Successful control in the first recapture of the sweet potato weevil Cylas formicarius (Coleoptera: Brentidae) since its eradication from Kume Island, Japan

The sweet potato weevil Cylas formicarius is a notorious underground pest in sweet potato (Ipomoea batatas L.). However, little is known about the effects of cadmium (Cd) stress on weevil biology and resistance to pesticides and biotic agents. Therefore, we fed sweet potato weevils with Cd-contaminated sweet potato and assessed adult food intake and survival and larval developmental duration and mortality rates, as well as resistance to the insecticide spinetoram and susceptibility to the entomopathogenic fungus Beauveria bassiana. With increasing Cd concentration, the number of adult weevil feeding holes, adult survival and life span, and larval developmental duration decreased significantly, whereas larval mortality rates increased significantly. However, at the lowest Cd concentration (30 mg/L), adult feeding was stimulated. Resistance of adult sweet potato weevils to spinetoram increased at low Cd concentration, whereas Cd contamination did not affect sensitivity to B. bassiana. Thus, Cd contamination affected sweet potato weevil biology and resistance, and further studies will investigate weevil Cd accumulation and detoxification mechanisms.

Iotrochota birotulata, an abundantly occurring sponge collected off the coast of Port Royal, Jamaica was investigated to identify its main constituents and evaluate the bioactivity associated with its crude extracts. The compounds renierapurpurin and the tyrosine derivative 1,3-dibromo-5-{2-[(p-hydroxyphenyl)-acetamido]ethyl}-2-[3-(-methyl-2-butenamido)-propoxy] benzene were isolated from the crude extract along with the common steroid β-sitosterol. The carotenoid derivative renierapurpurin was identified in this species for the first time. The structures of these compounds were elucidated using spectral analysis. When the crude extracts of the sponge were tested against the sweet potato weevil Cylas formicarius elegantulus, 100% mortality was observed at a concentration of 2 µg/mL after 72 hours.

Sweet potato weevil Cylas formicarius is a major insect pest in Siang valley of Arunachal Pradesh which inflicts damage on the leaves, vines, and tubers as part of their normal feeding and survival habit. The study was conducted to evaluate 29 local genotypes of Northeast India, along with two commercial cultivars, Sree Bhadra and ST-14, for their relative susceptibility to pest. Sweet potato weevil and grasshopper incidence on the vines were lowest in CHFSP-10, while thrips infestations was lowest in CHFSP-07. In terms of tuber incidence, the genotypes CHFSP-10, CHFSP-14and CHFSP-15 performed better against C. formicarius. The substantially decreased sensitivity of CHFSP-10, CHFSP-14 and CHFSP-15 to sweet potato weevil indicates the feasibility of using them in varietal development to improve breeding programmes.

Screening of wild Ipomoea sp. and identification of new sources of resistance to the sweet potato weevil (Cylas formicarius Fabricius) with I. palmata, I. mauritiana, I. obscura, I. triloba were carried out. The leaves, vines and tubers of the different Ipomoea sp. were screened using multiple choice bioassay. The insect feeding holes on I. mauritiana leaves (1.67+1.528), vines (7.67±2.96) and tubers (12.67+2.309) was significantly less compared with other Ipomoea sp. Further, the two-choice bioassay was done, using I. batatas and I. mauritiana for comparison. Based on the morphological screening different phytochemical constituents was identified using GC-MS analysis of the methanolic extract of roots of selected Ipomoea sp. (I. mauritiana, I. palmata and I. batatas). The results indicated that the phytochemical constituent of I. mauritiana viz., undecane, quinic acid which is to have insecticidal activity. The major constituent of I. batatas comprises of melezitose (38.53%) and alpha-I-rhamnopyranose (21.26%). It can be concluded that the phytochemical constituents of I. mauritiana was responsible for the antibiosis.

As many 80 species of insects and non-insect species are known to attack sweet potato. The important pests include sweet potato weevil Cylas formicarius, vine borer Omphisa anastomosalis, leaf folder Brachmia convolvuli, sweet potato Hawk moth Agrius convolvuli, Bihar hairy caterpillar Spilosoma obliqua, syntomid caterpillar Euchromia polymena, tortoise beetle Aspidomorpha miliaris and spiny beetle Oncocephala tuberculata. Management of the key pests is also discussed.

The sweetpotato weevil Cylas formicarius (Fabricius) (Coleoptera: Brentidae) and West Indian sweetpotato weevil Euscepes postfasciatus (Fairmaire) (Coleoptera: Curculionidae) are major pests of sweet potato Ipomoea batatas (L.) Lam., in tropical and subtropical regions. Effects of intra‐ and inter‐specific competition on the number of progeny (fecundity), body weight and developmental time of C. formicarius and E. postfasciatus were examined in single‐ and mixed‐species treatments under laboratory conditions. Cylas formicarius tended to outcompete E. postfasciatus, whereas E. postfasciatus rather than C. formicarius tolerated higher conspecific densities. We discuss the implications of the results for pest management and resource partitioning of pestiferous weevils.

Simple SummaryTonic immobility (TI) is an essential anti-predator behavior to reduce the effect of predators. To know the relationship between mating behavior and TI, the effect of TI on courtship and copulation, as well as the effect of courtship and copulation on TI, were investigated in the sweetpotato weevil (SPW), Cylas formicarius. In the present study, we found the duration of TI was significantly reduced in the stage of courtship and copulation. The pairs with males from the L-strain (SPW with longer period of TI) showed lower frequency and longer duration of courtship than pairs with males from the S-strain (SPW with shorter duration of TI). Similarly, males from L-strain pairs showed a longer period of copulation than pairs with males from the S-strain. However, there is no significant difference in the frequency of copulation and the success of insemination. The results of our study clearly demonstrate that SPW mating behavior and TI are negatively correlated.Numerous studies have confirmed that the trade-off between anti-predator behavior and mating behavior occurs in certain insect species. This suggests that insects invest more in anti-predator behavior, and fewer resources or time can be used in mating behavior. However, few studies focus on tonic immobility, an important anti-predator behavior in nature, and different stages in mating behavior. Tonic immobility (TI) is considered to be an important anti-predator behavior. Herein, we investigated the relationship between TI and mating behavior in the sweetpotato weevil (SPW), Cylas formicarius. As the first step, we artificially selected SPWs for the longer duration of TI (L-strain) and the shorter duration of TI (S-strain). The effect of courtship and copulation on the duration of TI in two artificial selection strains was tested. Furthermore, we compared the frequency and duration of two mating behaviors in four kinds of pairs (LF×LM, LF×SM, SF×LM, and SF×SM: LM—L-strain male; SM—S-strain male; LF—L-strain female; SF—S-strain female). Finally, we tested insemination success in four kinds of pairs (male and female SPWs from the L-strain or the S-strain). The courtship and copulation significantly reduced the duration of TI. Pairs with males from the L-strain showed lower frequency and longer duration of courtship than pairs with males from the S-strain. Similarly, males from L-strain pairs showed a longer period of copulation than pairs with males from the S-strain. However, there is no significant difference in the frequency of copulation and the success of insemination. These results support that there was a significant trade-off between TI and courtship as well as copulation in the SPW.

Inadvertent selection is an important genetic process that frequently occurs during laboratory culture. The mass-reared strain of the sweet potato weevil Cylas formicarius exhibits stronger inbreeding depression than the wild strain does. When inbreeding depression occurs in a population, mating with a close relative is often considered maladaptive; however, in some contexts, the inclusive fitness benefits of inbreeding may outweigh the costs, favoring individuals that tolerate a low level of inbreeding depression. Theory predicts that mass-reared strain weevils will avoid inbreeding while wild strain weevils will tolerate inbreeding. To examine this prediction, we compared the effect of relatedness on the mating and insemination successes in mass-reared and wild strains of C. formicarius. While close relative pairs of the wild strain copulated less frequently than non-kin pairs, almost all mass-reared strain pairs copulated irrespective of relatedness. The results showed that the strain with weak inbreeding depression (wild strain) avoided inbreeding, whereas the strain with strong inbreeding depression (mass-reared strain) tolerated inbreeding. The contradiction between the theoretical prediction and our results is discussed from the perspective of laboratory adaptation, mating systems, and life history of C. formicarius.

The aim of our study was to examine the effect of mass‐rearing, in which there is no exposure to predators, on antipredator traits of insects for improving sterile insect technique programs. The duration of death‐feigning (antipredator behaviour) in sweet potato weevil Cylas formicarius (Summers) (Coleoptera: Brentidae) after mass‐rearing for 71 generations were compared with those in wild strain. There was no significant difference in the duration of death‐feigning between wild and mass‐reared strains. This indicated that the death‐feigning behaviour of mass‐reared strain was maintained for 71 generations even in the absence of predators. We discuss the reasons why death‐feigning behaviour is maintained after mass‐rearing.

Efficacy of <i>Piper betle</i> Leaf extracts against sweet potato weevil <i>Cylas formicarius</i> (F.)

Biotransformation of squamulosone by Curvularia lunata ATCC 12017

A new triterpene, A(1)-1-benzoate-19α-hydroxy-urs-2(3),12(13)-dien-28-oic acid (1), was isolated from Hyptis verticillata, in addition to the known triterpenes tormentic acid, isolated as the diacetate (2), betulinic acid (3), α- and β-amyrin, oleanolic acid and ursolic acid. The structure of 1 was elucidated by spectroscopic analysis. Compounds 1–3 exhibited insecticidal activity against the sweet potato weevil Cylas formicarius elegantulus (Summers).

Because life‐history theory predicts that risky behaviours such as mating should increase as life expectancy decreases, predatory avoidance is expected to decrease with age. However, this prediction has not been examined. In the present study, the effect of age on death‐feigning behaviour, a form of predatory avoidance behaviour in the sweetpotato weevil Cylas formicarius (Summers) (Coleoptera: Brentidae), is investigated by performing a longitudinal study. Because the effects of mating history and age usually cannot be distinguished, mating history is controlled. The results show that only female weevils decrease the investment in death‐feigning behaviour with age, whereas male weevils do not show any age‐related change. In addition, death‐feigning behaviour of mated females is longer than that of virgin females, possibly because additional mating partners would be not needed by mated females.

Gamma radiation from isotopic sources has been used in sterile insect technique (SIT) programs worldwide, but it might be difficult to continue using these sources in future SIT programs because of social issues. Therefore, an alternative sterilization source to gamma rays, such as X-rays, needs to be developed. The physical properties of radiation are different between gamma rays and X-rays: for example, X-rays have a shorter penetration depth than gamma rays. Therefore, X-rays may not fully confer male sterility, depending on the target pest insects. The present study investigated whether the West-Indian sweetpotato weevil Euscepes postfasciatus (Fairmaire) and the sweetpotato weevil Cylas formicarius (Fabricius) are sterilized by X-rays generated in a low-energy X-ray irradiator, without deterioration of male mating ability, at the doses currently used in the eradication programs for E. postfasciatus (150 Gy) and C. formicarius (200 Gy) using gamma rays at Okinawa, Japan. The results demonstrated that it is possible to use X-rays in future SIT programs for E. postfasciatus and C. formicarius, because X-ray irradiated males were almost completely sterilized without deterioration of their mating ability.

In sterile insect technique (SIT) programs, the released sterile males are important for their effectiveness. The use of sex pheromones to collect males is economical; however, pre-exposure to sex pheromones may affect male mating behavior, and would thus reduce the effectiveness of the SIT programs. Males exposed to sex pheromone may become attractive to other males due to pheromone adsorption on their body impregnation, prevent mating and reduce the dispersal of sterile males. We examined the effect of pre-exposure to sex pheromone on the mating behavior of male sweetpotato weevil Cylas formicarius. Pre-exposure to high-dose sex pheromone for 24 h did not affect the male mating behavior of C. formicarius, and the exposed males did not attract other males. These results suggest that male C. formicarius that were collected from a mass-rearing facility using sex pheromone can be effectively used in SIT programs.