Cylas Formicarius Research Articles

Sweetpotato Weevil Resistance to Stem and Root Injury Sweetpotato Plant Introductions

The sweetpotato weevil is the most-destructive worldwide pest of sweetpotato and only low to moderate levels of resistance to the insect are available in acceptable cultivars. No sources of high resistance levels have been identified; consequently, there is a need to identify additional sources of resistance genes to develop high resistance levels. To begin a search for sources of resistance, plant introductions were evaluated for injury levels. In 1993, 100 plant introductions were evaluated for sweetpotato weevil injury and 62 of the least injured were tested again in 1994. In 1995, 36 of the least injured in 1993 and 1994, plus 24 additional PIs were evaluated. Control cultivars included `Regal', moderately resistant; `Jewel', intermediate; and `Beauregard' and `Centennial', susceptible. Measurements of injury were percentage of roots injured, and, stem and root injury scores based on a 0–5 scale, with 0 being no injury. First year results indicated that a low level of resistance to stem injury is available in the PIs tested. Stem injury was more severe in the following year and no differences were found. Lower weevil populations will be required to screen for low levels of stem injury resistance. Percentage injured roots and root injury scores were lower over the 3 years for five PIs than for `Regal'.

Enhanced Resistance to West Indian Sweetpotato Weevil (Euscepes Postfasciatus) in Transgenic `Jewel' Sweetpotato with Cowpea Trypsin Inhibitor and Snowdrop Lectin

Euscepes postfasciatus is one of the most important sweetpotato pests in the South Pacific, Caribbean basin, and some countries of Central and South America. Development of host resistance will greatly improve the effects of integrated pest management (IPM) for this pest. Ten transgenic clones of `Jewel' sweetpotato with cowpea trypsin inhibitors and snowdrop lectin, developed by Axis Agri. Genetics, Ltd., were assayed for weevil resistance using a no-choice bioassay. A replicated experiment was conducted in the screenhouse. Five storage roots from each clone were infested with five pairs of adults. Non-transformed `Jewel' was used as a check. Resistance was assessed 60 days after infestation by estimating the percentage of internal damage and the weevil population in the storage roots. A five-grade damage index was recorded. The experiment was repeated twice. Significant enhancement of resistance was found in the transgenic clones. Clone CTI-13 with cowpea trypsin inhibitor and clone PCG-7 with both cowpea trypsin inhibitor and snowdrop lectin demonstrated moderate resistance to E. postfasciatus, whereas the non-transformed `Jewel' was susceptible. This result shows that resistance to Euscepes postfasciatus can be achieved through genetic transformation.

Sperm numbers, their storage and usage in the flyDryomyza anilis

In the fly Dryomyza anilis females have two kinds of sperm storage organs: one bursa copulatrix and three spermathecae (two spermathecae with a common duct form the doublet, and the third is a singlet spermathecal unit). At the beginning of a mating the male deposits his sperm in the bursa copulatrix. After sperm transfer the male taps the female's abdomen with his claspers. This behaviour has been shown to increase the male's fertilization success. After mating, the female discharges large quantities of sperm before oviposition. To find out where the sperm remaining in the female are stored, I counted the number of sperm in the droplet and in the female's sperm storage organs after different types of mating. I carried out three mating experiments. In experiment 1, virgin females were mated with one male and the matings were interrupted either immediately after sperm transfer or after several tapping sequences. The results show that during male tapping more sperm moved into the singlet spermatheca. In addition, the total number of sperm correlated with sperm numbers in all sperm storage organs, and male size was positively related to the number of sperm remaining in the bursa. In experiment 2, females mated with several males. The number of sperm increased with increasing number of matings only in the doublet spermatheca. No increase in the number of sperm in the singlet spermatheca during consecutive matings suggests that sperm were replaced or did not reach this sperm storage organ. In experiment 3, virgin females were mated with a single male and half of them were allowed to lay eggs. The experiment showed that during egglaying, females primarily used sperm from their singlet spermatheca. The results from the three experiments suggest that sperm stored in the singlet spermatheca is central for male fertilization success and male tapping is related to sperm storage in the singlet spermatheca. The different female's sperm storage organs in D. anilis may have separate functions during sperm storage as well as during sperm usage.

Dispersal Potential of Male Cylas formicarius (Coleoptera: Brentidae) Over Land and Water

To determine the size needed for buffer zones in an eradication program, dispersal ability of male Cylas formicarius (F.) was evaluated by the mark-release-capture method in the central part of Okinawa Island, Japan. Approximately 36,700 marked males were released from 2 islets. Forty-five pheromone traps were placed on 6 islets near Okinawa Island and 24 on the eastern seashore of Okinawa Island. Two traps were put at the 2 release points on the last day of the experiment. Of 71 recaptured males, 34 were caught by 3 traps on the Sea Road (a 5-km bank connecting Okinawa Island and an islet) located 2 km northwest of a release point. Sixty-two traps did not capture marked males. This result suggests that for C. formicarius eradication projects, a buffer zone with a minimum radius of 2-4 km should surround the area targeted for control.

Evaluation of Selected Soil and Foliar Insecticides on Sweetpotato Weevil, White Grubs and Banded Cucumber Beetles, 1995

Abstract A test was conducted in Hessmer, LA, to determine the efficacy of two soil insecticides and three foliar applied insecticides for control of sweetpotato weevil, banded cucumber beetle, and white grubs. Treatments were arranged in a CRB design with four replications. The cultivar ‘Beauregard’ was planted in Jun. Plots were 4 rows wide (4 feet/row) and 50 ft long. Insecticides were applied at planting day (soil insecticides) and at weekly intervals starting three weeks after transplanting. A CO2 pressurized backpack sprayer was used (30 psi) with a single row boom (20 inches wide) containing three nozzles (Cone Jet SX-10) and calibrated to deliver 25 gpa. Sweetpotatoes were harvested on 13 Oct and field graded into number 1, 2, or 3. From each plot, in each of the 3 grades, 50 potatoes were randomly selected and evaluated for insect damage. The number of potatoes infested with sweetpotato weevil, the number of white grub feeding scars, and the number of holes present caused by banded cucumber beetles (or wireworms) were counted. All data were analyzed by ANOVA and treatment means were separated by DMRT at P = 0.05.

Evaluation of Selected Foliar Insecticides on Sweetpotato Weevil, Banded Cucumber Beetle, and White Grub on Sweetpotatoes, 1995

Abstract A test was conducted on the Burden Research Plantation, LSUAC, Baton Rouge, LA, to determine the efficacy of 9 insecticide treatments for the control of sweetpotato weevil, banded cucumber beetle, and white grub. Treatments were arranged in an RCB design with four replications. The cultivar ‘Beauregard’ was planted on 18 May. Plots were 3 rows wide (f ft./row) and 30 feet long. Insecticides were applied on an approximately weekly basis starting two months after transplanting (18, 23 Jul, 1,8, 14, 22 and 29 Aug). A CO2 pressurized back pack sprayer was used (30 psi) with a single row boom (20 inches wide) containing 3 nozzles (Cone Jet sx-10) and calibrated to deliver 25 gpa. Sweetpotatoes were harvested on 6 Sep and rated for damage. From each plot, 50 roots were randomly selected and the number of white grub feeding holes, the number of banded cucumber beetle holes, and the presence or absence of weevil damage was noted.

天敵糸状菌Ｂｅａｕｖｅｒｉａ ｂａｓｓｉａｎａのアリモドキゾウムシ成虫に対する感染性に及ぼす温度，湿度，分生子密度の影響

Beauveria bassiana infected Cylas formicarius irrespective of temperature between 15 and 31°C. No infection was observed at relative humidities of less than 43%. The median tolerance limit for conidia density per cm2 was 2.2×109 (male) and 3.7×109 (female).

Reproductive Sharing in Different Types of Kin Associations

Reproductive Sharing in Different Types of Kin Associations

Infectivity and Reproduction of Three Heterorhabditid Nematodes (Rhabditida: Heterorhabditidae) in Two Insect Hosts

The infectivity, incubation time, and reproduction of three heterorhabditid nematodes, Heterorhabditis sp. Bacardis and FL2122 strains and H. bacteriophora Poinar HP88 strain were studied in two insect hosts, an apionid weevil, Cylas formicarius (F.), and a pyralid moth, Galleria mellonella (L.). Two of the nematodes, Heterorhabditis sp. Bacardis and FL2122 strains, were of tropical or subtropical origin, whereas the third nematode, H. bacteriophora HP88 strain, was of temperate origin. Infectivity did not differ among nematodes within each host; however, it did differ between hosts for the Bacardis strain. Cylas formicarius was more susceptible to this nematode than G. mellonella. Incubation times also did not differ among nematodes within hosts; however, incubation times were 3.2-4.3 d shorter in C. formicarius than in G. mellonella. Progeny production differed (although not significantly consistent) among nematodes and was highest for Heterorhabditis sp. Bacardis followed by the Heterorhabditis sp. FL2122 and H. bacteriophora HP88 in both hosts. Percentages of infected cadavers that produced progeny were consistently higher for the tropical and subtropical nematodes, Heterorhabditis sp. Bacardis and FL2122, than for the temperate nematode, H. bacteriophora HP88, in both hosts. Patterns of emergence from cadavers were consistent in G. mellonella; most progeny emerged by 23 d after inoculation and emergence lasted for up to 48 d after inoculation. Conversely, emergence patterns varied markedly in C. formicarius. Emergence lasted for up to 29 d after inoculation and peak emergence varied between 12 and 28 d after inoculation. Progeny production in C. formicarius was not related to the biomass of the host cadaver.

Effect of Sweetpotato Latex on Sweetpotato Weevil (Coleoptera: Curculionidae) Feeding and Oviposition

Latex in some laticiferous plants acts as a natural defense system against certain herbivores. The potential of latex produced by the sweet potato as a defense mechanism against the sweet potato weevil, Cylas formicarius (F.) was investigated. Genetic and environmental differences were found in latex production in a broad cross section of sweet potato germ plasm (96 lines). Most lines produced 2.6-10 mg fresh weight x vine -1 of latex when the 2nd inter node from the apex was severed. Some lines, however, produced more, the highest being 48.3 mg X vine-1. Young vine material produced more latex and had less weevil feeding damage than older more mature portions of the vine. Application of latex to the surface of root cores reduced feeding and oviposition. Addition of latex to a semi-artificial media also significantly reduced the number of feeding punctures. Leaf feeding location (veins) and direction (basipetal), however, were not indicative of a major deterrent role for latex against the sweet potato weevil.

風洞内におけるサツマイモの異なる器官と被害塊根のイモゾウムシ成虫に対する誘引性

Many more adults of the West-Indian sweet potato weevil, Euscepes postfasciatus (FAIRMAIRE), were attracted by tubers and stems than by leaves of the sweet potato in a wind tunnel. Tubers damaged by larvae were much less attractive than undamaged tubers.

Estimating the Reproductive Properties of the Sweet Potato Weevil, Cylas formicarius (FABRICIUS) (Coleoptera, Brentidae)

The reproductive properties of the sweet potato weevil were studied at 27°C, 70% RH and 14L10D. The mature female laid, at most 3 to 4 eggs per 2 days, and a total of 64 eggs on average throughout her life time of 96 days. Females that first mated on the 40th day after eclosion laid as many eggs as those first mating on the 10th day. Males and females were fertile until death from the 7th day and the 5th-7th day after eclosion, respectively. Most females were fertile on the day of emergence from the tuber. Virgin females older than 5 days attracted males strongly, but their attractivity disappeared once they mated. This is likely to be related to female secretion of a sex pheromone. Males mated repeatedly throughout their lives. Females, if given a chance to mate, could mate multiply for 40 days after eclosion. However, in the field, females rarely remated because secretion of the pheromone was inhibited after the first mating.

Dispersal of Male Sweetpotato Weevils (Coleoptera: Curculionidae) in Fields with or without Sweet Potato Plants

Dispersal distance of the male sweetpotato weevil, Cylas formicarius elegantulus (Summers), was estimated in the field. Two experiments were conducted. In experiment 1, release and capture were replicated 3 times from September to October in the same locality consisting mainly of sweet potato fields. Approximately 8,000 marked males were released and ≈30% of released males were captured by pheromone traps each time. Median dispersal distances per 2 d were 325.7 m in September, 119.8 m in early October, and <50 m in late October. The maximum dispersal distance in September was 500 m, whereas it was 200 m in October. In experiment 2, the dispersal distances were compared in the fields with and without sweet potato plants. The dispersal distance in the field without sweet potato plants was longer than that obtained in the sweet potato cultivated area. The maximum dispersal distance in the fields with sweet potatoes was 500 m, whereas it was 1,000 m in the fields without sweet potatoes.

Irrigation Affects Yield and Sweetpotato Weevil [Cylas formicarius elegantus (Summers)] Infestation of Sweetpotato

A study was conducted to evaluate the effect of irrigation on yield and sweetpotato weevil (SPW) infestation of sweetpotato storage roots. Sweetpotato was grown in plots under controlled soil moisture regimes. The treatments were rainfed (no applied irrigation) and irrigation applied to maintain soil moisture levels at 20, 40, and 60 kPa, based on tensiometer readings. The 40- and 60-kPa treatments produced the highest yield of root biomass. Irrigation applied at 40 kPa produced significantly more medium-sized storage roots (8.1 t·ha–1) than the rain-fed treatment, which produced 4.4 t·ha–1. All of the irrigation treatments produced significantly more marketable storage roots with a lower mean damage index (MDI) than the rain-fed treatment. There was an inverse relationship between MDI and soil moisture levels among the irrigation treatments. A significantly higher percentage of storage roots (51.5%) from the 20-kPa treatment were rated in the Damage Index (DI)-1 (uninfested roots) category than from the rain-fed treatment (27.7%). Additionally, the percentage (29.4%) of storage roots from the rain-fed treatment rated in the DI-6 (most severe) category was significantly higher than the applied irrigation treatments, with 13.9%, 13.9%, and 6.0% respectively, for the 60-, 40-, and 20-kPa treatments. Irrigation therefore has potential to increase sweetpotato yields while reducing SPW infestation levels.

Sweet Potato Weevils in Jamaica:

The sweet potato weevils (Cylas formicarius and Euscepes postfasciatus) have probably been in Jamaica for as long as sweet potato (Ipomoea batatas) has been cultivated. Yet, farmers have been unqilling to adopt cultural control measures, one of which has been known for 300 years. The social and economic aspects of growing sweet potato and the implications for control of the weevils have been ignored by researchers and extension agents. It appears that the pest is more acceptable to the farmers than the control measures. The authors interviewed producers of sweet potato to understand the social and economic reasons why farmers do not adopt, or only partially adopt, recommended weevil control practices. Extension staff were interviewed to determine what control practices they are recommending, and how the control practices are presented to farmers. The reasons why a technological package which has been repeatedly demonstrated to farmers has been rejected could help direct research and enable extension to ...

Mortality of Sweet potato Weevil (Coleoptera: Apionidae) Stages Exposed to Gamma Irradiation

Sweet potato weevil, Clyas formicarius (F.), eggs; first, seeoud, and third insstars; pupae; and adults in roots of sweet potato, Ipomoea balatas (L.) Lam., cultivar Jewel, were exposed to gamma irradiation doses ranging from 100 to 1,000 Gy. Criterion of effectiveness of the irradiation dose was based on preventing adults emerging from treated roots infested with different stages of the weevil. Dose-mortality data were analyzed by logistic, Gompertz, and normal probit probability density functions with and without log 10 conversions. Gompertz probability density function analysis gave the best 99.9968% mortality estimates (and 95% FL) against stages of sweet potato weevil in roots: 37 Gy (35-42 Gy) for eggs (no log 10 conversion); 73 Gy (53-132 Gy) for first instars (log 10 conversion); 38 Gy (31-55 Gy) for second instars (log 10 conversion); 28 Gy (23-4.5 Gy) for third instars (no log 10 conversion); and 1,497 Cy (963-2,229 Gy) for pupae (log 10 conversion). Pupae irradiated With ≥800 Gy produced no adults when efficacy tests were done. Irradiating adults in roots with 1,000 Gy did not prevent adult emergence. However, males exposed to 150 Gy were sterile, and females exposed to 300 Gy were sterile.

Characteristics of infestation of sweet potato by sweet potato weevilCylas formicarius(Coleoptera: Apionidae)

Studies were conducted to examine the characteristics of infestation of vines of sweet potato plants by the sweet potato weevil, Cylas formicarius (F.). The use of terminal tender vine cuttings, taken even from heavily weevil‐infested sweet potato, to grow a new crop and planting such a crop in plots surrounded by barriers to reduce weevil migration from the outside to the newly planted area, produced a practically weevil‐free crop. On the contrary, crop planted to old vine cuttings in an open field was severely damaged by the weevil. Consequently, crop planted using tender vine cuttings produced significantly more root yield than the one planted to old vine cuttings, irrespective of whether the planting was done in an open field or in an insect‐protected field. Sweet potato weevil infestation of 1‐ to 8‐week‐old plants increased significantly with plant age. The insect preferred sweet potato roots over sweet potato vines when both plant parts were available for infestation. Dipping the vine cuttings for 30 min in carbofuran solution prior to planting protected the newly planted sweet potato crop for up to 6 weeks after planting.

カルボスルファン３％粒剤のイモゾウムシ，アリモドキゾウムシの成虫に対する忌避効果と幼虫に対する殺虫効果

カルボスルファン３％粒剤のイモゾウムシ，アリモドキゾウムシの成虫に対する忌避効果と幼虫に対する殺虫効果

Farmers’ cultural practices and their effects on pest control in sweetpotato in South Nyanza, Kenya

Abstract Sweetpotato weevils (Cylas puncticollis (Bohe.) and C. brunneus (Fabr.) Coteoptera: Apionidae) are the most important insect pests in South Nyanza, Kenya's principal sweetpotato‐growing district. A pest of secondary importance is the sweetpotato butterfly (Acraea acerata (Hew.) Lepidoptera: Nymphalidae). Cultural control is currently the most promising component of an integrated pest management strategy for subsistence sweetpotato farmers in Kenya. A survey of fanners’ cultural practices in South Nyanza suggests that crop protection workers should concentrate their research and extension efforts on crop sanitation and the avoidance of adjacent planting of successive crops. The life cycle and behaviour of the sweetpotato weevils and butterfly should be explained to farmers, so that they better understand the insects’ modes of dispersal and thus see the need for sanitation and adjacent planting.

Insecticidal activity of synthetic 2-carboxylbenzofurans and their coumarin precursors

Several 2-carboxylbenzofurans and their coumarin precursors, compounds 1–6, and the novel compound 7 were synthesized and their insecticidal activity studied using adult sweet potato weevils (Cylas formicarius elegantulus (Summer)) at 24 μg, 48 μg and 72 μg per insect in 0.5 ml litre−1 piperonyl butoxide (PPB) in acetone. The order of toxicity of the compounds as judged by the percentage mortality at 24 μg per insect at 48 h was 2 (100%) > 6 (95%) > 7 (85%) > 4 (75%)) > 3 (65%) > 1 (60%) > 5 (45%) > piperonyl butoxide (0.0%). Compound 2 was equitoxic to 24 μg of technical grade dimethoate. When administered in acetone alone, however, the compounds were only moderately active (i.e. > 120 μg per insect was required for 60% mortality at 48 h). The test compounds were more active at lower doses (48–72 μg per insect) when dissolved in dimethylsulfoxide or in an oil extract obtained from the fruit of Blighia sapida Koenig.