Trophic web associated with the South American tomato moth Tuta absoluta: implications for its conservation biological control in Argentina

相似文献   

Oviposition decisions in an endoparasitoid under self-superparasitism conditions

Superparasitism is a widespread phenomenon. Having accepted superparasitism, mated female parasitoids must decide on the sex of each egg they subsequently lay into the same host. Theory predicts that this decision is either based on host quality, when more male eggs are laid in hosts that are already parasitized because they are perceived to be of poorer quality; or more eggs are laid of the sex that is most likely to be a strong larval competitor, i.e. generally females.Anastatus disparis is a facultative endoparasitic egg parasitoid. We used ‘artificial’ hosts to explore outcomes of decision making by A. disparis during superparasitism under a manipulated absence of larval competition. When only one egg was laid it was always female. As the number of eggs laid increased, so more of them were male. This supports the theory that oviposition decisions are based on host quality; more male eggs were laid in hosts that were already parasitized and thus of poorer quality.In a second experiment, eggs were exposed to parasitoids for different periods of time. Half the eggs were dissected to determine the number of parasitoid eggs that had been laid. The remaining eggs were incubated and the number and sex of offspring that ultimately emerged, following larval competition, were recorded. Under superparasitism conditions fierce larval competition ensued; only one offspring survived and they were predominantly female.In conclusion, oviposition decisions by female A. disparis accepting self-superparasitism were made based on host quality.     

Biology and performance of two indigenous larval parasitoids on Tuta absoluta (Lepidoptera: Gelechiidae) in Sudan

Tuta absoluta is an alien invasive pest in Sudan. Since it was detected in the country, the pest continues to cause major tomato losses. Alarmed by its devastating nature and the speed of spread, tomato growers resorted to the indiscriminate use of broad-spectrum insecticides. Promising indigenous parasitoid(s) may contribute to suppression of this pest. The biology and performance of the native parasitoids, Bracon nigricans Szépligeti (Braconidae) and Dolichogenidea appellator (Telenga) (Braconidae), was therefore evaluated against different immature stages of T. absoluta under laboratory conditions. A significantly higher number of fourth instar larvae was accepted for oviposition by B. nigricans. Similarly, fourth instar larvae yielded a considerably higher number of parasitoid offspring compared to third instar larvae. The male ratio of B. nigricans offspring which emerged from both larval instars was high, 0.96 and 0.66 for third and fourth instar larvae of T. absoluta, respectively. There was, however, no significant difference in the number of males and females that emerged from fourth instar larvae. Conversely, the number of hosts killed by stinging behaviour or host feeding was significantly higher on third instar larvae. B. nigricans potential fecundity varied with the age of the wasp with the lowest fecundity on the day of eclosion. The performance of D. appellator in terms of the total number of offspring produced and female progeny was similar for second and third instar larvae of T. absoluta. The preimaginal developmental time for both parasitoid species did not vary with either host stage or sex of the parasitoid. B. nigricans adult longevity was similar for both sexes, while that of D. appellator significantly varied with females living longer than males. Prospects for conservative biological control of T. absoluta are discussed in the light of the results of this study.     

Diving Into The Water: Cues Related to the Decision‐Making by an Egg Parasitoid Attacking Underwater Hosts

Although adult parasitoids spend a majority of their lives above ground, females of several species must search for their host in the water or on the soil. Adult parasitoids above ground can use a variety of sensory cues to detect their hosts from a distance. However, their sensory cues can be impaired from volatile chemicals, and their visual stimuli can be decreased while submerging or burrowing in the water of soil during their search for their hosts. Searching underwater or underground would incur high foraging costs, that is, time and energy consumption and increase risk of drowning. Therefore, to reduce such costs and increase searching efficiency, the decision on where to start submerging or burrowing for attacking hosts is important for parasitoids. Furthermore, there are no studies that have examined the cues of submerging or burrowing parasitoids on their exploit for the decision to attack their hosts. We have examined the cues used by the egg parasitoid Tiphodytes gerriphagus attacking underwater hosts. We compared the searching behaviors of T. gerriphagus among four oviposition site conditions. The four sites investigated were oviposition site with both host adult chemical residues and presence of eggs, with only the presence of eggs, with only the host adult chemical residues, and without any cue. Our results indicated that T. gerriphagus more frequently contacted and submerged at oviposition sites with the adult residues rather than at oviposition sites without them. Nonetheless, the presence of underwater host eggs did not affect the host‐searching behavior. This suggests that T. gerriphagus decided to submerge at the oviposition site in response to the adult residues. Furthermore, our observation also suggested that T. gerriphagus has already detected that the adult residues might be volatile before contacting the oviposition site. Finally, we will discuss the exploitation patterns of host‐searching cue by parasitoids that need to submerge from the context of its reliability and detectability problems.     

Age and parasitism status of Tuta absoluta eggs alter the foraging responses of the predator Nabis pseudoferus

We studied the effect of Trichogramma brassicae Bezdenko (Hymenoptera: Trichogrammatidae) parasitism of Tuta absoluta Meyrick (Lepidoptera: Gelechiidae) eggs on the foraging behavior of Nabis pseudoferus Remane (Hemiptera: Nabidae) feeding on T. absoluta eggs of different ages. Older parasitized eggs (48–72 h old) were rejected after probing with the probosis. A separate experiment showed that probing did not harm developing parasitoids. Bugs greatly reduced their feeding times on older parasitized eggs and spent more time grooming and probing eggs and leaves. Predators exhibited a type III functional response to 24 h-old eggs, but a type II response to older eggs, whether parasitized or not. 24 h-old eggs suffered higher attack rates, and required less handling time than older eggs. Although the predatory efficiency of N. pseudoferus was reduced in the presence of parasitized eggs, the partial refuge enjoyed by T. brassicae in older eggs may permit an additive impact on the pest, and should facilitate the joint augmentation of both species against T. absoluta.

     

Oviposition behaviour of Tamarixia radiata: effects of host density and exposure time

1. The number of hosts attacked as a function of host density is considered to be an important characteristic of parasitoid behaviour and is used to estimate key parameters such as handling time and ‘instantaneous rate of discovery’. However, little has been done to validate functional response models by direct observation of parasitoid oviposition behaviour. 2. Tamarixia radiata is the most promising parasitoid for biological control attacking Diaphorina citri. Mass rearing and augmentative release seen as a potential strategy for suppression of D. citri has been documented in abandoned citrus, residential areas, and organic groves. Nevertheless, parasitism rates in culture and in the field are only moderate, leading to questions about oviposition behaviour in response to host density. 3. Behaviours of gravid T. radiata females presented with susceptible host instars were categorised and documented by direct observation for 30 min and by camera recordings made over 12 h. Frequency of searching and antennating increased with host density during the 30 min. Probing rejection rates and search duration increased significantly with host density over 12 h. These factors resulted in significantly lower fecundity than expected, possibly due to host mark‐mediated deterrence within the small searching area. Females took approximately 3.6–4.2 min to probe and parasitise a host regardless of host density and exposure duration. These results were markedly different from the 52.2 min estimated from the functional response equation. 4. Further experiments are required to assess the range and persistence of the putative host‐marking pheromone, and to better understand the relationship between functional response parameters and actual behaviour.     

Acceptability and suitability of Tuta absoluta eggs from irradiated parents to parasitism by Trichogramma nerudai and Trichogramma pretiosum (Hymenoptera: Trichogrammatidae)

相似文献   

Egg allocation by Bracon hylobii Ratz., the principal parasitoid of the large pine weevil (Hylobius abietis L.), and implications for host suppression

1 The braconid parasitoid Bracon hylobii Ratz. is one of the few specialist natural enemies of the large pine weevil, Hylobius abietis L., a destructive pest of conifer transplants. An assessment of its role as an agent of biological control requires a detailed knowledge of the allocation of its reproductive effort. 2 Parasitoid females were continuously observed in laboratory culture with individually reared host larvae in bark discs. The outcome of sequential parasitoid–host encounters was recorded by subsequent examination of hosts and by rearing all parasitoids. 3 Parasitoids avoided ovipositing on host larvae < 100 mg fresh weight, even though such larvae represented sufficient biomass for complete parasitoid development. All larger larvae were vulnerable to attack, which leaves a window of vulnerability for parasitoids of about 90% of weevil larval life. 4 Parasitoids presented with a range of host sizes showed no preference above 100 mg for the size of host first attacked, but allocated more eggs and a greater total handling time to larger hosts. 5 Most eggs were deposited on the first host attacked, with progressively fewer allocated to subsequent hosts. However, oviposition experience did not affect the time spent on the next host. 6 From these results it is anticipated that when weevil larval size is reduced by less favourable feeding substrates, fewer parasitoid eggs will be allocated to each but more host larvae will ultimately be attacked. 7 Generation time, host finding, oviposition rate, clutch size, life expectancy and diapause induction are strongly affected by temperature. Life expectancy is substantially shorter for parasitoids deprived of non‐host food supplement. At 15 and 20 °C the number of hosts attacked and the number of eggs deposited decreased with female age. 8 Bracon hylobii is inevitably poorly synchronized with a variable life‐cycle host; it is egg‐limited and can enter diapause at a relatively high field temperature. None of these characteristics suggest that it could stabilize the abundance of its host below an economically acceptable threshold density. However, the reproductive potential of the parasitoid suggests that it could make a significant contribution to larval mortality and suppress adult recruitment, thus complementing other control strategies.     

Oviposition and reproductive performance of a generalist parasitoid (Trichogramma pretiosum) exposed to host species that differ in their physical characteristics

The response of generalist egg parasitoids to alternative natural hosts that are present simultaneously is not well known. We investigated the behavior of Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae) in relation to two field hosts Helicoverpa armigera Hübner and Spodoptera litura Fabricius, in choice and no choice tests. We quantified the effects of natal host species and post-emergence adult age on the oviposition preference of the parasitoids. H. armigera eggs were consistently preferred over S. litura eggs, regardless of the natal host and adult age. When only S. litura eggs were available as hosts, they were parasitized at statistically similar rates to H. armigera eggs (average of 17 ± 2.7 vs. 13 ± 3.0, H. armigera to S. litura). The adult lifespan and lifetime fecundity of T. pretiosum were variable but were affected by natal host species and/or host species to which they were exposed. Mean lifespan and fecundity of parasitoids that had developed in H. armigera eggs and were exposed to H. armigera eggs for oviposition were 13.9 ± 1.8 days and 98.7 ± 11.0 adult offspring. By contrast, those that developed in S. litura eggs and were exposed to S. litura eggs for oviposition lived for 7 ± 0.9 days and produced 53.8 ± 8.0 adult offspring. The ovigeny index (OI) was significantly lower in the parasitoids exposed to H. armigera eggs than in those exposed to S. litura eggs, regardless of the natal host, indicating that H. armigera eggs sustain the adult parasitoids better than S. litura eggs. These results are used to predict parasitoid behavior in the field when both hosts are available.     

Temporary host paralysis and avoidance of self-superparasitism in the solitary endoparasitoid Meteorus pulchricornis

We suggest a new mechanism for the avoidance of self-superparasitism by a solitary endoparasitoid of free-living hosts. Meteorus pulchricornis (Wesmael) (Hymenoptera: Braconidae) is a solitary larval endoparasitoid of a wide range of Lepidoptera. First, we tested the tendency to avoid multiple oviposition on Spodoptera litura (Fabricius) (Lepidoptera: Noctuidae) larvae, examining the distribution pattern of eggs deposited in 20 hosts in 24 h. The standardized Morisita index of dispersion (Ip) for the number of eggs in a host larva was almost always below zero, and the 95% confidence limits of the means were lower than zero for both experienced and inexperienced females, indicating that parasitoids tend to avoid multiple oviposition, although not completely. Second, we observed changes in host movements (head shaking and forward movement) after oviposition and the occurrence of additional ovipositions in pre-oviposited hosts, because a recent study indicated the necessity of visual cues provided by host movements for oviposition by this species. The incidence of host movements decreased markedly after oviposition and remained at a low level for approximately 1 h, during which time additional ovipositions were rarely observed. Temporary host paralysis after oviposition would be a new mechanism for the avoidance of self-superparasitism in a solitary endoparasitoid using visual cues from moving hosts for oviposition.     

Effects of Asobara japonica venom on larval survival of host and nonhost Drosophila species

Abstract Ovipositing Asobara japonica females inject venom (containing paralysis‐inducing factors) immediately after the insertion of their ovipositors into Drosophila larvae, and lay eggs a little later. Interruption of their oviposition behaviour before egg laying causes high larval mortality in host Drosophila species, whereas normal oviposition does not. This suggests that venom of this parasitoid is toxic to larvae of these host species but its toxicity is suppressed by factor(s) provided by parasitoid females at the time of laying egg or by parasitoid embryos developing in the hosts. On the other hand, venom does not show toxicity to larvae of nonhost Drosophia species. Possible functions of venom are discussed.     

Effect of host deprivation on egg quality,egg load,and oviposition in a solitary parasitoid,Chetogena edwardsii (Diptera: Tachinidae)

Solitary parasitoids are limited to laying one egg per host because larvae compete within hosts. If host encounter rate is low, females should not increase the number of eggs/host in response. The tachinid fly, Chetogena edwardsii,was used to evaluate the effect of host deprivation on egg accumulation, oviposition behavior, and egg quality in a solitary parasitoid. Females deprived of hosts for 2– 7 days accumulate about 1 day's supply of eggs. Egg output of deprived females once hosts are restored does not differ from that of control females. Deprived females retain one egg in the uterus where it undergoes embryogenesis. Maggots emerging from retained eggs are more likely to survive in hosts molting in 40 h or less after receipt of an egg than are maggots emerging from eggs fertilized shortly before oviposition. Egg retention is a consequence of host deprivation that permits females to broaden the range of hosts they can exploit to include soon-to-molt hosts and possibly multiply parasitized hosts.     

Superparasitism strategies by a native and an exotic parasitoid species attacking the Mexican fruit fly,Anastrepha ludens (Diptera: Tephritidae)

Superparasitism refers to the action of parasitoids ovipositing eggs in hosts that are already parasitized; this inevitably results in the elimination of supernumerary larvae in solitary parasitoids. Here, we investigated superparasitism performed by two species of solitary parasitoids on the larvae of Anastrepha ludens (Loew; Diptera: Tephritidae): a native species, Doryctobracon crawfordi (Viereck; Hymenoptera: Braconidae), and an exotic species, Diachasmimorpha tryoni (Cameron; Hymenoptera: Braconidae). Tests were conducted under laboratory conditions evaluating the behaviour of females acting alone (self-superparasitism) or in groups (conspecific superparasitism). Parasitism strategies were different between these two species. In D. crawfordi, the number of first instar larvae found in each dissected host pupa was never greater than two, regardless of the number of oviposition scars observed per pupa. In contrast, there was a positive correlation between the number of oviposition scars and the number of first instar larvae in D. tryoni. The survival and fecundity of D. crawfordi females emerging from pupae with one scar was higher than in females emerging from pupae with more scars. In D. tryoni, the number of oviposition scars did not show deleterious effects on life history traits and was positively correlated with the proportion of emerging females. An understanding of the superparasitism strategy adopted by parasitoid species could be of great interest to augmentative biological control programmes because the mass rearing of natural enemies could be negatively or positively affected by this condition.     

Patch-leaving rules for parasitoids with imperfect host discrimination

Abstract.

• 1 The solitary parasitoid Anagrus delicatus attacks hosts (plant-hopper eggs) that exist in distinct batches and that are readily detectable to the foraging parasitoid. However, Anagrus delicatus attacks only a small fraction of the available hosts within a batch of eggs and then disperses (Cronin & Strong, 1993a). Here we address the question: Why is A.delicatus abandoning seemingly high quality patches?
• 2 A parasitoid with an imperfect ability to discriminate between unparasitized hosts and hosts that it has attacked earlier within the same patch experiences a risk of self-superparasitism when attacking multiple hosts within a single patch. Self-superparasitism can incur costs in the form of lost time and eggs. Early patch leaving can be favoured as a means of avoiding the costs of self-superparasitism.
• 3 A simple static model demonstrates that patch leaving is favoured by low costs of travelling to a new patch, high error rates in discriminating previously self-parasitized hosts, and high levels of parasitism in the currently occupied patch.
• 4 A more detailed dynamic state variable model, parameterized for A.delicatus, demonstrates that this parasitoid's seemingly enigmatic behaviour can be explained under our hypothesis. In order for this to be the case, we predicted that A.delicatus cannot recognize previously parasitized hosts. Subsequent to our prediction, Cronin & Strong (1993b) demonstrated that experienced A.delicatus do not avoid ovipositing in previously self-parasitized hosts.
• 5 Optimal patch leaving rules can be highly sensitive to even very low host discrimination error rates, which may be widespread among parasitoids.

     

Efficiency,intrinsic competition and interspecific host discrimination of Copidosoma desantisi and Trichogramma evanescens,two parasitoids of Phthorimaea operculella

Trichogramma evanescens West. (Hymenoptera: Trichogrammatidae) and Copidosoma desantisi Annecke & Mynhardt (Hymenoptera: Encyrtidae) are potential parasitoids of the potato tuber moth (PTM), Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae) in Egypt. Discrimination of a parasitized host from an unparasitized host would prevent wasting of time, eggs and reduce competition with conspecifics or heterospecifics. Therefore, we evaluated interspecific host discrimination, multiparasitism and intrinsic competition between the two wasp species. In a choice test, females of T. evanescens showed high interspecific host discrimination only when they were offered 2-day-old C. desantisi parasitized and unparasitized PTM eggs. In contrast, C. desantisi showed high host discrimination and preferred unparasitized eggs to PTM eggs harboring 2-h- or 2-day-old T. evanescens’ eggs. We also evaluated the effect of different introduction sequences on the efficacy of the two wasps. Dissection data indicated that the two parasitoids had a negative impact on each other. There was a significant reduction in the total number of deposited eggs as well as total number of parasitized hosts by each parasitoid. Regarding the rearing experiment, the total number of T. evanescens-induced black eggs or C. desantisi formed mummies in combined treatments was significantly lower than in single parasitoid treatments (control). Moreover, C. desantisi was inferior and did not develop from any multiparasitized host regardless of oviposition order. It was suggested that combined release of the two wasps would not elevate rate of parasitism over that of single parasitoid treatments and competition between them would reduce their efficacy.     

Benefits of self-superparasitism in a polyembryonic parasitoid

Macrocentrus grandii is a polyembryonic parasitoid, with embryos that divide asexually within the host (European corn borer, Ostrinia nubilalis) to produce broods of clonal offspring. From a biological control standpoint, polyembryony seems advantageous because each parasitized host yields multiple parasitoids with minimal time and egg investment. When we observed M. grandii in the field, however, we found that the parasitoid virtually always invested additional time and, if possible, stings into hosts that it had already stung, apparently reducing some of the advantages of polyembryony. We therefore investigated and found support for two potential benefits that can be gained by self-superparasitism in this system. First, multiple stings allowed production of mixed-sex broods: 27% of multiply-stung versus 0% of singly-stung hosts produced mixed-sex broods. Second, multiple stings increased mean parasitoid progeny produced per host, primarily by reducing the chance of complete brood failure. Our results indicate substantial benefit for a second sting, but little benefit for three or more stings, even though M. grandii was sometimes observed to invest more than two stings within a single host. However, we also found that within-host larval competition is prevalent, suggesting that supernumerary stings may pay off in competition against conspecific larvae. Such additional investment within a single host would be particularly beneficial when hosts, rather than eggs, are limiting, but would decrease the overall efficacy of M. grandii as a biological control agent.     

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.     

Herbivore egg deposition induces tea leaves to arrest the egg‐larval parasitoid Ascogaster reticulata

Plants are able to activate direct and indirect defences against egg deposition by herbivorous insects. A known indirect defence is the production of synomones to help egg‐ and egg‐larval parasitoids to locate their hosts. The wasp Ascogaster reticulata Watanabe (Hymenoptera: Braconidae) is a solitary egg‐larval parasitoid of the moth Adoxophyes honmai Yasuda (Lepidoptera: Tortricidae), which lays eggs and feeds as caterpillars on the leaves of the tea plant Camellia sinensis (L.) Kuntze (Theaceae). Here, we studied whether or not oviposition by A. honmai induces tea plants to produce synomones that help the parasitoid to locate its host. An olfactometer bioassay suggested that synomones produced by the infested plants did not attract the parasitoid over a short range. However, a contact bioassay showed that tea leaves were induced to arrest the parasitoid 24 h after egg deposition and remained induced until the host‐egg masses were no more attractive to the parasitoids. Wing scales and deposits of adult moths and the contents of the egg masses did not induce the tea leaves to arrest the parasitoid, but the contents of the female moth's reproductive system did. Synomone induction was systemic: uninfested leaves in the vicinity of egg‐laden leaves also arrested the parasitoid.     

Impact of mating status on egg-laying and superparasitism behaviour in a parasitoid wasp

Most parasitoid female wasps can distinguish between unparasitized and parasitized hosts and use this information to optimize their progeny and sex allocation. In this study, we explored the impact of mating on oviposition behaviour (parasitism and self‐ and conspecific superparasitism) on both unparasitized and already parasitized hosts in the solitary parasitoid wasp Eupelmus vuilleti (Crw.) (Hymenoptera: Eupelmidae). Virgin and mated females had the same oviposition behaviour and laid eggs preferentially on unparasitized hosts. The sex ratio (as the proportion of females) of eggs laid by mated females in parasitism and conspecific superparasitism was 0.67 ± 0.04 and 0.57 ± 0.09, respectively. Likewise, females laid more eggs in conspecific superparasitism than self‐superparasitism under our experimental conditions. These experiments demonstrate that E. vuilleti females can (i) discriminate between unparasitized and parasitized hosts and adapt the number of eggs they lay accordingly, and (ii) probably discriminate self from conspecific superparasitized hosts. Finally, mating does not appear to influence the host discrimination capacity, the ovarian function, or the oviposition behaviour.     

Life history parameters of the microtype parasitoid fly Pales pavida (Diptera: Tachinidae), and effects of host age and number of eggs ingested by host on parasitism success

With the aim of developing better procedures for rearing the microtype tachinid fly Pales pavida (Meigen), we performed ecological studies in the laboratory using the natural host Mythimna separata (Walker), investigating larval development, mating behaviour, individual oviposition patterns and relationships between parasitisation and number of eggs ingested (NEI) per host. The host instar at the time of parasitoid egg ingestion significantly affected the development time of the immature parasitoid: development took longer when the hosts ingested eggs when at the fifth instar than at the sixth (last) instar. There was no difficulty obtaining mated females in the laboratory when day 0–1 female flies were kept with day 2–4 males. Mean lifetime fecundity was 5805?±?568 eggs per female. Daily rates of oviposition by individual females varied widely; the greatest number of eggs laid in a day was exactly 1700. When the NEI by day 1 fifth instars or day 0 or 3 last instars was 1, 3, 6 or 10, the parasitisation percentage tended to increase with increasing NEI, although it did not differ significantly between NEI 6 and 10. Therefore, the percentage adult emergence per egg ingested decreased from NEI 6 to 10, particularly in the case of last instars. Using day 0 last instars, with six eggs ingested per host, should increase parasitisation rates and shorten the development time of the parasitoid for rearing.