Search

To provide fundamental information for the biological control of aphids in vegetable greenhouses, we compared the host ranges of four aphid parasitoid species, Aphidius colemani Viereck, Aphidius gifuensis Ashmead, Diaeretiella rapae (M’Intosh), and Ephedrus nacheri Quilis (Hymenoptera: Braconidae: Aphidiinae). The acceptability as host of 11 vegetable-pest aphids, Acyrthosiphon pisum (Harris), Aphis craccivora Koch, Aphis gossypii Glover, Aulacorthum solani (Kaltenbach), Brevicoryne brassicae (Linnaeus), Chaetosiphon fragaefolii (Cockerell), Lipaphis erysimi (Kaltenbach), Macrosiphoniella sanborni (Gillette), Macrosiphum euphorbiae (Thomas), Myzus persicae (Sulzer), and Uroleucon formosanum (Takahashi), in addition to five aphid species, Melanaphis sacchari (Zehntner), Rhopalosiphum maidis (Fitch), Rhopalosiphum padi (Linnaeus), Schizaphis graminum (Rondani), and Sitobion akebiae (Shinji) (Hemiptera: Aphididae) that serve as alternative hosts in banker–plant systems for the four aphid parasitoid species, were investigated. A newly emerged pair of parasitoid adults were provided to 100 aphids of each species on caged host plants in a 25 °C chamber for 24 h. The numbers of mummified aphids and emerged adults were counted in 10 trials for each aphid species. Aphidius colemani, A. gifuensis, D. rapae and E. nacheri parasitized four, two, three, and eight pest species, respectively, and four, three, three, and five alternative host species, respectively. Ephedrus nacheri had the broadest host range among the four species, and all the four species parasitized M. persicae, R. maidis, and S. graminum. This information will be useful for selecting candidate of biological control agents for aphids and for constructing banker–plant systems.

The reproductive durations of Myzus persicae (Sulzer) after parasitization by three species of Aphidiinae were compared and the mechanisms for differences in duration were examined. The lifetime fecundities of adult aphids parasitized by Aphidius colemani Viereck, Aphidius gifuensis Ashmead, and Diaeretiella rapae (McIntosh) were 3.96, 6.40, and 6.48, respectively. These values were much smaller than that of healthy adults (61.43 nymphs). The time of termination of reproduction by the aphids coincided with the time that the parasitic wasp larvae reached second instar. We infer that first-instar larvae of all three species initially attack conspecific and/or heterospecific competitors and that consumption of the aphid’s ovaries and other reproductive organs commences in the second instar. The modified intrinsic rates of natural increase (r parasitized) calculated from post-parasitized fecundity were 0.185 by A. colemani, 0.233 by A. gifuensis, and 0.234 by D. rapae. Parasitization of 100 % of the adult aphids by A. gifuensis or D. rapae decreased the growth rate to a minimum of 24.4 % while A. colemani more moderately suppressed the growth of the aphid population (39.9 %). We propose the possibility that the effectiveness of species of Aphidiinae as biological control agents is influenced by differences in the duration of aphid reproduction following parasitization.

We investigated the recruitment of specific parasitoids using a specific blend of synthetic herbivory-induced plant volatiles (HIPVs) as a novel method of pest control in greenhouses. In the Miyama rural area in Kyoto, Japan, diamondback moth (DBM) (Plutella xylostella, Lepidoptera: Plutellidae) larvae are an important pest of cruciferous crops in greenhouses, and Cotesia vestalis (Hymenoptera: Braconidae), a larval parasitoid of DBM, is found in the surrounding areas. Dispensers of HIPVs that attracted C. vestalis and honey feeders were set inside greenhouses (treated greenhouses). The monthly incidence of DBMs in the treated greenhouses was significantly lower than that in the untreated greenhouses over a 2-year period. The monthly incidences of C. vestalis and DBMs were not significantly different in the untreated greenhouses, whereas monthly C. vestalis incidence was significantly higher than monthly DBM incidence in the treated greenhouses. Poisson regression analyses showed that, in both years, a significantly higher number of C. vestalis was recorded in the treated greenhouses than in the untreated greenhouses when the number of DBM adults increased. We concluded that DBMs were suppressed more effectively by C. vestalis in the treated greenhouses than in the untreated greenhouses., 植物の香りで特定の天敵を誘引し、標的とした害虫の発生抑制に成功 --植物の香りを用いた新しい害虫防除法--. 京都大学プレスリリース. 2020-12-02.

Banker-plant systems with Aphidius species have been used to control pest aphids in greenhouses in Japan. However, the occurrence of secondary parasitoids, which lead to aphid-control failures, and of minor aphid species, are problematic. In this work the ecological characteristics of Ephedrus nacheri Quilis (Hymenoptera: Braconidae), an alternative biological control agent to Aphidius species against the pest aphids Aphis gossypii and Myzus persicae, were examined under laboratory conditions at 25 °C. Attack rate, success of parasitization, and offspring sex ratio were highly dependent on aphid species and instar stage. Development time and offspring body size depended on aphid species. Because of insufficient honeydew production, survival of the female wasp decreased when the host density was low; as a result, a type III functional response curve was observed for the two aphid species in most stage combinations. The intrinsic rate of natural increase estimated by use of the bootstrap method ranged from 0.128 to 0.258, depending on the larval mortality, host species, and stage. These values were insufficient to support inoculative use of E. nacheri for aphid control. In future work we will conduct a survey to discover a better combination of banker plant and host aphid which maintains a sufficient population and offspring sex-ratio, and decide the scale of the banker-plant system in the greenhouse that will supply a sufficient wasp population.

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.

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.

We report here on the development of a system for producing cruciferous vegetables without using chemical pesticides. This system enables small-scale farmers in hilly and mountainous areas in the western region of Japan to grow products of equivalent volume and quality to those produced by standard practices. The first steps in developing the system involved modifying and creating methods to protect cruciferous vegetables against insect pests. Crops were protected from flying pests, such as the white cabbage butterfly, cabbage armyworm, diamondback moth, cabbage sawfly, leafminer fly, cabbage bug, striped flea beetle, and brassica leaf beetle using a 0.6 mm mesh screen. Bacillus thuringiensis preparations, the use of which is permitted by Japanese Agricultural Standards for organic plants and organic processed foods of plant origin, were used to prevent damage caused by butterfly larvae, (white cabbage butterfly, cabbage armyworm, and diamondback moth) that hatch from eggs deposited on the outer surface of the screen through which they can invade. Invasion by crawling pests, such as the striped flea and brassica leaf beetles, was suppressed by covering the ground around the greenhouse with a mulching sheet to control weeds that form the habitat for these pests. Aphids passing through the 0.6 mm mesh screen were eliminated by a banker plant system employing the aphid parasite Diaeretiella rapae (McIntosh), a natural predator. Solarizing the soil before cultivation destroyed the pests' larvae, pupae, or eggs residing underground, such as those of the striped flea beetle and cutworm, while pest damage by vegetable weevils was prevented by inserting our newly invented traps just underground. The second step in developing the system involved dealing with higher greenhouse temperatures during summer that would result from the 0.6 mm mesh screen cover. To keep the wet bulb globe temperature (WBGT) around the worker within acceptable limits, a battery-powered ventilator consisting of a cart, fan, solar battery, and ordinary battery was used as well as installing simple roof windows, all of which effectively lowered the WBGTs. By combining these methods, we were able to demonstrate that the system was highly effective for producing quality cruciferous vegetables in greenhouses and in open fields.

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.

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)Oecologia109, 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 silkwormBombyx moriinfected with the baculovirusB.morinucleopolyhedrovirus (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 ofB.moriinfected with a BmNPVptpknockout mutant (BmPTPD). However, when a silkworm-derivedptpgene (Bmptp-h) was inserted into BmPTPD, ELA was partially recovered.Bmptp-hwas identified from silkworms at 2 days after the start of the natural wandering stage. The deduced amino acid sequence ofBmptp-hshowed 48.2% identify (80.7% similarity) to the deduced amino acid sequence of BmNPVptp. On the basis of the high homology and larval stage at whichBmptp-hwas isolated, we postulate that the modern baculovirus may have acquired itsptpgene from an ancestral host and that this gene was selectively maintained because it increases virus transmission.

Theory predicts that plants should employ constitutive (fixed) defenses when herbivory is consistently strong among years and induced (plastic) defenses when herbivory varies among years but is predictable within a season. We tested this theory by examining the herbivore species and damage censused over three seasons for 20 populations of wild radish in northern California. We conducted assays of constitutive resistance by challenging undamaged plants from these 20 populations with their common herbivores in the greenhouse. We assayed induced resistance by comparing the performance of herbivores on plants that had been experimentally damaged to undamaged plants from the same populations. Following damage, plants generally became more resistant to chewing herbivores (caterpillars) but more susceptible to sucking herbivores (aphids). Constitutive resistance to caterpillars was not stronger for populations that had high levels of herbivory that varied little among years, contrary to theory. Induced resistance may be stronger for plants from populations where herbivory varied more among years, consistent with expectations, although low power makes this conclusion equivocal. Induced resistance was not stronger for populations where early herbivory was a good predictor of late season herbivory. This lack of support for theory could have been caused by inadequacies with the experimental tests or with the theory and its assumptions. The theory assumes a coevolutionary equilibrium; however, high gene flow that has been reported for wild radish could disrupt matches between risk of herbivory and plant defense. The theory also assumes that resistance traits evolved as defenses against herbivory although these traits also serve other functions. Finally, the correlation we measured between early and late season herbivory may be at a temporal scale that is irrelevant since wild radish appears to adjust its defenses very rapidly.

1. The ways of using host plants were compared among the three Athalia sawflies [A. japonica (Klug), A. rosae ruficornis Jakovlev, and A. infumata (Marlatt)] feeding on crucifers in Japan to determine whether host specialisation can explain the difference in their life-history traits. The occurrence of their larvae was examined on each crucifer species in the field, and the suitability of each crucifer species for the three successive steps of host use by the sawflies was evaluated: microhabitat selection by adult females, female oviposition, and larval growth. 2. There were 11 species of crucifer in the study area, and A. japonica, A. rosae, and A. infumata used nine, seven, and eight species respectively. Thus, sawfly host ranges overlapped. 3. Adult females of A. japonica, A. rosae, and A. infumata preferred shady clumps of crucifers, sunny clumps of crucifers, and disturbed areas respectively. 4. Unsuitable hosts for larval performance such as Brassica oleracea and Arabis plants were eliminated from the host ranges of the three sawflies. 5. Once they chose microhabitats, the suitability of each host plant for female oviposition and larval growth was similar. 6. Because of the divergent preferences for microhabitats, the host plants that were suitable for all the three steps were restricted to different sets of plants among the sawflies: Cardamine for A. japonica, cultivated crucifers (Raphanus and Brassica) for A. rosae, and Rorippa for A. infumata. These plants could be recognised as the respective primary host plants. 7. The spatio-temporal distributions of primary hosts were consistent with and explained the pattern of diapause and migration of each sawfly, suggesting that host specialisation caused their life-history traits to differentiate.

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.

Green larvae of the butterflyPieris rapae and black larvae of the sawflyAthalia rosae feed on green leaves of the same cruciferous plants. To demonstrate thatP. rapae has concealing coloration and thatA. rosae has warning coloration, the larvae of the two species were supplied to naive chicksGallus gallus on white, green or black backgrounds.P. rapae larvae were palatable and their green body color acted as a concealing coloration. On the other hand,A. rosae larvae were unpalatable and their black body color acted as a warning coloration.

This report assesses the primary factor for the evolution of summer diapause of the three species of sawfly,Athalia japonica, A. rosae andA. infumata that feed on cruciferous plants and coexist in the same area.A. japonica has two discrete spring and autumn generations, butA. rosae andA. infumata 5–6 generations. OnlyA. japonica enters summer diapause in response to the long daylengths in spring. Although these three sawflies usually feed on the same cultivated crucifers, they differ markedly in the utilization of wild crucifers. They oviposit only on young leaves.A. japonica mainly usesCardamine plants which sprout in spring and autumn.A. rosae andA. infumata primarily use hosts with new leaves all the year round, i.e. cultivated crucifers andRorippa indica, respectively. The thermal threshold for development is lower inA. japonica than in the other two species. The low heat tolerance ofA. japonica is adapted only to cool shady habitats whereCardamine grows. Presumably, summer diapause ofA. japonica is adaptation to the deterioration of the primary host plants rather than unfavorable climatic conditions. This interpretation is supported by the movement patterns of the threeAthalia sawflies, alternative means to escape from deteriorated habitat conditions.

I compared the differences in the movement intensity of three species of sympatricAthalia sawflies,A. japonica, A. rosae andA. infumata feeding on cruciferous plants. Mark-release-recapture census was conducted to estimate movement distance, sex ratio and age composition of adult sawflies. In addition, the sex ratio of newlyemerged adults was examined by rearing field-collected larvae until adult emergence. Age composition and longevity of adults were estimated experimentally. The movement intensity was evaluated mostly with the indirect information thus obtained.

ThreeAthalia sawflies,A. japonica, A. rosae andA. infumata, feeding on cruciferous plants, coexist in Japan. However, it is not known what ecological strategies they use and what environmental factors are crucial to such strategies. I attempted to explain these questions by examining the relationship between the spatio-temporal distribution patterns of threeAthalia sawflies and their habitats in three districts (Lowland, Intermediate and Mountain).