Interspecific interactions between two Tuta absoluta (Lepidoptera: Gelechiidae) larval parasitoids with contrasting life histories.

Interspecific interactions between two larval parasitoids of Tuta absoluta (Meyrick) with partially overlapping host niches were studied: the idiobiont ectoparasitoid Dineulophus phthorimaeae De Santis, and the koinobiont endoparasitoid Pseudapanteles dignus (Muesebeck). T. absoluta is an important pest of tomato crops worldwide, and its management could be improved by understanding the competitive interactions and potential coexistence between these two parasitoids. Firstly, a 15-min fixed time laboratory test evaluated the host-searching ability of adult D. phthorimaeae and P. dignus wasps on T. absoluta larvae. Secondly, D. phthorimaeae host discrimination against endoparasitized and non-endoparasitized hosts by P. dignus, at different adult female ages, was experimentally examined. D. phthorimaeae wasps spent significantly more time in general searching in the presence of its competitor than in its absence, but, parasitism was only effective by P. dignus. Older D. phthorimaeae wasps discriminated significantly less than young wasps between T. absoluta larvae parasitized and unparasitized by P. dignus, and an interaction took place by non-concurrent host-feeding. Intra-guild predation of P. dignus larvae by D. phthorimaeae female feeding behaviour might have a minor effect in this system. Results are discussed in the context of literature supporting diverse evidence of coexistence in other parasitoid-host systems, with implications for T. absoluta biological control.

Earthworm assemblages in different intensity of agricultural uses and their relation to edaphic variables.

The objective of this study was to relate earthworm assemblage structure with three different soil use intensities, and to indentify the physical, chemical, and microbiological soil variables that are associated to the observed differences. Three soil uses were evaluated: 1-Fifty year old naturalized grasslands, low use intensity; 2-Recent agricultural fields, intermediate use intensity, and 3-Fifty year old intensive agricultural fields, high use intensity. Three different sites for each soil use were evaluated from winter 2008 through summer 2011. Nine earthworm species were identified across all sampling sites. The sites shared five species: the native Microscolex dubius, and the introduced Aporrectodea caliginosa, A. rosea, Octalasion cyaneum, and O. lacteum, but they differed in relative abundance by soil use. The results show that the earthworm community structure is linked to and modulated by soil properties. Both species abundance and diversity showed significant differences depending on soil use intensity. A principal component analysis showed that species composition is closely related to the environmental variability. The ratio of native to exotic species was significantly lower in the intensive agricultural system when compared to the other two, lower disturbance systems. Microscolex dubius abundance was related to naturalized grasslands along with soil Ca, pH, mechanical resistance, and microbial respiration. Aporrectodea caliginosa abundance was related to high K levels, low enzymatic activity, slightly low pH, low Ca, and appeared related to the highly disturbed environment. Eukerria stagnalis and Aporrectodea rosea, commonly found in the recent agricultural system, were related to high soil moisture condition, low pH, low Ca and low enzymatic activity. These results show that earthworm assemblages can be good indicators of soil use intensities. In particular, Microscolex dubius, Aporrectodea caliginosa, and Aporrectodea rosea, showed different temporal patterns and species associations, due to the changes in soil properties attributable to soil use intensity, defined as the amount and type of agricultural operations.

The importance of transients' dynamics in spatially extended populations.

Recent theoretical works on the dynamics of metapopulations have highlighted the existence of very long transients (supertransients) with abrupt changes in behaviour which occur following perturbation of the system away from its attractor. If this phenomenon is common in natural systems, populations that do not oscillate can begin to fluctuate wildly without any change in the environmental conditions. However, the frequency of occurrence of supertransients is currently poorly understood even in model systems. Here we explore their occurrence in metapopulation models which relax the important assumption of global synchrony of events implicit in all the coupled map lattice models for which supertransients have so far been demonstrated. We find supertransients in all the models but always only for a very restricted range of parameter combinations. However, we also report for the first time another type of longer-lived transient (mesotransients) that occurs on shorter time-scales than supertransients and is found for a much wider set of conditions. We argue that these medium-term changes in the dynamics of populations can be of more ecological relevance than the long-term changes of supertransients.