A new symbiont associated with the South American locust Schistocerca cancellata.

PLISCHUK, S.; POCCO. M. E.; QUINTANA S.; DE WYSIECKI, M. L.; LANGE, C. E.

Agadir

Congreso; 13th International Congress of Orthopterology; 2019

The Orthopterist Society

After several decades of recession, an outbreak of historical magnitude of the South American locust Schistocerca cancellata has recently occurred in parts of Argentina, Paraguay, and Bolivia. Gregarious-phase older nymphs and adults were collected in fields near San Pedro, Jujuy province, in northwestern Argentina. The locusts were taken to the laboratory where they were sacrificed in order to scrutinize them for parasites and pathogens. All individuals were examined by ventral, longitudinal dissection under a stereo zoom microscope. Several adults and last-instar nymphs harbored gregarine-like microorganisms in their digestive tract, which were extracted and stored in absolute ethyl alcohol for DNA extraction. Using three different primer sets, DNA fragments were amplified, purified, and directly sequenced (ABI 3500 Genetic Analyzer, Applied Biosystems). The sequences similarities were determined by the Basic Local Alignment Search Tool (BLAST, NCBI). Morphological observations of the different developmental stages of the symbiont were carried out using a compound microscope. Measurements were taken using Micrometrics® SE Premium 4.0. Its presence was corroborated in the midgut as well as the gastric caeca. Sporozoites, trophozoites, gamonts, gametocysts, and oocysts were individualized. Both the diversity of the stages and their morphology were characteristic of a septate eugregarine. Trophozoites presented a globular epimerite (mean diameter = 24 μm) and averaged 176.8 μm long; the mean length of gamonts was 265.4 μm, protomerites measuring 67.2 μm x 90.4 μm, and deutomerites 198.2 μm x 129.8 μm on aver-age. Syzygy was in all cases frontal-caudal being primite and satellite of similar size but showing slight differences in the anterior end. Both immature and mature gametocysts were observed in the posterior portion of the gut and feces. Gametocysts were spherical structures of 459 μm mean diameter. Two-three days after being passed out with the feces about 30 equidistant basal discs (20.7 μm of average diameter) were observable on the surface of gametocysts. Two days after (under rearing room conditions, i.e.: 30 oC; 40% R. H.; 14 L: 10 D photoperiod) chains of oocysts were ejected from basal discs. Oocysts were doliform, measuring on average 7.4 μm x 4.5 μm. Considering that I) features of the few septate eugregarines described in South America associated with Acrididae members are far from beeing in agreement with those described here, II) morphological characters fit with those described for genus Gregarina, and III) after sequencing, BLAST locates it within that genus but without a clear association, the possibility that the septate eugregarine found in S. cancellata would be a new, undescribed Gregarina species appears highly likely.