Plastic responses of some life history traits and cellular components of body size in Aphidius ervi as related to the age of its host Acyrthosiphon pisum

Phenotypic plasticity of wing size and shape has been evaluated in Aphidius ervi developing in its host, Acyrthosiphon pisum, parasitized at seven different ages. The parasitoid wing size was used as an estimator of both whole body size and its cellular composition. No size difference was observed in A. ervi adults emerged from aphids 1, 2 or 3 days old at parasitization. Body size then increased in A. ervi emerged from hosts older at parasitization. Body size values as related to host age at parasitization were achieved by adjusting developmental time, developmental rate or both. Parasitoids of similar size, but developed in hosts parasitized at different ages, had different wing cellular composition, while the increase of parasitoid body size was related to a general increase in both cell area and cell number. These results seem to suggest a trade-off between adult size and developmental time, at least for parasitoids developed at the two extremes of host ages at parasitization, and that A. ervi can reach the same adult size via different trajectories, adapting its ontogenetic processes. Wing shape was typical for all the different parasitoid classes considered and differed strongly between males and females, independent of their size. Parasitoid males (haploids) and females (diploids) did not differ in either cell area or cell number, suggesting a possible sex-determined dosage compensation in somatic tissue endoreplication

Plastic responses of some life history traits and cellular components of body size in Aphidius ervi as related to the age of its host Acyrthosiphon pisum

Phenotypic plasticity of wing size and shape has been evaluated in Aphidius ervi developing in its host, Acyrthosiphon pisum, parasitized at seven different ages. The parasitoid wing size was used as an estimator of both whole body size and its cellular composition. No size difference was observed in A. ervi adults emerged from aphids 1, 2 or 3 days old at parasitization. Body size then increased in A. ervi emerged from hosts older at parasitization. Body size values as related to host age at parasitization were achieved by adjusting developmental time, developmental rate or both. Parasitoids of similar size, but developed in hosts parasitized at different ages, had different wing cellular composition, while the increase of parasitoid body size was related to a general increase in both cell area and cell number. These results seem to suggest a trade-off between adult size and developmental time, at least for parasitoids developed at the two extremes of host ages at parasitization, and that A. ervi can reach the same adult size via different trajectories, adapting its ontogenetic processes. Wing shape was typical for all the different parasitoid classes considered and differed strongly between males and females, independent of their size. Parasitoid males (haploids) and females (diploids) did not differ in either cell area or cell number, suggesting a possible sex-determined dosage compensation in somatic tissue endoreplication

Prey abundance and intraguild predation between Adalia bipunctata (Coleoptera: Coccinellidae) and Macrolophus pygmaeus (Hemiptera: Miridae)

Macrolophus pygmaeus Rambur (Hemiptera: Miridae) and Adalia bipunctata (L.) (Coleoptera: Coccinellidae) are two predatory insects commonly used as biological control agents. In order to determine the incidence with which both species attack and eat each other [Intraguild predation (IGP)], the direction and symmetry of the interaction between A. bipunctata and M. pygmaeus were characterized. In addition, whether the intensity of IGP between these two predators increased when the number of extraguild prey Acyrthosiphon pisum (Harris) (Hemiptera: Aphididae) decreased, was also determined. Unidirectional sensu stricto IGP between A. bipunctata and M. pygmaeus was recorded: when IGP occurred, A. bipunctata was always the IG predator that killed and ate M. pygmaeus, the IG prey. However, the intensity of IGP was a function of the abundance of the extraguild prey, A. pisum, since IGP increased when the number of extraguild prey decreased. These results are discussed in terms of theoretical models that predict stability and the outcome of using natural enemies to control pests

Transgenerational plasticity in aphids reared in a poor-resource environment

: The changing environmental conditions can affect insect biology over multiple generations and phenotypic plasticity is important for coping with these changes. Transgenerational plasticity occurs when the environment in which the parents developed influences the plastic response of the offspring phenotype. In the present study, the plastic effects of resource limitation on important life history traits such as body size, fecundity, survival, and resistance to starvation of the pea aphid Acyrthosiphon pisum were investigated over two generations. This study focused on understanding how resource limitation can determine an adaptive expression of maternal effects and transgenerational plasticity in fitness-related traits. Aphids showed phenotypic plasticity for the life history traits investigated, as they performed better when grown in an optimal environment than in a resource-poor one. Also, aphids had a poorer performance if their mothers were raised in a resource-poor environment. The effects of transgenerational plasticity were observed only in response to resistance to starvation, through increased survival in the offspring of the mother reared in a resource-poor environment, suggesting an evolutionary bet-hedging strategy. The results of this study showed that the effects of adaptive transgenerational plasticity may be partially masked in stressful environments, where developmental problems instead predominate. More information on the transgenerational response to resource limitation across generations can contribute to a better understanding of aphid biology

Effect of irrigation regimes and artificial mycorrhization on insect pest infestations and yield in tomato crop

A 2-year field experiment was carried out to test the effect of root symbionts treatments in combination with different watering levels on tomato yield and pest infestation rates. A split-plot experimental design was followed, where the main treatments were three irrigation regimes, and the subplot factor was the mycorrhizal treatment (two mycorrhizal treatments [M1 and M2] and the control). The M1 treatment consisted in the use of a commercial preparation (Micosat F; CCS Aosta, Italy) containing a mixture of vesicular-arbuscular mycorrhizae (VAM), bacteria of the rhizosphere and saprophytic fungi, while M2 treatment used only arbuscular mycorrhizal fungi. Insect pests sampled in the field during the 2 years of experiment were all sap-feeders (Trialeurodes vaporariorum, Macrosiphum euphorbiae, Frankliniella occidentalis and an unidentified species of leafhopper). Results did not show any impact of root symbionts on pests, whereas water deficit significantly reduced plant infestation rates. Both mycorrhization treatments and water supply resulted in a significantly positive effect on crop yield

I funghi entomopatogeni

Fungal entomopathogens are very interesting as biocontrol agents against important arthropods pests of crops and forests. These fungi infect their hosts mainly by penetrating through the cuticle and as consequence they can infect sucking insects, unlike entomopathogenic virus and bacteria. Most research on fungal entomopathogens only looks on a dozen species of commercially produced fungi, contained in over 170 products, and many scientific papers aim at improving production, storage and distribution techniques. The potential of using entomopathogenic fungi in biocontrol strategies different than inundative biological control was insufficiently explored because of the poor attention paid to ecological aspects. In the recent years accumulating evidence shows that several fungal entomopathogens, among them Beauveria bassiana, can colonize plants endophytically, they can be recovered from plant surface as an epiphyte, and finally they can suppress plant diseases. These interesting observations open new prospects of research and application for these versatile organisms

L'impiego di impollinatori come bioindicatori di impatto ambientale

Lo scopo dello studio è stato quello di sviluppare una approfondita conoscenza delle relazioni fra insetti impollinatori e piante con riferimento ai due aspetti seguenti: a) il potenziale impatto di piante geneticamente modificate (PGM); b) le possibilità di contaminazione dell’ambiente attraverso la dispersione di polline. Tale lavoro è stato effettuato utilizzando come casi studio quello di PGM esprimenti tossine di tipo Cry per la resistenza ad insetti. Sono state studiate tre diverse colture: colza, melanzana e pomodoro

Effetti diretti di shock termici su due specie afidiche (Acyrthosiphon pisum e Macrosiphum euphorbiae) e sull’imenottero parassitoide Aphidius ervi

La capacità degli organismi viventi di rispondere ai cambiamenti climatici e gli aspetti genetici interessati a queste risposte hanno enormi implicazioni pratiche in settori come la selvicoltura e l’agricoltura. Nel presente studio sono stati indagati gli effetti diretti di uno stress termico (esposizione per 30 minuti alla temperatura di 40°C) sulla sopravvivenza di mummie e parassitoidi adulti di Aphidius ervi e sulla sopravvivenza e fecondità in due distinte specie di afidi (Acyrthosiphon pisum e Macrosiphum euphorbiae, entrambe ospiti di A. ervi) La sopravvivenza di M. euphorbiae in seguito allo shock termico applicato è del tutto simile a quella di A. pisum (80% circa). A 24 ore dal trattamento, la capacità riproduttiva degli afidi sopravvissuti risulta essere simile al controllo per A. pisum, mentre in M. euphorbiae è ridotta del 60% circa. A 48 ore dallo shock termico non si registrano differenze di produttività tra controlli e afidi sperimentali sopravvissuti. La sopravvivenza delle femmine adulte di A. ervi è decisamente più bassa rispetto a quella dei due afidi: alla temperatura di 40°C la sopravvivenza degli adulti è del 20% circa, mentre alla stessa temperatura la sopravvivenza delle mummie è del 89% circa