Intrinsic competition between two European egg parasitoids of the brown marmorated stink bug

Following the accidental introduction and spread of the invasive polyphagous agricultural pest Halyomorpha halys (Stål) (Hemiptera: Pentatomidae), the two European egg parasitoids Anastatus bifasciatus (Geoffroy) (Hymenoptera: Eupelmidae) and Ooencyrtus telenomicida (Vassiliev) (Hymenoptera: Encyrtidae) have been investigated for inundative biological control. Since the competititve outcome between the two generalist parasitoids is difficult to predict, intrinsic competition was investigated with a time-course development study. Both species readily oviposited in H. halys eggs containing eggs and early instar larvae of the competitor, but oviposition decreased when eggs contained late instar larvae and pupae. Ooencyrtus telenomicida offspring emergence from multiparasitized eggs was significantly lower than that from rearing controls, independent of the order of parasitization. Anastatus bifasciatus offspring emergence was not influenced by the presence of O. telenomicida when it parasitized as the first species, but emergence was decreased after oviposition in eggs containing O. telenomicida larvae and pupae. There was no indication that O. telenomicida can act as a facultative hyperparasitoid of A. bifasciatus. These results suggest that A. bifasciatus is the superior intrinsic competitor and no or minor negative implications for A. bifasciatus are expected if released in combination with O. telenomicida.     

Genetic variability in the area searched by a parasitic wasp: analysis from automatic video tracking of the walking path

The ability of foraging hymenopterous parasitoid females to discover their hosts, and thus to be efficient agents in biological control programs, is likely to be related to the surface they are able to prospect per unit of time. However, this behavioural trait has never been accurately estimated, and its implication in female efficiency has never been really demonstrated. This paper provides an algorithmic method that can be used to estimate this trait from an automatic recording of the females' walking path. Using stochastic procedures simulating walking tracks, this trait is shown to be strongly related to the number of hosts that parasitoid females are able to attack per unit of time. This trait was estimated for individual females of Trichogramma brassicae Bezdenko (Hymenoptera; Trichogrammatidae). On average, females of this species are able to prospect about 28mm(2)s(-1). Finally, the genetic variation in this trait was studied using the iso-female line method. A significant genetic variability was observed. It provides the basic information that is necessary to start a genetic selection of mass-reared Trichogramma in order to improve their efficiency in controlling target pests in biological control programs. The functional and evolutionary implications of these results are discussed.     

Behavioral response of the egg parasitoid <Emphasis Type="Italic">Ooencyrtus telenomicida</Emphasis> to host-related chemical cues in a tritrophic perspective

The response of the generalist egg parasitoid Ooencyrtus telenomicida (Vassiliev) (Hymenoptera: Encyrtidae) to host-related chemical cues from tomato plants, Solanum lycopersicum L., and adults of Nezara viridula (L.) (Heteroptera: Pentatomidae) was investigated in laboratory-based no-choice and paired-choice tests. In Y-tube olfactometer experiments, when female wasps were exposed to volatiles from plants in different conditions, they were attracted only to volatiles produced by N. viridula adult-infested tomato plants. When female wasps were exposed to adults of N. viridula, they were attracted to volatiles from virgin males, and, at a lower level, to volatiles from mated females in preoviposition state. Finally, studies in open arena showed that chemical footprints left by adults of N. viridula did not induce arrestment responses in wasp females. These results are discussed in terms of extrinsic competition with other beneficial egg parasitoids that in field can compete for the same egg mass, since intraguild interactions may affect the success of a biological control program.     

First report of Melittobia australica Girault in Europe and new record of M. acasta (Walker) for Italy

Melittobia acasta and Melittobia australica are newly recorded from Sicily, Italy, and the second species is reported in Europe for the first time. A short historical background about Melittobia parasitoid wasps, their hosts, and distribution, with emphasis in those two species is presented together with illustrations to facilitate their identification. Brief discussion about the presence and possible distribution of the species in Sicily is also included.     

Chemo-orientation responses in hymenopteran parasitoids induced by substrate-borne semiochemicals

Hymenopteran parasitoids can utilize substrate-borne semiochemicals released by conspecifics or by their hosts, increasing the likelihood of successful mating and host location. According to the literature, two substrate-borne chemo-orientation patterns can occur: (1) biased random searching, a non-directional reaction toward the chemicals (kinesis), and (2) trail-following searching, a directional response toward the source emitting the chemical compounds (taxis). These two different strategies can be adopted by parasitoids to locate hosts and mates. In host location, random searching is induced by allelochemicals indirectly associated with the host, whereas trail-following behavior is induced by allelochemicals directly emitted by the target organism. In mate finding, sex pheromones emitted by conspecifics can induce either the random searching or the trail-following behavior, although the spatial distribution of virgin conspecifics could be an important factor driving the evolution of substrate-borne chemo-orientation patterns. The chemical nature of substrate-borne semiochemicals has not yet been fully elucidated. Most studies have shown that crude extracts are biologically active for eliciting parasitoid arrestment response, but few studies have clearly characterized their chemical nature. However, experimental evidence indicates that cuticular lipids located in the external layer of insects’ bodies play a role in parasitoid–parasitoid and host–parasitoid communication. The ecological role of parasitoid chemo-orientation in host and mate location is discussed from a biological control perspective.     

Fortuitous Introduction and Successful Establishment ofTrichopoda pennipesF.: Adult Parasitoid ofNezara viridula(L.)

While the accidental introduction of insect pests is becoming increasingly common due to intense and rapid commercial exchanges, the incidence of accidental introduction of their parasitoids seems to be much less frequent or is overlooked. The case reported here, for a tachinid Phasiinae, is both fortuitous and fortunate since the parasitoid has been carried from the New World by a pest that is already present in the new country, Italy, where there are virtually no competitors. Establishment and specificity of the parasitoid was confirmed by the first follow-up studies immediately after its discovery.     

The ovipositing female of Ooencyrtus telenomicida relies on physiological mechanisms to mediate intrinsic competition with Trissolcus basalis

Ongoing studies by our group showed that the outcome of the intrinsic competition between two solitary egg parasitoids, Trissolcus basalis (Wollaston) (Hymenoptera: Scelionidae) and Ooencyrtus telenomicida (Vassiliev) (Hymenoptera: Encyrtidae), is dominated by O. telenomicida. In this article we investigated the role played by the ovipositing O. telenomicida female in the suppression of a T. basalis competitor. Laboratory experiments were conducted by allowing an O. telenomicida female to puncture the eggs of Nezara viridula (L.) (Heteroptera: Pentatomidae) with her ovipositor (= no oviposition) or to parasitize them. The results show that O. telenomicida relies on some physiological mechanisms to mediate its interspecific intrinsic competition with T. basalis. In fact, the emergence of T. basalis was strongly reduced in host eggs that were parasitized either before or after being punctured by O. telenomicida at fixed time intervals (5, 15, 30, or 45 h). The low percentage of emergence of T. basalis (ranging from approximately 4–20%) was a consequence of the delay and growth rate reduction of larval development. Furthermore, the percentage of eclosion of N. viridula nymphs was negatively affected by the O. telenomicida female’s punctures (96% from healthy host eggs, 4% from punctured host eggs). Host eggs punctured or oviposited in by O. telenomicida showed alterations in the ooplasm including some melanized‐like areas near the hole made with the ovipositor; such alterations indicate that the adult parasitoid releases substances that affect the host eggs survival. These results suggest that the O. telenomicida female influences both the physiological interspecific parasitoid‐parasitoid interaction, as well as the host‐parasitoid interaction, providing, for the first time in egg parasitoids, evidence that physiological suppression of some competitive egg parasitoids is mediated by the ovipositing female.     

Behavioral responses of the parasitoid Melittobia digitata to volatiles emitted by its natural and laboratory hosts

Responses of macropterous females of the ectoparasitoid Melittobia digitata Dahms (Hymenoptera: Eulophidae) to direct and indirect cues emitted by its natural hosts as well as laboratory hosts were investigated using a Y‐tube olfactometer. To locate the nest of mud dauber wasps, Trypoxylon politum Say (Hymenoptera: Crabronidae), and one of their inquilines, Anthrax spec., parasitoids exploit volatiles from the freshly built nest mud and the empty cocoon constructed by the wasps, as well as their meconium. However, the parasitoids did not respond to odors emitted by older nest mud or by the host stages that are attacked (T. politum prepupae and Anthrax spec. larvae). Melittobia digitata was not attracted to direct volatiles released by the dipteran hosts Anastrepha ludens Loew (Diptera: Tephritidae) (a natural host) and Sarcophaga bullata (Parker) (Diptera: Sarcophagidae) (a laboratory host). Based on our results, we suggest that M. digitata adopts a ‘sit and wait’ strategy to locate mud dauber wasps, relying mainly on indirect host‐related cues: females search for nests that are under construction and once found, they wait inside the cell until the host completes its cocoon and releases meconium, an indicator that is associated with host suitability. No attraction was found to dipteran hosts, suggesting that parasitization of these hosts may be incidental, due to the broad host plasticity of Melittobia wasps.     

Volatile compounds released by disturbed and undisturbed adults of Anchomenus dorsalis (Coleoptera, Carabidae, Platynini) and structure of the pygidial gland

Volatile compounds produced by adults of Anchomenus dorsalis under undisturbed and disturbed conditions were investigated with an all-glass aeration apparatus. GC-MS analysis of the crude extracts from undisturbed and disturbed adults highlighted four major volatile compounds, undecane, heneicosane, Z-9 tricosene and tricosane, of which significantly more undecane was released by disturbed adults compared to undisturbed beetles. The pygidial glands of adults of Anchomenus dorsalis were investigated using light and Transmission Electron Microscopy (TEM). Each gland showed dense aggregates of secretory cells organized into visually distinct lobes; a long collecting canal that drains the secretion towards the reservoir, a bean-shaped double lobed muscular reservoir in which secretion is stored and a short duct (efferent duct) through which the secretion is discharged. The function of the pygidial glands and the possible role played by undecane as a defensive allomone and/or chemical signalling molecule are discussed.     

Emergence,dispersal, and mate finding via a substrate‐borne sex pheromone in the parasitoid Metaphycus luteolus

Metaphycus luteolus Timberlake (Hymenoptera: Encyrtidae) is a facultatively gregarious parasitoid of soft scale insects. We conducted behavioral experiments to better understand the mating structure of this species. Emergence of male and female offspring is synchronized, beginning at the onset of photoperiod. Both sexes are able to disperse, although dispersal of males from natal patches appears to take longer than dispersal of females. We demonstrated the presence of a female‐produced contact pheromone using open arena bioassays and motion tracking software, testing residues deposited by walking females, and extracts of females. Males responded to the females' ‘chemical footprints’ and to acetone and hexane extracts of females by searching and arrestment on the chemical residues. Responses of males were dose dependent and diminished with time since the stimulus was deposited. Our findings support the hypothesis that non‐local mating among wasps emerging from different hosts may be quite common in these parasitoids. The implications of our results for the mating structure and previously documented sex ratio patterns of these parasitoids are described.