Statistical study ofTrichogramma brassicae efficiency in relation with characteristics of the European corn borer egg masses

The efficiency ofTrichogramma brassicae inundative releases in biological control of the European corn borerOstrinia nubilalis was analyzed in seven plots of 504 plants, each situated in a corn field naturally infested by the European corn borer. Different strategies ofTrichogramma releases were defined on the seven plots. These inundative releases were concluded to be highly efficient even on plots where there were either no parasitoid release or only one parasitoid release at the beginning of the egg mass laying period.     

Biology ofTrichogramma ostriniae (Hym.: trichogrammatidae) reared onOstrinia nubilalis (Lep.: pyralidae) and survey for additional hosts

Trichogramma ostriniae has been identified as a candidate for biological control ofOstrinia nubilalis. As little was known about the biology of this parasitoid when reared onO. nubilalis, we undertook experiments to quantify biological parameters important to mass-rearing and ase ofT. ostriniae. When reared continuously onO. nubilalis, femaleT. ostriniae on average lived 2.7 days and produced 24 progeny. Continuous access to honey resulted in a four-fold increase in longevity and fecundity and a significant increase in the percentage of females parasitizing eggs. Rates of fecundity and parasitism decreased with age of female. Likewise, emergence rates and percentage of female progeny decreased with age of parental female.T. ostriniae successfully parasitizedO. nubilalis eggs until the blackhead stage. Most parasitism of eggs and eclosion of adults occurred during the first half of photophase. Eggs of 13 Lepidopterans were parasitized byT. ostriniae. Eggs of the Noctuidae, Pyralidae, and Plutellidae experienced higher levels of parasitism than others tested.T. ostriniae appears to be similar to other species ofTrichogramma in several respects and does not possess any characteristics that limit its potential for mass rearing and use for augmentative biological control ofO. nubilalis.     

Locomotor activity ofTrichogramma brassicae (Hymenoptera) under the influence of high-temperature shocks

In order to assess the effects of high temperatures prevailing during the releases ofTrichogramma brassicae Bezdenko parasitoid used against the European corn borerOstrinia nubilalis Hübner, we exposed wasps in the white pupa stage (WP) to single or double shocks (at 35 or 44°C for 6 h) in the laboratory. The locomotor activity of adults in the presence ofO. nubilalis egg masses is greater than in pure air. Single or double shocks at 35°C have little effect on the females. On the contrary, wasps exposed to single or double shocks at 44°C had a lower motility than control wasps.     

Ovarian cycle in immature and adult stages ofTrichogramma cacoeciae andT. Brassicae (Hym.: Trichogrammatidae)

The ovarian cycle was studied in two species ofTrichogramma, the thelytokousT. cacoeciae and the arrhenotokousT. brassicae. For both species, egg development was recorded (1) in the immature stages (2) in adult females before and after one bout of oviposition. The two species differed in the numbers of immature eggs formed and stored in the ovaries, and in the pattern of egg replenishment after oviposition.     

The Response Specificity of <Emphasis Type="Italic">Trichogramma</Emphasis> Egg Parasitoids towards Infochemicals during Host Location

Parasitoids are confronted with many different infochemicals of their hosts and food plants during host selection. Here, we investigated the effect of kairomones from the adult host Pieris brassicae and of cues present on Brussels sprout plants infested by P. brassicae eggs on the behavioral response of the egg parasitoid Trichogramma evanescens. Additionally, we tested whether the parasitoid’s acceptance of P. brassicae eggs changes with different host ages. The wasps did not discriminate between olfactory cues from mated and virgin females or between mated females and males of P. brassicae. T. evanescens randomly climbed on the butterflies, showing a phoretic behavior without any preference for a certain sex. The parasitoid was arrested on leaf parts next to 1-day-old host egg masses. This arrestment might be due to cues deposited during oviposition. The wasps parasitized host eggs up to 3 days old equally well. Our results were compared with former studies on responses by T .brassicae showing that T. evanescens makes less use of infochemicals from P. brassicae than T. brassicae.     

Effect of Inoculative Releases of Trichogramma ostriniae on Populations of Ostrinia nubilalis and Damage to Sweet Corn and Field Corn

European corn borer (Ostrinia nubilalis) is one of the most injurious pests of sweet and field corn in the United States. We report here on controlled experiments in which an egg parasitoid (Trichogramma ostriniae) was released inoculatively (75,000 females ha⁻¹) early in the growing season (when corn plants were at the early to mid-whorl stage) to test its efficacy as a biological control agent of O. nubilalis. Releases were made in fields of sweet corn and field corn. Numbers of eggs laid in experimental plots, larval tunnels, and larvae and proportion of damaged ears were determined. Mass of ears was determined for field corn plots. In sweet corn, despite greater oviposition by O. nubilalis in T. ostriniae release plots, the number of borer larvae, stalk tunnels, and damaged ears was reduced by ∼50% compared with those in nonrelease plots. This reduction in damage was consistent for early and late-planted sweet corn. In the field corn plots, larger numbers of O. nubilalis eggs were again laid in some release plots than in control plots. However, O. nubilalis damage appeared to be suppressed in T. ostriniae release plots, although no significant differences were found in most. These results were promising, but further work is required in field corn. The results for sweet corn demonstrated that inoculative releases of T. ostriniae provide suppression of O. nubilalis populations adequate to reduce damage significantly.     

Oviposition behaviour ofEphedrus cerasicola [Hym.: Aphidiidae] parasitizing different instars of its aphid host

The parasitoidEphedrus cerasicola Starý oviposited in all 4 nymphal instars and in newly moulted adults ofMyzus persicae (Sulzer). The different host categories were offered with no choice. The duration of an oviposition increased with the age of nymphs, being about 13, 18, 21, 22, and 17 s from 1 st instars to adults, respectively. Observations of number of stabbing attacks prior to oviposition, percent of the encounters not resulting in oviposition, time from first encounter to oviposition, handling time and aphid defensive behaviour also indicated that 1 st instarM. persicae are most easily parasitized. The behaviour ofE. cerasicola in encounters with unparasitized and parasitized hosts, suggested that the parasitoid could discriminate. In encounters with parasitized 1 st to 4th instar aphids,E. cerasicola used only the antennae in 80% of the encounters that resulted in discrimination.     

Analysis of oviposition behaviour in the parasitoidEpidinocarsis lopezi (Hym.: Encyrtidae): Comparison of flow charts on factorial maps

Females ofEpidinocarsis lopezi (De Santis) are presented with groups of unparasitized hosts or groups containing different ratios of parasitized hosts (Phenacoccus manihoti). Oviposition behaviour sequences obtained in various situations are filmed and split into units of behaviour or patterns. The succession of patterns is analyzed and translated into flow charts on factorial maps characteristic of each type of sequence. Comparison of flow charts reveals host discrimination by female parasitoids since the relative importance of behaviour patterns is modified according to the level of parasitized hosts encountered; it also gives clues to the strategy adopted by the female parasitoid during the search of a patch. In addition, the analysis divides the oviposition sequence into three separate patterns, specific to host search, oviposition act and post-oviposition behaviour. This series of patterns is closely related to factorial axes which indicates the fundamental trends of oviposition behaviour.     

RETRACTED ARTICLE: Foraging of Host-Habitat and Superparasitism in <Emphasis Type="Italic">Cotesia glomerata</Emphasis>: A Gregarious Parasitoid of <Emphasis Type="Italic">Pieris brassicae</Emphasis>

The study investigates differences in the oviposition pattern of a braconid parasitoid, Cotesia glomerata (Linn.) in Pieris brassicae (Linn.) in relation to their use of different cruciferous food plants. The response of P. brassicae to superparasitism and consequences for the parasitoid were examined in order to elucidate the ecological significance of this behaviour. Female parasitoid located various crucifers and searched for host more frequently almost on all the host plants tested i.e. cabbage, cauliflower, Chinese cabbage, broccoli and radish. According to the estimated relative number of female locating hosts, cabbage was the most attractive plant for C. glomerata and total number of eggs laid in host larvae feeding on it was higher than in larvae feeding on other plants. Laboratory experiments demonstrated that superparasitism reduced survivorship of P. brassicae larvae. Superparasitism lengthened parasitoid development and prolonged the feeding period of host larvae. Sex ratio and the body weight of emergent wasps correlated negatively with brood size. Despite a trade-off between maximising brood size and optimising the fitness of individual offspring, two or three ovipositions on P. brassicae larvae resulted in a greater female dry mass than did a single oviposition on the host. Thus, superparasitism might be of adaptive significance under certain circumstances, especially when host density is low and unparasitized hosts are rare in a habitat.     

Host plant constituents as oviposition stimulants for a generalist herbivore: European corn borer

Oviposition response of the polyphagous European corn borer,Ostrinia nubilalis (Hübner) (Lepidoptera: Pyralidae), to chemical constituents in host plants was investigated in the laboratory using two-choice bioassays. Foliar extracts of corn (Zea mays L.), pepper (Capsicum annuum L.) and potato (Solanum tuberosum L.) were prepared using the solvents pentane, acetone and methanol. In all three host plants, chemicals soluble in pentane stimulated oviposition. In potato, chemicals extractable in acetone also elicited a positive oviposition response. When presented with a choice between pentane extracts of corn and pepper, females preferred corn. No preferences were exhibited between pentane extracts of corn and potato or pepper and potato. Pentane extracts of corn husks, tassels, silk, and corn leaves from plants at early whorl and tassel (pre-pollen shed) stages of development also stimulated oviposition. Similar extracts from plants at 2-leaf and blister (when kernels resemble blisters) stages were not stimulatory. This indicates that plant phenology affects chemically mediated oviposition response in European corn borer. The potential use of plant chemicals for management ofO. nubilalis in the field is suggested.     

Patch leaving decision rules and the Marginal Value Theorem: an experimental analysis and a simulation model

The patch exploitation strategy of females of the insect parasitoid Trichogramma brassicae was studied on patches containing different proportions of hosts that were previously attacked by conspecificfemales. On average, T. brassicae females spent more time onpatches of higher quality, and all patches were reduced tothe same level of profitability before being left. This appearedto be in accordance to the optimal predictions of the CharnovMarginal Value Theorem. The proximate leaving mechanisms involvedwere analyzed by means of a Cox proportional hazards model.Each oviposition in a healthy host appeared to have an incremental influence on the patch residence time, whereas each rejectionof a healthy host or of a host that was previously attackedby the same female (i.e., self-superparasitism) had a decrementaleffect. These patch leaving mechanisms did not change accordingto the quality of the patch the females were exploiting. AMonte Carlo simulation was developed around the results of the Cox regression model. The results suggest that this set of patchleaving rules seems to provide the females with a sufficientway to reach the predictions of the Charnov model. Among thedifferent mechanisms involved, the incremental effect associatedwith each oviposition in a healthy host appeared to play the most important role. The relationship between the proximatemechanistic rules adopted by the females and the ultimate predictionof the Charnov model is discussed.     

Parasrnzatlon of bemisia argentifolii (Hom.: Aleyrodidae) by encarsia pergandiella (Hym.: Apheunidae)

The biology of the arrhenotokous autoparasitoid,Encarsia pergandiella Howard, was studied in the laboratory on the silverleaf whitefly,Bemisia argentifolii Bellows & Perring. Egg to adult development of parasitoid females averaged ca. 14 days at about 25.3+0.2?C regardless of whether the whitefly host was reared on tomato, eggplant or squash. While all instars ofB. argentifolii were accepted for primary parasitization, a greater percentage of third and fourth instars were parasitized. Mortality of whitefly nymphs in the absence of parasitization did not differ among instars and averaged about 35%. Second instar to pupal parasitoid females were accepted for secondary parasitization although a greater percent of pupal females were parasitized. About 40% of immatureE. pergandiella females more than 4 days old died in the absence of secondary parasitization when exposed to adultE. pergandiella females.     

The role of host species, age and defensive behaviour on ovipositional decisions in a solitary specialist and gregarious generalist parasitoid (Cotesia species)

The main objective of this study was to determine the extent to which host acceptance behaviour as related to host species, age, and defensive behaviour might explain the differences in host use that exist between two congeneric and sympatric species of parasitic wasps. Cotesia glomerata (L.) (Hymenoptera: Braconidae) is gregarious and generalist on several species of Pieridae, whereas C. rubecula (Marshall) is solitary and specific to Pieris rapae (L.). Cotesia species differed in their responses to host species (P. brassicae (L.), P. napi (L.) and P. rapae) and developmental stage (early and late 1st, 2nd and 3rd instars). In no-choice tests, host acceptance by C. rubecula was higher for p. rapae and females did not distinguish among the 6 host ages. In contrast, when foraging for P. brassicae and P. napi, C. rubecula females more readily attacked early first instar. Cotesia glomerata showed a higher degree of behavioural plasticity towards acceptance of Pieris host species and host age than did C. rubecula. Cotesia glomerata females parasitized the three Pieris species and showed higher acceptance of first and second instars over third instar. Oviposition success was also influenced by host defensive behaviour. The frequency and the effectiveness of defensive behaviour rose with increasing age of the host, P. brassicae being the most aggressive Pieris species. Furthermore, the mean duration of C. glomerata oviposition was significantly reduced by the defensive reactions of P. brassicae, which would likely affect parasitoid fitness as oviposition time is positively correlated to clutch size in C. glomerata. Acceptance frequencies corresponded well to field reports of Pieris-Cotesia associations and to patterns of parasitoid larval performance, suggesting that the acceptance phase might be used as a reliable indicator of Cotesia host-specificity.     

The parasitoidCotesia glomerata (Hymenoptera: Braconidae) discriminates between first and fifth larval instars of its hostPieris brassicae,on the basis of contact cues from frass,silk, and herbivore-damaged leaf tissue

Adult females of the larval parasitoidCotesia glomerata (L.) respond to chemical cues associated with feeding damage inflicted on cabbage plants by its host,Pieris brassicae (L.). The use of these infochemicals by the parasitoid during selection of the most suitable host instar was investigated. The parasitoid can successfully parasitize first-instar host larvae, while contacts with fifth-instar larvae are very risky since these caterpillars react to parasitization attempts by biting, spitting, and hitting, resulting in a high probability of the parasitoid being seriously injured or killed. Observations of the locomotor behavior of individual wasps on leaves with feeding damage inflicted by the first and the fifth larval instars and on host silk and frass showed that several cues affect the duration of searching by the parasitoids after reaching a leaf: cues on the margin of the feeding damage and cues in the host frass and silk. Whole frass, silk, and hexane extracts of frass obtained from first-instar elicited parasitoid's searching behavior significantly longer than frass, silk, and hexane extract of frass from the fifth instar. The results demonstrate thatC. glomerata can discriminate between first instars, which are more suitable hosts, and fifth instars ofP. brassicae without contacting the caterpillars, by exploiting instar-related cues.     

Specificity and instar preference ofDiplazon laetatorius (Hym.: Ichneumonidae) parasitizing aphidophagous syrphids (Dipt.: Syrphidae)

D. laetatorius is one of the most important natural enemies of aphidophagous syrphid flies, in terms of abundance, in crops and pastures in Argentina. In order to increase the database on this parasitoid, its prey selection behaviour was studied. Laboratory experiments were made to investigate its preference of host species and instars within species. This parasitoid showed a fastidious behaviour, choosing more often than predicted by chance, first instars ofAllograpta exotica (Wied.).     

Within-patch foraging behaviour of the aphid parasitoidAphidius funebris: plant architecture, host behaviour, and individual variation

The influence of plant architecture, host colony size, and host colony structure on the foraging behaviour of the aphid parasitoidAphidius funebris Mackauer (Hymenoptera: Aphidiidae) was investigated using a factorial experimental design. The factorial design involved releasing individual parasitoid females in aphid colonies consisting of either 10 or 20 individuals ofUroleucon jaceae L. (Homoptera: Aphididae) of either only larval instar L3 or a mixture of host instars, both on unmanipulated plants and on plants that had all leaves adjacent to the colony removed. Interactions between the parasitoid and its host were recorded until the parasitoid had left the plant. The time females spent on the host plant and the number of eggs laid varied greatly among females. Host colony size significantly affected patch residence time and the number of contacts between parasitoids and aphids. Plant architecture influenced the time-budget of the parasitoids which used leaves adjacent to the aphid colony for attacking aphids. Female oviposition rate was higher on unmanipulated plants than on manipulated plants. No further significant treatment effects on patch residence time, the number of contacts, attacks or ovipositions were found. Oviposition success ofA. funebris was influenced by instar-specific host behaviour. Several rules-of-thumb proposed by foraging theory did not account for parasitoid patch-leaving behaviour.     

Short-range cues mediate parasitoid searching behavior on maize: The role of oviposition-induced plant synomones

Host searching by egg parasitoids faces a main constraint due to low detectability of cues from host eggs. Therefore egg parasitoids have developed distinctive strategies by exploiting cues that originate from non-target instars of the host and/or from plants. The scelionid Telenomus busseolae is specialized on concealed eggs of Sesamia nonagrioides and other noctuid stemborers. In this paper we show that oviposition by S. nonagrioides induces changes in the cues present on maize leaf surface, which arrest naïve females of T. busseolae. The induction appears to be systemic as the parasitoid also responds to leaves and leaf portions that are not directly affected by ovipositing females. Such oviposition-induced, short-range, plant synomones, acting in sequence with the kairomonal cues from scales left on the plant by the ovipositing host female, significantly increases parasitoid efficiency during host finding. The elicitor of plant response originates from the host female reproductive system, being contained both in the host’s ovarian eggs and in the colleterial gland secretion. Induction starts 24 h after oviposition and lasts at least till 72 h. The ecological role of this oviposition-induced plant synomone in host searching by T. busseolae is discussed.     

Preference and performance of the hyperparasitoid Syrphophagus aphidivorus (Hymenoptera: Encyrtidae): fitness consequences of selecting hosts in live aphids or aphid mummies

Abstract.  1. Theoretical models predict that ovipositional decisions of parasitoid females should lead to the selection of the most profitable host for parasitoid development. Most parasitoid species have evolved specific adaptations to exploit a single host stage. However, females of the aphid hyperparasitoid Syrphophagous aphidivorus (Mayr) (Hymenoptera: Encyrtidae) display a unique and atypical oviposition behaviour by attacking either primary parasitoid larvae in live aphids, or parasitoid pupae in dead, mummified aphids.
2. In the laboratory, the correlation between host suitability and host preference of S. aphidivorus on the host Aphidius nigripes Ashmead parasitising the aphid Macrosiphum euphorbiae (Thomas) was investigated.
3. The relative suitability of the two host stages was determined by measuring hyperparasitoid fitness parameters (survival, development time, fecundity, sex ratio, and adult size of progeny), and calculating the intrinsic rate of population increase ( r _m). Host preference by S. aphidivorus females and the influence of aphid defence behaviour on host selection was also examined.
4. Hyperparasitoid offspring performance was highest when developing from hosts in aphid mummies and females consistently preferred this host to hosts in parasitised aphids. Although aphid defensive behaviour may influence host selection, it was not a determining factor. Ecological and evolutionary processes that might have led to dual oviposition behaviour in S. aphidivorus are discussed.     

Larvicidal activity of lectins onLucilia cuprina: mechanism of action

Foraging behaviour and host-instar preference of young and old females of the solitary aphid parasitoid,Lysiphlebus cardui Marshall (Hymenoptera: Aphidiidae), were studied in the laboratory. The analysis of interactions between parasitoids and different stages ofAphis fabae cirsiiacanthoidis Scop. (Homoptera: Aphididae) revealed that encounter rates between aphids and parasitoid females and defence reactions of the aphids influenced the degree to which a particular aphid age class is parasitized. Encounter rates between hosts and parasitoid females depended on the foraging pattern of the parasitoid, which varied with age. In mixed aphid colonies patch residence time increased with parasitoid age. Furthermore, younger parasitoids (≦1 day old) laid more eggs into second and third instars, while older parasitoids (≧4 days old) did not show distinct host instar preferences. It is suggested that the oviposition behaviour ofL. cardui is influenced by the physiological state, i.e. the age of the wasp.