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Insect parasitoids have been widely studied, particularly due to their ecological implications through the study of the special relationships observed among this kind of species, as well as to their expression in mathematical models. However, there are still scarce studies on parasitoid relationships and their expression in more realistic mathematical models. The present work is aimed at deepening into competition relationships among parasitoids. Bearing this purpose in mind, the system shaped by two parasitoids was chosen: Trichogramma brassicae (idiobiont egg parasitoid) and Chelonus oculator (koinobiont egg-larval parasitoid). Both species compete against each other for the same host species (Lepidoptera). The results obtained in the laboratory point out that T. brassicae may be considered a better competitor than Ch. oculator. This is the result of the extrinsic competition due to the substances injected by the female during parasitization. However, our results show this classification into better and worse competitors inaccurate. Thus, these interspecific competition influences are detrimental to both parasitoid species. This is the first time that the effect of this competition is mentioned regarding parasitoid functional response. Our results and their ecological implications are reported and discussed.

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The parasitization behaviour of Chelonus oculator (F.), egg-larval parasitoid of noctuid lepidopteran species, has been studied under laboratory conditions, using Ephestia kuehniella Zeller as host, at four different temperature levels (10,20, 30 and 40±1 °C) and five densities of host eggs (50,100,150, 200 and 250). A significant effect of temperature and parasitism density was observed. At 10 °C, there was no parasitism, whilst at 40 °C it was very low; presenting adequate values at the two other temperatures (20 and 30 °C). With regard to these facts, the functional responses of this parasitoid species were adjusted and we noted that they display Holling type III. Estimating the handling times from the respective mathematical expressions, we obtained 10.944 and 15.250 min, at 20 and 30°C, respectively. These values are considerably higher than the respective times obtained by direct observation, 0.597 and 0.560 min for these temperatures (this difference is due to the fact that in the first case, unlike the second one, the time used for the search of the host is also included). The results obtained from the parasitization behaviour of Ch. oculator are discussed, also considering it as a candidate biological control agent against Spdoptera exigua (Hübner), beet armyworm, with a view to its possible use in greenhouse crops in Spain.

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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.

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Community Ecology
Authors: F. J. Fernandez-Maldonado, J. R. Gallego, A. Valencia, M. Gamez, Z. Varga, J. Garay, and T. Cabello

Cannibalism is a common phenomenon among insects. It has raised considerable interest both from a theoretical perspective and because of its importance in population dynamics in natural ecosystems. It could also play an important role from an applied perspective, especially when using predatory species in biological control programmes. The present paper aims to study the cannibalistic behaviour of Nabis pseudoferus Remane and the functional response of adult females. In a non-choice experiment, adult females showed clear acceptance of immature conspecifics as prey, with relatively high mortality values (51.89 ± 2.69%). These values were lower than those occurring for heterospecific prey, Spodoptera exigua Hübner, under the same conditions (80.00 ± 2.82%). However, the main result was that the rate of predation on heterospecific prey was reduced to 59.09 ± 7.08% in the presence of conspecific prey. The prey-capture behaviour of adult females differed when they hunted conspecific versus heterospecific prey. This was shown in the average handling time, which was 23.3 ± 3.3 min in the first case (conspecific) versus 16.6 ± 2.5 min in the second (heterospecific). Furthermore, the values increased in the former case and declined in the latter according to the order in which the prey were captured. The difference in handling time was not significant when adjusting the adult female functional response to conspecific nymphs. We argue that these results likely indicate risk aversion and a fear of reprisal among conspecifics.

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