Effects of different Philosamia ricini (Lepidoptera: Saturniidae) cold storage periods on Ooencyrtus pityocampae and Ooencyrtus kuvanae (Hymenoptera: Encyrtidae) rearing.

Ooencyrtus pityocampae and Ooencyrtus kuvanae are egg parasitoids that are considered potential candidates for the control of different pest species through inundative release. The aim of this study was to assess the effects of different cold-storage periods of Philosamia ricini eggs (host) on the rearing parameters of O. pityocampae and O. kuvanae. Host eggs were stored at 3 °C, and a factorial experiment involving two parasitoid species, nine host storage periods (1, 5, 10, 15, 30, 45, 60, 75 and 90 days) and a control, and two host ages (1 and 2 days) was conducted, with 10 replications including 40-P. ricini eggs each. Adult emergence, development time, longevity, and fecundity were investigated. The parasitoid adult emergence percentage significantly varied with storage duration. These values were lower in O. kuvanae than in O. pityocampae. The development time of O. kuvanae progeny increased in both host age groups except in the 1-day storage period subgroup. However, the development times of the progeny of O. pityocampae reared on one-day-old eggs stored for 5, 10, 60, and 75 days were increased, and the development times of the progeny of O. pityocampae reared on 2-day-old eggs stored for 45 and 90 days were increased. The longevity of the F1 progeny of O. kuvanae was negatively affected by storage time. There was no difference in the longevity of the F1 progeny of O. pityocampae compared to that of the control. Additionally, the fecundities of the F1 progeny of O. pityocampae and O. kuvanae were 54.7 and 47.0 offspring/female, respectively. These results provide useful information for guiding the development of mass rearing methodologies for both parasitoid species.

Hormones and carbohydrates are both involved in the negative effects of reproduction on vegetative bud outgrowth in the mango tree: consequences for irregular bearing.

The negative effects of fruit production during one cycle on reproduction during the following cycle are generally explained by two complementary processes: hormone synthesis and carbohydrate mobilization. Our study focused on mango (Mangifera indica L.) for which it has been shown that reproduction decreases and delays vegetative bud outgrowth. This, in turn, affects flowering and fruiting in the following cycle. Vegetative growth therefore plays a pivotal role in irregular fruit production patterns across consecutive years. Our aim was to decipher the respective roles of hormones and carbohydrates on the negative effects of reproduction on vegetative growth. We analyzed the changes in various hormone (auxin, cytokinin, abscisic acid) and carbohydrate (glucose, sucrose, starch) concentrations in terminal axes with vegetative and reproductive fates of two mango cultivars, Cogshall and José, characterized by different bearing patterns, across consecutive phenological periods during a growing cycle. Auxin concentrations were high in inflorescences, fruit peduncles and axes bearing inflorescences or fruit, suggesting auxin-induced inhibition of vegetative bud outgrowth in the flowering and fruiting axes. Moreover, growing fruits, which are strong sink organs, depleted carbohydrates from non-fruiting axes. During vegetative growth, this starch depletion probably contributed to decreasing the probability of and to delaying vegetative bud outgrowth of reproductive axes for Cogshall, and of reproductive and nonreproductive axes for José. Starch dynamics in quiescent and flowering growth units during early fruit growth and their starch concentrations at fruit maturity differed between the two cultivars, presumably in relation to the observed contrasted crop loads and/or to differences in photosynthetic capacity or carbohydrate allocation. These differences between the two cultivars in terms of starch concentration in terminal axes during vegetative growth could partly explain their different bearing patterns.

Deciphering the Costs of Reproduction in Mango - Vegetative Growth Matters.

Irregular fruit production across successive years is a major issue that limits the profitability of most temperate and tropical fruit crops. It is particularly affected by the reciprocal relationships between vegetative and reproductive growth. The concept of the costs of reproduction is defined in terms of losses in the potential future reproductive success caused by current investment in reproduction. This concept, developed in ecology and evolutionary biology, could provide a methodological framework to analyze irregular bearing in fruit crops, especially in relation to the spatial scale at which studies are done. The objective of this study was to investigate the direct effects of reproduction during a growing cycle on reproduction during the following growing cycle and the indirect effects through vegetative growth between these two reproductive events, for four mango cultivars and during two growing cycles. Two spatial scales were considered: the growth unit (GU) and the scaffold branch. Costs of reproduction were detected between two successive reproductive events and between reproduction and vegetative growth. These costs were scale-dependent, generally detected at the GU scale and infrequently at the scaffold branch scale, suggesting partial branch autonomy with respect to processes underlying the effects of reproduction on vegetative growth. In contrast, the relationships between vegetative growth and reproduction were positive at the GU scale and at the scaffold branch scale in most cases, suggesting branch autonomy for the processes, mainly local, underlying flowering and fruiting. The negative effect of reproduction on vegetative growth prevailed over the positive effect of vegetative growth on the subsequent reproduction. The costs of reproduction were also cultivar-dependent. Those revealed at the GU scale were related to the bearing behavior of each cultivar. Our results put forward the crucial role of vegetative growth occurring between two reproductive events. They are discussed in the context of irregular bearing considering both the spatial scale and the various bearing habits of the mango cultivars, in order to formulate new hypotheses about this issue.

Explanatory ecological factors for the persistence of desiccation-sensitive seeds in transient soil seed banks: Quercus ilex as a case study.

BACKGROUND AND AIMS: Dominant tree species in northern temperate forests, for example oak and beech, produce desiccation-sensitive seeds. Despite the potentially major influence of this functional trait on the regeneration and distribution of species under climate change, little is currently known about the ecological determinants of the persistence of desiccation-sensitive seeds in transient soil seed banks. Knowing which key climatic and microsite factors favour seed survival will help define the regeneration niche for species whose seeds display extreme sensitivity to environmental stress METHODS: Using the Mediterranean Holm oak (Quercus ilex) forest as a model system, an in situ time-course monitoring of seed water status and viability was performed during the unfavourable winter season in two years with contrasting rainfall, at an instrumented site with detailed climate records. In parallel, the characteristics of the microhabitat and their influence on the post-winter water status and viability of seeds were investigated in a regional survey of 33 woodlands representative of the French distribution of the species. KEY RESULTS: Time-course monitoring of seed water status in natural conditions confirmed that in situ desiccation is the main abiotic cause of mortality in winter. Critical water contents could be reached in a few days during drought spells. Seed dehydration rates were satisfactorily estimated using integrative climate proxies including vapour pressure deficit and potential evapotranspiration. Seed water status was therefore determined by the balance between water uptake after a rainfall event and water loss during dry periods. Structural equation modelling of microhabitat factors highlighted the major influence of canopy openness and resulting incident radiation on the ground. CONCLUSIONS: This study provides part of the knowledge required to implement species distribution models which incorporate their regeneration niche. It is an important step forward in evaluating the ecological consequences of increasing winter drought and environmental filtering due to climate change on the regeneration of the most dominant Mediterranean tree species.