Masami Takagi

The reproductive strategy of the gregarious parasitoid, Pteromalus puparum (Hymenoptera: Pteromalidae)

SummaryPteromalus puparum is a gregarious parasitoid of lepidopterous pupae. To determine in which phase of a host outbreak superparasitism occurs, field investigations were carried out on seasonal prevalence of the host, Papilio xuhtus, and parasitism by P. puparum in a citrus grove in Fukuoka, Japan in 1974. Host pupation occurred from May to November and the parasitoid attacked the host throughout this period. Pupal density increased rapidly after mid-August and the percentage parasitism decreased during this period. A high level of parasitism was attained after one or more parasitoid generations in mid-September. The superparasitism was observed after mid-September when the parasitoid attained extremely high density, and resulted in an increase in the proportion of males, high mortality, and a decrease in the size of the progeny.

Population dynamics of the citrus swallowtail,Papilio xuthus Linné (Lepidoptera: Papilionidae): Mechanisms stabilizing its numbers

The citrus swallowtail, Pa#ilio xuthus LINN~, is widely distributed in Japan and the commonest among swallowtail butterflies in its suburban areas, As the larvae feed on Rutaceae, the present species is a pest of citrus in the suburban areas. However, it never outbreaks and its population is maintained at a low level. Population dynamics of various insect species have been studied, but most of them are pests characterized by high levels or violent fluctuations in abundance. In spite of the fact that the majority of insect species remain at relatively low levels in abundance for a long period, we do not fully understand mechanisms of natural regulation in numbers of such low-density species. Studies on the population dynamics of the citrus swallowtail may well contribute to the understanding of the mechanisms. Life tables of the butterfly have recently been reported by TSUBAKI (1973, 1977) and WATANABE (1976), but the mechanisms stabilizing its numbers have remained unknown. Independent of the life table studies made by these two workers, population studies of the butterfly were begun in a suburban area of Fukuoka in 1970. During the course of tho population studies, these have developed into ecological studies of its important natural enemies. The results of the studies of adult dispersal (SUZUKI et al., 1974), spatial distribution of the eggs in a citrus grove (SuzuKI et al., 1976) and adult fecundity (YAMANAKA et al., 1978) have been published as parts of the former studies. The results of the studies of parasitoids (TAKAGI, 1976; HIROSE et al., 1976; HIEHATA et al., 1976) and predators (YAMASAKI et al., 1978) have also been published as parts of the latter studies. This paper presents the life table data of the butterfly in the suburban area and discusses mechanisms stabilizing its numbers on the basis of a life table analysis and the above-mentioned studies on both the butterfly and its natural enemies.

Perspective of practical biological control and population theories

We have not yet had sufficient theoretical explanation for successful biological control in which a key pest is controlled after an introduction of natural enemies. I compare here real features of successful biological control and theoretical host–parasitoid population models to reduce the gap between theory and practice. I first review the historical interaction between classical biological control projects and theoretical population models. Second, I consider the importance of host refuges in host–parasitoid population dynamics as concerns the mechanisms of low and stable host density. The importance of density–dependent parasitism through parasitoid reproduction in multivoltine host–parasitoid systems and supplemental generalist natural enemies are also discussed. Finally, I consider the difference in tactics for classical biological control and for augmentation of natural enemies in annual crop systems.

Costs and benefits of larval jumping behaviour of Bathyplectes anurus

Bathyplectes anurus, a parasitoid of the alfalfa weevils, forms a cocoon in the late larval stage and exhibits jumping behaviour. Adaptive significance and costs of the cocoon jumping have not been thoroughly studied. We hypothesised that jumping has the fitness benefits of enabling habitat selection by avoiding unfavourable environments. We conducted laboratory experiments, which demonstrated that jumping frequencies increased in the presence of light, with greater magnitudes of temperature increase and at lower relative humidity. In addition, when B. anurus individuals were allowed to freely jump in an arena with a light gradient, more cocoons were found in the shady area, suggesting microhabitat selection. In a field experiment, mortality of cocoons placed in the sun was significantly higher than for cocoons placed in the shade. B. anurus cocoons respond to environmental stress by jumping, resulting in habitat selection. In the presence of potential predators (ants), jumping frequencies were higher than in the control (no ant) arenas, though jumping frequencies decreased after direct contact with the predators. Body mass of B. anurus cocoons induced to jump significantly decreased over time than cocoons that did not jump, suggesting a cost to jumping. We discuss the benefits and costs of jumping behaviour and potential evolutionary advantages of this peculiar trait, which is present in a limited number of species.

Cage evaluation of augmentative biological control of Thrips palmi with Wollastoniella rotunda in winter greenhouses

Cage trials of an anthocorid predator, Wollastoniella rotunda Yasunaga et Miyamoto, as a biological control agent of Thrips palmi Karny were conducted in Fukuoka, Japan, under winter greenhouse production conditions. Females of W. rotunda were released on caged eggplants, and placed in two greenhouses on 27 October. The development, population growth, and effectiveness of W. rotunda were observed until early March. Results from the cage trials showed that W. rotunda successfully developed, reproduced, and suppressed T. palmi populations under the conditions found in winter greenhouses. During the experiment, one full generation and a second generation of adult predators occurred. The T. palmi population which was exposed to predators remained at a low density throughout the trial period, but it increased dramatically on eggplants without W. rotunda. The maximum difference between predator treatments and controls was approximately 10‐fold by the end of January. Wollastoniella rotunda has the potential to be an effective control agent for T. palmi on eggplant, even during the winter in temperate regions.

Host-plant dependent population genetics of the invading weevil Hypera postica

Population genetics of invading pests can be informative for understanding their ecology. In this study, we investigated population genetics of the invasive alfalfa weevil Hypera postica in Fukuoka Prefecture, Japan. We analyzed mitochondrial tRNALeu-COII, nuclear EF-1α gene fragments, and Wolbachia infection in relation to three leguminous host plants: Vicia angustifolia, Vicia villosa, and a new host Astragalus sinicus cultivated as a honey source and green manure crop. A parsimony network generated from mitochondrial gene sequences uncovered two major haplotypic groups, Western and Egyptian. In contrast to reported Wolbachia infection of the Western strain in the United States, none of our analyzed individuals were infected. The absence of Wolbachia may contribute to the stable coexistence of mitochondrial strains through inter-strain reproductive compatibility. Hypera postica genetic variants for the mitochondrial and nuclear genes were associated neither with host plant species nor with two geographic regions (Hisayama and Kama) within Fukuoka. Mitochondrial haplogroups were incongruent with nuclear genetic variants. Genetic diversity at the nuclear locus was the highest for the populations feeding on V. angustifolia. The nuclear data for A. sinicus-feeding populations indicated past sudden population growth and extended Bayesian skyline plot analysis based on the mitochondrial and nuclear data showed that the growth of A. sinicus-feeding population took place within the past 1000 years. These results suggest a shorter history of A. sinicus as a host plant compared with V. angustifolia and a recent rapid growth of H. postica population using the new host A. sinicus.

Life History Parameters and Temperature Requirements for Development of an Aphid Parasitoid Aphelinus asychis (Hymenoptera: Aphelinidae)

ABSTRACT We assessed the life history parameters and temperature requirement of a Korean population of the endoparasitoid Aphelinus asychis Walker (Hymenoptera: Aphelinidae), using Aphis gossypii Glover (Hemiptera: Aphididae) as a host. We first measured the time from egg to mummification (i.e., pupation) and mummification to adult emergence (i.e., pupal period) at 25°C. The pupal period was significantly longer than the egg to pupation period in both genders, unlike in other regional populations of the species. Females produced an average of 342.9 mummies, he highest reported fecundity among the various regional populations of this species. Age-specific realized fecundity peaked between the 4th and 7th day (23.3–24.8 mummies a day). The intrinsic rate of increase (rm) was 0.255 offspring per female per day. The parasitoids were then reared at eight constant temperatures between 15 and 32.5°C. The developmental time from egg to adult emergence decreased from 27.8 to 9.8 d. The lower developmental thresholds (T0), estimated by linear regression, for the egg to mummy, mummy to adult, and egg to adult stages were 6.7, 6.8 and 6.7, respectively. The thermal constants for each of the three periods were 115, 126, and 243 DD. We compared these parameters with published data of A. asychis from other regions reared on different hosts and representative species of aphid parasitoids in Aphidiinae (Braconidae) reared on hosts including A. gossypii. The T0s of A. asychis were higher than those of Aphidius colemani and Aphidius matricariae when using A. gossypii.

Dynamics of infection with Wolbachia in Hypera postica (Coleoptera: Curculionidae) during invasion and establishment

The process of loss or gain of parasites during invasion of new lands is not well understood. The alfalfa weevil Hypera postica is an invasive pest of various leguminous crops and consists of three major mitochondrial haplotypes, ‘Western’, ‘Egyptian’ and ‘Eastern’. The Western strain is infected with the endosymbiotic proteobacteria Wolbachia, that cause unidirectional complete reproductive incompatibility, in its native (Europe) and an introduced (the United States) ranges. However, our preliminary screening of a few introduced populations in Northern Kyushu, southwestern Japan, failed to detect Wolbachia from the Western strain. A larger-scale and historical assessment of Wolbachia infection may allow to estimate when and how the bacteria were lost, and current geographical distribution of infection among host haplotypes. In this study, we aim to assess the Wolbachia-infection status of H. postica populations throughout Northern Kyushu, where H. postica invasion to Japan was first found. A total of 228 individuals from seven regions in Northern Kyushu collected in different time periods from 1982 to 2015 and 14 individuals from Europe were subjected to PCR diagnostics for Wolbachia. Wolbachia from the Western strain was not detected, irrespective of the time periods and geographic areas in Northern Kyushu. We found ‘Egyptian’-strain H. postica collected most recently from an island off Kyushu harboured a supergroup-B Wolbachia variant. This variant was genetically different from the European Wolbachia variant infecting Western-strain H. postica. The infection was new to the Egyptian haplotype and was estimated to have taken place independently of the loss in the Western strain.

Effects of Temperature on the Immature Development of the Stone Leek Leafminer Liriomyza chinensis (Diptera: Agromyzidae)

Abstract The effect of nine constant temperatures (15, 17.5, 20, 22.5, 25, 27.5 30, 32.5, and 35°C) on the development of the stone leek leafminer, Liriomyza chinensis (Kato), on Japanese bunching onion, Allium fistulosum L., was studied in the laboratory. Developmental times for immature stages were inversely proportional to temperature between 15 and 30°C but increased at 32.5°C. Total developmental times from egg to adult emergence decreased from 69.6 to 17.1 d for temperatures from 15 to 30°C, with pupae requiring more time for development than the combined egg and larva stages. Both linear and nonlinear (Logan equation VI) models provided a reliable fit of development rates versus temperature for all immature stages. The lower developmental thresholds that were estimated from linear regression equations for the egg, first, second, and third instars, total larva, egg-larval, pupa, and total combined immature stages were 12.1, 10.6, 13.6, 8, 9.6, 11.3, 11.2, and 11.4°C, respectively. The degree-day accumulation was calculated as 312.5 DD for development from egg to adult emergence. By fitting the nonlinear models to the data, the upper and optimal temperatures for egg, larva, pupa, and total immature stages were calculated as 37.8 and 31.7, 34.9 and 30.1, 35.8 and 30.6, and 35.0 and 30.9°C, respectively. These data are useful for predicting population dynamics of L. chinensis under field conditions and determining the maximum proportion of susceptible individuals for facilitating improved timing of application of control measures.

Biophoton Emission from Kidney Bean Leaf Infested with Tetranychus Kanzawai Kishida

We studied spontaneous photon emission from kidney bean leaves infested with spider mites. Strong photon radiation was observed from the leaf veins where spider mites were crowding. Photon emission intensity increased with the decreases in chlorophyll content and photosynthesis yield; these decreases represented the degree of damage caused by the pest. When both infested and un-infested leaves were put on the same wet cotton, photon emission from the un-infested leaf increased, too. Photon emission from the un-infested leaf might be induced by an aqueous elicitor released from the infested leaf. Such an elicitor activates the plant defense response. Therefore, it is suggested that photon emission from an infested leaf conveys information on the direct injury (physical stresses) and physiological (biochemical) actions associated with the defensive response.