Arthropod pests continue to occur throughout the year by inter-plant movement and dispersal between cultivated host plants that are applied with pesticides and wild host plants that serve as refuges in the area of cultivation. This paper reviews the relationship between the host range and status of pesticide resistance in agricultural arthropod pests in Japan. The decisive factors for determining the development of pesticide resistance were concluded with attention paid to wild host plants as refuges. The arthropod pests that developed pesticide resistance were as follows: (1) monophagous species infesting cultivated crops treated with pesticides, (2) polyphagous species with a host range restricted to cultivated plants lacking wild host plants, and (3) certain populations of polyphagous species develop resistance in habitats such as tea fields and greenhouses with year-round cultivation because they are relatively isolated from the surrounding populations that do not develop resistance due to the abundance of refuges. In all cases, pest populations inhabit environments where they are restricted to mate with the susceptible populations from refuges of wild host plants.
Severe flower bud rot was observed in hydrangeas (Hydrangea macrophylla) growing in Shimane Prefecture, Japan. This symptom was observed in potted hydrangeas grown under forcing culture in greenhouses during winter. A gray mold pathogen (Botrytis cinerea) was isolated from rotten buds, and the original rot symptom was reproduced via inoculation with the isolates. The identification of the pathogen was confirmed by morphology and molecular phylogeny. This is the first report of hydrangea flower bud rot caused by B. cinerea in Japan.
In this study, we examined the relationships between plant growth stage and disease severity in hydrangeas infected with stem and root rot. Hydrangeas were inoculated with four oomycete pathogens (Pythium myriotylum, Globisporangium splendens, Globisporangium spinosum, and Globisporangium sp.) at 0, 1, 2, 3, and 4 months post-transplantation. Plants inoculated with all four pathogens showed disease symptoms until at least 1 month after transplanting; however, the damage caused to plants was found to become less severe with a lengthening of the post-transplantation period prior to pathogen inoculation. Only one of the four oomycete pathogens (Globisporangium sp.) caused significant damage to hydrangeas when inoculated at 4 months after transplanting.
Five isolates of the pathogen that causes downy mildew in spinach, Peronospora farinosa f. sp. spinaciae, collected in Fukuoka Prefecture, Japan, in 2019 were identified as two races, which were distinct from races 1–17 authorized by the International Working Group on Peronospora. The races were temporarily named J19-1 and J19-2. J19-1 reacted to race-differential cultivars similar to an isolate from the United States, UA201502. However, the response of J19-2 to race-differential cultivars differed from any reported races.
Shiso mosaic disease is caused by the perilla mosaic virus (PerMV) and transmitted by shiso rust mites (Shevtchenkella sp.). Twenty PerMV-infected shiso rust mites were released in the center of a perilla plant field to investigate horizontal disease transmission. Disease in the surrounding plants started developing after 19 days; 47% of plants displayed symptoms after 40 days; and all plants displayed symptoms after 69 days. The diseased-plant density was the highest in the northeast, northwest, and southeast of the inoculated field, and was lowest in the southeast. The wind direction frequency during the one to two weeks before the field observation seemingly correlated with the density of disease-developed plants in the field.
To estimate the infection period of a root rot pathogen of ginger (Pythium myriotylum Drechsler) under an open-field cultivation condition, an inoculation test was conducted under field conditions for two cultivation seasons. The pathogen infection was confirmed by the LAMP method and symptoms were observed from late May 2016 to mid-September and 2017. This demonstrates that the pathogen can infect ginger tubers for more than four months from early to mature stages of the plant under field conditions.
Tomato bacterial wilt, caused by Ralstonia solanacearum, is one of the most damaging soil-borne diseases. One of the most effective control methods is the use of disease-resistant rootstocks. In this study, we evaluated the degree of the resistance of 17 commercial rootstock cultivars. We also evaluated the effects of cultivars with different resistance levels combined with different soil disinfection treatments (soil solarization, chloropicrin, or dazomet with flooding). The rootstock cultivars ‘Magnet’ and ‘Green Force’ did not completely suppress the disease with soil solarization or chloropicrin, but the suppression was enhanced by dazomet with flooding. Conversely, a highly resistant cultivar, ‘King Barrier,’ suppressed the disease under all experimental conditions. Highly resistant cultivars can be expected to suppress the disease regardless of soil disinfection.
We obtained 458 Botrytis cinerea isolates from tomato plants in Gifu Prefecture, Japan, and evaluated them for their sensitivity to the fungicide fludioxonil using mycelial plugs and potato dextrose agar containing 0.2 ppm fludioxonil, as previously reported. Of the isolates, 3.9% had clear growth and were estimated to be ‘low-susceptibility’ isolates based on a microplate or in vivo assay. In addition, we attempted to improve the mycelial plug method because unclear growth was observed in some of the susceptible isolates. The use of mycelial homogenate or paper disks soaked in a spore suspension allowed the sensitivity to be evaluated more clearly than with the use of mycelial plugs.
To clarify the sites that are used for hibernation by stink bugs that diapause in the adult stage, we attempted to search for diapausing adults in the scrubs and levees beside paddy fields during winter. The adults of Plautia crossota stali and Glaucias subpunctatus, which cause serious damage to many kinds of fruit, hibernated under the fallen leaves in the scrubs. Similarly, the adults of Cletus punctiger and Leptocorisa chinensis, which are insect pests that feed on rice grains, and Riptortus pedestris and Piezodorus hybneri, which are soybean pests, hibernated under the fallen leaves in the scrubs or at the bottom of the stocks of dead gramineous plants in the levees beside the paddy fields. The hibernating sites of Lagynotomus elongatus adults, which are pests of rice plants, were not investigated in detail. However, we found diapausing adults at the bottom of the stocks of dead gramineous plants in the levees beside the paddy fields or in the dead grasses in the sunny scrubs.
We evaluated the susceptibility of Kanzawa spider mites, Tetranychus kanzawai Kishida, and two-spotted spider mites, T. urticae Koch, populations from eggplants and adzuki beans to pesticides sprayed on kidney bean leaves. Results showed that the susceptibility of adult females varied among species. Of the 20 pesticides applied with a spray tower (20 pesticides against T. kanzawai and 17 pesticides against T. urticae), acynonapyr and spinetoram were the most toxic to adult females of both Tetranychus species. Chlorfenapyr, cyflumetofen, tebufenpyrad, bifenazate, milbemectin, acequinocyl, avermectin, emamectin benzoate, and cyenopyrafen caused high mortality in T. kanzawai, whereas decanoyloctanoylglycerol, spinetoram, and fluxametamide caused high mortality in T. urticae.
Thrips that damage carrot leaves have been observed in Kyotanba Town and Nantan City, Kyoto Prefecture, from September 2013; however, the thrip species are unknown. The species composition of thrips was surveyed by collecting female adults from the foliage of carrot leaves in three greenhouses in Kyotanba Town and Nantan City, Kyoto Prefecture, in 2020. Thrips tabaci, T. nigropilosus, Frankliniella occidentalis, F. intonsa, and Phlaeothripidae sp. were found. T. tabaci and T. nigropilosus were predominant among the five species.
We investigated the relationship between the density of the tea green leafhopper, Empoasca onukii Matsuda, in tea fields and damage to new shoots of the tea crop. The density of E. onukii, determined by beating the tea canopy, was investigated twice before plucking, and the damage rates of plucked new shoots were determined. The correlation between the density and damage rate was higher when the cumulative density from the two survey times were used than when data from only one survey were used. The relationship between the cumulative density from two surveys (x) and the damage rate (y) produced the following regression equation: y = 1 – exp(–0.0227x), R2 = 0.76, n = 99. The relationship between the damage rate (x: angle conversion value) and the damage indexes: Σ(each grade × number of damaged shoots, applying grade values from 0 to 6)/6 × total number of shoots checked (y: angle conversion value), showed a high correlation (R2 = 0.99, n = 30). It is suggested that these results can contribute to the development of a technique for controlling the density of E. onukii to produce special tea containing diol induced by E. onukii damage.
Twenty insecticides were used as treatments against striped flea beetle adults with Japanese mustard spinach leaves. At three days after treatment, 13 insecticides were found to have high toxicity at commercial concentrations. These insecticides are thought to be highly effective for chemical control of this population but confirming the effectiveness for other populations is necessary.
Eighteen insecticides were used against brassica leaf beetle adults with Japanese white radish leaves. At three days after treatment, 16 insecticides were found to have high toxicity at commercial concentrations. However, only five insecticides were found to have high toxicity at 1/4 of the commercial concentration: fipronil, permethrin, thiocyclam, metaflumizone, and fluxametamide. These results suggest that these five insecticides are a highly effective chemical control for brassica leaf beetles at high densities.
We investigated the control effect of hot-water treatment on the moth fly Tinearia alternata in a polyurethane substrate of hydroponic Welsh onions. We collected polyurethane substrate inhabited by T. alternata with Welsh onions from the field, squeezed it lightly to reduce its water content, and put it in hot water (48 or 50°C) for 1, 2, or 3 min. We then soaked it in cold water and held it at room temperature under an ambient photoperiod and counted the number of adults that appeared every day for 8 days. Hot-water treatment at 50°C for ≥2 min proved effective. No damage was observed on the green onions in any treatment.
To determine rust symptoms caused by shiso rust mites (Shevtchenkella sp.), perilla leaf color was quantified by image analysis, and symptomatic and healthy leaves were compared. On symptomatic leaves, the blue (B) value in the red, green, and blue (RGB) color system was lower on the back side of the leaf, whereas the red/green (a*) values in the L*a*b* color system were lower on both sides of the leaves, compared with those of healthy leaves. Complex color elements were investigated by principal component analysis to determine rust occurrence. Using the RGB system, less green (B) on the back indicated rust. Using the L*a*b* system, a* value on the front indicated rust and suggested that size may also contribute to the results.
Effects of six insecticides were investigated on two species of flower thrips, Frankliniella occidentalis (Pergande) and F. intonsa (Trybom), collected from strawberry greenhouses in Nara Prefecture. Spinosad was found to be the most effective insecticide against two species of flower thrips in terms of corrected mortality and leaf damage. Fluxametamide was found to be an effective insecticide. Cyantraniliprole showed low corrected mortality but low leaf damage. Flometoquin was found to be effective against F. occidentalis, but ineffective against F. intonsa. Acetamiprid results differed in terms of corrected mortality and leaf damage according to the population. These results suggest that spinosad and cyantraniliprole are effective insecticides against two species of flower thrips, F. occidentalis and F. intonsa, from strawberry plants in Nara Prefecture.
The effectiveness of potential trap baits for the apple snail Pomacea canaliculata was evaluated in a rice field in Hyogo Prefecture, Japan. Four kinds of baits were tested: rice bran, carp pellets, goldfish pellets, and a mixture containing rice bran, carp pellets, and rice malt in a 1:1:1 ratio. The trap yields were investigated three times (1, 6, and 7 days) after deployment. Traps with mixed bait attracted the highest number of snails for all investigations. The yield decreased over time with other bait types, but the mixed bait remained an effective lure for the longest time, probably because rice malt continued to produce sugar and slowed the decay of the bait.
We aimed to easily make an automatic monitoring insect trap by combining a commercially available IoT monitoring camera with a sticky pheromone trap that was assembled from parts of commercially available sticky traps in order to grasp the number of daily trap catches of insect pests on the same day. This trap is hereafter referred to as the IoT camera-equipped sticky pheromone trap. In the present study, we applied the IoT camera-equipped sticky pheromone trap to Spodoptera exigua (Hübner) and examined whether it was possible to record the daily catches of S. exigua males by the trap. According to the predetermined settings, the IoT camera automatically took a picture (3 million pixels) of the sticky board capturing S. exigua males at 9:00 AM and then immediately sent the image with lowered resolution (0.3 million pixels) to a designated e-mail address via mobile networks (LTE) of a cellular carrier (NTT docomo). Trapped S. exigua males appearing in the sent images of the sticky board could be distinguished from other insects and counted on the monitor screen of a personal computer. The number of trapped males was also counted by directly checking the sticky board in the field every 2–4 days. On each day that trapped S. exigua males were directly counted in the field, the number of S. exigua males coincided with that counted through viewing the e-mailed image. These results suggest that the daily catches of S. exigua males can be grasped using the IoT camera-equipped sticky pheromone trap. Thus, this trap might be useful for monitoring the daily occurrence of insect pests, but this needs to be verified by applying it to various insect pest species.
In 2020, we surveyed the relative abundance of a native grasshopper, Atractomorpha lata (Motschoulsky), and an exotic congener, A. sinensissinensis Bolívar, on agricultural crops, including eggplant, cockscomb, Chinese cabbage, and crown daisy, in Habikino City, Osaka Prefecture, and found that A. sinensis sinensis was predominant on all investigated crops. In addition, we assessed the toxicity of nine insecticides against A. sinensis sinensis adults collected in Habikino City using the cabbage leaf-dipping method, which revealed that MEP, fipronil, and tetraniliprole are the most effective insecticides against this grasshopper species.
Nesidiocoris tenuis (Reuter) (Hemiptera: Miridae) is a zoophytophagous predator used for biological control in greenhouse cultivation. We investigated the seasonal abundance of N. tenuis in six fields of open cultivated sesame in Miyazaki Prefecture, Japan, in 2018. We surveyed each field during the following periods until just before harvest: July to August in three May-sowing fields and August to September in three July-sowing fields. The first individual of N. tenuis was observed on July 10 in a May-sowing field, earlier than that of a previous study in eastern Japan. The mean numbers of N. tenuis individuals per plant in the final survey were 9.1 to 13.2 in the May-sowing fields, whereas they were 21.0 to 31.0 in the July-sowing fields. These results will be useful for the application of indigenous N. tenuis populations for biological control.
We investigated the toxicity of 31 insecticides to adult loquat psyllids, Cacopsylla biwa, collected from loquat trees in Wakayama Prefecture. Alanycarb, chlorpyrifos, malathion, methidathion, phenthoate, ethiprole, silafluofen, and cartap were toxic, resulting in a corrected mortality of more than 90%.
The residue of pesticide inside a power sprayer and a water tank were measured after washing with water. After spraying pesticides (acetamiprid, pyribencarb, and boscalid), we rinsed the applicators five or six times and analyzed cleaning solution samples with LC/MS/MS. More than 90% of the pesticide residues in the power sprayer and tank were removed after rinsing two times. There tended to be more pyribencarb and boscalid left in the apparatus compared with acetamiprid.