The Hypopus Formation And Completion In Rhizoglyphus Echinopus

Rhizoglyphus echinopus (Fumouze & Robin) (Acari: Acaridae) is a worldwide pest of rootstalk. It is often found in storage and frequently intercepted in the international trade. Hypopi of R. echinopus were produced to resist the worsening habitat or adverse environmental conditions and to disperse by means of other animals. Hypopi are obviously different from other phases in shape. The flatten body, ossified and browned cuticle and degraded mouth lead the difficulty in field prevention and quarantine. Researches addressed that hypopus formation and completion were determined by genetic factors and influenced by one or more environmental factors such as temperature, humidity, nutrition and population density.The research status of hypopus formation, phoresy, development, prevention and the economic importance of R. echinopus were comprehensively reviewed.We studied the influence of environmental factors (temperature, humidity, density and feed) in hypopus formation and completion and provided theoretical basis for further research on the mechanism about hypopus formation and completion. We also tested the toxicity of acaricide for the protonymph and hypopus of R. echinopus. The induce function for hypopus formation and completion of sublethal doses of different acaricides were also studied. Some advises were given for efficient deracinate R. echinopus in process of quarantine and production.The result indicated that temperature, humidity, nutrition, density and pesticide were influencing hypopus formation and completion in different degree.(1) 25℃, 100% RH is the ideal condition for eggs of R. echinopus hatching and developing.(2) In different grades of temperature at 100%RH and dark condition, hypopus produce the most (32.25%) at 15℃. The proportion of hypopi produced were significantly different from others.(3) Relative humidity had influence on the hypopus incidence. Hypopus formation had significant difference when protonymph treated under different periods of time of lower humidity (76%RH).(4) In the test of comparing the influence of 3 different factors, temperature, humidity and population density, humidity was the key factor in determine hypopus formation and population density was less important than temperature.(5) Food quality, quantity and starvation duration influenced the proportion and speed of hypopus formation at 15±0.5℃, 100% RH and dark condition (P<0.05).(6) The livability of hypopus in 24 hours overpassed 50% at -8℃, but all hypopi died at 64%RH in 3 days. Hypopi were strongly resistant to the lower temperature, but not to the lower humidity.(7) The hypopus completion was influenced by temperature and humidity. Hypopi started earlier to moult under 25℃, 100%RH and dark condition. Proportion of hypopus reached the highest at 35℃and 96%RH. The sex ratio of female to male was about 1:1 when the hypopi exuviated to tritonymphs. The lower temperature induced the hypopi termination, it can also induce the hypopus completion.(8) All the 6 acaricides were effective to kill the protonymphs of R. echinopus. The higher dose of pesticides could control the hypopi to a certain extent. Avermectins had the lowest LC₅₀ to the protonymphs and hypopus. The higher concentration of pesticides the better effection it produced.(9) Sublethal dose of acaricides had no induction for hypopus formation, but played an important role in hypopus completion. They restrained the process of exuviating and reduced the percentage of hypopus completion.Therefore, we advise to use extremely lower temperature (about -18℃) and drying conditions to control hypopus in the process of quarantine, choosing suitable acaricides to reduce the damage of R. echinopus in the field. Higher dose of pesticides could be considered as an alternative measure when high population of hypopus occurred.