The pH of the artificial diet used for insect rearing generally affects the bacterial contamination of the diet. We examined the effect of adding hydrochloric acid (HCl) to the artificial diet of Euscepes postfasciatus on bacterial contamination of the diet. First, we reared the species using diets prepared with various HCl concentrations to determine the concentration that does not adversely affect the survival and development of E. postfasciatus. The use of HCl at a lower concentration than 0.12% does not remarkably affect insects. Next, we compared bacterial contamination among the following four groups. Insect eggs were inoculated with three of these groups: 0.072% HCl diet, 0.036% HCl diet, and diet without HCl added (positive control). In the fourth group, HCl was not added to the diet, and the eggs were not inoculated (negative control). The contamination rate in the 0.036% diet was not significantly lower than in the positive control, whereas the rate in the 0.072% diet was lower than in the positive control but not significantly higher than in the negative control. We concluded that adding HCl to the artificial diet of E. postfasciatus was quite effective for preventing bacterial contamination of the diet.
The braconid wasp, Apanteles baoris, is a gregarious larval parasitoid of the rice-plant skipper, Parnara guttata guttata (Lepidoptera: Hesperiidae), which is an important insect pest of the rice plant in Japan. To investigate the developmental relationship of these species, host larvae experimentally parasitized by A. baoris at the 1st to 5th instars were reared at 25°C under 16L8D. A. baoris was able to parasitize all instars of larval P. g. guttata, and egression of A. baoris occurred in the late final instar of the host. The rate of hosts from which A. baoris egressed was 27–72% and there was no significant difference among the rates irrespective of the host instar. The number of A. baoris adults emerging per host, or “parasitoid brood size”, ranged 4–112 (mean, 51). The mean periods from oviposition to egression of A. baoris were 15–31 days, longer than the corresponding developmental periods of unparasitized hosts. Most parasitized hosts made a 5th larval molt and became 6th-instar larvae, while all unparasitized host larvae pupated after the 5th instar. The mean maximum weight of parasitized hosts was significantly less than that of unparasitized hosts when they oviposited at 1st–3rd instars. The maximum weight of parasitized hosts was significantly and positively correlated with parasitoid brood size, and the parasitoid brood size and weight of A. baoris adults emerging from hosts were negatively correlated in both sexes.
Although sodium ions induce puddling behavior in males of some butterfly species, the role of sodium ions in the male life history is unclear. Effects of saline intake until the second mating on the mass of spermatophore and accessory substances, as well as the number of eupyrene sperm bundles and apyrene spermatozoa, were examined in the male swallowtail butterfly, Papilio xuthus Linnaeus. The virgin male transferred 6 mg spermatophore and 8 mg accessory substances with 38 eupyrene sperm bundles and 350,000 apyrene spermatozoa to a virgin female during copulation. A small spermatophore, a little accessory substance, and a low number of eupyrene sperm bundles and apyrene spermatozoa in the second mating of mated males the day after the first copulation were found. Mated males fed on both 20% sucrose solution and 0.01 M saline solution for two days after the first copulation transferred similar ejaculates at the first copulation. Saline intake recovered the ejaculate mass. Because a large spermatophore and a large number of sperm must be advantageous to the male under sperm competition in female polyandry, puddling behavior might be important to increase reproductive success in males.
To determine the optimum time for chemical control, I investigated the infestation and damage of citrus fruits by Scirtothrips dorsalis Hood in four experimental plots where insecticide was applied at different times. The peak days of adult immigration into citrus orchards from the 2nd to the 7th generation were predicted by real-time calculation of the total effective temperature in 2000, 2001, and 2002. The four experimental plots were set up as follows: insecticides were applied at 6.6±1.5 days before the peak days, at 1.0±1.7 days before the peak days, at 5.2±2.1 days after the peak days; no insecticides were applied to one plot, which was considered the control plot. In the two plots where the insecticides were applied at 6.6 or 1.0 days before the peak days, the density of S. dorsalis and the rate of damage caused to the fruits were significantly lower than those in the control plot. However, in the plot where insecticides were applied at 5.2 days after the peak days, the density of adults temporally increased and the rate of damage caused to the fruits were higher than in those in the above two plots.
The effect of breaking up the artificial diet of Euscepes postfasciatus into small pieces before egg seeding on the diet was examined as a possible method for improving larval survival rate in the mass rearing of the species. Breaking up the diet realized a 10-fold increase in number of emerging adults compared to the use of a non-broken up diet. Although the air permeability of the rearing tray was previously shown to affect survival of the species in a rearing method with a non-broken up diet, it did not significantly affect the survival rate when a broken up diet was used in the present study; therefore, a broken up diet is considered to be effective for ensuring good survival of the species, particularly in terms of a stable survival rate irrespective of the air permeability of the rearing tray.