Effects of an optical brightener and an abrasive on iridescent virus infection and development of Aedes aegypti

The insecticidal properties of certain entomopathogenic viruses can be greatly improved in mixtures with substances that affect the integrity of the insect peritrophic membrane, particularly optical brighteners. We aimed to determine the effect of an optical brightener, Blankophor BBH, and an abrasive compound, silicon carbide, alone and in mixtures, on the prevalence of patent and covert infection of Aedes aegypti (L.) (Diptera: Culicidae) by Invertebrate iridescent virus 6 (IIV‐6) (Iridoviridae). The prevalence of patent infection by IIV‐6 was < 1.5% in all treatments involving virus. Contrary to predictions, there were significantly fewer patent infections in virus treatments involving Blankophor with or without silicon carbide compared with controls. Covert infection of adults detected by insect bioassay was between 6.7 and 12.2%, although no significant differences were observed between treatments. Exposure to IIV‐6 alone or silicon carbide alone did not significantly increase larval mortality compared to the controls, whereas exposure to Blankophor alone, or in any combination with IIV‐6 or silicon carbide, clearly increased larval mortality. These effects did not carry‐over to the pupal stage. Adult females emerged ～1.5 days later than males. Compared to control insects, female development rate was extended by 11.4 and 12.6% in the treatments involving IIV‐6 alone and silicon carbide alone, respectively. The sex ratio at adult emergence did not differ significantly between control insects and those of other treatments. These results support the hypothesis that the gut is unlikely to represent the principal point of infection of mosquito larvae by iridescent viruses.     

Ethephon application induces symptoms of fruit tissue degeneration in watermelon

Vegetable Research Division, NHRI, 475 Imok-dong, Jangan-gu, Suwon, Gyeonggi-do, 440-706, Republic of Korea Flesh tissue degeneration (called blood-black heart; BBH) of watermelon (Citrullus vulgaris S.) is occasionally observed in Korea. Fruits with BBH have lower quality, a dark-red flesh, and reduced firmness of the rind, often producing an unpleasant flavor. Although causal factors are thought to be undesirable soil moisture conditions, e.g., drought or water-logging, temperature extremes, or virus infection, the mechanism for this physiological disorder is not clearly understood. It is possible that ethylene gas (C₂H₄) is involved in degrading the cell walls. To determine such an implication for ethylene in the occurrence of BBH, we foliar-applied various concentrations of ethephon (100, 200, 400, 800, or 1000 mg L^-1) to watermelon plants at 5 or 10 d prior to harvesting, then monitored the development of this disorder in their fruits. At 400 mg L^-1 or higher, quality was diminished and the fruit had softer rind tissues. About 25% of the fruits harvested at that level exhibited BBH versus 100% of the fruits exposed to 800 or 1000 mg L^-1 ethephon. Concomitant with the onset of BBH, those affected fruits produced elevated amounts of ethylene gas during the 4-d measurement period. Therefore, a high incidence of BBH may well be related to this increased ethylene production, which can be triggered by both unfavorable environmental conditions and inappropriate cultural practices.     

Fluorescent brightener inhibits apoptosis in baculovirus-infected gypsy moth larval midgut cells in vitro

Fluorescent brighteners significantly lower the LC₅₀ and LT₅₀ in a variety of nucleopolyhedrovirus-insect host systems. In larvae of the gypsy moth, Lymantria dispar (L.), a European NPV strain of virus (LdMNPV) does not normally replicate in the midgut, but addition of a fluorescent brightener (Calcofluor M2R) to the virus suspension results in productive infections. In the current study, we show that LdMNPV also does not replicate in a larval midgut primary cell culture system unless a fluorescent brightener (Blankophor P167) is added. Morphological and cellular changes characteristic of apoptotic cell death were noted in infected midgut cells in vitro. We used the TUNEL assay to measure apoptosis in virus-challenged midgut cell cultures at 24-48 h post-inoculation. A significant decrease in apoptotic midgut cells was noted in the presence of 0.01 M brightener. The inhibition of apoptosis and presumptive inhibition of shedding of infected midgut cells in the presence of fluorescent brightener in the insect midgut appeared to promote virus replication and are likely to be partly responsible for enhancement of LdMNPV activity that is observed in gypsy moth larvae.     

Identification of the composite parameters of the BBH-B model specifying the effects of biohydrologic processes on the water balance of crop fields

A model of soil hydrology incorporating rainfall interception and macropore flow, which are representative biohydorologic processes, (BBH-B model) has two composite parameters, Π and Φ. These parameters express the ratios of rainfall interception and macropore flow to gross rainfall, respectively. Their values, however, change widely with the vegetation, soil texture and wetness. The results of experiments that have been carried out for various objectives under various conditions by the present authors were reanalyzed to evaluate these two parameters. Further, two supplemental experiments were designed to identify the two parameters. In the experiments, the monthly mean of Π for a cornfield ranged from 0.18 to 0.64 in the summer months, while Φ for a weed-grown field reached a maximum of 0.8 when daily rainfall was more than 40 mm day⁻¹. From these analyses and experiments, we concluded that the effects of biohydrologic processes on the water balance of crop fields are rather large and not negligible.