Koukichi Nagasaka

Bio: Koukichi Nagasaka is an academic researcher from National Agriculture and Food Research Organization. The author has contributed to research in topics: Aphid & Myzus persicae. The author has an hindex of 5, co-authored 10 publications receiving 194 citations. Previous affiliations of Koukichi Nagasaka include National Agricultural Research Centre.

A baculovirus-encoded protein tyrosine phosphatase gene induces enhanced locomotory activity in a lepidopteran host.

Abstract: Enhanced locomotory activity (ELA), such as wandering, is a normal behavior that occurs at the end of the larval stage in lepidopteran (butterflies and moths) insects. Baculovirus infection can also induce ELA in lepidopteran larvae. The belief is that the virus induces this behavior to increase its transmission [Goulson, D. (1997) Oecologia 109, 219–228]. Here we show that a baculovirus-encoded protein tyrosine phosphatase (PTP) gene (ptp) induces ELA that is activated by light. ELA was induced in silkworm Bombyx mori infected with the baculovirus B. mori nucleopolyhedrovirus (BmNPV) beginning at ≈3.75 days postinfection (p.i.) and continued until 4.75 days p.i. The intensity of the ELA was dramatically reduced immediately before death at 5.25 days p.i. Light activated the intensity of the ELA by ≈3-fold, and larvae with ELA showed positive phototropism. ELA was not induced in larvae of B. mori infected with a BmNPV ptp knockout mutant (BmPTPD). However, when a silkworm-derived ptp gene (Bmptp-h) was inserted into BmPTPD, ELA was partially recovered. Bmptp-h was identified from silkworms at 2 days after the start of the natural wandering stage. The deduced amino acid sequence of Bmptp-h showed 48.2% identify (80.7% similarity) to the deduced amino acid sequence of BmNPV ptp. On the basis of the high homology and larval stage at which Bmptp-h was isolated, we postulate that the modern baculovirus may have acquired its ptp gene from an ancestral host and that this gene was selectively maintained because it increases virus transmission.

Impact of secondary parasitism on Aphidius colemani in the banker plant system on aphid control in commercial greenhouses in Kochi, Japan

Abstract: In order to elucidate the impact of secondary parasitism on a banker plant system, aphid parasitoids on banker plants were surveyed for four years in commercial greenhouses producing eggplant and sweet pepper in Kochi Prefecture, Japan. A banker plant system using Aphidius colemani was introduced into the greenhouses in November or December for the control of pest aphids from February through May. The mean rate of secondary parasitoids to total parasitoids on the alternative host aphid (Rhopalosiphum padi) on banker plants was less than 35% in the early season. In March or April, the mean rate exceeded 40%, and was more than 70% by May or June. Three main species of secondary parasitoids, Alloxysta sp. nr victrix, Dendrocerus laticeps and Syrphophagus sp., occurred throughout the season. In addition, Asaphes suspensus and Pachynouron aphidis occurred later in the season. In greenhouses where the banker plant system of aphid control failed, the increase of secondary parasitism on banker plants was sharper than in greenhouses with successful aphid control. In March and April, the higher rates of secondary parasitism on banker plants had a significant influence on the failure of aphid control.

A food-supply device for maintaining Cotesia vestalis , a larval parasitoid of the diamondback moth Plutella xylostella , in greenhouses

Abstract: The limited availability of sugar sources (e.g., flowers) in greenhouses may affect biological pest control by parasitoid wasps. However, few studies have focused on feeding devices to provide parasitoids with sugar foods. We investigated the accessibility of a yellow-colored bottle-type feeding device to adult Cotesia vestalis (Halliday), a larval endoparasitoid of the diamondback moth Plutella xylostella (L.). All parasitoids died within four days in a room with no sugar source, whereas 66.7 % of individuals survived if a bottle-type feeding device providing honey solution was installed. We also investigated female longevity in response to different sugar solutions presented in a bottle-type feeding device. Honey and sugar mixtures (glucose and fructose) improved female longevity (38.4 and 39.2 days, respectively) much more than water (3.1 days), indicating these feeding devices containing sugar foods to be potentially useful for maintaining C. vestalis in greenhouses where natural food sources are limited.

Abundances of a Bean Bug and Its Natural Enemy in Seminatural and Cultivated Habitats in Agricultural Landscapes

Abstract: To determine differences in distribution patterns between the soybean pest Riptortus pedestris F. (Hemiptera: Alydidae) and its egg parasitoid Ooencyrtus nezarae Ishii (Hymenoptera: Encyrtidae) in source and cultivated habitats, we compared their abundances in soybean fields and forest edges, which were assumed to be the overwintering sites of R. pedestris. We set synthetic attractant-baited traps for both species over 2 yr in mid-August, just before R. pedestris normally colonizes soybeans. During one of the 2 yr, we also examined the rate of parasitism using an egg trap. The numbers of both R. pedestris and O. nezarae trapped at forest edges were higher than the numbers caught in soybean fields, suggesting that forest edges are important source habitats. Compared with R. pedestris, the abundance of O. nezarae in soybean fields was considerably lower than in forest edges, presumably because of differences in their dispersal abilities and their responses to landscape structure and resource distribution. Better pest control service by O. nezarae was provided at forest edges than in soybean fields. Therefore, when using pest control by O. nezarae in soybean fields, spatial arrangement and distance from the forest edge should be considered.

Development and parasitization of an aphid’s secondary parasitoid, Dendrocerus laticeps (Hymenoptera: Megaspilidae), on Aphidius colemani (Hymenoptera: Braconidae)

Abstract: Banker-plant systems using Aphidius species have been employed to control pest aphids in greenhouses growing eggplant and sweet pepper in Japan. However, a strong negative correlation between the occurrence of secondary parasitoids and aphid-control success by this system was reported by Nagasaka et al. (2010). To control secondary parasitoid populations, detailed knowledge of their ecological characteristics is needed. In this paper, the development and parasitization ability of Dendrocerus laticeps (Hedicke) (Hymenoptera: Megaspilidae), a major secondary ectoparasitoid of Aphidius species in Japan, were examined under 25 °C laboratory conditions. The maximum female longevity was about 11 days when honeydew was available. Parasitization occurred only on mummified aphids, and the age of mummified aphids did not influence the ecological value of offspring. The maximum parasitization ability was 18.9 hosts/day estimated by Holling’s disc equation. Possible lifetime fecundity was 100.35. The intrinsic rate of natural increase estimated by the bootstrap method ranged from 0.211 to 0.321, depending on the assumptions made about larval mortality. The countermeasures for avoiding the negative impacts of D. laticeps in a banker-plant system include the development of a refuge for mummified aphids and increasing the temperature around the banker plants.

Approaches to conserving natural enemy populations in greenhouse crops: current methods and future prospects

Abstract: Biological pest control in greenhouse crops is usually based on periodical releases of mass-produced natural enemies, and this method has been successfully applied for decades. However, in some cases there are shortcomings in pest control efficacy, which often can be attributed to the poor establishment of natural enemies. Their establishment and population numbers can be enhanced by providing additional resources, such as alternative food, prey, hosts, oviposition sites or shelters. Furthermore, natural enemy efficacy can be enhanced by using volatiles, adapting the greenhouse climate, avoiding pesticide side-effects and minimizing disrupting food web complexities. The special case of high value crops in a protected greenhouse environment offers tremendous opportunities to design and manage the system in ways that increase crop resilience to pest infestations. While we have outlined opportunities and tools to develop such systems, this review also identifies knowledge gaps, where additional research is needed to optimize these tools.

Virus infection causes specific learning deficits in honeybee foragers

Abstract: In both mammals and invertebrates, virus infections can impair a broad spectrum of physiological functions including learning and memory formation. In contrast to the knowledge on the conserved mechanisms underlying learning, the effects of virus infection on different aspects of learning are barely known. We use the honeybee (Apis mellifera), a well-established model system for studying learning, to investigate the impact of deformed wing virus (DWV) on learning. Injection of DWV into the haemolymph of forager leads to a RT-PCR detectable DWV signal after 3 days. The detailed behavioural analysis of DWV-infected honeybees shows an increased responsiveness to water and low sucrose concentrations, an impaired associative learning and memory formation, but intact non-associative learning like sensitization and habituation. This contradicts all present studies in non-infected bees, where increased sucrose responsiveness is linked to improved associative learning and to changes in non-associative learning. Thus, DWV seems to interfere with molecular mechanism of learning by yet unknown processes that may include viral effects on the immune system and on gene expression.

Baculovirus Pesticides: Present State and Future Perspectives

Abstract: Baculoviruses pesticides are ideal tools in integrated pest management programs as they are usually highly specific to their host insects; thus, they do not affect other arthropods including pest predators and parasitoids. They are also safe to vertebrates and plants and to the biosphere. Over 50 baculovirus products have been used against different insect pests worldwide, and all have been produced in vivo, mostly on insects reared on artificial diets. However, there are cases of significant viral production in the field by applying a baculovirus against natural populations of the insect host and collecting dead or moribund larvae for further processing into a formulated product. Despite the considerable number of programs worldwide utilizing baculoviruses as biopesticides, their use is still low compared to another biological insecticide based on the bacterium Bacillus thuringiensis Berliner. As of the present, there are no programs using in vitro commercial production of baculovirus due to several technical limitations, and further developments in this area are much needed. Use of the baculovirus of the velvetbean caterpillar in Brazil has experienced a setback over the past 7 years due to modifications in cultural practices by soybean growers. Slow speed of kill by viral pesticides is a limitation that has led to considerable research effort toward developing faster killing agents through genetic modifications by either deleting or inserting toxin genes from scorpions and spiders into their genomes. However, these GMOs have not been used in practice due to significant resistance by the public to modified baculovirus genomes. Effective public extension services and farmer education toward application of biopesticides are much needed to expand the use of these products worldwide.

Secondary plants used in biological control: A review

Abstract: In crop systems, different types of plant or secondary crop may be grown together with the primary crop for pest management purposes. These additional plants – henceforth called secondary plants – may increase the efficiency and sustainability of biological control of pests by natural enemies. Such plants fall into several categories: companion, repellent, barrier, indicator, trap, insectary, and banker. Despite their effectiveness and accepted function in biological control, to date the full potential of secondary plants in integrated pest management has not been put to good use. This may be partly attributed to a lack of detailed knowledge of the way the secondary plant–crop systems operate, including the effects of the secondary plants on tritrophic interactions. The biggest constraint upon progress, however, has been confusion over definitions and terminology. In this paper, we review the knowledge of the currently employed plant categories and provide clear definitions.