Effect of temperature, photoperiod, flooding, and drying on the hatching pattern of the eggs of Strelkovimermis spiculatus (Nematoda: Mermithidae)

We assessed the number of Strelkovimermis spiculatus preparasites obtained from a known initial number of nematode eggs and the effect of abiotic conditions (temperature, photoperiod, flooding–drying) on the number of emerged preparasites. Two egg groups were maintained: one continuously flooded, another with flooding–drying cycles (every 15, 30, 60 days). Each egg group was studied at 25 °C and 14:10 (L:D) and 16 °C and 12:12 (L:D). The flooded eggs contained a higher overall percentage of S. spiculatus preparasites compared to the wet–dry-cycle eggs. The conditions of continuous flooding at 16 °C and 12:12 (L:D) produced the maximum percent of emerged J2s (30 ± 15%). Preparasites were recorded by 7 (25 °C) and 14 (16 °C) days, suggesting this period as the minimum time for embryonic development. The preparasite-emergence time observed from the same flooded-egg batch (98 and 112 days at 25 °C and 16 °C, respectively) suggested a nonsynchronous hatching, possibly through nonuniform egg embryonation. The time of exposure to drought in the assays did not significantly affect the total average percentage of J2s obtained at 25 °C and 14:10 (L:D), whereas at 16 °C the number of emerged J2s diminished with a prolongation of the drying period. The oviposition period was also recorded only at 16 °C and 12:12 (L:D): S. spiculatus eggs were detected at 12.6 days after postparasite emergence, and oviposition was complete at 51 days under those conditions. We propose a flooding schedule to optimize the mass-rearing of S. spiculatus.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Effect of abiotic factors on Strelkovimermis spiculatus preparasite emergence from numbered eggs. ► Maximum percent J2 emergence under flooding at 16 °C and 12:12 (L:D) photoperiod. ► First preparasites at Day 7 (25 °C) or 14 (16 °C) implied as minimum embryogenesis time. ► Prolonged J2 emergence after oviposition with flooding implied hatching asychrony. ► Higher J2 emergence when kept flooded than with any flooding–drying cycle.