Augmentative release of two parasitoid species decreased Drosophila hosts without mutual suppression in a vineyard

The acute thermal tolerances of six Daphnia species were compared at three acclimation temperatures. Of the species tested, all but one showed an increase in thermal tolerance when acclimated at higher temperature. Comparison of the regression relationships between thermal tolerances and acclimation temperature revealed no significant interspecific differences among species in their improvement of thermal tolerance caused by acclimation. However, significant intraspecific differences in thermal tolerance were noted. Daphnia obtusa had the highest tolerance, while D. pulex had the lowest. Among the other species acclimated at 10 C, thermal tolerance declined in a sequence of D. ambigua, D. magna, D. carinata, and D. nivalis. The differences in thermal tolerance noted among species were correlated with maximum temperatures of the environment from which they originated. While comparison of clones of D. pulex from several geographic localities revealed up to 2 C differences in acute thermal tolerance, there was no evidence of clonal variation in thermal tolerance of D. magna.

Baumwolle ist eine der ökonomisch wichtigsten Nutzpflanzen in Ägypten. Im Jahr 1991 begann in Ägypten die organische Produktion, um die Nachfrage nach organisch gewachsener Baumwolle in den Ländern der westlichen Hemisphäre, besonders Europas, zu befriedigen. Baumwolle wird von einem grossen Spektrum von Insekten befallen. Die größten Schäden werden dabei von Helicoverpa armigera, einer Schmetterlingsart, verursacht. Biologische Maßnahmen für die Kontrolle der Schädlingsarten sind bisher jedoch in den meisten Fällen noch nicht etabliert. Daher wurden dieser Studie mit dem Ziel durchgeführt, die Wirksamkeit verschiedener biologischen Kontrollmaßnahmen gegenüber H. armigera in einer organischen Baumwollproduktion zu überprüfen. Folgende Fragestellungen standen im Mittelpunkt: 1. Die Wirksamkeit der Parasitisierung von Helicoverpa armigera durch zwei Ei-Parasitoide, Trichogramma pretiosum und T. minutum unter Labor- und Gewächshausbedingungen. 2. Die Effizienz räuberischer Florfliegen Eier und Larven von Helicoverpa zu fressen. 3. Die Auswirkung einer kombinierten Freilassung von Florfliegen und Parasitoiden. 4. Der Einfluss der chemischen und morphologischen Merkmale verschiedener Baumwollsorten auf das Suchverhalten und die Parasitierungsrate der Trichogramma-Arten. 5. Die Auswirkung einer Behandlung der Pflanzen mit Jasmonat auf das Verhalten der natürlichen Feinde von H. armigera in Labor- und Freilandexperimenten. 1) Die Parasitisierungsrate der Trichogramma Arten wurde signifikant durch die Temperatur beeinflusst, wobei T. pretiosum effektiver war als T. minutum. Im Gegensatz dazu lebten adulte T. minutum im Durchschnitt etwas länger als adulte T. pretiosum. Die Langlebigkeit hing von der Wirtsart ab. Aus Eiern von Helicoverpa schlüpfende Parasitoide lebten länger als aus Eiern von Sitotroga schlüpfende Parasitoide. Die Parasitierungsrate wurde außerdem stark von der Baumwollsorte verändert, welche die Wirtsfindung und -behandlung suchender Parasitoide zu beeinflussen. 2) Die Prädationsrate von C. carnea stieg während der ersten zwei Larvenstadien an und erreichte ein Maximum im dritten Larvenstadium. Die dritten Larvenstadien frassen ungefähr 80% der Eier und Larven von Helicoverpa. Die Entwicklungszeit von mit Helicoverpa-Eiern gefütterten C. carnea war kürzer als bei einer Fütterung mit Larven. Die Position der Eier auf den Baumwollepflanzen beeinflusste die Wirksamkeit der Räuber erheblich; Eier auf dem fünften Blatt wurden häufiger als solche auf dem erste Blatt konsumiert. Die Baumwollsorten hatten keinen signifikanten Einfluss auf die Frassrate der Prädatoren. 3) Die Zeit zwischen dem Ende der Parasitisierung und dem Beginn der Prädation beeinflusste sowohl die Frass- als auch die Parasitisierungsrate. Je älter die parasitisierten Eier, desto weniger wurden sie noch vom Räuber akzeptiert, unabhängig davon, ob es sich beim Wirt um Eier von Helicoverpa oder Sitotroga handelte. Trotzdem ergab eine Kombination von Trichogramma spp. mit C. carnea eine bessere Kontrolle von H. armigera als Trichogramma alleine, weil die Mortalität der Eier erhöht war. Chrysoperla frass jedoch fast keine parasitisierten Eier. 4) T. minutum und T. pretiosum unterschieden sich erheblich in ihrem Erfolg, vertikal verteilte Eier zu finden. Die Parasitisierungsraten waren auf den oberen und unteren Blattetagen verschiedener Baumwollsorten höher als auf den mittleren Blättern. Außerdem waren die Parasitisierungsraten negativ mit der Distanz zwischen dem Ort der Freisetzung der Parasitoide und dem Ort der Eierposition korreliert. Morphologische Merkmale der Baumwollpflanzen, d.h. Vorhandensein von Drüsen oder die Dichte von Trichomen, beeinflussten das Verhalten von Trichogramma signifikant. Die Parasitisierungsrate auf Sorten mit Blattdrüsen und verringerter Trichomdichte war signifikant höher als auf Sorten ohne Blattdrüsen und hoher Trichomdichte. Eine Analyse der volatilen Substanzen mittels GC-MS zeigte, dass sich die Baumwollsorten erheblich sowohl bei diesen Substanzen als auch in der Zusammensetzung ihrer Phytosterole unterschieden. 5) Weibchen der Parasitoidenart Cotesia marginiventris wurden verstärkt von Pflanzen angezogen, wenn diese mit Jasmonat behandelt oder von Larven des Beet Armyworm beschädigt waren. Jasmonat-induzierte Pflanzen waren signifikant attraktiver als durch Pflanzen, die durch 2 Beet Armyworm Larven geschädigt worden waren; am wenigsten attraktiv waren Pflanzen, die von 1 Larve befressen wurden. Weibchen von Cotesia bevorzugten die Jasmonat behandelten Zonen im Vergleich zu von Larven beschädigten Zonen auf BT-Baumwoll- sowie Nicht-BT-Baumwollpflanzen. In Experimenten ohne Jasmonat- Behandlung besuchten die Weibchen Bt-Pflanzen häufiger als Nicht-Bt-Pflanzen und verbrachten dort mehr Zeit mit dem Suchen und Auswählen von Wirten. 6) In einem Freilandexperiment fanden sich auf den mit Jasmonat behandelten Pflanzen sieben Tage nach der Anwendung 70% weniger Arten schädlicher Insekten als auf den Kontrollpflanzen. Der Effekt einer einzelnen Jasmonat-Behandlung erhöhte sich mit Zeit; er war am ersten und dritten Tag nach der Anwendung klein und wurde am siebenten Tag nach der Behandlung mittel bis stark. BT-Baumwollsorten (mit oder ohne Jasmonat-Behandlung) hatten die höheren Anzahlen von natürlichen Feinden als konventionelle Sorten. Ausgebrachte Beet Armyworm Eier wiesen jedoch ähnliche Parasitisierungs- und Prädationsraten auf bei Jasmonat behandelten oder unbehandelten Pflanzen. Die Resultate dieser Experimente werden hinsichtlich der Nachfrage nach biologischen Kontrollstrategien in organisch angebauter Baumwolle diskutiert. Großflächige Feldexperimente sind nötig, um abschätzen zu können, ob diese Maßnahmen auch im Freiland zur Anwendung kommen können.

In the face of global warming, both the absolute thermal tolerance of an ectotherm, and its ability to shift its tolerance level via acclimation, are thought to be fundamentally important. Understanding the links between tolerance and its plasticity is therefore critical to accurately predict vulnerability to warming. Previous studies in a number of ectotherm taxa suggest trade-offs in the evolution of thermal tolerance and its plasticity, something which does not, however, apply to Deronectes diving beetles, where these traits are instead positively correlated. Here we revisit the relationship between thermal tolerance and plasticity in these beetles, paying attention to a recently discovered morphological adaptation supporting under water respiration – setal tracheal gills. Hollow setae on the elytra interconnect with the beetle’s tracheal system, providing a gas exchange surface that allows oxygen to be extracted directly from the water. This enables individuals to stay submerged for longer than their subelytral air stores would allow. We show that hypoxia reduced heat tolerance, especially when individuals were denied access to air, forcing them to rely solely on aquatic gas exchange. Species with higher densities of these gas-exchanging setae exhibited improved cold tolerance, but reduced heat tolerance and lower plasticity of heat tolerance. Differences in setal tracheal gill density across species were also related to habitat use: species with low gill density were found mainly in intermittent, warmer rivers, where underwater gas exchange is more problematic and risks of surfacing may be smaller. Moreover, when controlling for differences in gill density we no longer found a significant relationship between heat tolerance and its plasticity, suggesting that the previously reported positive relationship between these variables may be driven by differences in gill density. Differences in environmental conditions between the preferred habitats could simultaneously select for characteristic differences in both thermal tolerance and gill density. Such simultaneous selection may have resulted in a non-causal association between cold tolerance and gill density. For heat tolerance, the correlations with gill density could reflect a causal relationship. Species relying strongly on diffusive oxygen uptake via setal tracheal gills may have a reduced oxygen supply capacity and may be left with fewer options for matching oxygen uptake to oxygen demand during acclimation, which could explain their reduced heat tolerance and limited plasticity. Our study helps shed light on the mechanisms that underpin thermal tolerance and plasticity in diving air-breathing ectotherms, and explores how differences in thermal tolerance across species are linked to their selected habitat, morphological adaptations and evolutionary history.

Although studies increasingly disentangle phenotypic plasticity from evolutionary responses to environmental change, few test for transgenerational plasticity in this context. Here, we evaluate whether phenotypic divergence of acorn ants in response to urbanization is driven by transgenerational plasticity rather than evolution. F2 generation worker ants (offspring of laboratory‐born queens) exhibited similar divergence among urban and rural populations as field‐born worker ants, suggesting that evolutionary divergence rather than transgenerational plasticity was primarily responsible for shifts toward higher heat tolerance and diminished cold tolerance in urban acorn ants. Hybrid offspring from matings between urban and rural populations also indicated that evolutionary divergence was likely the primary mechanism underlying population differences in thermal tolerance. Specifically, thermal tolerance traits were not inherited either maternally or paternally in the hybrid pairings as would be expected for strong parental or grandparental effects mediated through a single sex. Urban–rural hybrid offspring provided further insight into the genetic architecture of thermal adaptation. Heat tolerance of hybrids more resembled the urban–urban pure type, whereas cold tolerance of hybrids more resembled the rural–rural pure type. As a consequence, thermal tolerance traits in this system appear to be influenced by dominance rather than being purely additive traits, and heat and cold tolerance might be determined by separate genes. Though transgenerational plasticity does not appear to explain divergence of acorn ant thermal tolerance, its role in divergence of other traits and across other urbanization gradients merits further study.

Populations of common killifish, Fundulus heteroclitus, are distributed along the Atlantic coast of North America through a steep latitudinal thermal gradient. We examined intraspecific variation in whole-animal thermal tolerance and its relationship to the heat shock response in killifish from the northern and southern extremes of the species range. Critical thermal maxima were significantly higher in southern than in northern fish by approximately 1.5 degrees C at a wide range of acclimation temperatures (from 2-34 degrees C), and critical thermal minima differed by approximately 1.5 degrees C at acclimation temperatures above 22 degrees C, converging on the freezing point of brackish water at lower acclimation temperatures. To determine whether these differences in whole-organism thermal tolerance were reflected in differences in either the sequence or regulation of the heat shock protein genes (hsps) we obtained complete cDNA sequences for hsc70, hsp70-1 and hsp70-2, and partial sequences of hsp90alpha and hsp90beta. There were no fixed differences in amino acid sequence between populations in either hsp70-1 or hsp70-2, and only a single conservative substitution between populations in hsc70. By contrast, there were significant differences between populations in the expression of many, but not all, of these genes. Both northern and southern killifish significantly increased hsp70-2 levels above control values (T(on)) at a heat shock temperature of 33 degrees C, but the magnitude of this induction was greater in northern fish, suggesting that northern fish may be more susceptible to thermal damage than are southern fish. In contrast, hsp70-1 mRNA levels increased gradually and to the same extent in response to heat shock in both populations. Hsc70 mRNA levels were significantly elevated by heat shock in southern fish, but not in northern fish. Similarly, the more thermotolerant southern killifish had a T(on) for hsp90alpha of 30 degrees C, 2 degrees C lower than that of northern fish. This observation combined with the ability of southern killifish to upregulate hsc70 in response to heat shock suggests a possible role for these hsps in whole-organism differences in thermal tolerance. These data highlight the importance of considering the complexity of the heat shock response across multiple isoforms when attempting to make linkages to whole-organism traits such as thermal tolerance.

The life history of parasitoids is divided into a parasitic immature stage living in or on a host invertebrate and a free‐living adult stage. We still have little consensus on how larvae and adult parasitoids differ in their responses to environmental heat waves. We tested the performance of two cosmopolitan drosophila pupal parasitoids, Pachycrepoideus vindemiae (Hymenoptera: Pteromalidae) and Trichopria drosophilae (Hymenoptera: Diapriidae), when exposed to 35 and 40°C heat waves in the larval and adult stage, respectively. Additionally, we tested if heat hardening in the larval stage influenced the thermal tolerance of adult parasitoids. P. vindemiae had a higher tolerance to heat waves than T. drosophilae in both the larval and adult stages. We did not find significantly increased thermal tolerance of adult wasps that experienced heat hardening during the larval stage. A 35°C heat wave had no effect on P. vindemiae. Larval T. drosophilae that experienced a 35°C heat wave had longer development times, but individuals that survived showed no significant decrease in longevity and fecundity compared with those without warming experience. By contrast, adult T. drosophilae suffered less mortality from the 35°C heat wave, but individuals that survived had significantly reduced longevity and fecundity. A 40°C heat wave resulted in higher mortality in the larval stage than in the adult stage for both parasitoid species. Our study clearly revealed the contrasting responses to heat waves in the larval and adult stages of two parasitoids and highlighted the importance of ontogenetic differences in thermal tolerance in predicting parasitoid distributions and population dynamics.

Influence of intra- and inter-specific competition between egg parasitoids on the effectiveness of biological control of Euschistus heros (Hemiptera: Pentatomidae)

Heat-wave tolerance in tropical intertidal animals: accounting for thermal and desiccation tolerances

BackgroundTwo Trichogramma spp., Trichogramma evanescens Westwood and Trichogrammatoidea bactrae Nagaraja (Hymenoptera: Trichogrammatidae), were studied to control one of the most cereal pests attacking various grains, Sitotroga cerealella (Olivier) (Gelechiidae: Lepidoptera). Experiments were carried out to evaluate S. cerealella egg-ages, parasitoids’ emergence time and cold storage host eggs on rearing the two tested parasitoids’ spp.ResultsThe age of S. cerealella eggs had significantly influenced the parasitization and adult emergence rates of the two parasitoid species. Parasitism rate resulted from old host eggs (32 h old) (44.93%) decreased than those of the fresh ones (2 h old) (95.85%). Emergence rate ranged between (62.64–97.85%) for T. evanescens and (62.90–95.54%) for T. bactrae from different S. cerealella egg-ages (0–32 h). Regardless to late emerged parasitoids, their population affected. T. evanescens parasitized rate ranged (73.79–95.06%), which comparatively lower than those of T. bactrae (88.81–96.90%), at parasitoid emerging times (0–64 h), respectively. Emergence times had significantly differences in the emergence rate of T. evanescens and/or T. bactrae. On the other hand, percentage of parasitism of the non-stored S. cerealella eggs was higher than the other cold-stored ones. The emergence rate of adult parasitoids, T. evanescens (66.00–91.16%) and T. bactrae (71.16–94.11%), was decreased at the cold storage durations (5–40 days) increased. In comparison to the tested biological aspects between the two parasitoid species, non-significant differences were recorded, at the three assessment parameters, which include host egg-ages, parasitoid emergence time and cold-stored eggs. Meanwhile, there were significant differences between F1 emerged rates for T. evanescens and T. bactrae obtained at each of the three tested parameters.ConclusionIt was concluded that low emergence time of the parasitoids, T. evanescens and T. bactrae, was relatively more effective when they parasitized the fresh egg-age and less cold storage periods of S. cerealella.

Intraspecific differences in thermal tolerance of the diamondback watersnake ( Nerodia rhombifer): effects of ontogeny, latitude, and sex

Ecological communities are composed of many species, forming complex networks of interactions. Current environmental changes are altering the structure and species composition of ecological networks, which could modify interactions, either directly or indirectly. To predict changes in the functioning of communities, we need to understand whether species interactions are primarily driven by network structure (i.e. topology) or the specific identities of species (i.e. nodes). Yet, this partitioning of effects is challenging and thus rarely explored. Here we disentangled the influence of network structure and the identities of species on the outcome of consumer-resource interactions using a host-parasitoid system. We used four common community modules in host-parasitoid communities to represent network structure (i.e. host-parasitoid, exploitative competition, alternative host and a combination of exploitative competition and alternative host). We assembled nine different species combinations per community module in a laboratory experiment using a pool of three Drosophila hosts and three larval parasitoid species (Leptopilina sp., Ganaspis sp. and Asobara sp.). We compared host suppression and parasitoid performance across community modules and species assemblages to identify general effects linked to network structure and specific effects due to species community composition. We found that multiple parasitoid species enhanced host suppression due to sampling effect, weaker interspecific than intraspecific competition between parasitoids, and synergism. However, the effects of network structure on parasitoid performance were species specific and dependent on the identity of co-occurring species. Consequently, multiple parasitoid species generally strengthen top-down control, but the performance of the parasitoids depends on the identity of either the co-occurring parasitoid species, the alternative host species or both. Our results highlight the importance of preserving parasitoid diversity for ecosystem functioning and show that other effects depend on species community composition, and may therefore be altered by ongoing environmental changes.

Population dynamics models suggest that the over-all level of resource productivity plays an important role in community dynamics. One such factor of resource productivity is the quality of the host plant, which can determine the effectiveness of entomophagous (predatory and parasitoid) species by altering the growth rate of the phytophagous population via effects on fecundity, survival, and rate of development. These effects have been studied in relation to the distribution of host plants and their physiological state. However, few studies have considered the differences among plant cultivars. The objective of this study was to identify a continuous-time dynamic model, to describe the effects of different tomato cultivars on a one predatortwo prey model. The experiment was carried out under greenhouse conditions using ten tomato cultivars, with the predatory species Nesidiocoris tenuis (Reuter) (Insecta, Hemiptera, Miridae) and two prey species: the phytophagous species Bemisia tabaci (Gennadius) (Insecta, Hemiptera, Aleyrodidae) and the parasitoid species Trichogramma achaeae (Nagaraja & Nagarkatti) (Insecta, Hymenoptera, Trichogrammatidae); the latter was used as the intraguild-prey. Using the software SIMFIT, we found that a three-dimensional Lotka-Volterra type system could be well fitted to the data, estimating the phytophagous species´ growth rate, the parasitoid and predator mortality rates, the predation and parasitism rates, and the parasitoid emergence rate according to the cultivar type. The results showed an important effect of the host plant quality, by cultivar, on intraguild predation, resulting in important changes in the dynamics of phytophagous populations. These results are also discussed in relation to their importance in the biological control of pest species in greenhouse crops.

Sex differences in thermal tolerance may significantly impact population responses to climate change, yet most studies examining geographic variation in thermal tolerance focus on a single sex. Here, we investigate how males and females might vary in their capacity to tolerate the heat along a latitudinal cline using the Australian water flea, Daphnia carinata. We measured heat knockdown times in males and females using clones of Daphnia from six populations spanning eastern Australia, raised under two acclimation temperatures (20°C and 25°C). Females consistently showed higher thermal tolerances than males, with greater capacity for thermal acclimation. Critically, we discovered that latitudinal clines in thermal tolerance were sex-specific: females showed a much steeper decline in heat tolerance with increasing latitude compared with males. As a result, sexual dimorphism in thermal tolerance was more than twice as large in northern populations compared with southern populations. These results suggest that sex-specific selection, potentially driven by differential habitat use or the female-biased demography of cyclical parthenogenesis, may be driving divergent thermal adaptation between the sexes. Our findings highlight the importance of considering both sexes when predicting population vulnerability to climate change, as sex-averaged estimates may misrepresent the heat tolerance of populations along environmental gradients.

The efficiency of two Trichogramma species as biocontrol agents against the European corn borer (ECB) Ostrinia nubilalis (Lepidoptera: Crambidae) was investigated under field conditions. Five inundative releases of Trichogramma ostriniae and T. brassicae (Hymenoptera: Trichogrammatidae) were done in sweet corn plots. Ostrinia nubilalis sentinel egg masses were placed on corn plants in order to compare the efficiency of the two Trichogramma species. The parasitism rate of O. nubilalis egg masses by T. ostriniae was 13% higher than egg masses parasitized by T. brassicae. Likewise, the percentage of eggs parasitized per mass by T. ostriniae was significantly higher following two of the five releases. Attacked egg masses showed an average of 29% of eggs parasitized by T. ostriniae, versus 14% of eggs parasitized by T. brassicae. The rate of parasitoid emergence from sentinel egg masses was also significantly higher for T. ostriniae than for T. brassicae. Damages to plants due to ECB did not differ significantly in presence of the two parasitoid species. However, plants in plots receiving parasitoids showed less damage than plants in control plots. Overall, T. ostriniae was clearly more efficient than T. brassicae to parasitized egg masses of O. nubilalis in sweet corn.

Aedes aegypti (L. 1762), the yellow fever mosquito, and Culex quinquefasciatus Say 1823, the southern house mosquito, are prevalent in tropical and subtropical areas worldwide and are responsible for the spread of a number of devastating diseases to humans and livestock. The development of new control methods, as well as continued study of mosquito biology, is vital for improving human health. This study aimed to examine the efficacy of sugar alcohols as a novel means for mosquito control, as well as how sugar alcohols and other factors are involved in thermal tolerance in mosquitoes. No-choice tests with the sugar alcohols erythritol, sorbitol, and xylitol resulted in significant mortality in at least one species, with erythritol resulting in the highest mortality. A two-choice test between sucrose with or without added erythritol showed no significant preference between the two in either Ae. aegypti or Cx. quinquefasciatus. Based on our findings, erythritol and other sugar alcohols have good potential as novel mosquito toxins, and further study should be conducted into the efficacy of deployment in the field. Thermal tolerance assays demonstrated that the consumption of sugar alcohols does not improve cold tolerance in Cx. quinquefasciatus, but that consumption of mannitol can decrease heat tolerance. We observed similar levels of cold tolerance between all diets tested. However, we found that Cx. quinquefasciatus was inherently significantly more cold tolerant than Ae. aegypti, while Ae. aegypti had improved heat tolerance compared to Cx. quinquefasciatus. There were no differences in thermal tolerance between sexes within either species. Our results suggest that although dietary factors such as sugar alcohols and sugars may play a role in thermal tolerance in mosquitoes, there are likely physiological and genetic factors that can have a greater influence on the limits of thermal tolerance within a species.