It was investigated that the effects of multiple tillage treatments on the Tyrophagus similis Volgin (Acari: Acaridae) populations and on the physical properties of soil. From May to June 2014, spinach was cultivated twice in greenhouses in Hokkaido. T. similis was released at a rate of 500/ m2 with 50 kg/10 a of fishmeal pellets, 9 days before seeding. After 2 days, the entire area was tilled once, followed by one to three tillage treatments, 1 week before sowing. The density of T. similis in the soil, the number of T. similis acarid mites captured inside the traps, and the degree of damage caused to spinach were significantly lower in the triple-processed land plots than in the unprocessed (control) land plots. No significant difference in the water content was observed between the processed and control plots. However, the weight of the dried soil per 100 ml was significantly higher in the triple-processed land plots than in the controls. This weight did not change when the soil was pressed (48 g/cm2) without being tilled. Moreover, the density of T. similis and the number of T. similis acarid mites captured inside the traps were also significantly lower in the pressed land plots than in the control plots.
In recent years, damage caused by Tyrophagus similis Volgin(Acari: Acaridae)to greenhouse spinach increased and it is threatening the stable production of spinach. However, details of the climbing behavior of mites on spinach sprout and influence of soil surface algae on mite behavior in the greenhouse remain unknown. It is known that T. similis colonizes soil surface algae under a high humidity condition and that it shows good population increase after feeding algae. In this study, we investigated proximate factors for T. similis to move to spinach sprout. In 2012, we conducted laboratory tests to observe behavior of T. similis which aggregated on soil surface algae under two aerial humidity conditions(65%RH and 95%RH). The total number of mites, after 24 hs without algae, was largest on spinach sprout at the 65%RH condition and in the soil at the 95%RH condition, respectively. With algae as well as spinach sprout, mite numbers were also highest on spinach sprout at 65%RH but most mites moved to algae at the 95%RH condition. To test the feasibility of our findings, algal occurrence and mite damage were investigated in the greenhouse in Yamaguchi pref. in April 2013. Algae covered all soil surfaces when spinach was young, and then depending on dryness, algal distribution was sporadic at the harvest time. Areas without algae showed a high damaging index of mites showing a significant negative relationship between algal occurrence and mite damage. These results suggested that soil inhabiting mites aggregated on algae in humid condition and dry condition triggered their movement to spinach sprout.
The Japanese water strider, Aquarius paludum(Fabricius), exhibits wing dimorphism: long- and short-winged adults. In order to clarify the reproductive strategy in each morph, changes in the number of eggs in the nonsexual period were examined by dissection. Immediately after emergence, a few immature eggs were found in the ovaries of females in both morphs. The number of immature eggs increased with age, and a maximum of 50 eggs had accumulated in 5-day-old females of each morph. Submature eggs were found in 3-day-old long-winged females, but in 1-day-old short-winged females. Additionally, mature eggs appeared at 5 days of age in long-winged females, later than in short-winged ones. Although the number of mature eggs increased with age, by 13 days, the maximum number of mature eggs in long-winged females was lower than that in short-winged ones. Females younger than 11 days of age showed mate refusal behavior. Females began to oviposit 2 days after copulation. The size of the first clutch of long-winged females was significantly smaller than that of short-winged ones. However, after the fourth clutch, there were no significant differences in clutch size between the two morphs. Therefore, more eggs produced by short-winged females were found during the pre-reproductive period.
Damage by the foxglove aphid, Aulacorthum solani(Kaltenbach), to sweet pepper leaves and fruit was investigated under laboratory and field conditions. A. solani caused yellowing of young and mature leaves, deformation(twisting and curling)of young leaves, and necrotic spots on fruit. Such damage occurred at 2 days on fruit and 6 days on leaves after the release of A. solani at first to second nymphal stage on sweet pepper plants, irrespective of the aphid density. In greenhouses with forcing culture, A. solani occurred irregularly. The percentage of damaged plants at the first occurrence ranged from 0.6% to 6.0%. The distribution of damaged plants suggested that the occurrence of A. solani was due to invasion through roof ventilators.