Effect of Furcellaran Solution as an Egg-seeding Agent on Post-hatching Survival and Development of the West Indian Sweetpotato Weevil,Euscepes postfasciatus (Coleoptera: Curculionidae)

Mass rearing the West Indian sweetpotato weevil, Euscepes postfasciatus (Fairmaire), using artificial diets is essential for eradicating this serious sweetpotato pest by the sterile insect technique. We tested the use of the furcellaran solution (a viscous liquid, hereafter FS) as an egg-seeding agent on an artificial diet as an important step in extending small-scale rearing of this species to a mass-rearing technique. We recently detected no effect of FS on egg hatching; however, this study revealed significant adverse effects of FS on post-hatching survival and development of the species, i.e. more than 50% reduction in the survival rate and a 1.3- to 1.5-fold extension of the development period. The number of larvae remaining on the diet surface but not feeding into the diet was consistently higher in the FS-treated groups throughout the experiment period. These results suggests that FS may physically or chemically inhibit the normal feeding of larvae, leading to the observed adverse effects on survival and development of insects. The survival rate among FS-treated replicates was significantly related to variations of the diet conditions (shrunk by desiccation) that might be caused by uncontrollable environmental differences. The shrunk diets yielded two to three times more adults than those not shrunk. This implies that post-hatching survival of E. postfasciatus can be improved by drying the contents of the rearing trays after egg-seeding.     

Moisture during Egg Incubation Adversely Affects Hatching of the West Indian Sweetpotato Weevil,Euscepes postfasciatus (Coleoptera: Curculionidae), When the Eggs are Incubated En Masse

We compared the egg-hatching of Euscepes postfasciatus (Fairmaire) with and without moisture treatment to test whether moisture is necessary during egg incubation when a large number of eggs are gathered into a mass. Moisture treatment exhibited significant undesirable effects on hatching (reduction of hatchability, delay of hatching, and increase of the variance of hatching date) compared to no moisture treatment. In addition, moisture treatment significantly increased the incidence of fungus on the egg surface, which can subsequently contaminate the larval artificial diet. Based on these results, we concluded that moisture is not necessary for incubating E. postfasciatus eggs. Two possible explanations for the undesirable effects of moisture on hatching were discussed: a direct effect by preventing respiration of the eggs and an indirect effect through fungal infection of the eggs.     

Population dynamics of the West Indian sweetpotato weevil Euscepes postfasciatus (Fairmaire): a simulation analysis

The West Indian sweetpotato weevil Euscepes postfasciatus (Fairmaire) is a major pest of the sweet potato Ipomoea batatas (L.) Lam. and this weevil is a target of an eradication program using the Sterile Insect Technique in Okinawa Prefecture, Japan. Understanding the population ecology is essential in the planning of an eradication program; hence, a host‐plant infestation survey and light trap survey have been conducted to monitor the population dynamics of the weevil on Kume Island (Okinawa Prefecture), which is the target area of the trial weevil eradication project. Seasonal tendencies of weevil density were found in these field surveys, but the tendency found in the host‐plant infestation survey was not seen every year, and the effectiveness of the light trap is somewhat suspect. To confirm the reliability of the tendency observed in these field surveys, the present study attempted to explain the tendency by a seasonal temperature change using a temperature‐based model of weevil population dynamics. The seasonal changes of weevil density differed according to host plants and host‐plant fields. The seasonal changes of weevil density inside the host plant Ipomoea indica and outside the host plants in I. indica fields were consistent with those predicted by the model. However, those inside the host plant Ipomoea pes‐caprae in the host‐plant infestation survey were contrary to the predicted ones, and those observed outside host plants in I. pes‐caprae fields by the light trap survey were not in good agreement with the predicted ones. It was concluded that the seasonal change of the weevil density observed in I. indica and I. indica fields can be explained by a seasonal temperature change, but factors other than seasonal temperature change are needed to explain those in I. pes‐caprae and I. pes‐caprae fields.     

Suppressing effect of gamma-irradiated weevils on progeny production in the West Indian sweetpotato weevil Euscepes postfasciatus (Coleoptera: Curculionidae)

The West Indian sweet potato weevil Euscepes postfasciatus (Fairmaire) (Coleoptera: Curculionidae) is a major pest of sweet potato Ipomoea batatas (L.) in the tropical and subtropical regions. The sterile insect technique (SIT) could be used as one of the most effective methods for suppression or eradication of the weevil. The effectiveness of SIT depends on the ability of the released sterile males to mate with and inseminate wild females. However, the effect of sterile weevils on the fitness of E. postfasciatus has not been evaluated on natural density. Here, we investigated the effect of gamma-irradiated weevil density on the number of weevil progeny. When irradiated weevils were released in numbers equal to those of non-irradiated weevils, the number of progeny was reduced by half of that in the control treatment, and it remained at this state for 2?weeks. Our results show that irradiated weevils ensure adequate and efficient suppression of wild weevils. We conclude that the SIT programs will be employed as effective eradication method for E. postfasciatus.     

The Effect of Inbreeding on Mating Behaviour of West Indian Sweet Potato Weevil Euscepes postfasciatus

When there is an inbreeding depression, mating with a kin individual is generally considered maladaptive behaviour. However, in some conditions, the inclusive fitness benefits from inbreeding may outweigh the costs of inbreeding depression, and thus, inbreeding tolerance is often adaptive. Inbreeding depression and the effect of relatedness on mating behaviour in the West Indian sweet potato weevil Euscepes postfasciatus were examined. No significant inbreeding depression was detected as indicated by body weight and number of progeny emerging from sweet potato roots. Male mating performance (i.e. number of mating occurrences per night) was adversely affected by inbreeding depression, but the effect was low (fitness loss was 6.3%). Although there were no significant differences in latency to mounting, pre‐copulatory guarding, copulation and post‐copulatory guarding duration between full‐sib and non‐kin pairs, the copulation rate of full‐sib pairs was significantly higher than that of non‐kin pairs. These results support the theoretical prediction that when inbreeding depression is weak, copulation with close relative individuals is favoured.     

Male body size does not affect the refractory period of females in the West Indian sweet potato weevil Euscepes postfasciatus (Fairmaire) (Coleoptera: Curculionidae) and the seed bug Togo hemipterus (Scott) (Heteroptera: Lygaeidae)

Journal of Ethology - Multiple mating by females increases both the risk and intensity of sperm competition for males. The ability to temporarily or permanently inhibit female receptivity to...     

Fractionated irradiation improves the mating performance of the West Indian sweet potato weevil Euscepes postfasciatus

• 1 The sterile insect technique (SIT) is widely used to suppress or eradicate target pest insect populations.
• 2 The effectiveness of SIT depends on the ability of released sterile males to mate with and inseminate wild females. The use of gamma radiation to induce sterility, however, negatively affects both somatic cells as well as reproductive cells. Consequently, mating performance of sterilized individuals decreases drastically over time. The mating propensity of sterilized Euscepes postfasciatus (Fairmaire) males irradiated with a single dose of 150 Gy (the current standard of the Okinawa Prefecture SIT programme) is equal to that of non‐irradiated weevils for the first 6 days.
• 3 Fractionated irradiation, in which a sterilizing dose is delivered over time in a series of smaller irradiations, reduces the damage of irradiation in insects. In the present study, we evaluated the effect of fractionated irradiation on male fertilization ability, longevity and mating propensity of E. postfasciatus for a period of 16 days after irradiation.
• 4 Although fractionated irradiation totalling 150 Gy was found to induce full sterility regardless of the number of individual doses, the mating propensity of male weevils sterilized by fractionated irradiation was maintained for the first 12 days. These results demonstrate that fractionated irradiation can be highly advantageous in programmes aimed at eradication of E. postfasciatus.

     

Trail Marking and Processionary Behavior of the Larvae of the Weevil Phelypera distigma (Coleoptera: Curculionidae)

We present here the results of an investigation of the behavioral bases of the first documented instance of trail marking and processionary behavior in a beetle. The larvae of Phelypera distigma (Coleoptera: Curculionidae) forage communally, moving over the host plant in head-to-tail processions. Our study shows that the larvae secrete a pheromone from the ventral surface of the posterior abdomen that both elicits and guides the collective locomotion of the cohort. The pheromone is soluble in acetone and other nonpolar solvents and is relatively short-lived, eliciting trail following for less than 4 h after its deposition. When in processionary formations, larvae stimulate locomotion in others by rapidly bobbing their heads against sets of setae that occur on the lateral flanks of the posterior tips of the abdomens of precedent individuals. Larvae are also strongly attracted to tactile or chemotactile stimuli found at the tip of the abdomen of other larvae and their response to lures made of eviscerated abdomens show that such stimuli take precedence over the trail pheromone in eliciting and orienting locomotion. The cycloalexic formations adopted by resting larvae maximize the amount of body contact possible in a two-dimensional aggregate and allow tactile signals to rapidly radiate through the groups, alerting all members of a cohort to the onset of bouts of activity.     

Cuticular Compounds Recognition and Mating Behavior of the Rice Water Weevil Oryzophagus oryzae (Coleoptera, Curculionidae)

Oryzophagus oryzae mating behavior and mate recognition were investigated. Bioassays revealed that couples had intense sexual activity in the first 3 h of photophase and scotophase. Adults mated and re-mated at any time of day in the presence of water; however, in the absence of water, only 10 % of adults mated, meaning that water was important for couples to find each other. In the sequence of pre-mating behaviors bioassay four steps were observed and females were always attracted to males, seeking them, before copulation; after mating, males showed guarding activity of variable duration, allowing remating. Cuticule extractions revealed that both sexes had similar cuticular chemical compounds. They were identified as aldehydes and a ketone, probably because of its aquatic life habits. Bioassays suggested that males recognized females by their cuticle composition.     

Evaluation of partial sterility in mating performance and reproduction of the West Indian sweetpotato weevil,Euscepes postfasciatus

The sterile insect technique (SIT) is based on population and behavioral ecology and is widely used to suppress or eradicate target pest insect populations. The effectiveness of SIT depends on the ability of the released sterile males to mate with and inseminate wild females. The use of gamma‐radiation to induce sterility is, however, associated with negative impacts not only on reproductive cells but also on somatic cells. Consequently, irradiation for sterilization diminishes mating performance over time. In this study, we evaluated the balance between the irradiation dose and both fertility and mating propensity in Euscepes postfasciatus (Fairmaire) (Coleoptera: Curculionidae) for 22 days following irradiation. The mating propensity of males irradiated with a 150‐Gy dose, as currently used to induce complete sterility of E. postfasciatus in the SIT program in Okinawa Prefecture, was equal to that of non‐irradiated weevils for up to 6 days, and the mating propensity of males irradiated with a dose of 125 Gy was equal to that of non‐irradiated weevils for twice this period (12 days). The fertilization ability of weevils irradiated with a dose of 125 Gy was reduced by 4.6% in males and 0.6% in females, compared to the potential fertilization ability. We also discuss the possibility of the application of partially sterilized insects in eradication programs.     

Social Behavior of Larvae of the Neotropical Processionary Weevil Phelypera distigma (Boheman) (Coleoptera: Curculionidae: Hyperinae)

Socially gregarious behavior among free‐living leaf‐eating insect larvae occurs mostly among Lepidoptera, Symphyta, and a few Chyrsomelidae (Coleoptera). However, the Neotropical hyperine curculionid Phelypera distigma has also evolved this lifestyle, exhibiting a suite of social behaviors unique among beetles. The larvae are nomadic processionary foragers that punctuate foraging bouts with rosette‐shaped resting formations (cycloalexy). Larvae also vibrate or bob their heads rapidly when moving, especially when in contact with conspecifics, and this suggests acoustic or vibrational communication. In this study we used observational and experimental approaches to investigate the basis of processionary, cycloalexic,and head‐vibration behavior of this species. Larvae used both trail pheromones and thigmotactic signals to organize themselves into head‐to‐tail processionary columns. The trail pheromone, produced from the center of the abdomen, remains active for up to 4 h. Processions are not consistently led by particular individuals, but dynamically change over time and often temporarily break into two or more subprocessions. Subprocessions reunite through use of the trail pheromone. We found no evidence that head‐bobbing generates attraction through substrate‐borne or acoustic signals, but this behavior functions in direct contact to excite group activity. Time‐lapse videography used to analyze cycloalexic group formation showed that larvae transition from feeding in a line along the leaf margin to cycloalexic formations on the upper leaf surface via a coordinated back‐up movement that brings the posterior tip of their abdomens into contact. We identify three phases of cycloalexic formation: line‐up, back‐up, and an adjustment phase. Complete assembly can be achieved in as little as 5 s, but often the two phases establishing the basic rosette lasts 5–10 min, while the adjustment phase slowly tightens the group over a period of up to an hour. Collectively these studies present the first documented case of chemical trail marking in a beetle, and provide insight into a remarkable social‐behavioral repertoire convergent in key respects with the better‐studied social caterpillars and sawflies.     

Effect of temperature on the development of the West Indian sweet potato weevil, <Emphasis Type="Italic">Euscepes postfasciatus</Emphasis> (Fairmaire) (Coleoptera: Curculionidae) on an artificial diet

The relationship between temperature and the development of the West Indian sweet potato weevil, Euscepes postfasciatus, on an artificial larval diet containing powdered sweet potato root, was examined at different fixed temperatures from 22 to 31°C. The developmental periods for egg, larvae, and pupae stages shortened in correlation with increased temperature. The thermal constant was 769.2 degree-days and the developmental zero for female and male was 11.1 and 11.7°C, respectively. Although we can rear this weevil at temperatures ranging from 22 to 31°C, rearing temperatures should be kept between 25 and 28°C because the developmental stages were too long at 22°C and the larval period was delayed at 31°C. The basis for these developmental data will be a useful key factor in designing a plan to eradicate the weevil by using a mass-rearing system and SIT.     

Ultraviolet light-emitting diode (UV LED) trap the West Indian sweet potato weevil, <Emphasis Type="Italic">Euscepes postfasciatus</Emphasis> (Coleoptera: Curculionidae)

The West Indian sweet potato weevil Euscepes postfasciatus (Fairmaire) is a troublesome pest insect of sweet potato that originally came from the Caribbean, but is now expanding its distribution into the Pacific Islands. Although sterile insect techniques have been used against this pest in a demonstration experiment on Kume Island [Ohno et al. (2006) Kontyu to Shizen 41:25–30], effective methods of monitoring E. postfasciatus are scarce. It is necessary to detect the weevils at an early stage of invasion in uninvaded areas, and an attractant trap can be used to achieve this. Thus, we developed an ultraviolet (UV) light-emitting diode trap, invented a method for diffusing the light to attract more insects, and investigated the attractiveness of the light trap to E. postfasciatus under laboratory conditions. Our results indicate that diffused UV light has a higher potential to attract E. postfasciatus than direct UV light. Furthermore, sweet potato is an effective bait to use to capture the weevils attracted by UV light. Thus, E. postfasciatus can be trapped using diffused UV light and sweet potato bait.     

Irradiation as a methyl bromide alternative for postharvest control of Omphisa anastomosalis (Lepidoptera: Pyralidae) and Euscepes postfasciatus and Cylas formicarius elegantulus (Coleoptera: Curculionidae) in sweet potatoes

Irradiation studies were conducted with three sweet potato, Ipomoea batatas (L.) Lam., pests to determine an effective dose for quarantine control. Dose-response tests indicated that the most radiotolerant stage occurring in roots was the pupa of sweetpotato vine borer, Omphisa anastomosalis (Guenee), and the adult of West Indian sweetpotato weevil, Euscepes postfasciatus (Fairmaire), and sweetpotato weevil, Cylas formicarius elegantulus (Summers). In large-scale confirmatory tests, irradiation of 60,000 C. formicarius elegantulus adults, 62,323 E. postfasciatus adults, and 30,282 O. anastomosalis pupae at a dose of 150 Gy resulted in no production of F1 adults, demonstrating that this dose is sufficient to provide quarantine security.     

A New Species of the Weevil Genus Dermatodina Faust (Coleoptera,Curculionidae) from Vietnam

Entomological Review - Dermatodina prosvirovi sp. n. from Vietnam is described as new to science. The taxonomic composition of the genus Dermatodina Faust, 1895 is discussed.     

Appropriate number of inoculated eggs for mass-rearing the West Indian sweet potato weevil, <Emphasis Type="Italic">Euscepes postfasciatus</Emphasis> (Coleoptera: Curculionidae)

It is necessary to establish an economical mass-rearing system for the West Indian sweet potato weevil Euscepes postfasciatus (Fairmaire) so that large numbers can be created for use in the sterile insect technique (SIT) to control wild infestations. Both the quality of offspring and the number of adult weevils produced are important. As an adult female with a dry weight of less than 1.4 mg has an extremely low rate of production of offspring, we investigated the effect of an inoculated dose of egg suspension on both yield rate and body size, in order to determine the appropriate dose to attain the maximum yield of productive females. The number of emerged weevils increased as the inoculated dose of egg suspension increased. In brief, both yield rate and female body size significantly decreased as the inoculated dose of egg suspension increased, perhaps as a result of density effects. We conclude that the appropriate dose of inoculated egg suspension to attain the maximum yield from productive females of E. postfasciatus in the current mass-rearing system is 3 mL (containing approximately 450 eggs) per rearing container.     

Effects of high CO2 on mating success,mating duration,and sperm transfer in the West Indian sweet potato weevil,Euscepes postfasciatus

Most terrestrial animals live in natural atmospheric conditions, but some are also adapted to low oxygen (hypoxic) or high-carbon dioxide (hypercapnic) conditions, such as in social insect nests, soil, caves, wood, and decaying material. Although it is possible that individuals adapt their behaviour to the environmental condition of their habitats, mating behaviour under ecologically possible ranges of CO₂ has not been well studied. We compared walking activity, duration of mating behaviour, and sperm transfer ability in the West Indian sweet potato weevil, Euscepes postfasciatus Fairmaire (Coleoptera: Curculionidae), in high CO₂ (10 000 p.p.m.) vs. normal atmospheric conditions (laboratory air, ca. 800 p.p.m.). We found that high CO₂ enhanced walking activity and mounting frequency. Under such circumstances, we predicted that enhanced activities under a high-CO₂ environment would increase the risk of sperm competition, which induces an extended copulation period and an increase in sperm transfer. However, weevils shortened the mating period and did not alter their sperm transfer ability under high CO₂. These findings are, as far as we are aware, the first report of the effect of ecologically relevant high CO₂ on insect mating behaviour under mass-rearing conditions. The effect of ambient conditions on mating behaviour and sperm transfer is discussed in relation to the intensity of female refusal behaviour directed against males.     

New Taxa and Host Associations of the Weevil Subfamily Ceutorhynchinae (Coleoptera,Curculionidae) from Thailand

A new subgenus of Mecysmoderes Sch., Enzoellus Korotyaev, subgen. n. (type species Mecysmoderes carinatus Faust), two new genera of the tribe Hypohypurini Colonnelli, Siamohypurus Korotyaev, gen. n. (type species S. samuelsoni Korotyaev, sp. n.), Glikmanellus Korotyaev, gen. n. (type species G. rosti Korotyaev, sp. n.) and eleven new species of the weevil subfamily Ceutorhynchinae are described: Mecysmoderes (Memecyderes) sarukhanovi Korotyaev, sp. n. from Thailand, M. (Enzoellus) gressitti Korotyaev, sp. n. from Thailand and Laos, M. (Enzoellus) muratovi Korotyaev, sp. n., Megahypurus oroszi Korotyaev, sp. n., Cyphohypurus suppantschitschi Korotyaev, sp. n., Siamohypurus samuelsoni Korotyaev, sp. n., S. attilai Korotyaev, sp. n., Glikmanellus rosti Korotyaev, sp. n., all from Thailand; G. baloghi Korotyaev, sp. n. from Sri Lanka; G. obrieni Korotyaev, sp. n. and G. louisae Korotyaev, sp. n., both from India. A key to three species of Megahypurus from Thailand is given. Host plants are determined for Megahypurus alexandri Kor. and Glikmanellus rosti sp. n. from Koh Kood Island in southern Thailand, which were repeatedly collected from a tree of the family Rubiaceae.