Publications
The Fruits of My Labor
Here you will find information about my research publications I’ve been involved with. Throughout my research, I’ve had the opportunity to work on many interesting projects with various Professors, Scientists, PIs, laboratories and Research Institutions that have enriched my understanding of Plant/crop Protection, Pest Management, Plant-Insect-(Microbe) Interactions and paved the path towards my successful Post-Graduate career. I’m proud to showcase the fruits of my labor (and that hard work does get rewarded) with the list of publications below.
December 16, 2021
Success of plants largely depends on their ability to defend against herbivores. Since emergence of the first voracious consumers, plants maintained adapting their structures and chemistry to escape from extinction. The constant pressure was further accelerated by adaptation of herbivores to plant defenses, which all together sparked the rise of chemical empire comprised of thousands of specialized metabolites currently found in plants. Metabolic diversity in plant kingdom is truly amazing, and although many plant metabolites have already been identified, a large number of potentially useful chemicals remain unexplored in the plant bio-resources. Similarly, biosynthetic routes for plant metabolites involve many enzymes, some of which still wait for identification and biochemical characterization. Moreover, regulatory mechanisms that control gene expression and enzyme activities in specialized metabolism of plants are scarcely known. Finally, understanding of how plant defense chemicals exert their toxicity and/or repellency against herbivores remains limited to typical examples, such as proteinase inhibitors, cyanogenic compounds and nicotine. In this review, we attempt summarizing the current status quo in metabolic defense of plants that is predominantly based on the survey of ubiquitous examples of plant interactions with chewing herbivores.
February 2019
Feeding of sucking insects, such as the rice brown planthopper (Nilaparvata lugens; BPH), causes only limited mechanical damage on plants that is otherwise essential for injury-triggered defense responses against herbivores. In pursuit of complementary BPH elicitors perceived by plants, we examined the potential effects of BPH honeydew secretions on the BPH monocot host, rice (Oryza sativa). We found that BPH honeydew strongly elicits direct and putative indirect defenses in rice, namely accumulation of phytoalexins in the leaves, and release of volatile organic compounds from the leaves that serve to attract natural enemies of herbivores, respectively. We then examined the elicitor active components in the honeydew and found that bacteria in the secretions are responsible for the activation of plant defense. Corroborating the importance of honeydew-associated microbiota for induced plant resistance, BPHs partially devoid of their microbiota via prolonged antibiotics ingestion induced significantly less defense in rice relative to antibiotic-free insects applied to similar groups of plants. Our data suggest that rice plants may additionally perceive herbivores via their honeydew-associated microbes, allowing them to discriminate between incompatible herbivores—that do not produce honeydew—and those that are compatible and therefore dangerous.
April 2020
Bemisia tabaci is a notorious agricultural pest that causes serious damage to many crops via herbivory and spread of viral diseases. Effective control measures are, therefore, required. Integrating entomopathogenic fungi into the chemical control system offers promise for B. tabaci management. In-vitro assays on the augmentative effect of Beauveria bassiana GHA strain with insecticides, and its compatibility with fungicides were tested. Varying egg mortality was observed for most insecticides except for milbemectin. Pyrifluquinazon was less effective against the nymphs. Flonicamid showed no insecticidal effect on either nymphs or adults. However, increased mortality in nymphs and adults was observed when flonicamid was mixed with Beauveria bassiana GHA strain. Furthermore, no significant synergistic effect of mixing pesticides with B. bassiana GHA strain was observed. Most insecticides (when not mixed with B. bassiana) showed high (>80%) mortality against B. tabaci nymphs and adults. Most fungicides tested showed no inhibitory effects on B. bassiana GHA strain against B. tabaci nymphs and adults. Fungistatic effect was observed in the mycelial and spore germination inhibition studies. Weekly rotation of some pesticides with B. bassiana GHA strain in greenhouse conditions yielded significant reduction in different growth stages of B. tabaci. However, no significant difference in viral incidence was observed. Laboratory and field tests showed positive effects of augmenting pesticides and B. bassiana GHA strain against B. tabaci nymphs and adults. Therefore, augmentation of pesticides and B. bassiana GHA strain is one prospect towards developing an effective B. tabaci IPM system.
August 2019
Plants use many natural products to counter pests and diseases in nature. In rice, direct defense mechanisms include broad range of secondary metabolites, such as phenolamides (PA), diterpene phytoalexins, and flavonoid sakuranetin. Recently, accumulation of PAs in rice was shown to be under control of microbial symbionts in honeydew (HD), digestive waste from the rice brown planthopper (Nilaparvata lugens; BPH), but whether HD microbiota can also promote diterpene phytoalexins, momilactone A (MoA) and MoB, has not been reported. Here, we demonstrate that crude HD, but not a filtered one, induces MoA and MoB in rice, suggesting the involvement of BPH-HD endosymbionts. Consequently, microbial strains previously isolated from HD could promote MoA and MoB levels in wounded rice leaves, suggesting that rice indeed responds to BPH by cumulative chemical defense that involves both PA and diterpene phytoalexin pathways.
March 2021
Nesidiocoris tenuis (Hemiptera: Miridae) is an important biocontrol agent of several key arthropod pests, such as greenhouse and tobacco whiteflies, the South American tomato pinworm, thrips, plant mites, and other pests in the greenhouse. However, optimizing N. tenuis utilization in the greenhouse to control greenhouse pests such as whiteflies still needs further studies, especially in Japan. Here, we showed that factitious supplementary dietary in the form of Artemia cysts enhanced with high fructose corn syrup and honey, and delivered using a hemp rope could promote N. tenuis proliferation and spread among tomato plants. Nesidiocoris tenuis spread among tomato plants therefore, can maintain whitefly (Bemisia tabaci) eggs and nymph numbers at minimum in the greenhouse conditions.
April 2021
This is an excerpt giving an overview of the insects MPDI Special Issue: Biology and Management of Sap-Sucking Pests.
January 2015
A population survey of phytoseiid mites and of spider mites on randomly selected trees and their groundcover plant Paederia foetida L. (Rubiaceae) was conducted in Japanese peach orchards that used different pesticide practices. An organic orchard with wild groundcover and no synthetic chemicals used for pest control and a conventionally managed orchard with bare ground had no trees on which spider mite density was beyond the control threshold density (one mite per leaf). On the other hand, spider mite densities in some trees at conventionally managed orchards with wild groundcover were temporary beyond the control threshold level. The phytoseiid mite species composition on peach leaves estimated by previously established method using quantitative sequencing changed during the survey period and varied among orchards. PCR amplification of the internal transcribed spacer (ITS) region of ribosomal genes of Tetranychus kanzawai Kishida and Panonychus mori Yokoyama from three phytoseiid mite species, Neoseiulus californicus (McGregor), Amblyseius eharai Amitai and Swirski, and Euseius sojaensis (Ehara), collected on peach leaves was conducted. Results showed that the feeding preference for the three phytoseiid mite species was greater for T. kanzawai than for P. mori in the field. PCR amplification of the ITS sequences of Petrobia harti (Ewing) inhabiting Oxalis corniculata L. (Oxalidaceae) showed that phytoseiid mites move from groundcover plants to peach leaves, possibly through ambulatory and aerial dispersal.
July 2016
To examine the utilization of plant food resources by the phytoseiid mite species Amblyseius eharai Amitai & Swirski, Euseius sojaensis (Ehara), and Neoseiulus californicus (McGregor) (Acarina: Phytoseiidae), we collected phytoseiid mites on peach leaves in Japanese peach orchards. Then, phytoseiid mite samples that had been estimated to contain a single phytoseiid mite species using quantitative sequencing were selected. Simultaneously, we surveyed pollen available for phytoseiid mites in peach orchards and selected Digitaria ciliaris (Retz.) Koeler (Poales: Poaceae), Eleusine indica (L.) Gaertn. (Poales: Poaceae), and Pinus densiflora Siebold & Zucc. (Pinales: Pinaceae) as pollen source plants. Subsequently, the internal transcribed spacer sequences of ribosomal genes or the non-coding region of the chloroplast DNA of the three plant species were amplified from phytoseiid mite samples using polymerase chain reaction. Results showed that phytoseiid mite species with different feeding habits use plant food sources, possibly pollens, of D. ciliaris and P. densiflora.
July 2014
A population survey of phytoseiid mites and spider mites was conducted on peach leaves and wild plants in Japanese peach orchards having different pesticide practices. The phytoseiid mite species composition on peach leaves and wild plants, as estimated using quantitative sequencing, changed during the survey period. Moreover, it varied among study sites. The phytoseiid mite species compositions were similar between peach leaves and some wild plants, such as Veronica persica, Paederia foetida, Persicaria longiseta, and Oxalis corniculata with larger quantities of phytoseiid mites, especially after mid-summer. A PCR-based method to detect the ribosomal ITS sequences of Tetranychus kanzawai and Panonychus mori from phytoseiid mites was developed. Results showed that Euseius sojaensis (specialized pollen feeder/generalist predator) uses both spider mites as prey in the field.
Simplified insecticide toxicity determination method for Nesidiocoris tenuis using contaminated diet
January 2021
Nesidiocoris tenuis is a zoophytophagous mirid bug widely studied for its role in preying on major greenhouse pests. Since N. tenuis has now been known for its vigorous predation potential on pests such as Bemisia tabaci, many applied entomologists are now recommending that N. tenuis be merged into the Integrated Pest management (IPM) systems. However, successful integration of N. tenuis into any IPM system depends on thorough evaluation with compatible pesticides, as incompatible pesticides can offset the whole idea of IPM. Here, we simulate the field situation where N. tenuis feeds directly on a contaminated B. tabaci nymph or leaves. However, instead of using live B. tabaci nymphs, we used brine shrimp eggs, Artemia salina (Linnaeus, 1758). Brine shrimp eggs have been reported to be an excellent factitious supplementary diet in augmenting N. tenuis populations. Thus, we use brine shrimp eggs to determine the toxicity of pesticides, to which the calculated mortality rates can be used to determine which pesticides can be used together with N. tenuis in an IPM system against any related pest.
October 2020
New succinate dehydrogenase inhibitor fungicides (SDHIs), isopyrazam, pyraziflumid and isofetamid were introduced in the Japanese market in 2017–2018 to control powdery mildew on cucumber. SDHI resistance of the disease fungus (Podosphaera xanthii) was first reported during 2008–2009 against boscalid. Then, penthiopyrad which belongs to SDHIs was introduced in 2010, but subsequent monitoring study was not performed. We investigated the sensitivity of P. xanthii field isolates from Ibaraki Prefecture, Japan, to SDHIs and SdhB, SdhC and SdhD gene mutations, using a leaf disc assay and SDH gene analysis. A total of 19 out of the 22 selected isolates showed resistance to SDHIs. The 19 isolates were phenotypically categorized into three types: Resistant I as moderately and Resistant II as highly resistant to penthiopyrad, isopyrazam and pyraziflumid but sensitive to isofetamid and Resistant III as highly resistant to isofetamid but sensitive to the other three SDHIs. SDH gene analysis revealed that Resistant I and III isolates carried a substitution in PxD-S121P and PxC-A86V, respectively. Resistant II carried three different substitutions: PxC-G151R, PxC-G172D, and PxD-H137R. Among 127 isolates sampled from 16 cucumber greenhouses, 54 exhibited Resistant I phenotype and carried only PxD-S121P. Fifty-six isolates exhibited Resistant II and carried PxC-G151R (four isolates), PxC-G172D (24), and PxD-H137R (28). Only two isolates expressed the Resistant III phenotype carrying PxC-A86V. To the best of our knowledge, this is the first report demonstrating cross-resistance patterns and the molecular characterization of SDHIs in P. xanthii.
March 2020
In Japan, Hirschmanniella diversa is an important pest in lotus cultivation in paddy fields and only lime nitrogen is registered for its control. Therefore, additional nematicides are required to control the nematode. The objective of this study was to screen for an effective nematicide. Fourth-stage juveniles and adults of H. diversa sampled from a lotus field were tested in in vitro solution experiments against 37 pesticides that are registered for the pest control of crops in Japan. Carbamate-based benfuracarb, organophosphate-based fenthion, nereistoxin-based cartap hydrochloride and cyanamide showed nematicidal effects against H. diversa. Benfuracarb at 1 μg/mL showed a nematostatic effect on H. diversa in an agar plate assay. Further, H. diversa treated with benfuracarb did not resume activity 7 days post nematicide treatment when transferred to distilled water. Benfuracarb was tested in micro-field experiments, in which H. diversa density and lotus tuber damage levels were monitored. Results showed that benfuracarb reduced H. diversa densities in the roots during the cultivation period in 2012 and consistently reduced damage levels during a five year study period. Thus, benfuracarb is recommended as an effective nematicide to be used for H. diversa control in lotus cultivation.
March 2021
The stone leek leafminer Liriomyza chinensis Kato is one of the most important pests of Allium spp. In recent years, a new genotype of L. chinensis, genotype B, has been shown to cause more severe damage to Allium spp. compared with the native genotype A in Japan. Thus, identification of the genotypes is important for establishing L. chinensis control strategies. In this study, we developed a simple and rapid method of genotype identification using PCR-restriction fragment length polymorphism (RFLP). Primers were designed to mitochondria cytochrome oxidase subunit I gene (mtCOI) nucleotide sequences from both genotypes. Genotypes A and B were successfully identified using the restriction enzymes PvuI and DdeI, respectively. Using PCR-RFLP, we identified the genotype of L. chinensis samples (n = 108) collected in seven Japanese bunching onion fields in Ibaraki Prefecture, Japan. All individuals were shown to be genotype B, as expected.
February 2012
In addition to the allele frequencies of the L1014F and T929I mutations which are involved in nerve-insensitive resistance to a pyrethroid, those of the M918I mutation were examined using field strains obtained in China, Thailand, and Japan during 2009-2011. Results show that the resistance allele frequencies at the L1014F site were 89-100%, 97-100% and 65-85%, respectively, for strains in China, Thailand, and Japan. The respective allele frequencies at the T929I site were 86-100%, 70-97% and 58-84% for Chinese, Thai, and Japanese strains. With low frequencies up to 27%, M918I was found in Japan and China, but not in Thailand. The strain homozygous for the M918I and L1014F mutations was established and its resistance level to a pyrethroid was examined. The strain lacks a portion of the sodium channel gene corresponding to the 3' portion of exon 18a, intron 18, and the 5' portion of exon 18b. Nevertheless, the strain showed a similar level of resistance to that which was homozygous for the T929I and L1014F mutations
September 2019
The lotus root nematode, Hirschmanniella diversa Sher (Tylenchida: Pratylenchidae), causes damage to lotus tubers, and thus decreases its economic value. Few studies have elucidated the life cycle of H. diversa, which is essential to optimize control methods. Therefore, we collected H. diversa from lotus roots and investigated its seasonal population fluctuations, female mating rates, stylet, and body lengths to understand its seasonal occurrence and possibly predict its life cycle. Hirschmanniella diversa were sampled from two lotus paddy fields between 2010 and 2012 in Ibaraki Prefecture, Japan. The occurrence of H. diversa increased with time peaking around late August and early September, then depreciating thereafter. The seasonal breeding period determined by quantifying the number of H. diversa females with spermatheca filled with sperm peaked from April until mid-May and decreased subsequently. Furthermore, overwintered adult H. diversa females laid eggs around June, hence possibly mating between April and May. Second-stage juveniles emerged at the beginning of August and continued developing thereafter. The fourth-stage juveniles or adults overwintered in the lotus roots, weed roots, or soil. The population dynamics of H. diversa in lotus roots in paddy fields determined in this study will be useful for development of control strategies.
August 2017
Earlier studies have demonstrated that Paederia foetida L. (skunk vine) harbors larger numbers of phytoseiid mites for longer periods than any other wild plant in peach orchards. To assess the effectiveness of P. foetida in spider mite control, first, longevity and fecundity of Tetranychus kanzawai Kishida were examined in the laboratory using P. foetida and Phaseolus vulgaris L. as host plants. Results showed that all T. kanzawai larvae died without molting and that female adults laid few eggs on P. foetida. No such adverse effect on larvae or female adults was observed on P. vulgaris. Then, population surveys of spider mites and phytoseiid mites were conducted on peach trees with and without P. foetida. Results showed that the presence of P. foetida itself was inadequate to achieve decreased spider mite populations on peach leaves under any circumstances.