitat of its host, the cassava mealybug, Phenacoccus manihoti

In the field, the encyrtid wasp, Epidinocarsis lopezi (DeSantis) can find its host, the cassava mealybug (Phenacoccus manihoti Matile-Ferrero) on cassave plants when the host is scarce. As a step towards understanding the parasitoid's effectiveness we investigated the cues with which it locates its host-habitat. Using a fourarmed olfactometer, we determined the attactivity of various host-and host-plant odours to female E. lopezi which had been previously exposed to infested plants. Attractivity or preference of an odour was determined from the proportion of 50 choices made between the odour and a blank, or between two odours. Female E. lopezi were attracted by mealybug-infested cassava leaves (CML), but not by the odour of cassava mealybugs (CMB) alone or by uninfested plants (ULU). An artificial combination of CMB and ULU was also not attractive. CML was preferred over ULU and CMB + ULU. These results suggest that the attractive element arises from the cassava plant itself in response to CMB infestation. We therefore tested the attractivity of uninfested leaves from partly infested plants, and found that these were indeed attractive. E. lopezi probably uses the odour which is emitted from infested cassava plants to guide it to its host in the field.

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Zusammenfassung Epidinocarsis lopezi ist imstande, seine Wirte auf den Cassavapflanzen zu finden, auch wenn die Wirte nur in geringer Dichte vorkommen. Die Reaktion der Schlupfwespe auf Gerüche der Wirte und der Wirtspflanzen wurde untersucht. Weibchen der Schlupfwespe, die vorher mit Schmierläusen auf Cassavapflanzen zusammengebracht worden waren, wurden individuell in einem vierarmigen Olfaktometer verschiedenen Kombinationen dieser Gerüche ausgesetzt. Die relative Attraktivität jedes Geruchs wurde bestimmt anhand von 50 Entscheiden zwischen dem Geruch und einer Kontrolle oder zwischen zwei Gerüchen. E. lopezi Weibchen wurden von schmierlausinfizierten Blättern angezogen, aber nicht von Cassavaschmierläusen (CMB), oder von uninfizierten Cassavapflanzen (ULU). Die künstliche Mischung von CMN und ULU wurde auch nicht anlockend. CML war relativ mehr attraktiv als ULU und als die Mischung. Die Vermutung liegt vor dass E. lopezi von einem Pflanzenduft angezogen wird, der von mit Schmierläusen infizierten Cassavapflanzen ausgeschieden wird. Die Parasitoide wurden auch von uninfizierte Blättern teilweise infizierter Pflanzen angezogen. Wahrscheinlich wird im Freiland der Geruch infizierter Cassavapflanzen durch E. lopezi zur Auffindung weiterer wirtstragenden Cassavapflanzen gebraucht.

     

Experimental evaluation of the efficiency of Epidinocarsis lopezi, a parasitoid introduced into Africa against the cassava mealybug Phenacoccus manihoti

The capability of Epidinocarsis lopezi (De Santis) (Hymenoptera: Encyrtidae) to control the cassava mealybug (CM) Phenacoccus manihoti Mat.-Ferr. (Homoptera: Pseudococcidae) was investigated in Nigeria using physical and chemical exclusion experiments. In two sleeve cage experiments CM populations, about 2 months after artificial infestation, were 7.0 and 2.3 x lower on artificially infested cassava tips covered with open cages than on tips in closed cages which excluded most parasitoids. On similarly infested but uncovered tips, CM populations were 24.3 and 37.5 x lower, and parasitisation rates were higher. In an artificially infested field which was treated weekly with carbaryl, parasitisation rates were below 10% and CM populations exceeded 200 per tip. In the chemically untreated plot, parasitisation rates were up to 25% and CM densities were mostly below 10 per tip. This study demonstrates the efficiency of E. lopezi in controlling its host under the experimental conditions.

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Résumé La capacité d'E. lopezi de contrôler la cochenille farineuse du manioc a été évaluée au Nigéria en excluant le parasitoïde de son hôte par des moyens physiques et chimiques. Dans deux expériences utilisants des manchons les populations de la cochenille deux mois après l'infestation artificielle étaient 7.0 et 2.3 fois plus basses sur les branches couvertes d'un manchon ouvert que sur les branches couvertes par un manchon fermé, qui excluait la plupart des parasitoïdes. Sur les apex sans manchons, également infestés artificiellement, les populations de la cochenille étaient 24.3 et 37.5 fois plus bas tandis que le degré de parasitisme était plus élevé. Dans un champ infesté artificiellement et partiellement traité chaque semaine avec du carbaryl, le pourcentage de parasitisme restait au-dessous de 10%, et les populations de la cochenille dépassaient 200 par apex. Dans la partie non-traitée, le parasitisme atteignait 25% et la densité de la cochenille restait pour la plupart du temps au-dessous de 10 cochenilles par apex. Ces expériences démontrent la capacité d'E. lopezi de maintenir son hôte à un bas niveau dans des conditions expérimentales.

     

Melanization and encapsulation of eggs and larvae of Epidinocarsis lopezi by its host Phenacoccus manihoti; effects of superparasitism and egg laying patterns

Encapsulation of Epidinocarsis lopezi (De Santis) (Hymenoptera, Encyrtidae) by the cassava mealybug Phenacoccus manihoti Matile-Ferrero (Homoptera, Pseudococcidae) was studied in the laboratory under controlled conditions (thermohygrometry and photoperiod as close as possible to field conditions): temperature, 26±1 °C; relative humidity, 80±10%; photoperiod, 12 h. Encapsulation began with melanin deposits forming on the parasitoid envelopes at different developmental stages: egg chorion and cuticle of L2 and L3 larvae. It led to the formation of an amorphous capsule from which parasitoids could occasionally escape. Encapsulation affected 26.7% of all parasitoids in solitary parasitism. There was a highly significant increase in the level of encapsulation (83.3%) in superparasitism. Encapsulation was more likely when egg laying occurred in the median body zone of host mealybugs but it was not related either to the sequence of eggs deposited or to the duration of egg laying. These results have significant implications for the assessment of E. lopezi parasitoid efficiency and should be considered in the current biological control program on P. manihoti in Africa.

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Mélanisation et encapsulement des ufs et des larves d'Epidinocarsis lopezi par son hôte Phenacoccus manihoti: effets du superparasitisme et des modalités de la ponte

Résumé L'encapsulement d'Epidinocarsis lopezi (De Santis) (Hyménoptère, Encyrtidae) par la cochenille du manioc Phenacoccus manihoti Matile-Ferrero (Homoptère, Pseudococcidae) a été étudié au laboratoire en conditions standardisées de thermohygrométrie et de photopériode aussi proches que possible de celle existant sur le terrain: température: 26±1 °C; hygrométrie relative: 80±10%; photopériode: 12 heures.Le phénomène débute par un dépot de mélanine sur les enveloppes du parasitoïde à différents stades de son développement: chorion de l'uf ou cuticule des larves L2 et L3. Il aboutit à la formation d'une capsule amorphe dont le parasitoïde parvient parfois à s'échapper. L'encapsulement affectant 26,7% des individus en situation de parasitisme solitaire est très significativement augmenté dans le cas de superparasitisme où ce taux concerne jusqu'à 83,3% des Hyménoptères en développement mais dans ces situations de superparasitisme, un Hyménoptère adulte est toujours obtenu d'une cochenille infestée.L'encapsulement est par ailleurs favorisé lorsque la ponte du parasitoïde s'effectue dans la région médiane de la cochenille mais ne dépend pas du rang de ponte des ufs et de la durée de la piqûre.Nos résultats, confirmés par des travaux de terrain au Congo, indiquent qu'un tel taux d'encapsulement a une incidence sur l'efficacité parasitaire d'Epidinocarsis lopezi et qu'il doit être pris en considération dans le progamme de lutte biologique en cours en Afrique contre Phenacoccus manihoti.

     

Release and establishment in Nigeria of Epidinocarsis lopezi, a parasitoid of the cassava mealybug, Phenacoccus manihoti

The encyrtid wasp Epidinocarsis (= Apoanagyrus) lopezi (De Santis) was imported from Paraguay into Nigeria for the biological control of the cassava mealybug, Phenacoccus manihoti Matile-Ferrero. It was mass-reared and released at four localities in Nigeria. The parasitoid is now established and it is dispersing throughout cassava growing areas of Nigeria.

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Libération et installation au Nigéria d'Epidinocarsis lopezi, parasitoïde de la cochenille du manioc Phenococcus manihoti

Résumé Epidinocarsis lopezi (Apoanagyrus) lopezi a été introduit du Paraguay au Nigéria pour lutter contre la cochenille du manioc, Phenacoccus manihoti. Il a été lâché dans quatre champs de manioc pour étudier son acclimatation et son installation au Nigéria. Trois ans après les lâchers, les résultats ont permis de conclure que E. lopezi s'est établi avec succès et se disperse dans la plupart des zones de culture du manioc au Nigeria; il a aussi survécu à trois saisons pluvieuses pendant lesquelles les populations de P. manihoti ont été très faibles. Quatorze mois après les premiers lâchers, cet encyrtide a été obtenu à environ 150 km du lieu de libération.

     

Interspecific interference between Apoanagyrus lopezi and A. diversicornis, parasitoids of the cassava mealybug Phenacoccus manihoti

The parasitoids Apoanagyrus lopezi De Santis and A. diversicornis (Howard) (Hymenoptera: Encyrtidae) have been introduced into Africa for the biological control of the cassava mealybug Phenacoccus manihoti Matile-Ferrero (Homoptera: Pseudococcidae). We have studied competition between these species to investigate if they can coexist. Here we report on the influence of the simultaneous presence of non-conspecific adult females on searching efficiency on patches. Wasps of either species foraged on discs of cassava leaf with mealybugs, while at the same time different numbers of non-conspecifics were also depleting the patch. Patch area per parasitoid and number of hosts available to each parasitoid were equal in all treatments.In both species, the presence of other foragers clearly affected several aspects of the parasitoids' behaviour. Patch residence time increased with the number of non-conspecifics in A. diversicornis. In both parasitoid species, the proportion of hosts left unparasitized after the patch visit decreased with increasing numbers of females on the patch. The proportions of super- and multiparasitism did not change with the number of females. Both species produced more offspring during a patch visit in the presence of more non-conspecifics. These behavioural changes did not, however, lead to a change in the offspring production rate on patches. A. diversicornis produced offspring at a rate three times that of A. lopezi when one A. lopezi and one A. diversicornis foraged simultaneously. This is the first report of an aspect of interspecific competition where A. diversicornis has an advantage over A. lopezi. Interference between adult females thus promotes coexistence of the two species on P. manihoti.     

The role of kairomones in prey finding by Diomus sp. and Exochomus sp., two coccinellid predators of the cassava mealybug, Phenacoccus manihoti

We studied searching behaviour of Diomus sp., a coccinellid predator introduced into Africa as a natural enemy of the cassava mealybug, when searching on cassava leaves, and compared its behaviour with the searching behaviour of Exochomus sp., an African predator of mealybugs (MB's). Female adults of Diomus and Exochomus spent more time searching on cassava leaves previously infested with cassava MB than on clean cassava leaves, in response to substances produced by MB's (wax and/or honeydew) still present on these leaves as kairomones after removal of the MB's. Both species were also arrested by wax and/or honeydew of the citrus mealybug, Planococcus citri. When offered a choice between kairomones of both MB species only experienced Diomus (reared on cassava MB) showed a clear preference for kairomone of cassava MB. Separate influences of wax and honeydew were tested. Wax from cassava MB was an arrestment stimulus for both coccinellid species. Honeydew produced by cassava MB arrested Exochomus and inexperienced Diomus.

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Zusammenfassung Das Suchverhalten auf Cassaveblätter des coccinelliden Raübers Diomus, eines aus Süd Amerika importierten natürlichen Feindes der Cassaveschmierlaus wurde studiert und verglichen mit dem Suchverhalten eines afrikanischen Räubers von Schmierläusen, Exochomus sp.. Weiblichen Adulten von Diomus un Exochomus verwendeten mehr Zeit auf Cassaveblätter wenn diese Blätter vorher mit Cassaveschmierläuse infiziert waren als auf uninfizierte Blätter, und gebrauchten Substanzen (Wachs und/oder Honigtau) die von Schmierläuse produziert wurden und nach der Entfernung der Schmierläuse auf die Blätter zugeblieben waren als Kairomonen.Beide Arten wurden auch von Wachs und/oder Honigtau der Citrusschmierlaus, Planococcus citri, auf den Blätter arretiert. Wenn die Tiere wahlen könnten zwischen Kairomone der beiden Schmierlausarten wurden die Kairomonen der Cassaveschmierlaus nur von erfahrenen Diomus-Individuen, die auf Cassaveschmierlaüse aufgezogen wurden, bevorzugt.Die Einflüsse von Wachs und Honigtau wurden separat geprüft. Wachs von Exuvien der Cassaveschmierlaus ist ein Arretierungsstimulus für beide Räuberarten. Von Cassaveschmierläusen produzierten Honigtau arretierte Exochomus-und unerfahrene Diomus-Individuen.

     

The influence of constant temperature on population growth rates of the cassava mealybug, Phenacoccus manihoti

Life table studies were conducted to assess the effect of constant temperature on the rate of population growth of the cassava mealybug, Phenacoccus manihoti Matile-Ferrero. Four temperatures, between 20 and 30.5°C, were tested. An inverse relationship was observed between temperature and most demographic parameters.The intrinsic rate of natural increase (r_m) increased from 0.1 at 20°C to 0.2 at 27°C and 30.5°C. The net reproductive rate varied between 426.3 at 30.5°C and 584.7 at 20°C. The mealybug population reached 50% mortality after 37.5, 21.5, 19.0 and 19.0 days respectively at 20, 23.5, 27 and 30.5°C. The results indicate that P. manihoti can persist and increase in numbers within the range between 20 and 30.5°C.

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Influence de températures constantes sur les taux de croissance de populations de la cochenille du manioc Phenococcus manihoti

Résumé Des tables de vie ont été établies pour déterminer l'effet de températures constantes sur les taux de croissance de populations de la cochenille du manioc, Phenacoccus manihoti Mat.-Ferr., et ainsi comprendre les changements au sein des populations du ravageur dans les champs et mener à bien le programme de lutte biologique organisé à l'I.I.T.A. contre cette cochenille. P. manihoti, introduit à partir de l'Amérique latine en Afrique, y menace la production du manioc (Manihot esculenta Crantz).Le taux intrinsèque d'accroissement natural (r_m) a augmenté de 0.114 à 20°C, à 0.185 à 27°C, avant de descendre à 0.182 à 30.5°C. Le taux net de reproduction (R_o) a été relativement élevé (426–584 oeufs femelles/génération). Dans nos conditions expérimentales, la mortalité a atteint 50% au bout de 37.5, 21.5, 19.0 jours respectivement à 20, 23.5, 27 et 30.5°C. La durée du cycle et le coefficient d'accroissement () étaient inversement liés à la température. Le ravageur possède la capacité de doubler sa population en 6.08 jours à 20°C alors que 3.81 jours seulement suffisent pour doubler la population à 30.5°C.Ces résultats nous ont permis de comprendre et d'expliquer l'énorme pouvoir de pullulation de la cochenille observé dans les champs pendant la saison sèche; il s'ensuit que les lâchers des entomophages produits en élevages doivent se faire très tôt au début de la saison sèche, afin de contrecarrer la grande fertilité et la capacité d'augmentation rapide des populations de P. manihoti.

     

Effect of native natural enemies on the population dynamics of the grape mealybug,Pseudococcus maritimus (Hom.: Pseudococcidae), in apple and pear orchards

The impact of native natural enemies on populations of the grape mealybug,Pseudococcus maritimus (Ehrhorn) in apple and pear orchards was assessed using a combination of techniques, including exclusion cages, limb-banding, and visual inspection of shoots and fruits. The complex of native natural enemies (which included two encyrtid parasitoids, (Pseudaphycus websteri Timberlake andMayridia species), a coccinellid beetle (Hyperaspis lateralis Mulsant), and a chamaemyiid fly (Leucopis verticalis Malloch), provided reasonably good control in orchards that had not been treated with insecticides for one to two years. However, surveys indicated that most of these species were absent from orchards regularly sprayed with pesticides.     

Influence of secondary compounds in the phloem sap of cassava on expression of antibiosis towards the mealybugPhenacoccus manihoti

Identification and assay of cyanogenic and phenolic compounds in phloem sap of cassava (Manihot esculenta Crantz, Euphorbiaceae) and in honeydew of the cassava mealybugPhenacoccus manihoti Matt. Ferr. (Homoptera, Pseudococcidae) were realised. Cyanogenic glucosides and three flavonoid glycosides (rutin, kaempferol glycoside-1 and kaempferol glycoside-2) were found to be translocated in cassava phloem sap and consumed by the mealygug. Differences in profiles of secondary compounds of phloem sap and honeydew samples, characterised mainly by the appearance of free cyanide and of a free flavonoid, suggest the metabolic processing of at least some of the ingested compounds. The relationship between foliar concentrations of these different compounds and expression of the antibiotic resistance of cassava towardsP. manihoti was also investigated in 7 varieties of cassava and in the ‘faux-caoutchouc’ hybrid. Infestation by mealybug was followed by a clear increase in levels of both rutin and kaempferol glycoside-2, while no modification in cyanide contents was noted. The best rank correlation between antibiotic resistance (measured by the intrinsic rate of increase r _c ) and secondary compounds analyzed is observed with rutin contents of infested plants (ρ=−0.73; p=0.05). The possible implication of this compound in the biochemical mechanisms accompanying cassava defence reaction to mealybug attack is discussed.

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Résumé Ce travail présente l'identification et le dosage des substances secondaires (composés cyanés et phénoliques) présentes dans la sève phloémienne du manioc (Manihot esculenta Crantz, Euphabiaceae) et dans le miellat de la cochenille farineusePhenacoccus manihoti Matt. Ferr. (Homoptera, Pseudococcidae). Des glycosides cyanogéniques et trois flavono?des glycosylés majeurs (rutine, kaempferol glycoside-1 et kaempferol glycoside-2) sont transportés par la sève phloémienne du manioc et consommés par la cochenille. Le profil sensiblement différent des composés secondaires du meillat de la cochenille, en particulier l'apparition d'un flavonoide libre et de cyanure, suggère une modification de certains composés lors du transit intestinal. La relation entre les teneurs de ces différentes substances dans le liquide foliaire de 7 variétés de manioc et du ‘faux-caoutchouc’ (hybride deM. esculenta et deM. glaziovii) et l'expression de leur résistance antibiotique vis-à-vis deP. manihoti a également été étudiée. L'infestation par la cochenille se traduit par une importante augmentation des teneurs en rutine et en kaempferol glycoside-2, alors qu'aucune modification des teneurs en cyanure libre n'est enregistrée. La meilleure corrélation entre la résistance par antibiose, exprimée par la capacité intrinsèque d'accroissement r _c , et les teneurs en substances secondaires analysées est observée avec les teneurs en rutine des plants infestés (ρ=−0.73; p=0.05). L'association éventuelle de ce glycoside aux mécanismes biochimiques de défense du manioc à la cochenille farineuse est discutée.

     

杭州地区扶桑绵粉蚧危害调查及系统进化分析

【背景】扶桑绵粉蚧是近年来入侵我国的重要检疫性害虫,在我国多个省份均有发生,造成了严重的经济损失。【方法】于2009—2015年对杭州地区扶桑绵粉蚧的发生危害情况进行了实地调查,同时结合mt DNA COI分子标记方法,对扶桑绵粉蚧进行分子鉴定和系统进化分析。【结果】杭州市余杭区、萧山区和临安市3个地区发现扶桑绵粉蚧分布,共调查到寄主植物38科61属68种,以辣椒、茄子、番茄、南瓜、棉花、芝麻、菊花、苦荬菜、大花马齿苋和五色梅受害最严重。系统进化分析表明,杭州地区的扶桑绵粉蚧未发生明显的遗传分化,与我国其他地区扶桑绵粉蚧mt DNA COI基因相似度为99.4%~100%。【结论与意义】本研究为进一步研究扶桑绵粉蚧的遗传进化、可能的侵入途径以及科学防控提供了理论基础。     

Temperature-dependent growth rates for the cassava mealybug, Phenacoccus herreni, and two of its encyrtid parasitoids, Epidinocarsis diversicornis and Acerophagus coccois in Colombia

Developmental rates for Phenacoccus herreni Cox & Williams were determined at 18°, 20°, 22°, 25°, 30° and 35°C for the egg, all juvenile male and all juvenile female stadia. Longevity was determined for adult females and adult males. Developmental rates for the P. herreni parasitoid Epidinocarsis diversicornis (Howard) were determined at 18°, 20°, 25° and 30°C for the oviposition-to-mummy-formation period and the mummy-formation-to-adult-eclosion period. Developmental rates were determined for the P. herreni parasitoid Acerophagus coccois Smith for the same two life stages at 20°, 25° and 30°C. Least-squares-derived polynomial equations or logistic equations were fitted to each data set (except for A. coccois) so that rates could be interpolated for temperatures between observed points for use in an analysis of the impact of these parasitoids on population dynamics of P. herreni. Results of this analysis are presented separately.

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Résumé Les vitesses de développement des oeufs et de tous les stades larvaires mâles et femelles de P. herreni Cox & Williams ont été déterminées à 18°, 20°, 22°, 25°, 30° et 35°C. La longévité des adultes mâles et femelles a été déterminée. Les vitesses de développement de la ponte à la formation du cocon et de celleci à l'émergence de E. diversicornis Howard, encyrtide parasite de P. herreni ont été déterminées à 18°, 20°, 25° et 30°C. Il en a été de même pour un second encyrtide parasite A. coccois Smith à 20°, 25° et 30°C. Les équations polynomiales des derniers carrés dérivés et les équations logistiques ont été ajustées pour chaque lot de données (à l'exception de A. coccois) de façon à ce qu'elles aient pu être interpolées pour analyser l'impact de ces parasites sur la dynamique de population de P. herreni. Les résultats de cette analyse sont présentés à part.

     

Influence of water-stressed cassava on Phenacoccus herreni and three associated parasitoids

The influence of cassava Manihot esculenta Crantz grown under condition of water-stress on development and reproduction of the cassava mealybug, Phenacoccus herreni Cox & Williams, and levels of parasitism of three encyrtid parasitoids, Apoanagyrus diversicornis Howard, Aenasius vexans Kerrich, and Acerophagus coccois Smith, were studied in the laboratory. Two cassava cultivars were used: CM 507-37 (drought-tolerant) and CMC 40. A 30 day period of water stress, imposed by reducing the irrigation volume, led to a reduction in shoot development and stomatal conductance of leaves of both cassava genotypes. Phenacoccus herreni development and reproduction were favoured by cassava under water shortage. Parasitism decreased and water stress appeared to enhance the encapsulation of parasitoid eggs or larvae by the mealybug. In the case of the parasitoid A. diversicornis, there was a decrease in size of female progeny, suggesting a lower fitness in this species on cassava plants under water stress. All results indicated that cassava grown under low water availability favoured P. herreni development and reproduction, and affected the success of parasitism and, depending on the species, parasitoid development. The drought-tolerance characteristic of cassava genotypes and parasitoid species most suitable for controlling P. herreni in drought-stricken areas are discussed.     

Sustained biological control of the cassava mealybugPhenacoccus manihoti [Hom.: Pseudococcidae] byEpidinocarsis lopezi [Hym.: Encyrtidae] in Nigeria

Following the successful introduction ofEpidinocarsis lopezi (De Santis) for biological control of the cassava mealybug (CM)Phenacoccus manihoti Mat.-Ferr. in southwestern Nigeria in 1981 and 1982, 11 groups of cassava fields were sampled every 2 weeks up to 1988 for impact assessment. After 1984, CM populations remained mostly below 10 per tip despite the presence of native hyperparasitoids, demonstrating the long-term success of biological control byE. lopezi in the region. Indigenous polyphagous coccinellids were found only during peak host densities, whereas the specificE. lopezi was common throughout the year. During some periods, percentage parasitism indicated delayed density dependence. Since 89% of all sampled cassava tips had no CM at all and the parasitisme is very mobile, parasitization rates were also calculated for individual infested tips (N=4,878). Parasitism increased slightly with host density on tips having between 1 and 10 CM of the 3^rd and 4^th instars, indicating positive density dependence. Such tips comprised 64% of all infested tips. At higher host densities, parasitism rates fell rapidly. The results are discussed in view of different theories on population regulation by biological control agents.      

寄主植物对扶桑绵粉蚧体型及体内能源物质含量的影响

[目的]研究寄主植物对扶桑绵粉蚧雌成虫体型和体内能源物质含量的影响,为扶桑绵粉蚧的寄主适应性和风险分析提供科学参考.[方法]在室内用8种寄主植物连续饲养扶桑绵粉蚧5代后,测量7日龄雌成虫体长、体宽和体重,并测定体内能源物质(脂肪、可溶性蛋白质、可溶性糖)含量,分析上述指标在不同寄主间的差异.[结果]取食不同寄主后,扶桑...     

Host–plant relationships and natural enemies of the invasive mealybug,Rastrococcus iceryoides Green in Kenya and Tanzania

The invasive mango mealybug, Rastrococcus iceryoides Green (Hemiptera: Pseudococcidae), believed to be native to southern Asia has rapidly invaded Kenya and Tanzania. A survey was carried out from February 2008 to July 2009 to study its geographical distribution, host–plant relationships and associated parasitoids in both countries. Our results infer that R. iceryoides is widely distributed across the coastal belts of both countries. Rastrococcus iceryoides was recorded from 29 cultivated and wild host plants from 16 families. Twenty‐one of these host plants are new records. Among the cultivated host plants, M. indica (407.68 ± 9.26/twig and 75.68 ± 7.13/leaf in Kibaha, and 595.86 ± 17.2/fruit in Kinondoni) and Cajanus cajan (L.) Millspaugh (18.15 ± 4.22/leaf and 233.62 ± 18.9/twig in Morogoro) recorded the highest levels of infestation. Parkinsonia aculeata (394.62 ± 11.7/twig, 0.15 ± 0.03/leaf and 8.44 ± 0.94/fruit in Kinango), Caesalpinia sepiaria Roxb. (3.33 ± 0.76/leaf and 155.81 ± 9.16/twig in Kinondoni) and Deinbollia borbonica Scheff. (2.70 ± 0.66/leaf and 112.65 ± 5.3/twig in Kibaha) were found to be the most heavily infested wild host plants. Six parasitoid species were recovered and are reported here for the first time to parasitize R. iceryoides. Anagyrus pseudococci Girault was the most dominant species accounting for 21% parasitism on M. indica and 20% parasitism on P. aculeata in Tanzania and Kenya, respectively. Despite this, the ability of the parasitoid to regulate the population of R. iceryoides was inadequate. Therefore, there is a need for foreign exploration and introduction of efficient coevolved natural enemies from its aboriginal home of southern Asia to minimize its impact on horticulture in Africa.     

基于宏基因组测序的扶桑绵粉蚧内共生菌多样性研究

[目的] 扶桑绵粉蚧是一种重要的入侵害虫,也被列为我国的检疫性有害生物。内共生菌的群落结构及与扶桑绵粉蚧关系的研究,将为研究扶桑绵粉蚧的入侵生物学和防治提供新的思路和参考。[方法] 利用宏基因组测序技术对室内饲养扶桑绵粉蚧内共生菌的物种组成、丰度和多样性进行了研究。[结果] 共鉴定获得29个门,47个纲,105个目,178个科,245个属,299个种。变形菌门、γ-变形菌纲、肠杆菌目、肠杆菌科、伯克氏菌属、Candidatus分别为各分类阶元的优势种群。共预测了36505个基因,其中77.27%的基因分布在200~499 nt的范围内。基因集KEGG注释表明,扶桑绵粉蚧内共生菌代谢相关基因最多,达384个,占49.48%;环境信息处理基因最少,仅8个,占1.03%;代谢相关基因最多的为氨基酸代谢基因,为64个,占28.19%。基因集COG注释表明,翻译、核糖体结构和生物发生的基因最多,其次为氨基酸转运和代谢基因,分别占27.64%和12.31%。[结论] 初步确定了扶桑绵粉蚧内共生菌菌群的群落结构和优势菌群,并初步分析了这些内共生菌的功能基因情况,为进一步研究内共生菌与扶桑绵粉蚧之间的关系提供了基础,以期从内共生菌的角度为该虫的防控提供新的策略。     

Host specificity and comparative foraging behaviour of Aenasius vexans and Acerophagus coccois, two endo-parasitoids of the cassava mealybug

Two encyrtid parasitoids, Aenasius vexans Kerrich (Hymenoptera: Encyrtidae) and Acerophagus coccois Smith (Hymenoptera: Encyrtidae), were compared for their degree of dietary specialisation and the impact this has on their foraging strategies. Both parasitoid species are significant for biological control of the cassava mealybug, Phenacoccus herreni, Cox & Williams (Homoptera: Sternorrhyncha) a major Latin American pest of cassava, Manihot esculenta Crantz, an important root crop. Host acceptance and parasitism were analysed in seven mealybug species (with different levels of polyphagy) occurring in and around cassava fields. Results demonstrate that, in this ecosystem, An. vexans is a specialist for P. herreni while Ac. coccois is a generalist on the first and second trophic level. Of the seven mealybug species, P. herreni and P. madeirensis Green were the most acceptable hosts for Ac. coccois, followed by Ferrisia virgata Cockerell. Ac. coccois did not accept the other four mealybug species.The foraging and oviposition behaviour of individual parasitoids was observed in bioassays with cassava leaves infested by P. herreni. The two species used different strategies to locate their host. Aenasius vexans spent significantly more time walking and standing on an infested leaf and examined a host longer than did Ac. coccois. Acerophagus coccois, in contrast, spent more time for oviposition. As a consequence An. vexans parasitised more hosts in a given time than did Ac. coccois. Because the rate of offspring production of the two species did not differ, we conclude that the gregarious Ac. coccois's strategy to deposit several eggs at once might compensate for its relatively low number of ovipostitions, compared with the solitary An. vexans. These findings suggest that, given the advantages and limitations of each species, a multi-species approach to biological control of P. herreni may yield best results.     

云南扶桑绵粉蚧的发生及防治

扶桑绵粉蚧是一种全球恶性入侵害虫,2008年传入我国,目前已有13个省区报道其为害,2009年在云南省被发现,截至2013年3月,云南省共8个州(市) 10个县(市)已有分布。扶桑绵粉蚧寄主范围广,危害性大,适应性强。同时,云南省花卉、蔬菜调运及进出口贸易频繁,加之气候类型丰富、水热条件优越、自然地理环境复杂多样、动植物资源丰富等优势,有利于扶桑绵粉蚧的入侵、定殖与扩散,易造成较大的经济损失。目前,关于云南省扶桑绵粉蚧的研究仍然缺乏,现就扶桑绵粉蚧在云南的发生现状、潜在风险和防治措施等方面进行概述,以期为该虫的有效防范提供参考。     

Host preferences of two encyrtid parasitoids for the Columbian Phenacoccus spp. of cassava mealybugs

In a choice test among six life stages of Phenacoccus herreni Cox & Williams, Epidinocarsis diversicornis (Howard) used its antennae to examine adult and 3rd stadium females more than other stages and preferentially attempted to oviposit in these plus 2nd stadium females. Success of ovipositor insertion was unaffected by host stage. The outcome of these behaviors was preferential oviposition by E. diversicornis in the large female host stages. Acerophagus coccois Smith also preferentially examined larger female mealybugs (second and third stadium nymphs and adults) more than other stages and successfully inserted its ovipositor in these stages more often than in second stadium male nymphs and male cocoons, resulting in a similar preference in this species for larger female host stages. When given a choice between adult female hosts of two species, P. herreni and Phenacoccus gossypii Townsend & Cockerell, E. diversicornis exhibited a clear preference for P. herreni; whereas A. coccois preferred P. gossypii.

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Résumé Epidinocarsis diversicornis (Howard), ayant la possibilité de choisir entre six stades différents de Phenacoccus herreni Cox & Williams, examine avec ses antennes plus particulièrement les adultes et les larves femelles du 3ème stade, et essaie de pondre de préférence dans ces stades et les larves femelles de second stade. L'insertion de la tarière s'effectue aussi bien quel que soit le stade de l'hôte. Il résulte de ces différents aspects du comportement que E. diversicornis pond de préférence dans les femelles des stades les plus avancés. Acerophagus coccois Smith préfère aussi examiner les cochenilles femelles les plus grosses (second et 3ème stade larvaires et adulte), et introduit sa tarière avec succès dans ces stades plus souvent que dans les larves mâles de second stade ou les cocons mâles; il en résulte aussi pour cette espèce une préférence pour les femelles des stades les plus gros.Quand on leur a donné le choix entre des femelles des deux espèces de cochenilles (P. herreni et Phenacoccus gossypii Towsend & Cockerell), E. diversicornis manifestait une nette préférence pour P. herreni, tandis que A. coccois préférait P. gossypii.

     

Attraction of the predatory mites Typhlodromalus manihoti and Typhlodromalus aripo to cassava plants infested by cassava green mite

The attraction of the predatory mites, Typhlodromalus manihoti and Typhlodromalus aripo, to the host plant-spider mite complex, Manihot esculenta – Mononychellus tanajoa, was investigated with a Y-tube olfactometer. Factors examined included predator starvation period, several combinations of cassava leaf biomass and initial M. tanajoa infestations, M. tanajoa-damaged leaves with mites and/or their residues removed, M. tanajoa alone, and mechanically damaged cassava leaves. We found that females of T. manihoti and T. aripo were significantly attracted to M. tanajoa-infested cassava leaves when the predators were starved for 2, 6, or 10 h. Satiated T. aripo was significantly attracted to infested cassava leaves whereas satiated T. manihoti did not discriminate between infested and non-infested leaves. When a choice was given between either two or four leaves infested with 200 female M. tanajoa and an equivalent number of non-infested leaves, 2 h-starved T. manihoti and T. aripo were significantly attracted to each of the infested groups of cassava leaves. At a density of 12 female M. tanajoa per leaf on four leaves, 2 h-starved T. manihoti was still attracted to M. tanajoa-infested leaves whereas 2 h-starved T. aripo was not attracted. When a choice was given between non-infested cassava leaves and either infested leaves from which only M. tanajoa females had been removed, or infested leaves from which all M. tanajoa and their visible products (web, feces) had been wiped off, T. aripo preferred odors from both types of previously infested leaves. Typhlodromalus manihoti was only attracted to infested leaves from which the M. tanajoa females only had been removed. Finally, the two predators were not attracted to 400 female M. tanajoa on clean cotton wool or to mechanically wounded leaves. This supports the hypothesis that M. tanajoa damage induces volatile cues in cassava leaves that attract T. manihoti and T. aripo to M. tanajoa-infested leaves.