Biology of two key Palaearctic larval ectoparasitoids when parasitizing the invasive pest Tuta absoluta

During the last few years following the invasion of European tomato crops by the invasive South American tomato leafminer, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae), several indigenous larval parasitoid species were recorded as natural enemies of this pest. Necremnus cf. artynes (Walker) and to a lesser extent Stenomesius sp. nr. japonicus (Ashmead) (Hymenoptera: Eulophidae) have been frequently reported attacking T. absoluta in tomato greenhouses in Europe and they are considered as possible biocontrol agents. Few biological data are available on these two species, notably when they parasitize T. absoluta. Therefore, the present study documents their biology when parasitizing T. absoluta, and provides scientific bases for potential development of biological control programs relying on larval ectoparasitoids in invaded areas. We demonstrated the ability of the two parasitoid species to reproduce on T. absoluta as host on tomato plants. On average, N. cf. artynes female parasitized 28.5 larvae and killed 26.2 larvae during its life time whereas S. sp. nr. japonicus female was more long-lived and consequently more efficient; it parasitized 144.3 larvae and killed 90.1 larvae. In a second step, we also explored the effect of T. absoluta larvae instar on parasitism by S. sp. nr. japonicus and subsequent development of the parasitoid offspring. Best results were obtained with the third larvae instar with a higher number of offspring produced, bigger individuals and a higher proportion of females. Our results support the hypothesis that the two species are good candidates for biological control programs targeting T. absoluta in Europe.     

Host discrimination ability in the tephritid parasitoid Psyttalia concolor (Hymenoptera: Braconidae)

Psyttalia concolor (Szépligeti) (Hymenoptera: Braconidae) is a koinobiont larval-pupal endoparasitoid of many Tephritidae of economic importance. Little has been reported on the ability of females to discriminate between healthy and parasitized hosts, as well as parasitized versus superparasitized larvae. Two-choice bioassays were conducted to evaluate the preferences of P. concolor naïve females for healthy or single-parasitized/superparasitized C. capitata larvae, as well as the host discrimination ability among medfly larvae which had been superparasitized by the same wasp or by a conspecific one. Psyttalia concolor preferred to oviposit in a unparasitized C. capitata larva than in a self-parasitized one. Females also showed an innate ability to discriminate between larvae parasitized twice or only once, preferring the latter. This ability helps the female to optimise its oviposition decisions by deliberately avoiding superparasitized hosts, since it is known that they give a lower return in offspring number and quality than do singly parasitized hosts. Our findings contribute to a better knowledge of the P. concolor host location behaviour and also to improve its mass-rearing technique through a rational management of the host/parasitoid ratio and the host exposure time. Indeed, the proper setting of these parameters allows to reduce the fraction of single-parasitized and heavily superparasitized larvae and to enhance P. concolor rearing in terms of parasitoid offspring.     

Übertragung zweler bakterieller Pathogene in den Körper von Sesamia cretica Led. (Lep., Tortricidae) mittels des Legebohrers von Bracon brevicornis Wesm. (Hym., Braconidae)

Laboratory trials were undertaken to investigate the transmission of 2 bacterial pathogens (Serratia marcescens Bizio andBacillus thuringiensis Berliner) by the ovipositor of a braconid parasitoid,Bracon brevicornis Wesmael into the body cavity ofSesamia cretica Lederer. The braconid's ovipositor was able to transmit the 2 bacterial pathogens and plays as inoculating needle. The host larvaeS. cretica were significantly immobilized faster by the contaminated ovipositor of a parasitoid (in case of the 2 pathogens). After successful transmission of the bacterial pathogen into the body cavity of host larvae, different deleterious effects were significantly found for the parasitoid and its progeny specially in case ofS. marcescens. Through contamination of the ovipositor, the non-sporeforming bacterium,S. marcescens has more pathogenic effects on the parasitoid and its progeny than the sporeforming bacterium,B. thuringiensis.     

Zur Morphologie und Entwicklung von Bracon instabilis Marsh. (Hym., Braconidae), eines Parasiten der Kartoffelmotte,Phthorimaea operculella Zell. (Lep., Gelechiidae) in Ägypten

Bracon instabilis Marshal is an ectoparasite attacking the larvae ofP. operculella in Egypt. According to available literatures, this is the first study onB. instabilis. The laboratory rearing of this parasite was undertaken on the third and fourth larval instars ofP. operculella and the method was mentioned in details. Certain aspects of the morphology of the immature and adult stages were given. The durations of the immature stages of the parasite were estimated at 15 and 25°C and 60±5% R.H. The total durations of the immature stages (from egg to adult) were 39.62 and 11.19 days at 15 and 25°C, respectively.     

Zur Wirkung der Nahrungspflanze auf die Entwicklung und Vermeharung der Baumwolleule,Spodoptera littoralis (Boisd.) (Lep.,Noctuidae)

Effect of some host plants on development and reproduction of Spodoptera littoralis (Boisd.) (Lep., Noctuidae) Investigations were performed to study the effect of some hostplants on development and reproduction capacity of the Egyptian cotton leaf-worm,Spodoptera littoralis (Boisd,), Larval and pupal weights, life span, average number of eggs laid per female and percent digestability for fifth instar larvae were measured. Cotton leafworm was able to complete its life cycle only when reared on eigher castor bean leaves, clover, sweet potato leaves, or the outer green cabbage leaves. Chlorophyl-free inner white cabbage leaves, maize, and grape vine are nutritionally insufficient to support growth and development of larvae and, in turn, cause increase in span of survived larvae and none of these larvae metamorph to pupae. It seems that there is a positive correlation between larval and pupal weights and average number of eggs laid per female; the greater the weight of larvae and pupae the higher the number of eggs laid. Castor bean leaves seem to be the most favorable host plant for rearing cotton leafworm in the laboratory. The differences and variations in the growth and development of cotton leafworm due to feeding on different host plants are discussed.     

Impact of neem and chinaberry fruit extracts on the pest/parasitoid (Pieris rapae/Hyposoter ebeninus) interactions

A new technique was performed to simulate exposure of the host Pieris rapae larvae to both botanical treatment and the parasitoid Hyposoter eheninus in different sequences. It was found that: host larvae subjected to both parasitoid and 1?% neem treatment showed significant or insignificant reductions both in pupal formation as well as adult emergence percentages when treatment preceded or followed parasitism, respectively. Both neem treatments revealed significant prolongation in the development of unparasitized and parasitized larvae (on average 4 to 5 days delay), whereas chinaberry caused significant prolongation only among parasitized larvae (on average 2.7 days delay in egg-larval duration). Fate of parasitism among untreated hosts was found to be faster than among neem-treated ones. Parasitism percentages among 1 and 0.5?% neem-treated third instar host larvae held 7 days before parasitism reached 3 and 2 times that achieved among those reared on untreated diet for the same period, ­respectively. It was concluded that prolongation of the preferred target instars of the host, due to neem treatments, increased the chance for parasitism. Nevertheless, treatment with neem at the LC₅₀ level exhibited a great reduction in parasitoid progeny. However, a lower concentration (LC₂₅) could reasonably potentiate parasitism without drastic losses in parasitoid emergence.     

Wechselseitige Beeinflussung des Entwicklungsablaufs bei entomophagen Parasiten und deren Wirten,erörtert am Beispiel vonColeophora-Arten(Lep., Coleophoridae) undUrophora-Arten(Dipt., Trypetidae)

Summary This study compares the host-parasite relation betweenColeophora ? alcyonipennella andAgathis sp., on the one hand, andUrophora spp. andEurytoma tibialis, on the other hand.Coleophora-Agathis is a striking example for a host-parasite relation where the larval development of the parasitoid is controlled by the endocrine system of the host, which results in an optimal synchronization between the life-cycles of the moth and its specialized Braconid parasite. Attempts to obtain adultAgathis during the winter season for the biological control ofColeophora in New Zealand have met with considerable difficulties because of the hormonal dependence of the parasite on the host. The rearing and the transfer of adult parasites was not possible until the diapause of the host could be ended experimentally. In the complexUrophora-E. tibialis the parasite larvae interferes with the hormonal system controlling the development of the host. In hibernating generations ofUrophora spp. the parasite induces a premature onset of the process of pupation of the host, but consumes the latter when it has formed its puparium. In both hosts the hormonal reactivation of the diapausing full-grown larva results in a change of the position of the larva in its case or gall, before the morphogenetic changes involved in pupation take place. The larvae ofAgathis as well asE. tibialis do not kill their hosts until the latter have reversed their position within the case or gall. In this way the emergence ofAgathis from the case ofColeophora and the emergence ofE. tibialis from the gall ofUrophora is facilitated.     

Eine verbesserte Technik zur Gewinnung eines höheren Weibchenanteils beim Parasitoiden Bracon brevicornis Wesm. (Hym., Braconidae)

The effect on sex ratio ofBracon brevicornis progeny when male, female, and host larva (Sesamia cretica) were placed together in different time sequences, was investigated. Placing a parasitoid female first, a male after 3 hours, and a host larva after 24 hours, yielded significantly the highest proportion of females (48%). In this case female/male sex ratio was 1∶1 approximately, while other manipulations, they ranged from 1∶4 to 1∶20 (with preponderance to males).     

Neue Wirtspflanzen des Ringelbocks,Oberea brevis Swed. (Col., Cerambycidae,Lamiinae) in Indien

Up to this time the girdle beetle,Oberea brevis has been recorded on soybean (Glycine max), beans (Lab-lab niger), cow pea (Vigna signensis), urid (Phaseolus mungo) and moong (Phaseolus radiatus) growing in the areas of Utter Prodesh, Madhya Pradesh and Jabalpur, India. The pest caused mortalities of plants up to 36.5 per cent. In 1975 and 1976 researchs were done to record the host range ofO. brevis. The infestation was ascertained by having two parallel girdles, which are made by the female beetles to reduce the moisture content of the plant and to lay the eggs between the girdles. Due to girdling on the plants, the apical parts dry and later drop off and larvae make their tunnels in the lower parts of the plants. 11 new host plants ofO. brevis were recorded.     

Relationships between the emergence and oviposition of ectoparasitoid Spathius agrili Yang and its host emerald ash borer, Agrilus planipennis Fairmaire

Emerald ash borer (EAB), Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), (= A. marcopoli Obenberger), is an important bark beetle attacking ash trees (Fraxinus spp.). It is very difficult to detect and control because of its highly concealed life history. This pest mainly distributed in partial Asian countries (China, Japan, Korea, Mongolia) and Far East Russia, while in China it presented in Heilongjiang, Jilin, Liaoning, Shandong, Inner Mongolia, Hebei, Taiwan Provinces and Tianjin City, etc. The important timber species F. mandshurica and gardening tree F. velutina were damaged severely in northern China. Spathius agrili Yang (Hymenoptera: Braconidae) is an important ectoparasitic wasp of the EAB larvae. This parasitoid has the potential to use as an excellent biological control agent for suppressing populations of EAB. The differences of emergence date between overwintered S. agrili and its host, parasitism rates at different periods, relations between parasitism rates and host densities, and relationships between ovipositions of braconid wasp and body sizes of host larvae were studied using methods of regular surveys in forests and observations in laboratory. Results revealed that the emergence of S. agrili was more than one month later than that of its host. It suggests good synchrony between parasitoid emergence and host availability. The overwintered S. agrili emerged from mid June to mid August with the peak in July in 2003, and it lasted from late May till late July with the peak during late June to early July in 2004. While the EAB emergence period ranged from mid May to late May in 2003, it ranged from mid April to mid May in 2004 (in laboratory). The emergence date of parasitoid asynchronously inosculated with the optimum developmental instars of the earliest host larvae, which was the result of a long-term co-evolution between the two species. It was also suggested that the parasitoid S. agrili could be a specialized natural enemy for EAB. The natural parasitism rates on the whole gradually increased in field with time. The body sizes of host larvae, i.e. larval instar, affected the decision of parasitoid S. agrili to lay eggs or not. Under natural conditions, this parasitoid usually oviposited only on those host larvae with a prontum and body width more than 1.5 mm, and a body length in excess of 12 mm, i.e. the third or fourth instar larvae. These findings would consequentially contribute to the further successfully biological control of the trunk borer. __________ Translated from Acta Ecologica Sinica, 2006, 26(4): 1,103–1,109 [译自: 生态学报]     

松褐天牛肿腿蜂对松褐天牛低龄幼虫控制作用的研究

研究测定了松褐天牛肿腿蜂对松褐天牛1～3龄幼虫的控制作用,采用林间和室内罩网相结合的方法研究了2组松褐天牛肿腿蜂对松褐天牛幼虫的寄生情况.结果显示:在室内试验条件下,松褐天牛肿腿蜂产卵之前的刺蛰、补充营养取食能直接造成松褐天牛1～3龄幼虫死亡,对1、2及3龄幼虫的平均致死率分别为95.66％、85.91％、57.88％,并可产卵寄生2、3龄幼虫;林间释放2组松褐天牛肿腿蜂后,在刺蛰和补充营养取食后能有效寄生寄主的肿腿蜂雌蜂数量比例变化较大,有效肿腿蜂率最高为14.9％,最低为2.3％.松褐天牛肿腿蜂寄生行为不受寄主聚集程度的影响,但刚羽化出茧肿腿蜂雌蜂的寄生效率比经饲喂后的雌蜂高近5倍.从肿腿蜂单一个体来看,每头雌蜂补充营养取食和产卵寄生致死的松褐天牛幼虫数为2.1～7.7头.松褐天牛肿腿蜂雌蜂的补充营养习性及刺蛰、取食致死寄主行为在防治中有很重要的作用,表明该种肿腿蜂是防治松褐天牛的重要天敌,在生物防治松褐天牛幼龄幼虫上具有良好的应用前景.     

Untersuchungen über die Eiparasiten (Hym.: Chalcidoidea) der rotgelben Kiefern-BuschhornblattwespeNeodiprion sertifer Geoff. (Hym.: Diprionidae)

IV. Summary 1. Four or five species of egg parasites ofNeodiprion sertifer have been found in central Europe.2.Dipriocampe diprioni is a primary parasite which overwinters as a first instar larva within the host's egg, The larvae complete feeding in early spring and enter an obligatory diapause which lasts until July–August. Under the influence of the parasite, the egg shell of the host turns brownish. The adults emerge from mid-August onward. The univoltine parasite is thus well synchronized with its major host,N. sertifer.3. A second species, or form, ofDipriocampe has been found, the taxonomic status of which is still unresolved. It is here referred to asDipriocampe sp. forma ignorata. Although not yet separable fromD. diprioni morphologically, its biology is quite different. The larvae mature before the winter and the adults emerge in April–May of the following year, being dependent on alternate hosts. This form is exceedingly rare in lowland areas but possibly common at high altitudes. It remains to be seen whether it is a separate species or a polymorphic, non-diapausing form ofD. diprioni. Host eggs attacked byDipriocampe sp.forma ignorata turn blackish.4. Two species ofAchrysocharella have been found,A. ruforum andA. ovulorum. In lowland areas,Achrysocharella spp. attack the eggs ofN. sertifer in a hyperparasitic capacity, developing at the expense of the larvae and pupae ofDipriocampe spp. or of larvae and pupae of their own kind. There are two or three such hyperparasitic generations during the summer, the last entering hibernation before the new eggs ofN. sertifer make their appearance, thus failing to attack them in a primary capacity.In mountainous areas, where the eggs ofN. sertifer appear earlier,Achrysocharella spp. pass the first generation as primary parasites in the sawfly eggs, and the second (summer) generation as hyperparasites of larvae and pupae ofDipriocampe spp. or of larvae and pupae of their own kind.5.Tetrastichus oophagus has been associated with the eggs ofN. sertifer in a few cases only, but has been more common as a parasite of the eggs ofDiprion pini.6. The importance of the egg parasites ofN. sertifer has to date been underestimated. Egg parasitism is apparently density-dependent and can reach high values during, and immediately after, the break-down of the sawfly populations.     

桉树蛀干新害虫--桉蝙蛾形态与生物学研究

桉蝙蛾是近年来在广西、广东新发现严重危害桉树的蛀干害虫,本文记述了该害虫的形态特征和生物学特性,该虫在广西分布于12个市49个县,10个自治区直属国有林场,232个乡镇,危害桉树面积达2 894.42 hm2,多数个体1年完成1代,以幼虫于12月中下旬开始在受害树干中越冬,次年2-3月化蛹,4月羽化,5月上旬初孵幼虫出现,6-8月幼虫上树转移危害,1年只有1次羽化;该虫主要分布在丘陵山地,以沟谷和坡底危害较严重,主要危害1～2年生巨尾桉和尾巨桉无性系.1年生和2年生受害桉树单株材积生长量下降率分别为16.70％和24.78％.沟谷和坡底1～2年生速生桉无性系是防治的主要对象.     

Host specificity of Asian parasitoids for potential classical biological control of <Emphasis Type="Italic">Drosophila suzukii</Emphasis>

The Asian spotted wing drosophila, Drosophila suzukii, has recently become a serious pest of soft fruits in Europe. Classical biological control through the introduction of larval parasitoids from its native range in Asia is presently being considered. However, host specificity of potential biological control agents has to be determined to avoid releasing species that may have unintended non-target impacts. Larvae of six different European non-target fly species and the target D. suzukii were exposed either on diet or blueberries to three Asian larval parasitoids, Asobara japonica, Leptopilina japonica, and Ganaspis cf. brasiliensis, and one European species, Leptopilina heterotoma. Asobara japonica showed the lowest specificity, attacking and developing in all Drosophilidae. Leptopilina japonica successfully parasitized two non-target Drosophilidae, D. melanogaster and D. subobscura, with one singly progeny emerging from D. immigrans. Ganaspis cf. brasiliensis had the highest level of specificity but variations occurred between two geographical populations tested. A Japanese population was strictly specific to D. suzukii, whereas another population from China parasitized D. suzukii, D. melanogaster and sporadically D. subobscura. The European L. heterotoma successfully developed in D. melanogaster, D. subobscura and occasionally in D. immigrans, but nearly all eggs and larvae in D. suzukii were encapsulated. These results show that Ganaspis cf. brasiliensis is the species with the highest potential for biological control, but more studies are needed on its taxonomic status and the existence of biotypes or cryptic species varying in their specificity before field releases can be conducted in Europe.     

Studies on biological control of the Bean-weevil (Bruchus chinensis L.) byApanteles flavipes (Cam.) (Hymen., Braconidae)

Bean-weevil (Bruchus chinensis L.) is commonly found in Sind region of Pakistan and it severely damages Mong seeds (Phaseolus mungo L.), and some other pulses in storage conditions. The parasitoidApanteles flavipes (Cam.), a gregarious Braconid parasite of Bean-weevil was reared under laboratory conditions with a view to exploiting it for the biological control techniques to be reported for the first time in Pakistan. This parasite completes its whole life cycle inside the body of the host by completing a number of generations in a year, and it successfully parasitisesBruchus spp. larvae inside the seed body; and its life cycle entirely depends upon the environmental factors like temperature and humidity as well as on the physiological condition of the host. It parasitised upto 45% in field population and 83% under laboratory conditions.     

Wirkungen zwischen Bacillus thuringiensis Berl. und Larven der Schlupfwespe Bracon brevicornis Wesm. in bzw. an den Raupen von Sesamia cretica Led. bei verschiedenen Temperaturen

Laboratory trials were undertaken to investigate the interactions which may occur when rearing the parasitoid,Bracon brevicornis on Sesamia cretica larvae after being injected with the pathogen,Bacillus thuringiensis under 5 constant temperatures. Bacillus-infected larvae ofS. cretica had detrimental effects on the parasitoid's progeny e. g. prolonged periods of both cocoon stage and total development at 20 or 25 °C; and decreased number of formed cocoons or produced adults at all tested temperatures. The most deleterious temperature for the parasitoid rearing under condition of the bacterial pathogen was 30 or 35 °C.     

For sex and more: attraction of the tephritid parasitoid Psyttalia concolor (Hymenoptera: Braconidae) to male sex pheromone of the olive fruit fly,Bactrocera oleae

The braconid parasitoid Psyttalia concolor foraging for larvae of Bactrocera oleae (Diptera: Tephritidae) uses olfactory cues from the larval microhabitat. However, it could rely on the sex pheromones of adults of its host, since B. oleae mating leks usually occur on olive plants and a high number of infested fruits can be easily located in their close proximity. We quantified the behavioural responses of P. concolor towards different doses of the two major sex pheromone components of B. oleae, the female-borne 1,7-dioxaspiro[5.5]undecane (DSU) and the male-borne (Z)-9-tricosene (ZT). Results showed that P. concolor females and males were attracted only to the highest amounts of ZT (10 B. oleae male equivalents), regardless of the mating status. Wasps remained longer on the surfaces treated with high ZT amounts over the control. P. concolor females could exploit the ZT produced by lekking olive fruit fly males as a foraging kairomone. This could allow them to rapidly track B. oleae-infested olive plants, thus raising their chances to locate host larvae during their lifespan. On the other hand, the perception of ZT by P. concolor males could raise their chances to locate receptive females emerging from parasitised B. oleae pupae or also ovipositing in olive fruits. This study increases the knowledge of the reproductive biology of P. concolor, highlighting a case of chemical espionage in which a sex pheromone component from adult stages of the host is exploited both as a foraging kairomone by female parasitoids and as a sexual kairomone by male wasps.     

Mesopolobus pinus Hussey, 1960 (Hym., Pteromalidae), ein neuer Parasit vonMegastigmus suspectus Borries, 1895 (Hym., Torymidae) in Weißtannensamen

A hitherto unknown parasite of theMegastigmus suspectus larvae, the pest of fir-seeds (Abies alba Mill.), was found and identified asMesopolobus pinus. It was stated from the Roztoczański National Park in Poland. That this parasite is able to play considerable role in the limitation ofMegastigmus suspectus population.     

Experimental release of a parasitoid, Doryctes yogoi Watanabe (Hymenoptera: Braconidae), onto Semanotus japonicus Lacordaire (Coleoptera: Cerambycidae) inoculated into live Japanese cedar trees (Cryptomeria japonica D.DON)

Release experiments of Doryctes yogoi Watanabe onto Semanotus japonicus Lacordaire larvae inoculated into Japanese cedar, Cryptomeria japonica D. Don, were conducted to clarify the role of the parasitoids in the mortality of S. japonicus and the efficiency of the parasitoid as a natural enemy of the beetle. S. japonicus larvae were inoculated into three types of samples: live trees, girdled trees, and logs, each of which was treated in three ways: D. yogoi was released into the sample, the sample was screened (excluding natural enemies), or the sample was used as a control. In live trees, more than 90% of the larvae were killed by resin flow, and the percentage of parasitism by D. yogoi was less than 6%. In girdled trees, most of the larvae were dead due to the resin in the trees, having survived inoculation as well as in live trees, but many larvae were parasitized by D. yogoi in dead trees like logs. The present study revealed three negative effects of resin flow on parasitism by D. yogoi in the live trees. First, most of the host larvae died before reaching a size suitable for parasitism. Second, parasitoid larvae were caught in the resin with their hosts and died. Third, the host-searching and oviposition of female D. yogoi were obstructed by resin flow on the surface of the trunk. The efficiency of D. yogoi as a natural enemy of S. japonicus is discussed.     

Untersuchungen zur überlebensfähigkeit und Entwicklung der Larven zweier Herkünfte des Schwammspinners Lymantria dispar L. (Lep.: Lymantriidae) in Abhängigkeit von der Fraßpflanze

The polyphagous gypsy moth (Lymantria dispar) is able to feed on about 400 different woody plant species. In general, oak species are preferred – on the other hand some other groups of plants are avoided on account of the presence of toxic substances. These unfavoured hosts are, for example, most of the Papilionaceae, like locust (Robinia pseudoacacia). We compared survival rate and development of two populations of different origin with long-term habituation to oak and locust, respectively. Larvae from the population habituated to oak proved unable to develop on locust food. There must be a lack of detoxification systems to modify the toxic alcaloids and flavenoids produced by Robinia pseudoacacia. On the other hand, larvae isolated from an locust stand were able to feed on oak leaves without problems in larval development or eclosion of adults. Gypsy moth larvae specialized on locust as host showed increased mortality (up to 27?%) in the early larval instars, but the surviving animals, especially female individuals, reached significantly higher pupal weights and showed better fecundity: 40?% higher egg numbers/egg mass compared to those feeding on oak. These results indicate that the gypsy moth population originating from the locust forest had achieved a high level of metabolic adaptation to this host plant and formed a 'biotype' of Lymantria dispar with optimal reproductive conditions in this special habitat.