Yoshimi Hirose

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.

Host discrimination in the parasitoid Ooencyrtus nezarae: the role of the egg stalk as an external marker

Laboratory experiments were conducted to examine the role of the egg stalk in host discrimination by Ooencyrtus nezarae Ishii (Hymenoptera: Encyrtidae), an egg parasitoid of the bean bug, Riptortus clavatus Thunberg (Hemiptera: Alydidae). These experiments showed that females that have oviposited in unparasitized hosts within 1 h before the test discriminated between parasitized and unparasitized hosts. When protruding parts of the parasitoids egg stalks were removed from hosts, the latter were accepted by experienced females. This suggests that the protruding portion of the parasitoid egg stalk functions as an external marker. This part of the egg stalk was responsible for host discrimination up to 8 days after parasitism. Internal discrimination was also observed on hosts 3 or 8 days after parasitism.

The parasitoidOoencyrtus nezarae (Hymenoptera: Encyrtidae) prefers hosts parasitized by conspecifics over unparasitized hosts

SummaryTwo laboratory experiments were conducted to examine the ovipositional preferences of the egg parasitoidOoencyrtus nezarae Ishii (Hymenoptera: Encyrtidae) for parasitized and unparasitizedMegacopta punctatissimum Montandon (Hemiptera: Plataspidae). Females that had never oviposited or that had not oviposite for 3 days preferred recently parasitized hosts more than unparasitized hosts. The preference for recently parasitized hosts appeared to be mediated by the punctures in already parasitized hosts made by the ovipositor of the first female. Survival of the parasitoid progeny was lower in recently parasitized hosts than in unparasitized hosts. However, handling time of parasitized hosts was extremely short relative to that of unparasitized hosts, because the superparasitizing female could use the punctures made by the previous females. It is concluded that the females preferred the parasitized hosts over unparasitized hosts because the benefit of saving time and energy for drilling was more than the cost of progeny survival.

Males second strategy in the allocation of sexes by the parasitic wasp, Gryon japonicum

SummaryPatterns of the sex ratio allocation of Gryon japonicum (Ashmead) (Hymenoptera: Scelionidae), a solitary egg parasitoid of Riptortus clavatus (Thunberg) (Heteroptera: Alydidae), were investigated in the laboratory, and the result was checked against the field data on the sex composition of the parasitoid. When five host eggs were presented simultaneously to each of the females of G. japonicum in a laboratory experiment, they had a strong tendency to lay a male egg in second host egg and female eggs in the others. However, when four host eggs were presented to each female more than 3 h after the completion of oviposition on a host egg, most of the females laid male eggs in the third oviposition, i.e. the second host eggs after the experimental interruption of oviposition. These results indicated that there was a mechanism for G. japonicum to produce a male egg in the second host egg in consecutive ovipositions, and that the mechanism was reset by more than 3 h intervals of oviposition. By this mechanism, G. japonicum is thought to produce the precise sex ratio in response to the size of a host egg batch. Field data on the size of a host egg batch and the sex composition of the parasitoid in a host egg batch supported this view.

Sex differences in foraging behaviour and oviposition site preference in an insect predator, Orius sauteri

The effects of patch quality on the foraging behaviour of an anthocorid predator Orius sauteri (Poppius) were compared between sexes. Prior experience in patches was also studied to determine whether this was a factor affecting oviposition decisions. Patch quality affected patch residence time differently for the two sexes; females stayed much longer in a patch with prey (60 Thrips palmi larvae) than a patch without prey, while males did not remain in any patch for extended periods. Most of the females remained in or moved to patches with prey, whereas males dispersed, irrespective of patch quality. Both females released in patches with prey and females released in patches without prey deposited more eggs per hour in patches with prey than in patches without prey. Females released in patches without prey laid eggs in patches with prey at higher rates than did females released in patches with prey. Causes for the sex difference in patch residence time and allocation are discussed in relation to optimal foraging theory. The significance of selective oviposition and the role of experience in oviposition decisions within heterogeneous environments are also discussed.

Trail sex pheromone as a cue for searching mates in an insect predator Orius sauteri

A critical event in sexual reproduction is mate location or recruitment. Low adult densities of both sexes pose mate location difficulties. Considering the small size of both insect females and males, in conjunction with environmental structural complexity, finding a mate appears a formidable task. Directed movements are often mediated by pheromones for a number of insects (Carde ́ & Baker, 1984). It is known that many heteropteran species use a sex pheromone to attract mates (Mitchell & Mau, 1971; Zdarek & Kontev, 1975; Ralph, 1977; Harris & Todd, 1980; Moriya & Shiga, 1984; Aldrich et al., 1986), however little information exists on a sex pheromone in predacious Heteroptera (James et al., 1994; Aldrich, 1996). For insects with well-developed flight abilities such as Lepidoptera, a volatile sex pheromone is an efficient way to locate females. These insects steer towards a distant pheromone source in a process known as optimotor anemotaxis (Kennedy & Marsh, 1974; Marshet al., 1978). In contrast with the windborne sex pheromone, a substrate-borne sex pheromone should be effective for cursorial animals, such as most insect predators and spiders (Hegdekar & Dondale, 1969), because males can detect the pheromone while walking. Adult females of Orius sauteri(Poppius) inhabit plants and search for prey by walking. Thus, males of this species may use a substrate-borne sex pheromone for locating females. Fauvergueet al. (1995) demonstrated recently that males of a parasitoid wasp, Aphelinus asychis Walker, search intensively areas where females have previously visited and leave a pheromone on the substrate which the authors described as a trail sex pheromone. Although this pheromone may be categorized as a substrate-borne sex pheromone, it differs from other such substrate-borne pheromones that are released with

Biological and ecological comparison of Trichogramma and Telenomus as control agents of lepidopterous pests1

The potential of Trichogramma (Hym., Trichogrammatidae) and Telenomus (Hym., Scelionidae) as natural control agents of lepidopterous pests from the viewpoint of their life history strategies are compared by reviewing the literature and more closely examining two case histories. The results suggested that Trichogramma can be a natural control agent when the hosts are present throughout a long growing season, due to the strong intergeneration response of this r‐selected parasitoid, while Telenomus can be a natural control agent if hosts are not always present during a long growing season, due to adult longevity and extended fecundity. In general, Telenomus should be a better control agent than Trichogramma in natural regulation of lepidopterous pests partly because it has greater longevity and higher searching ability.

Protandry in the parasitoidCardiochiles nigriceps, as related to its mating system

A laboratory study was conducted of the emergence times and mating success ofCardiochiles nigriceps Viereck (Hymenoptera: Braconidae), a larval parasitoid of the tobacco budworm,Heliothis virescens (F.) (Lepidoptera: Noctuidae), and in view of this information, the parasitoids mating system was explored. Observations on laboratory populations ofC. nigriceps confirmed the occurrence of two types of protandry, i.e. seasonal and diurnal; males emerged 2 days before females in a generation, and emerged about 1 hr before females on a given day. An experiment on mating success showed that newly emerged females are not receptive to males that emerged 1 hr earlier, but that these males and females often mate successfully after 1 more hr. The experiment also showed that 1- to 5-day-old males are more successful than 1-hr-old males in mating with 0- to 1-hr-old females. Thus, it is argued that males emerging on a given day have a disadvantage in competition for mates with males that emerged days earlier, and that this disadvantage may serve as a selection pressure toward diurnal protandry.A monogamous mating system for females ofC. nigriceps is suggested because sexual selection would be expected to be strong in species exhibiting both seasonal and diurnal protandry. A possibility of a sibling mating system inC. nigriceps is questioned partly because newly emerged females are unreceptive to males that emerged 1 hr earlier and partly because this parasitoid is solitary in what is considered highly dispersed hosts in the field.

Biological control of aphids and coccids: a comparative analysis

A comparison of the biological control of aphids and coccids was carried out by analyzing success rates for the three major types of biological control, i.e., classical, augmentative, and conservational. Because of the higher intrinsic rates of increase for aphids versus coccids, the working hypothesis that biological control of aphids is less successful compared to coccids was adopted. However, this hypothesis was not supported by an analysis of classical biological control using the BIOCAT database. In this analysis, parasitoids were more successful than predators when used against either aphids or coccids, but the control of Icerya spp. with Rodolia spp. (predators) was highly successful. Some reasons for success of Rodolia spp. are adduced, but field studies on the long-term population dynamics of Icerya–Rodolia systems are needed for determining the mechanisms of regulation. Comparative analyses of augmentative and conservational biological control of aphids and coccids were inconclusive, due to lack of adequate databases; some possible factors involved in the success of these types of biological control are discussed. It is suggested that parasitoids could be better control agents than predators in augmentative biological control of aphids in production greenhouses. Conservational biological control of either aphids or coccids should be aimed at enhancing populations of indigenous natural enemies, especially mobile generalist predators that are capable of keeping pace with mobile pests.

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.