Laura Baños-Picón

Are solitary progressive-provisioning wasps optimal foragers? A study with the digger wasp Bembix merceti (Hymenoptera: Crabronidae)

Summary Bembix merceti, a central-place forager that captures dipterans to feed its larvae, could be considered a suboptimal forager. The females tend to optimize their provisioning flights, capturing prey in proportions different from those present in the surrounding environment. These wasps make a positive selection of families of flies with greater mean weights even though they are less abundant and, within the families whose weight is not too great, capture individuals whose weight is larger than the mean. Selection is based on prey size and not on the type (family) to which the prey belongs. A significant correlation between the weight of each female and the weight of the largest prey captured by the wasp was found, suggesting that the females capture prey in consonance with their lift capacity. Nevertheless, captures were not optimized maximally; the females maintained a margin with respect to the maximum prey weights that they could transport efficiently. This margin could be related to the low availability of large prey in the environment; to the type of progressive provisioning shown by the females of this species; and to other factors, such as the good manoeuvrability of their prey and the pressure from their natural enemies and congeners.

Both landscape and local scale factors matter for the parental investment strategies of the pollinator Osmia caerulescens

Bees are important pollinators that use resources from both cropped and natural habitats in agroecosystems, and the amount of extant resources have proven to be critical in the adoption of parental investment decisions. Thus, the mixed effects that resource distribution and the organisms’ foraging and dispersal movements have on parental decisions cannot be adequately evaluated without the use of different spatial scales. We assess the effects of the landscape context and the local habitat type on the offspring traits of Osmia caerulescens L. Bees were obtained from standardized trap-nests established in Mediterranean crops. We analyzed the effects that the percentage of semi-natural habitats, the local habitat type, and the nest hole diameter have on offspring weight, the number of emergent progeny and offspring sex ratio. Both landscape and local scale factors affected the offspring traits in significant and interactive ways, and landscape-scale effects varied depending on local factors. Considering our results and taking into account the implications that offspring traits have on the population persistence, we stress the need to introduce these parameters in future studies. Maintaining agricultural landscape heterogeneity, with high crop diversity and the presence of semi-natural habitats is essential for the persistence of Osmia caerulescens populations.

Complex-to-predict generational shift between nested and clustered organization of individual prey networks in digger wasps.

Although diet has traditionally been considered to be a property of the species or populations as a whole, there is nowadays extensive knowledge that individual specialization is widespread among animal populations. Nevertheless, the factors determining the shape of interactions within food webs remain largely undiscovered, especially in predatory insects. We used an aggregation of the digger wasp Bembix merceti to 1) analyse patterns of individual prey use across three flying seasons in a network–based context; and 2) test the effect of four potential factors that might explain network topologies (wasp mass, nest spatial distribution, simultaneous nest-provisioning, prey availability). Inter-individual diet variation was found in all three years, under different predator-prey network topologies: Individuals arranged in dietary clusters and displayed a checkerboard pattern in 2009, but showed nestedness in 2008 and 2010. Network topologies were not fully explained by the tested factors. Larger females consumed a higher proportion of the total number of prey species captured by the population as a whole, in such a way that nested patterns may arise from mass-dependent prey spectrum width. Conversely, individuals with similar body mass didn’t form clusters. Nested patterns seemed to be associated with a greater availability of the main prey species (a proxy for reduced intra-specific competition). Thus, according with theory, clusters seemed to appear when competition increased. On the other hand, the nests of the individuals belonging to a given cluster were not more closely located, and neither did individuals within a cluster provision their nests simultaneously. Thus, a female-female copying behaviour during foraging was unlikely. In conclusion, wasp populations can maintain a considerable individual variation across years under different food web organizations. The tested factors only partially accounted for the shift in network properties, and new analyses should be carried out to elucidate how diet network topologies arise in wasp populations.

Falling Victim to Wasps in the Air: A Fate Driven by Prey Flight Morphology?

In prey-predator systems where the interacting individuals are both fliers, the flight performance of both participants heavily influences the probability of success of the predator (the prey is captured) and of the prey (the predator is avoided). While the flight morphology (an estimate of flight performance) of predatory wasps has rarely been addressed as a factor that may contribute to explain prey use, how the flight morphology of potential prey influences the output of predator-prey encounters has not been studied. Here, we hypothesized that flight morphology associated with flight ability (flight muscle mass to body mass ratio (FMR) and body mass to wing area ratio (wing loading, WL)) of Diptera affect their probability of being captured by specialized Diptera-hunting wasps (Bembix merceti and B. zonata), predicting a better manoeuvrability and acceleration capacity achieved by higher FMR and lower WL, and flight speed achieved by higher WL. In addition, wasp species with better flight morphology should be less limited by an advantageous Diptera flight morphology. Overall, the abundance of dipterans in the environment explained an important part of the observed variance in prey capture rate. However, it was not the only factor shaping prey capture. First, higher prey abundance was associated with greater capture rate for one species (B. merceti), although not for the other one. Second, the interaction observed between the environmental dipteran availability and dipteran WL for B. zonata suggests that greater dipteran WL (this probably meaning high cruising speed) decreased the probability of being captured, as long as fly abundance was high in the environment. Third, greater dipteran FMR (which likely means high manoeuvrability and acceleration capacity) helped to reduce predation by B. merceti if, again, dipterans were abundant in the environment. Wasp WL only varied with body mass but not between species, thereby hardly accounting for inter-specific differences in the wasps’ predatory patterns. However, the greater FMR of B. zonata, which implies better flight performance and greater load-lifting capacity, may explain why the capture rate in the two wasp species is affected by different factor interactions. In conclusion, although prey availability remains the primary factor shaping prey use, prey flight morphology seems to gain an additional role under conditions of abundant prey, when wasps can avoid flies with better flight ability.

Description of the Mature Larvae of Two Species of Liris with Notes on the Immature Stages of L. Niger (Hymenoptera: Crabronidae)

ABSTRACT The preimaginal stages of 2 species of Liris, including the egg, 2 mature and 1 immature larvae are described. The mature larva of L. niger (Fabricius) described is very similar to the previously known immature one. The mature larva of L. festinans praetermissus (Richards) differs only in minor details from that of L. niger, with the presence in the first one of parietal bands being outstanding. To date, the last larval stage of subtribe Larrina can be defined by the following character states: (a) head no higher than wide, (b) mandible with 4 or more teeth, (c) epipharynx with a large number of slender spinules, which tend to converge toward the midline, and (d) labrum rounded apically Within the Larrina, the mature larva of Liris is characterized by the autapomorphy “epipharynx spinulose, with a bare area in the center”.