Utilización de abejorros nativos como polinizadores de trébol rojo (Trifolium pratense) y tomate (Solanum lycospersicun)

Resumen de tesis doctoral

Abstract

The ecosystem service provided by insect pollinators is at risk due to the threat to their populations in the most parts of the world. This "pollinator crisis" would have important consequences in the maintenance of natural ecosystems and agricultural production. Bumblebees of the genus Bombus (Hymenoptera: Apidae), primitively eusocial bees with annual life cycle, are widely recognized as efficient pollinators of many crops. Its use as pollinators has been facilitated by obtaining colonies by artificial rearing in some species. In Uruguay, two native species are present, Bombus atratus distributed throughout the country and Bombus bellicosus located mainly south of the Rio Negro. In this thesis, the efficiency of B. atratus as pollinator of red clover (Trifolium pratense) and tomato (Solanum licopersicum) was studied, and the main parasites and viruses affecting this species were identified.  To pollinate a red clover seedset in its first bloom (December-January), B. atratus colonies obtained by artificial rearing were used. Bumblebees visited the red clover showing a clear decreasing distribution gradient from the nest location. Throughout the flowering period, thered clover was present in the bumblebees` corbicular pollen samples in a proportion between 32 % and 52 % and in the bumblebees`  nectar samples in a proportion between 19 % and 52 %. The average seed yield at 10, 80 and 160 meters from the nests was 709, 423, 327 kg/ha, respectively; while the percentage of fruit set was 42.7 %, 30.2 % and 25.7 % respectively. Honey bees were very abundant in the seedbed, however, by correlating seed production with the presence of bumblebees by means of a General Linear Model, it was determined that the latter were responsible for the production of almost 400 kg/ha of seeds. Seed yield values near the nests were significantly higher than those normally obtained by pollinating the legume with honey bees, which  opens the possibility of improving national seed production by using bumblebees as pollinators.  Three tomato pollination experiences were conducted to evaluate the effect of native bumblebees B. atratus on the percentage of fruit set and several fruit características: weight, diameter, number of seeds and number of locules (LAPATAIA and ELPIDA varieties were used). An experience was made in Canelones department, in which the fruits of flowers pollinated by bumblebees and flowers not visited by insects were compared, and two similar experiences in Salto but also including flowers treated with hormones. In the three greenhouses, bumblebee visits to flowers increased the percentage of fruit set between 13 and 47 % in relation to that obtained in flowers not visited by insects. The pollinator action of bumblebees also significantly improved fruit weight, size and number of seeds with respect to fruits obtained from flowers without access to pollinators in two of the three experiences. On the other hand, in the two tomato varieties a positive correlation was found between the number of seeds and fruit weight (R2= 0.37, R2= 0.53 for the varieties LAPATAIA and ELPIDA, respectively). This study is the first in Uruguay that shows the benefits of using native bumblebees to improve tomatoes production in greenhouses. The exhaustive analysis of queens, workers from wild nests and workers obtained by artificial rearing/breeding allowed to identify the microsporidia Nosema ceranae and Tubilonosema pampeana, a diptera of the family Conipidae, the nematode Sphaerularia bombi, the phoretic mites Tyrophagus putrescentiae, Pneumolaelaps longanalis, Pneumolaelaps longipilus, Kuzinia spp. And Parasitellus fucorum, the Deformed Wing Virus (DWV), the Black Queen Cell Virus (BQCV), the Sacbrood Virus (SBV) and the Acute Paralysis Virus (ABPV). The prevalence of N. ceranae was higher in the workers captured in the field (45.9 %) than in the workers obtained in the laboratory (13.0 %) and the queens (16.6 %). Conipidae larvae were found only in field workers (16.2 %) and queens (10.5 %). The S. bombi nematode was only found in queens with a low prevalence (10.5 %). The group with the highest prevalence of mites were queens (73.6 %), followed by laboratory workers (65.2 %) and field workers (40.5 %). In the queens there was the greatest diversity of mite species, 64.3 % presented more than one species. In 82.4 % of the bumblebees analyzed, at least one RNA virus was detected, with BQCV being the most prevalent appearing in 80.9 % of samples, with a wide difference from the others. Solo para el virus DWV se hallaron diferencias entre los tres grupos de abejorros estudiados, siendo más prevalente en las obreras de campo. Only for the DWV differences were found between the three groups of bumblebees studied, being more prevalent in field workers. The queens appear as the colony member most exposed to parasites, especially mites. Bumblebee colonies have an annual cycle and only queens survive the winter. This characteristic has shaped the behavior of parasites to reproduce and spread exceeding the period in which colonies disappear. The confinement of workers during artificial rearing/breeding and the availability of abundant food do not seem to generate important adverse conditions from a sanitary point of view. The results of this thesis constitute a contribution to the national agricultural production, demonstrating that the native bumblebee B. atratus is an efficient pollinator of two crops of great economic importance. Comprehensive information is also provided on the parasites and viruses present in this species and the potential damage that could be caused in natural populations or during artificial rearing.