Ryoko T. Ichiki

Attraction to Herbivore-induced Plant Volatiles by the Host-foraging Parasitoid Fly Exorista japonica

Responses of the tachinid fly Exorista japonica Townsend to odors from corn plants infested with the fly’s host, the larvae of the noctuid moth Mythimna separata (Walker), were examined in a wind tunnel. Naïve female flies showed a higher rate of landing on M. separata-infested corn plants from which the host larvae had been removed than on artificially damaged or intact corn plants. When paper impregnated with a solution of headspace volatiles collected from host-infested plants was attached to intact plants, females landed on the plants at a high rate. Females also responded to intact plants to which had been attached with paper impregnated with a synthetic blend of nine chemicals identified previously in host-infested plants. There was an optimum concentration of the synthetic blend for the females’ landing. Of the nine chemicals identified previously, four [(E)-4,8-dimethyl-1,3,7-nonatriene, indole, 3-hydroxy-2-butanone, and 2-methyl-1-propanol] released only by host-infested plants were classified as a host-induced blend. The other five [(Z)-3-hexen-1-yl acetate, (E)-2-hexenal, hexanal, (Z)-3-hexen-1-ol, and linalool] were classified as a non-specific blend released not only by infested plants but also by artificially damaged or intact plants. In the wind tunnel, E. japonica females did not respond to intact plants to which paper containing a solution of non-specific blend or host-induced blend was attached. However, they showed a high level of response to a mixture of the non-specific and host-induced blends. These results indicate that naïve E. japonica use a combination of non-specific and host-induced blends as an olfactory cue for locating host-infested plants.

The parasitoid fly Exorista japonica uses visual and olfactory cues to locate herbivore-infested plants

Some parasitoid flies exploit odors derived from plants as olfactory cues for locating the food plants of host insects, but the role of visual cues associated with plants remains largely unknown. The generalist tachinid Exorista japonica Townsend (Diptera: Tachinidae) is attracted to odors derived from maize plants [Zea mays L. (Poaceae)] infested by the larvae of Mythimna separata (Walker) (Lepidoptera: Noctuidae). In this study, we examined the effects of visual parameters on the olfactory attraction of female flies to host‐infested plants. A paper plant model of one of four colors (blue, green, yellow, or red) was placed in front of a host‐infested plant, which was hidden behind a mesh screen in a wind tunnel. The landing rate of females was significantly higher on the green plant model than on the other three models. When an achromatic plant model of one of four gray scales (white, light gray, dark gray, or black) was tested, the response rate of females was significantly higher towards the white model and decreased as the brightness of models decreased. Few female flies responded to the green plant model without odors of the host‐infested plants. When the four color plant models were placed together in a cage filled with odors of host‐infested plants, females remained significantly longer on the green model than on the other three models. These results showed that E. japonica females preferred the color green when odors of the host‐infested plants were present and suggest that E. japonica uses visual as well as olfactory cues to locate the host habitat.

Immature Life of Compsilura concinnata (Meigen) (Diptera: Tachinidae)

Abstract Development, location, and respiration of Compsilura concinnata (Meigen) (Diptera: Tachinidae) larvae were investigated using the silkworm, Bombyx mori (Linnaeus) (Lepidoptera: Saturniidae), as its host. C. concinnata was always found between the peritrophic membrane and the midgut of the host in the early larval stage. There they attached their posterior abdominal segment to or around the tracheoles of the host midgut using their anal hooks. C. concinnata at the later larval stage was found in the midgut cavity, where the peritrophic membrane had already been exuviated. The larvae actively took tracheae and tracheoles distributed on the coelomic surface of the host midgut into the midgut cavity.

Parasitisation of Tetrastichus brontispae (Hymenoptera: Eulophidae), a biological control agent of the coconut hispine beetle Brontispa longissima (Coleoptera: Chrysomelidae)

Abstract The gregarious endoparasitoids Tetrastichus brontispae Ferrière is one of the important natural enemies of the coconut hispine beetle Brontispa longissima (Gestro), a serious invasive pest on coconut palm plants (Cocos nucifera L.) in Southeast Asia. Development at different temperatures, effect of host and female ages, effect of food and oviposition frequency and superparasitism were investigated in the laboratory. Females were allowed only one attack against one host in all experiments. The wasp developed in a host between 19 and 30°C, whilst no wasp completed its immature development at 16 and 31°C. Host and female ages affected parasitisation. Parasitoid emergence was high on day 0 and day 1 pupal hosts, and younger females produced more offspring than older females. The longevity of the female was affected not only by food supply, but also by oviposition frequency. The female survived longer when oviposition frequency was low. However, the total number of hosts parasitised by the female during her lifetime did not differ at different oviposition frequencies. In superparasitism, although the percentage of adult emergence and body size of offspring decreased with an increasing number of attacks per host, a host parasitised by up to four females could produce parasitoid offspring.

A New Lavandulol-related Monoterpene in the Sex Pheromone of the Grey Pineapple Mealybug, Dysmicoccus neobrevipes

The grey pineapple mealybug, Dysmicoccus neobrevipes, is a serious pest that attacks a variety of crops in tropical regions. Recently, it was recorded on an island in southwestern Japan, suggesting that its distribution is expanding. As a measure against this expansion, a monitoring tool is urgently needed. In this study we determined the structure of the sex pheromone of D. neobrevipes in order to develop an efficient lure for monitoring traps. Volatiles collected from virgin adult females were fractionated by high performance liquid chromatography (HPLC) and gas chromatography, and fractions were tested for attractiveness to males in a laboratory bioassay. A single compound was isolated which was as attractive to males as the crude collections, and this was proposed to be the main, if not the only, component of the female-produced sex pheromone. The structure of this was determined to be (E)-2-isopropyl-5-methylhexa-3,5-dienyl acetate by gas chromatography/mass spectrometry and nuclear magnetic resonance analyses. This compound was synthesized through four steps, and the synthetic chemical was as attractive as the natural product in a greenhouse bioassay. The enantiomers of the synthetic acetate were obtained by enantioselective HPLC fractionation of the corresponding alcohols, and the natural pheromone was shown to be the (+)-isomer. The carbon skeleton of this novel compound is related to lavandulol, a monoterpene with an unusual non-head-to-tail connection of isoprene units that is often found in mealybug pheromones.

Artificial diets for rearing the coconut hispine beetle Brontispa longissima and its parasitoid Asecodes hispinarum

We tested artificial diets for rearing the coconut hispine beetle, Brontispa longissima, a serious invasive pest of coconut (Cocos nucifera) in Southeast Asia. We examined three artificial diets that were identical except for their agar content. The survival rate from hatching to adult emergence was 26.0% when beetles were reared on a ‘soft diet’ (20 g/l agar), 16.0% on a ‘hard diet’ (40 g/l agar), and 41.0% on a ‘mixed diet’, in which the hard diet was used for the first instar and the soft diet for later instars. Females raised as larvae on the mixed diet and then as adults on the soft diet laid few eggs, which did not hatch. However, females reared on the mixed diet as larvae and then on fresh leaves as adults consistently laid eggs that hatched. We then examined the suitability of B. longissima larvae reared on the mixed diet as hosts for the larval parasitoid Asecodes hispinarum, a specialist parasitoid of this beetle. Of the oviposited hosts, 75.0% became mummified and 41.7% produced adult wasps. These results indicate that the mixed diet may be useful for rearing B. longissima larvae as hosts for the rearing of A. hispinarum.

Reproductive biology of the microtype tachinid fly Zenillia dolosa (Meigen) (Diptera : Tachinidae)

Reproductive biology including mating, adult longevity, fecundity and development of the tachinid fly Zenillia dolosa was investigated for optimizing rearing procedures using Mythimna separata as a host in the laboratory. Females lay microtype eggs containing a first instar larva on food plants of the host and then the eggs must be ingested by the host for parasitization. Mating success was 58.5% with mating duration of 80.7 min. Mating was most successful when day 0–1 females were kept with day 2–4 male flies. Female body size was positively correlated with its fecundity but not with longevity. However, females that survived longer produced more eggs during their lifetime. Parasitoids successfully developed in 4th to 6th instar host larvae. Host instars at the time of parasitoid egg ingestion significantly influenced development time of the immature parasitoid, but did not affect body size of the emerging parasitoid. We suggest that pairing newly emerged females with day 2–4 males should result in higher mating success and using the last instar hosts for parasitization should minimize development time of the parasitoid for rearing.

Temperature‐sensitive eye colour mutation in the parasitoid fly Exorista japonica Townsend (Dipt.: Tachinidae)

Abstract:  An eye colour mutation was found in the tachinid fly Exorista japonica Townsend, and we established an isogenic line of the mutant. The phenotype of the mutant is red eye in adults; this can be clearly distinguished from the brown‐eyed phenotype of the wild type. Crossing experiments demonstrated that the mutant phenotype is controlled by a single autosomal recessive allele. As rearing temperature during the puparial stage rose, eye colour became lighter in the mutant but did not change in the wild type, indicating that the phenotype of the mutant is temperature dependent. No differences in the percentages of egg eclosion, pupariation and adult emergence were observed between the mutant and the wild type. This mutant of E. japonica– the first in the Tachinidae to be described – could be a useful marker in the laboratory experiments to test for paternity in multiple mating and to examine intraspecific competition.

Life history traits and damage potential of an invasive pest Brontispa longissima (Coleoptera: Chrysomelidae) on Satakentia liukiuensis

The coconut hispine beetle Brontispa longissima has been causing serious damage to the coconut palm Cocos nucifera in the Pacific, and Southeast and East Asia. This beetle also attacks Satakentia liukiuensis, an endemic palm on Ishigaki and Iriomote Islands, Japan. To assess the potential impact of B. longissima on S. liukiuensis, we examined the development period, survival rate, egg production and body size of B. longissima on S. liukiuensis at 22–31°C and consumption of S. liukiuensis leaf at 28°C. We also examined these life history traits on C. nucifera at 28°C to compare with those on S. liukiuensis. Brontispa longissima completed their development and reproduced on S. liukiuensis at 22–30°C. Linear regression analysis was used to estimate the effective cumulative temperature (k) as 891.2 degree‐days, and the lower developmental threshold as 13.3°C. On the basis of these values and monthly average temperatures on Ishigaki Island, it was estimated that B. longissima has four generations per year on the island. Satakentia liukiuensis was less suitable for B. longissima than C. nucifera in terms of immature survival, development time, resultant adult size and reproduction. The low quality of S. liukiuensis as a host‐plant may prevent the outbreak of B. longissima, which has not occurred yet on Ishigaki and Iriomote Islands.

Artificial diets for rearing the coconut hispine beetle, Brontispa longissima (Coleoptera: Chrysomelidae), and their suitability to two specialist parasitoids

Abstract The coconut hispine beetle, Brontispa longissima (Gestro), is a serious invasive pest that infests young unopened fronds of coconut palms (Cocos nucifera L.) in Southeast Asia. We previously developed the first artificial diet for rearing B. longissima larvae, which contained a leaf powder of young coconut fronds. Because the fronds are required for healthy growth of coconut palms, it is necessary to reduce their use for rearing the beetles. In this study, we tested two new artificial diets for the beetle larvae, which contained the leaf powders of mature coconut leaves or orchard grass (Dactylis glomerata L.). Brontispa longissima successfully developed from hatching to adulthood on both the mature coconut leaf diet and orchard grass diet. The beetles reared on the mature coconut leaf diet and orchard grass diet developed faster than those reared on the young coconut leaf diet. Fecundity and egg hatchability of beetles did not differ among the three diet treatments. We then examined the suitability of beetle larvae or pupae reared on each diet as hosts for two specialist endoparasitoids, Asecodes hispinarum Boucek and Tetrastichus brontispae Ferriere. The survival rate from oviposition to adult emergence for A. hispinarum was 43.8% in hosts reared on a young coconut leaf diet, 77.1% on a mature coconut leaf diet, and 85.7% on an orchard grass diet. For T. brontispae, the survival rate was 70.0% in hosts reared on the young coconut leaf diet, 38.1% on the mature coconut leaf diet, and 66.7% on the orchard grass diet. Our results indicate these artificial diets can be useful for rearing B. longissima and its two parasitoids, helping to reduce the costs of mass rearing these insects.