Landscape context on generalist and specialist aphid natural enemies

Report for the scientific sojourn at the University of Lund, Sweden, between May and September 2007. A landscape-scale research approach has been highlighted by a growing body of literature as essential for understanding important ecosystem services as biological control. Aphids are victims of a diversity of enemies making the aphid-enemy interaction a nice example for the role of enemy diversity for the functioning of biological control. Here it is examined the effects of landscape complexity on cereal aphids and associated natural enemies that varied in the degree of specialization. Parasitoids wasps abundance did not differ between landscape types but was strongly negatively related to the percentage of arable land. In contrast, abundances of generalist predators like Coccinellidae were significantly higher in simple landscapes since can benefit from the high availability of a variety of alternative resources within cropping systems. Consequently coccinellidae-to-aphid ratio was significantly higher in fields in homogenous landscapes as compared to fields included in an heterogeneous landscape, suggesting that enemy pressure on cereal aphids increases with landscape simplification. The landscape effect will depend mainly on the degree of specialization of functionally dominant natural enemies, so that the results imply that conservation actions aiming to optimise abundance for one taxonomic group in the agricultural landscape will not automatically increase abundance of other groups. Given that the strength of natural enemy impact on biocontrol depends on landscape features and the role of functionally dominant natural enemies. So, therefore it is essential to focus the future empirical work in examining the schedule of agricultural landscapes that maintain a diversity of generalist and specialist natural enemies.

First report of parasitism on pupae of Opsiphanes invirae amplificatus Stichel (Lepidoptera, Nymphalidae) by Conura (Conura) maculata (Fabricius) (Hymenoptera, Chalcididae) in Rio Grande do Sul, Brazil

First report of parasitism on pupae of Opsiphanes invirae amplificatus Stichel (Lepidoptera, Nymphalidae) by Conura (Conura) maculata (Fabricius) (Hymenoptera, Chalcididae) in Rio Grande do Sul, Brazil. This scientific note records the parasitism on pupae of Opsiphanes invirae amplificatus Stichel (1904) by Conura (Conura) maculata (Fabricius). This is a report of this interaction in the subtropical region of South America and the first report of the occurrence of this parasitoid in the state of Rio Grande do Sul, Brazil.

Five new associations of parasitoids in potter wasps (Vespidae, Eumeninae)

Five new associations of parasitoids in potter wasps (Vespidae, Eumeninae). New associations of host and parasitoids involving potter wasps: Toxophora leucon and Pleurochrysis sp. were found parasitizing Cyphomenes anisitsii, Chrysis sp. (gr. intricans) was found parasitizing Minixi suffusum, Plega beardi was found parasitizing Montezumia pelagica sepulchralis and Macrosiagon sp. was found parasitizing Pachodynerus nasidens.

Are wing size, wing shape and asymmetry related to field fitness of Trichogramma egg parasitoids?

The effects of wing shape, wing size, and fluctuating asymmetry in these measures oil the field fitness of T. nr. brassicae and T. pretiosum were investigated. Trichogramma wasps mass-reared on eggs of the factitious host Sitotroga cerealella were released in tomato paddocks and those females ovipositing on Helicoverpo spp. eggs were recaptured. Comparisons of the recaptured group with a sample from the release population were used to assess fitness. Wing data were obtained by positioning landmarks on mounted forewings. Size was then measured as the centroid size computed from landmark distances, while Procrustes analysis followed by principal component analysis was used to assess wing shape. Similar findings were obtained for both Trichogramma species: fitness of wasps was strongly related to wing size and some shape dimensions, but not to the asymmetries of these measures. Wasps which performed well in the field had larger wings and a different wing shape compared to wasps from the mass reared population. Both size and the shape dimensions were linearly associated with fitness although there was also some evidence for non-linear selection on shape. The results suggest that wing shape and wing size are reliable predictors of field fitness for these Trichogramma wasps.

Egg parasitoid wasps as natural enemies of the neotropical stink bug Dichelops melacanthus

The objective of this work was to determine the potential of five species of Scelionidae wasps - Telenomus podisi, Trissolcus basalis, Trissolcus urichi, Trissolcus teretis and Trissolcus brochymenae - as natural enemies of the neotropical stink bug Dichelops melacanthus, and to determine if the presence of eggs of other stink bug species influences the parasitism and development of the parasitoids. Two kinds of experiments were done in laboratory: without choice of hosts (eggs of D. melacanthus) and with choice (eggs of D. melacanthus and of Euschistus heros). Biological parameters, including proportion of parasitism, immature survivorship, progeny sex ratio, immature stage development period, and host preference were recorded. All the evaluated parasitoids can parasitize and develop on D. melacanthus eggs. The first choice of eggs did not influence the proportion of D. melacanthus eggs parasitized by Tr. basalis, Tr. teretis or Tr. brochymenae. However, D. melacanthus eggs as the first choice of Te. podisi and Tr. urichi increased, respectively, 9 and 14 times the chance for parasitism on eggs of this species. Behavioral and ecological aspects of parasitoids should be considered prior to their use in biological control programs.

Cross-resistance following artificial selection for increased defense against parasitoids in Drosophila melanogaster

An increase in resistance to one natural enemy may result in no correlated change, a positive correlated change, or a negative correlated change in the ability of the host or prey to resist other natural enemies. The type of specificity is important in understanding the evolutionary response to natural enemies and was studied here in a Drosaphila-parasitoid system. Drosophila melanogaster lines selected for increased larval resistance to the endoparasitoid wasps Asobara tabida or Leptopilina boulardi were exposed to attack by A. tabida, L. boulardi and Leptopilina heterotama at 15 degrees C, 20 degrees C, and 25 degrees C. In general, encapsulation ability increased with temperature, with the exception of the lines selected against L. boulardi, which showed the opposite trend. Lines selected against L, boulardi showed large increases in resistance against all three parasitoid species, and showed similar levels of defense against A. tabida to the lines selected against that parasitoid. In contrast, lines selected against A. tabida showed a large increase in resistance to A. tabida and generally to L. heterotoma, but displayed only a small change in their ability to survive attack by L. boulardi. Such asymmetries in correlated responses to selection for increased resistance to natural enemies may influence host-parasitoid community structure.

Functional and Taxonomic Diversity of Stinging Wasps in Brazilian Atlantic Rainforest Areas

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Parasitism by Ixodiphagus Wasps (Hymenoptera: Encyrtidae) in Rhipicephalus sanguineus and Amblyomma Ticks (Acari: Ixodidae) in Three Regions of Brazil

Hymenopteran parasitoids have been shown to be of potential value in tick biocontrol. Tick parasitoids has been reported only once in Brazil, over 95 yr ago when Ixodiphagus hookeri (Howard) was reported parasitizing Rhipicephalus sanguineus (Latreille) nymphs in Rio de Janeiro. Herein, we report the occurrence of Ixodiphagus spp. in ticks from three different regions of Brazil. In the state of Maranhao, in northeastern Brazil, parasitoids were detected in R. sanguineus nymphs on three occasions, during August 2009 and September 2010 (dry season), and January 2011 (rainy season). All parasitoids found in northeastern Brazil were identified as I. hookeri. In the state of Mato Grosso do Sul (westDcentral Brazil), one Amblyomma sp. engorged nymph was shown to be parasitized by I. hookeri. In the state of Rondonia (northern Brazil), one Amblyomma sp. engorged nymph was parasitized by Ixodiphagus texanus (Howard). Because Ixodiphagus spp. are present in ecologically distinct and geographically distant areas of Brazil, they are of potential use for biocontrol in the country.

New associations between native parasitoids and exotic insects introduced in Italy and in Europe

The introduction of exotic species is one of the most important threats to biodiversity.This phenomenon may cause economic and environmental damage. To prevent these invasions there are institutions like EPPO. Nevertheless, the introduction of exotic pests is an increasing issue, difficult to control. Classic biological control, based on importation of natural enemies from the country of origin, has been successfully used for over 120 years, but it has also raised some criticism. My research work has focused on the study of the new associations occurring between indigenous parasitoids and three exotic pests introduced in Italy and Europe. The three target insects considered were: Cacyreus marshalli Butler (Lepidoptera: Lycaenidae), a pest of Geranium plants; Dryocosmus kuriphilus Yasumatsu (Hymenoptera: Cynipidae), a plague of Castanea sp. and Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae). This ladybug has been introduced as a biological control agent, but since some years it considered as an invasive species. For C. marshalli I performed laboratory tests on acceptance and suitability of immature stages of this butterfly by Exorista larvarum (Diptera: Tachinidae) and Brachymeria tibialis (Hymenoptera: Chalcidicae). The experiments showed that these two parasitoids could be used to contain this pest. For D. kuriphilus I performed field samplings in an infested chestnut area, the samples were maintained in rearing chamber until gall wasp or parasitoids emergence. In the 3-year research many parasitoids of gall wasps were found; one of these, Torymus flavipes (Walker), was found in large number. For H. axyridis the research work included a first phase of field sampling, during which I searched indigenous parasitoids which had adapted to this new host; the only species found was Dinocampus coccinellae (Schrank) (Hymenoptera: Braconidae). Laboratory tests were performed on the wasp rearing, biology and capacity to contain H. axyridis.

A tritrophic signal that attracts parasitoids to host-damaged plants withstands disruption by non-host herbivores

Background: Volatiles emitted by herbivore-infested plants are highly attractive to parasitoids and therefore have been proposed to be part of an indirect plant defense strategy. However, this proposed function of the plant-provided signals remains controversial, and it is unclear how specific and reliable the signals are under natural conditions with simultaneous feeding by multiple herbivores. Phloem feeders in particular are assumed to interfere with plant defense responses. Therefore, we investigated how attack by the piercing-sucking cicadellid Euscelidius variegatus influences signaling by maize plants in response to the chewing herbivore Spodoptera littoralis.Results: The parasitoid Cotesia marginiventris strongly preferred volatiles of plants infested with its host S. littoralis. Overall, the volatile emissions induced by S. littoralis and E. variegatus were similar, but higher levels of certain wound-released compounds may have allowed the wasps to specifically recognize plants infested by hosts. Expression levels of defense marker genes and further behavioral bioassays with the parasitoid showed that neither the physiological defense responses nor the attractiveness of S. littoralis infested plants were altered by simultaneous E. variegatus attack.Conclusions: Our findings imply that plant defense responses to herbivory can be more robust than generally assumed and that ensuing volatiles convey specific information about the type of herbivore that is attacking a plant, even in complex situations with multiple herbivores. Hence, the results of this study support the notion that herbivore-induced plant volatiles may be part of a plant's indirect defense stratagem. © 2010 Erb et al; licensee BioMed Central Ltd.

The Role of Fresh versus Old Leaf Damage in the Attraction of Parasitic Wasps to Herbivore-Induced Maize Volatiles

The odor produced by a plant under herbivore attack is often used by parasitic wasps to locate hosts. Any type of surface damage commonly causes plant leaves to release so-called green leaf volatiles, whereas blends of inducible compounds are more specific for herbivore attack and can vary considerably among plant genotypes. We compared the responses of naïve and experienced parasitoids of the species Cotesia marginiventris and Microplitis rufiventris to volatiles from maize leaves with fresh damage (mainly green leaf volatiles) vs. old damage (mainly terpenoids) in a six-arm olfactometer. These braconid wasps are both solitary endoparasitoids of lepidopteran larvae, but differ in geographical origin and host range. In choice experiments with odor blends from maize plants with fresh damage vs. blends from plants with old damage, inexperienced C. marginiventris showed a preference for the volatiles from freshly damaged leaves. No such preference was observed for inexperienced M. rufiventris. After an oviposition experience in hosts feeding on maize plants, C. marginiventris females were more attracted by a mixture of volatiles from fresh and old damage. Apparently, C. marginiventris has an innate preference for the odor of freshly damaged leaves, and this preference shifts in favor of a blend containing a mixture of green leaf volatiles plus terpenoids, after experiencing the latter blend in association with hosts. M. rufiventris responded poorly after experience and preferred fresh damage odors. Possibly, after associative learning, this species uses cues that are more directly related with the host presence, such as volatiles from host feces, which were not present in the odor sources offered in the olfactometer. The results demonstrate the complexity of the use of plant volatiles by parasitoids and show that different parasitoid species have evolved different strategies to exploit these signals.

How caterpillar-damaged plants protect themselves by attracting parasitic wasps.

Parasitic and predatory arthropods often prevent plants from being severely damaged by killing herbivores as they feed on the plants. Recent studies show that a variety of plants, when injured by herbivores, emit chemical signals that guide natural enemies to the herbivores. It is unlikely that herbivore-damaged plants initiate the production of chemicals solely to attract parasitoids and predators. The signaling role probably evolved secondarily from plant responses that produce toxins and deterrents against herbivores and antibiotics against pathogens. To effectively function as signals for natural enemies, the emitted volatiles should be clearly distinguishable from background odors, specific for prey or host species that feed on the plant, and emitted at times when the natural enemies forage. Our studies on the phenomena of herbivore-induced emissions of volatiles in corn and cotton plants and studies conducted by others indicate that (i) the clarity of the volatile signals is high, as they are unique for herbivore damage, produced in relatively large amounts, and easily distinguishable from background odors; (ii) specificity is limited when different herbivores feed on the same plant species but high as far as odors emitted by different plant species and genotypes are concerned; (iii) the signals are timed so that they are mainly released during the daytime, when natural enemies tend to forage, and they wane slowly after herbivory stops.

Cannibalistic feeding of larval Trichogramma carverae parasitoids in moth eggs

Wasps of the genus Trichogramma parasitise the eggs of Lepidoptera. They may deposit one or many eggs in each host. Survival is high at low density but reaches a plateau as density increases. To reveal the mechanism by which excess larvae die we chose a lepidopteran host that has flattened, transparent eggs and used video microscopy to record novel feeding behaviours and interactions of larval Trichogramma carverae (Oatman and Pinto) at different densities. Single larvae show a rapid food ingestion phase, followed by a period of extensive saliva release. Ultimately the host egg is completely consumed. The larva then extracts excess moisture from the egg, providing a dry environment for pupation. When multiple larvae are present, the initial scramble for food results in the larvae consuming all of the egg contents early in development. All larvae survive if there is sufficient food for all to reach a threshold developmental stage. If not, physical proximity results in attack and consumption of others, continuing until the surviving larvae reach the threshold stage beyond which attacks seem to be no longer effective. The number of larvae remaining at the end of rapid ingestion dictates how many will survive to emerge as adults.

Bait and Habitat Preferences, and Temporal Variability of Social Wasps (Hymenoptera: Vespidae) Attracted to Vertebrate Carrion

In addition to feeding on carrion tissues and fluids, social wasps can also prey on immature and adult carrion flies, thereby reducing their populations and retarding the decomposition process of carcasses. In this study, we report on the occurrence and behavior of social wasps attracted to vertebrate carrion. The collections were made monthly from September 2006 to October 2007 in three environments (rural, urban, and forest) in six municipalities of southeast Brazil, using baited bottle traps. We collected Agelaia pallipes (Olivier, 1791) (n = 143), Agelaia vicina (Saussure, 1854) (n = 106), Agelaia multipicta (Haliday, 1836) (n = 18), and Polybia paulista Ihering, 1896 (n = 3). The wasps were observed feeding directly on the baits and preying on adult insects collected in the traps. Bait and habitat associations, temporal variability of social wasps, and possible forensic implications of their actions are discussed.

Phylogeography of Chelonus insularis (Hymenoptera: Braconidae) and Campoletis sonorensis (Hymenoptera: Ichneumonidae), Two Primary Neotropical Parasitoids of the Fall Armyworm (Lepidoptera: Noctuidae)

In a previous study, we observed no spatial genetic structure in Mexican populations of the parasitoids Chelonus insularis Cresson (Hymenoptera: Braconidae) and Campoletis sonorensis Cameron (Hymenoptera: Ichneumonidae) by using microsatellite markers In the current study, we Investigated whether for these important parasitoids of the fall armyworm (Lepidoptera: Noctuidae) there is any genetic structure at a larger scale Insects of both species were collected across the American continent and their phylogeography was Investigated using both nuclear and mitochondria] markers Our results suggest an ancient north-south migration of C insularis, whereas no clear pattern] could be determined for C sonorensis. Nonetheless, the resulting topology indicated the existence of a cryptic taxon within this later species. a few Canadian specimens determined as C. sonorensis branch outside a clack composed of the Argentinean Chelonus grioti Blanchard, the Brazilian Chelonus flavicincta Ashmead, and the rest of the C sonorensis individuals The individuals revealing the cryptic taxon were collected from Thichoplusia in (Hubner) (Lepidoptera. Noctuidae) on tomato (Lycopersicon spp) and may represent a biotype that has adapted to the early season phenology of its host. Overall, the loosely defined spatial genetic structure previously shown at a local fine scale also was found at the larger scale, for both species Dispersal of these insects may be partly driven by wind as suggested by genetic similarities between Individuals coming from very distant locations.