Sucrose octanoate toxicity to brown citrus aphid (Homoptera: Aphididae) and the parasitoid Lysiphlebus testaceipes (Hymenoptera: Aphidiidae)

We report the toxicological effects of a new biorational, synthetic sucrose octanoate (AVA Chemical Ventures L.L.C., Portsmouth, NH), on brown citrus aphid, Toxoptera citricida (Kirkaldy), nymphs and adults and to its native parasitoid Lysiphlebus testaceipes (Cresson). Sucrose octanoate topically applied was equally toxic to brown citrus aphid adults and nymphs with LC50 and LC90 values ranging from 356 to 514 and 1029 to 1420 ppm, respectively. Mortalities of both stages did not differ significantly over time during the 3-24-h sampling period. Dry residues of sucrose octanoate exhibited similar levels of toxicity to both nymphs and adults. Mortality ranged from 60 to 70% at 6,000 ppm 4 h after exposure. L. testaceipes was not harmed by treatments as high as 4,000 ppm of sucrose octanoate as long as the parasitoid had mummified before treatment. Based on these results, sucrose octanoate would be a useful biorational in citrus integrated pest management programs.     

Sources of mortality in colonies of brown citrus aphid, Toxoptera citricida

Sixteen cohorts of the brown citrus aphid, Toxoptera citricida, were followed from colony initiation to maturation/extinction in citrus groves at two sites in Puerto Rico and nine sites in Florida, USA. Infested citrus terminals were sampled repeatedly in a non-destructive manner and data recorded on the recruitment of natural enemies and the fate of aphid colonies. Coccinellidae were the most efficient predators of T. citricida, primarily Cycloneda sanguinea, and Coelophora inaequalis (Puerto Rico), C. sanguinea, Harmonia axyridis (Florida). Coccinellids were abundant in citrus year-round in Puerto Rico, but in Florida citrus their abundance peaked in spring and declined thereafter. Syrphid flies were other important predators, especially Pseudodorus clavatus (Florida and Puerto Rico) and Ocyptamus fuscipennis (Puerto Rico). Syrphids increased in abundance from spring to fall in both regions. Other predators included Cereaochrysa lineaticornis, Chrysoperla rufilabris (Chrysopidae) and Micromus posticus (Hemerobiidae). The parasitoid Lysiphlebus testaceipes was ubiquitous in T. citricida cohorts, but its impact on colony survival was usually low. The fungal pathogen Verticillium lecanii was a significant source of colony mortality at one site in Puerto Rico, but was not observed on T. citricida in Florida.     

Responses of Lipolexis oregmae (Hymenoptera: Aphidiidae) to different instars of Toxoptera citricida (Homoptera: Aphididae)

The effects of host instar of Toxoptera citricida Kirkaldy (Homoptera: Aphididae) on the performance of the parasitoid Lipolexis oregmae (Gahan) (Hymenoptera: Aphidiidae), originally Lipolexis scutellaris Mackauer, were evaluated in an effort to increase basic knowledge of this host-parasitoid association, improve field sampling methods, and potentially predict the success of parasitism in the field. L. oregmae was able to oviposit and develop in all four instars of T. citricida; however, there are differences in the quality of different host instars. Although second-instar hosts produce more L. oregmae progeny and a higher female-biased sex ratio, fourth-instar hosts produce L. oregmae progeny that are larger and have a higher realized fecundity. However, fourth-instar hosts require a longer handling time and expose the parasitoid female to more aphid behavioral defenses than do second-instar hosts. Additionally, results suggest that fourth-instar hosts may elicit a physiological immune response to parasitism; when aphids were observed being stung once, the number of L. oregmae larvae present on dissection after 4 d and the number of eclosed adults was lower in fourth- than in second-instar hosts. Pupal mortality of L. oregmae was also higher in fourth-instar hosts compared with second-instar hosts. The results of this study confirm that L. oregmae has a high reproductive rate and low incidence of incomplete parasitization on this host and is one of only a few natural enemies able to complete development in all instars of the brown citrus aphid in Florida.     

Development and parasitism of Lysiphlebus testaceipes (Cresson) and Aphidius colemani Viereck (Hymenoptera: Braconidae) on Aphis gossypii Glover (Hemiptera: Aphididae) on two chrysanthemum cultivars

The parasitoids Lysiphlebus testaceipes (Cresson) and Aphidius colemani Viereck play an important role on the regulation of aphid populations on chrysanthemum grown in greenhouses. This study evaluated the interaction of biological control and plant resistance by the development and the parasitism of L. testaceipes and A. colemani on Aphis gossypii Glover. The aphid host was kept on commercial cultivars of chrysanthemum susceptible Yellow Snowdon (YS) and resistant White Reagan (WR). The experiment was carried out in climatic chamber at 22 +/- 1 masculineC, 70 +/- 10% RH, and photophase 12h. Nymphs of 2nd and 3rd instars of A. gossypii attacked only once by the parasitoids were used in the experiment. The development time was 15.0 and 12.9 days for L. testaceipes and 17.0 and 16.3 days for A. colemani kept on A gossypii on cvs. YS and WR, respectively. The parasitoid L. testaceipes showed greater parasitism rate (68.4%) on A. gossypii on cv. YS than on WR (50%), and for A. colemani was not found significative difference on parasitism (46.8 and 35% to YS and WR, respectively). The emergence rates of L. testaceipes and A. colemani were 91.6% and 85.3% on A gossypii reared on YS, and 78.1% and 100% on WR, respectively. The longevity of A colemani and the parasitism rate of L. testaceipes were affected in a negative way by the cv. WR. The results indicated a positive interaction of biological control with parasitoids and the resistant cv. WR on A. gossypii control in protected cultivation.     

Status of biological control by egg parasitoids of Diaprepes abbreviatus (Coleoptera: Curculionidae) in citrus in Florida and Puerto Rico

Eggs of Diaprepes abbreviatus (L.) were routinely monitored in citrus groves at ten locations in Florida during 1997 and 1998 to study egg parasitism. One citrus location was studied in Puerto Rico. No native parasitoids were recovered from 1,337 D. abbreviatus egg masses studied in Florida citrus. In contrast, an average of 35.5% (range 12.5 to 68.8%) parasitism of egg masses was reported in Puerto Rico. The parasitoids Aprostocetus gala, Horismenus spp, and Quadrastichus haitiensis were recovered from the eggs of D. abbreviatusfstudied in Puerto Rico. The Horismenus parasitoids were suspected hyperparasitoids. Releases of the parasitoid Ceratogramma etiennei from Guadeloupe were initiated during 1998 at each of the Florida research sites. By the end of 1998, C. etiennei had been recovered from D. abbreviatus eggs at two of nine locations in Florida citrus. The parasitoid was recovered from 1 of 34 egg masses at one of these locations during the month of September and from 3 of 34 egg masses at the other location during the month of November. Whether or not C. etiennei establishes itself at one or more locations in Florida remains to be seen.     

Influence of plant resistance at the third trophic level: interactions between parasitoids and entomopathogenic fungi of cereal aphids

Host-plant resistance can affect herbivorous insects and their natural enemies such as parasitoids and entomopathogenic fungi. This tritrophic effect acts on interspecific interactions between the two groups of natural enemies distantly related in phylogenetic terms. The intra- and extra-host aspects of the interaction between the cereal aphid parasitoid Aphidius rhopalosiphi and the entomopathogenic fungus Erynia neoaphidis developing on the grain aphid, Sitobion avenae, on resistant and susceptible wheat (Triticum aestivum) cultivars, were studied. The competitive outcome of the intra-host interaction depended on the timing of parasitoid oviposition and fungal infection and was affected by wheat resistance. In particular, survival of the parasitoid was lower on the resistant wheat cultivar than the susceptible wheat cultivar, when the competitive outcome of the interaction was favourable for either parasitoid or fungal development. Before and after this period the influence of plant resistance was not significant. Furthermore, the extra-host interaction was not affected by the wheat cultivar, although an increase in fungal infection of S. avenae was observed when parasitoids foraged in the experimental arena with sporulating aphid cadavers compared with foraging in the absence of sporulating cadavers. Our results showed that the host plant may affect interspecific interactions between parasitoids and fungi and that these interactions depended on the timing of parasitoid oviposition and fungal infection. Received: 16 March 1998 / Accepted: 24 August 1998     

Behavioral and developmental effects of neem extracts on Clavigralla scutellaris (Hemiptera: Heteroptera: Coreidae) and its egg parasitoid, Gryon fulviventre (Hymenoptera: Scelionidae)

Extracts of neem, Azadirachta indica A. Juss, negatively affected feeding and development of Clavigralla scutellaris (Westwood), a coreid pest of pigeonpea, Cajanus cajan (L.) Millspaugh. Labial dabbing, pod wall penetration, and seed damage by fifth instars were significantly reduced on beans, Phaseolus vulgaris (L.), that had been dipped in aqueous, methanolic, or hexane extracts of neem seed kernel. When fourth instars were dipped directly into aqueous extract, developmental abnormalities of the wings occurred at all levels tested and fecundity dropped to zero at concentrations above 0.3125%. The LC50 value was 3.14% (220 ppm azadirachtin) at 8 d. The scelionid wasp Gryon fulviventre (Crawford) is an important natural enemy of Clavigralla spp.; egg mortality from this parasitoid ranged from 37 to 85% during the fall cropping season. Feeding by newly emerged wasps was dramatically reduced when honey was mixed with aqueous neem suspension, but 6-d survivorship of adults did not differ significantly from that of the control. Wasp oviposition behavior was altered slightly when coreid eggs were treated with neem: the period of antennation was significantly extended, but time for drilling, oviposition, and marking was unaffected. Neem-dipped eggs were accepted for oviposition and progeny emerged successfully from these treated eggs. Exposure of already parasitized eggs to neem did not interfere with progeny emergence, longevity, or sex ratio. Thus, neem extract and egg parasitoids seem to be compatible and promising control strategies for C. scutellaris. Our results suggest that use of neem against pod-sucking bugs will not interfere with natural control provided by G. fulviventre.     

Three homopteran pests of citrus as prey for the convergent lady beetle: suitability and preference

The convergent lady beetle, Hippodamia convergens Guérin-Méneville (Coleoptera: Coccinellidae), is an important predator of soft-bodied insect pests in many regions of the United States, but generally uncommon in Florida citrus. Certain citrus producers in Florida recently initiated releases of commercially available H. convergens from California against the Asian citrus psyllid Diaphorina citri Kuwayama, vector of Huanglongbing or citrus greening disease. However, there is little information on potential efficacy of this predator against the psyllid or other pests of citrus. Preference, development, and reproduction by H. convergens was evaluated on freshly collected nymphs of D. citri, brown citrus aphid Toxoptera citricida Kirkaldy, green citrus aphid Aphis spiraecola Patch, and frozen eggs of the flour moth Ephestia kuehniella Zeller. Larvae preferred D. citri over T. citricida in two-way choice tests and consumed more D. citri or A. spiraecola than T. citricida in no-choice tests. Adults consumed equal numbers of all three species in both tests. Development times of larvae at 25.5±0.05°C on A. spiraecola were longer than on the other three diets. Larval survival and pupation times did not differ among diets. Females lived longer than males irrespective of diet, and longevity of both genders was greatly increased on E. kuehniella compared with D. citri and A. spiraecola. Life table analysis indicated that H. convergens should increase on all three species, with a greater potential on psyllids than aphids. Further studies are warranted to assess establishment and persistence of this potential biological control agent in the Florida citrus environment.     

THE ROLE OF COCCOPHAGUS SCUTELLARIS (HYMENOPTERA: APHELINIDAE) IN THE BIOLOGICAL CONTROL OF SOFT SCALE INSECTS (HOMOPTERA: COCCIDAE) IN EGYPT

Abstract Coccophagus scutellaris (Dalman) is one of the specific parasitoids that attack soft scale insects in Egypt. In the present study, C. scutellaris was reared from 6 species of soft scale insects. These are Ceroplastes flori-densis Comstock, Coccus hesperidum L., Pulvinaria floccgera (Westwood), P. psidii Maskell, Saissetia coffeae (Walker) and S. oleae (Oliver). The abundance of C. scutellaris was monitored from July to Nov. 1999–2000 in five localities in Egypt, the Beni-Suef, Cairo, Giza, Gharbiya and the Northern coast. C. scutellaris is considered an effective parasitoid of S. coffeae and S. oleae with maximum parasitism rates reaching 26% and 22% in Nov. and Aug. 1999, respectively.     

聚寄生性蝶蛹金小蜂雌蜂体型大小对产卵策略的影响

在寄生蜂行为生态学研究中, 通常将寄主体型大小作为寄主品质的主要性状来探究寄生蜂的搜寻行为机理, 而忽略寄生蜂体型大小的意义。为揭示聚寄生蜂雌蜂体型大小对其产卵决策的影响, 在严格控制寄主菜粉蝶Pieris rapae蛹体型大小（体重）的情况下, 于室内观察了不同体型大小的蝶蛹金小蜂Pteromalus puparum雌蜂的产卵行为, 并调查了子代蜂数量（窝卵数）、 性比和体型大小的变化。结果表明： 雌蜂在寄主上的驻留时间随其自身体型增大而缩短, 但随寄主体重增大而延长。窝卵数和余卵量受到雌蜂体型大小的显著影响, 均随雌蜂体型增大而显著增加（P<0.05）; 但子代蜂性比不受雌蜂体型大小的显著影响 (P>0.05)。子代雌、 雄性体型大小均与雌蜂体型大小无关, 但子代雌蜂体型随寄主体重增大而增大。结果证实, 雌性蝶蛹金小蜂体型大小影响其部分产卵决策。因此, 在建立聚寄生蜂产卵决策模型中应考虑雌蜂体型大小这一重要变量因素。     

Tritrophic interaction of parasitoid Lysiphlebus testaceipes (Hymenoptera: Aphidiidae), greenbug, Schizaphis graminum (Homoptera: Aphididae), and greenbug-resistant sorghum hybrids

Interactions of the parasitoid Lysiphlebus testaceipes (Cresson) and the greenbug, Schizaphis graminum (Rondani), on greenbug-resistant 'Cargill 607E' (antibiosis), 'Cargill 797' (primarily tolerance), and -susceptible 'Golden Harvest 510B' sorghum, Sorghum bicolor (L.) Moench, were tested using three levels of biotype I greenbug infestation. The parasitoid infestation rate was 0.5 female and 1.0 male L. testaceipes per plant. For all three greenbug infestation levels, the parasitoid brought the greenbug under control (i.e., prevented the greenbugs from killing the plants) on both resistant hybrids, but it did not prevent heavy leaf damage at the higher greenbug infestation rates. At the low greenbug infestation rate (50 greenbugs per resistant plant when parasitoids were introduced), greenbugs damaged 5 and 18% of the total leaf area on 'Cargill 797' and 'Cargill 607E', respectively, before greenbugs were eliminated. Leaf damage was higher for the intermediate infestation study (120 greenbugs per plant), 21% and 30% leaf area were damaged on the resistant sorghum hybrids 'Cargill 797' and 'Cargill 607E', respectively. At the high greenbug infestation rate (300 greenbugs per plant), heavy damage occurred: 61% on 'Cargill 607E' and 75% on 'Cargill 797'. The parasitoids did not control greenbugs on the susceptible sorghum hybrid 'Golden Harvest 510B'. L. testaceipes provided comparable control on both greenbug-resistant hybrids. This study supports previous studies indicating that L. testaceipes is effective in controlling greenbugs on sorghum with antibiosis resistance to greenbugs. Furthermore, new information is provided indicating that L. testaceipes is also effective in controlling greenbugs on a greenbug-tolerant hybrid.     

Estimation of hymenopteran parasitism in cereal aphids by using molecular markers

Polymerase chain reaction (PCR) primers were designed and tested for identification of immature parasitoids in small grain cereal aphids and for estimation of parasitism rates. PCR technique was evaluated for 1) greenhouse-reared greenbugs, Schizaphis graminum (Rondani), parasitized by Lysiphlebus testaceipes Cresson and 2) aphids collected from winter wheat fields in Caddo County, Oklahoma. For greenhouse samples, parasitism frequencies for greenbugs examined by PCR at 0, 24, and 48 h after removal of L. testaceipes parasitoids were compared with parasitism frequencies as determined by greenbug dissection. PCR was unable to detect parasitism in greenbugs at 0 and 24 h postparasitism, but it was able to detect parasitoids 48 h after parasitoid removal at frequencies that were not significantly different from dissected samples. Field-collected samples were analyzed by rearing 25 aphids from each sample and by comparing parasitoid frequencies of mummies developed and PCR performed on another 50 aphids. Aphid samples included corn leaf aphids, Rhopalosiphum maidis (Fitch); bird cherry-oat aphids, Rhopalosiphum padi (L.); English grain aphids, Sitobion avenae (F.); and greenbugs. Mummies were isolated until adult emergence, whereupon each parasitoid was identified to species (L. testaceipes was the only parasitoid species found). Parasitism detection frequencies for PCR also were not statistically different from parasitism frequencies of reared aphids. These results indicate that PCR is a useful tool for providing accurate estimates of parasitism rates and especially for identification of immature parasitoids to species.     

埃及黄盾食蚧蚜小蜂在生物防治蚧壳虫中的作用

在埃及,黄盾食蚧蚜小蜂Coccophagus suteelaris(Dalman)是一种有效防治蚧壳虫的寄生蜂,研究中分别用6种蚧壳虫Ceroplastes floridensis Comstock,Coccus hesperidumL.,Pulvinaria floccifera (Westwood),P.psidii Maskell,Saissetia coffeae(Walker)以及S.oleae(Oliver)来饲养黄盾食蚧蚜小蜂,1999－2000年间,在埃及的Beni-Suef,Cairo,Giza,Gharbiya和北海岸等5个地方,C.scutellaris大规模的发生在7－11月间,C.scuteelaris对S.coffeae和S.oleae的最高寄生率分别是发生在1999年11月和8月的26％和22％,因此可以认为,黄盾食蚧蚜小蜂是对两种蚧壳虫有效的寄生蜂。     

Evaluation of green lacewings, Chrysoperla plorabunda (Fitch) (Neurop., Chrysopidae), for augmentative release against Toxoptera citricida (Hom., Aphididae) in citrus

Larvae of the lacewing Chrysoperla plorabunda (Fitch) were evaluated in laboratory and field tests for potential to control the brown citrus aphid, Toxoptera citricida (Kirkaldy) in inundative releases. Larvae surviving to pupation consumed an average of 1676, 1297, 392, 165 and 130 1st–4th instar T. citricida nymphs and apterous adults, respectively, and the mean developmental time was 27.0, 23.0, 16.5, 13.8 and 18.3 days, respectively. The average pupation rate was 37.5%, but only 6.3% of pupae yielded adults. Developmental time and survival to pupation varied with the life stage of aphids fed to larvae, 4th instars yielding the highest survival and shortest developmental time. Development of C. plorabunda was compared on diets of T. citricida and Aphis spiraecola . Only 6.3% of larvae completed development on T. citricida , whereas 37.5% yielded adults on A. spiraecola . Larvae consumed more of the brown T. citricida than the green A. spiraecola in a choice test on a white background, but no preference was evident when aphids were offered on a black background. Two separate field trials were performed in citrus groves with T. citricida infestations in which an average of 275 and 116 C. plorabunda larvae/tree were released, respectively. The rate of T. citricida colony maturation (= survival to alate production) was very low in the first trial, and relatively high in the second trial, but did not differ between control and release trees in either trial. The most apparent cause of aphid colony mortality was predation by the coccinellids Cycloneda sanguinea L. and Harmonia axyridis Pallas. Despite acceptance of T. citricida in the laboratory, very few C. plorabunda larvae were observed feeding on aphid colonies on release trees.     

Interspecific host discrimination and intrinsic competition between Aphelinus asychis and Aphidius gifuensis in Myzus persicae

Aphelinus asychis Walker (Hymenoptera: Aphelinidae) and Aphidius gifuensis Ashmead (Hymenoptera: Braconidae: Aphidiinae) are solitary kionobiont endoparasitoids, which can parasitize the green peach aphid, Myzus persicae (Sulzer) (Hemiptera: Aphididae). We determined the influence of oviposition sequence and various time intervals (0, 24, 48, and 72 h) between two ovipositions on self‐ and conspecific discrimination and interspecific intrinsic competition between A. asychis and A. gifuensis. When offered unparasitized M. persicae and those parasitized by the other parasitoid species, the two parasitoid species oviposited more often in unparasitized hosts. Aphelinus asychis and A. gifuensis could, however, not avoid to multiparasitize hosts parasitized by the other species. Both parasitoid species had a limited interspecific discrimination ability through ovipositor insertion to detect internal cues. Aphidius gifuensis most often out‐competed A. asychis. The outcome of this interspecific competition was not influenced by oviposition sequence or time intervals between two ovipositions. Aphidius gifuensis eliminated competitors by physical combat at the first instar and probably by physiological suppression in later stages; A. asychis possibly used physiological suppression in all larval stages.     

Influence of egg load and oviposition time interval on the host discrimination and offspring survival of Anagyrus pseudococci (Hymenoptera: encyrtidae), a solitary endoparasitoid of citrus mealybug, ++Planococcus citri (Hemiptera: pseudococcidae)

Oviposition and host discrimination behaviour of unmated Anagyrus pseudococci (Girault), an endoparasitoid of the citrus mealybug Planococcus citri (Risso), were investigated in the laboratory. Female parasitoids were able to discriminate between parasitized hosts and healthy ones. The mean number of ovipositions was significantly higher in unparasitized than in parasitized hosts. Conspecific-superparasitism occurred more often than self-superparasitism. Changes in consecutive ovipositions over three hours by A. pseudococci suggested that egg load influenced the discrimination behaviour of the parasitoids, with females which had low egg loads mostly avoiding oviposition in already parasitized hosts at time intervals ranging from 0 h to 96 h, and distributing their eggs in the high quality (unparasitized) hosts. The parasitized hosts were rejected more commonly through antennal perception of external markers than during ovipositor probing which could have encountered internal markers but this relationship changed with increasing time after oviposition. The parasitoid's oviposition rate in unparasitized and conspecific-parasitized hosts varied at the different oviposition time intervals when the females had fewer eggs in the ovaries. Percentage emergence of parasitized offspring was not significantly influenced by whether they developed in single or superparasitized mealybugs. The significance of host discrimination by A. pseudococci is discussed.     

Development and Reproduction of Ladybeetles (Coleoptera: Coccinellidae) on the Citrus Aphids Aphis spiraecola Patch and Toxoptera citricida (Kirkaldy) (Homoptera: Aphididae)

Seven species of Coccinellidae inhabiting citrus groves in Florida were evaluated for ability to develop and reproduce on the citrus aphids Toxoptera citricida (Kirkaldy) and Aphis spiraecola Patch. Choice tests performed with adults and larvae indicated that both aphid species were generally acceptable prey. Coccinella septempunctata L., Coleomegilla maculata fuscilabris (Mulsant), Coelophora inaequalis F., and Olla v-nigrum Mulsant were unable to complete development on either aphid. Hippodamia convergens Guerin larvae completed development on A. spiraecola with 68% survival; none survived on T. citricida. Only Cycloneda sanguinea (L.) and Harmonia axyridis Pallas completed development on both A. spiraecola (60 and 70% survival, respectively) and T. citricida (100 and 95% survival, respectively). Larval developmental time was shorter on T. citricida than on A. spiraecola, and resulting adults were heavier, differences being more pronounced in H. axyridis. Females of C. septempunctata, C. inaequalis, and O. v-nigrum produced viable eggs on T. citricida. O. v-nigrum did not produce eggs on A. spiraecola. Females of C. m. fuscilabris and H. axyridis produced no eggs on A. spiraecola and mostly infertile eggs on T. citricida. Female H. convergens laid twice as many eggs feeding on T. citricida as on A. spiraecola and egg viability was similar. C. sanguinea females laid similar numbers of eggs on both aphids, but eggs produced on A. spiraecola had higher fertility. Pollen added to the T. citricida diet temporarily improved the fertility of H. axyridis females, but not that of C. sanguinea females. C. sanguinea was judged the best candidate for augmentative biocontrol of T. citricida, the primary vector of citrus tristeza virus.     

Presence of a conspecific increases superparasitism but not infanticide under self‐ and conspecific superparasitism in a semisolitary parasitoid,Echthrodelphax fairchildii (Hymenoptera: Dryinidae)

Female parasitoids are expected to avoid superparasitism (ovipositing in and/or on parasitized hosts) when unparasitized hosts are available. However, when the supply of unparasitized hosts is restricted, they are expected to self‐ as well as conspecifically superparasitize. One of the cues of a reduced availability of unparasitized hosts is the presence of a conspecific. Moreover, if the focal species can perform infanticide, after encountering a conspecific female, the females are expected to kill eggs existing in and/or on hosts when superparasitizing, because the eggs are more likely to be laid by others. In this study we investigated whether females of an infanticidal semisolitary parasitoid, Echthrodelphax fairchildii, increase their frequencies of superparasitism and infanticide after encountering a conspecific female. Echthrodelphax fairchildii females are capable of discriminating between self‐ and conspecific superparasitism until up to 0.75 h after the first egg was laid (self‐superparasitism frequency < conspecific superparasitism frequency). As expected, the female parasitoids were more likely to perform self‐ and conspecific superparasitism after they had encountered a conspecific. In particular, the self‐superparasitism frequency increased highly within a short period after the first oviposition, so that no difference between the self‐ and conspecific superparasitism frequencies was found. In contrast, the infanticidal‐probing frequency remained extremely low, irrespective of whether or not the female parasitoids had encountered a conspecific. Moreover, when superparasitizing, females usually laid female eggs. Possible causes for the low frequency of infanticidal probing and the female‐biased sex ratio are discussed.     

Molecular analysis of predation on parasitized hosts

Predation on parasitized hosts can significantly affect natural enemy communities, and such intraguild predation may indirectly affect control of herbivore populations. However, the methodological challenges for studying these often complex trophic interactions are formidable. Here, we evaluate a DNA-based approach to track parasitism and predation on parasitized hosts in model herbivore-parasitoid-predator systems. Using singleplex polymerase chain reaction (SP-PCR) to target mtDNA of the parasitoid only, and multiplex PCR (MP-PCR) to additionally target host DNA as an internal amplification control, we found that detection of DNA from the parasitoid, Lysiphlebus testaceipes, in its aphid host, Aphis fabae, was possible as early as 5 min. post parasitism. Up to 24 h post parasitism SP-PCR proved to be more sensitive than MP-PCR in amplifying parasitoid DNA. In the carabid beetles Demetrias atricapillus and Erigone sp. spiders, fed with aphids containing five-day-old parasitoids, parasitoid and aphid DNA were equally detectable in both predator groups. However, when hosts containing two-day-old parasitoids were fed to the predators, detection of parasitoid prey was possible only at 0 h (immediately after consumption) and up to 8 h post consumption in carabids and spiders, respectively. Over longer periods of time, post-feeding prey detection success was significantly higher in spiders than in carabid beetles. MP-PCR, in which parasitoid and aphid DNA were simultaneously amplified, proved to be less sensitive at amplifying prey DNA than SP-PCR. In conclusion, our study demonstrates that PCR-based parasitoid and prey detection offers an exciting approach to further our understanding of host-parasitoid-predator interactions.     

Development of the parasitoid,Cotesia rubecula (Hymenoptera: Braconidae) in Pieris rapae and Pieris brassicae (Lepidoptera: Pieridae): evidence for host regulation

Several recent models examining the developmental strategies of parasitoids attacking hosts which continue feeding and growing after parasitism (=koinobiont parasitoids) assume that host quality is a non-linear function of host size at oviposition. We tested this assumption by comparing the growth and development of males of the solitary koinobiont endoparasitoid, Cotesia rubecula, in first (L1) to third (L3) larval instars of its preferred host, Pieris rapae and in a less preferred host, Pieris brassicae. Beginning 3 days after parasitism, hosts were dissected daily, and both host and parasitoid dry mass was determined. Using data on parasitoid dry mass, we measured the mean relative growth rate of C. rubecula, and compared the trajectories of larval growth of the parasitoid during the larval and pupal stages using non-linear equations. Parasitoids generally survived better, completed development faster, and grew larger in earlier than in later instars of both host species, and adult wasps emerging from P. rapae were significantly larger than wasps emerging from all corresponding instars of P. brassicae. During their early larval stages, parasitoids grew most slowly in L1 P. rapae, whereas in all other host classes of both host species growth to pupation proceeded fairly uniformly. The growth of both host species was markedly reduced after parasitism compared with controls, with the development of P. brassicae arrested at an earlier stage, and at a smaller body mass, than P. rapae. Our results suggest that C. rubecula regulates certain biochemical processes more effectively in P. rapae than in P. brassicae, in accordance with its own nutritional and physiological requirements. Furthermore, we propose that, for parasitoids such as C. rubecula, which do not consume all host tissues prior to pupation, that parasitoid size and host quality may vary independently of host size at oviposition and at larval parasitoid egression.