Cylas Formicarius Research Articles

Impact of Host Plant Resistance on Emergence, Body Parameters, and Supercooling Point of Cylas formicarius elegantulus (Coleoptera: Brentidae)

Sweetpotato weevil, Cylas formicarius elegantulus (Summers) (Coleoptera: Brentidae), an in-field and storage pest of sweetpotato, is the primary insect constraint to sweetpotato production in tropical and subtropical regions. Feeding by adult and larval sweetpotato weevil induces terpenes, rendering storage roots unmarketable. To reduce storage root damage and sweetpotato weevil populations, the present experiment tested the impact of sweetpotato cultivar on developmental time, adult emergence, body length, weight, and supercooling point of sweetpotato weevil. The cultivars tested were ‘Beauregard’ and ‘Evangeline,’ both orange fleshed cultivars susceptible to sweetpotato weevil, and ‘Murasaki,’ a white fleshed cultivar known to be resistant to sweetpotato weevil. There were no differences in developmental time with most adult sweetpotato weevils emerging 34 to 44 d after oviposition. However, the number of adult sweetpotato weevil that emerged from Beauregard (38.9 ± 3.3) and Evangeline (48.4 ± 6.2) roots were greater than numbers emerging from Murasaki (11.1 ± 3.5), indicating resistance is due to antixenosis. Although fewer in number, adults (male and female) emerging from Murasaki were heavier than males and females emerging from Beauregard and males from Evangeline. Supercooling points of sweetpotato weevil males emerging from Murasaki (–17.9 ± 0.4 °C) were significantly lower than Beauregard (–16.3 ± 0.5 °C) but similar to Evangeline (–17.1 ± 0.4 °C). Host plant resistance expressed by Murasaki may reduce sweetpotato weevil populations significantly, but those that emerge may be better suited to survive the cold.

Eradication of sweetpotato weevil, Cylas formicarius, from Tsuken Island, Okinawa, Japan, under transient invasion of males

AbstractAn eradication project against the sweetpotato weevil, Cylas formicarius (Fabricius) (Coleoptera: Brentidae), one of the most important pests of sweet potato in the world, was initiated in Oct. 2007 on Tsuken Island, Okinawa Prefecture, Japan. The sterile insect technique (SIT) and male annihilation technique (MAT) were employed as the main control measures to suppress and ultimately eradicate wild populations by impeding normal mating. In addition, two monitoring methods (host plant survey and trap survey) were used to evaluate the progress of the control actions. However, several years after the start of the project, wild male weevils were regularly captured by male‐attractant traps in seasonal patterns, although infestation was scarcely detected by host plant surveys. Evidently, the males flew to Tsuken Island from uncontrolled areas that were farther away than the weevils were previously expected to travel. Although the transient invasion of only males did not cause new colonization, it created a challenge for the progress of the project and the confirmation of the eradication of the weevil on Tsuken Island. To solve this problem, suppressive control measures in the uncontrolled area (Okinawa Island) to reduce transient invaders were implemented. In addition, to assess if control actions needed after eradication, a system was introduced to detect recolonization of the weevil based on trap catches of transient invading males. After the successive collection of 142,257 m of stem of host plants and 158.45 kg of root tubers of sweet potato without infestation (from February 2019 to November 2020), the eradication of C. formicarius from Tsuken Island was ultimately confirmed in November 2020.

Liquid Smoke of Red Fruit (Pandanus Conoideus. L.) Waste with Pyrolysis Method For Controlling Sweet Potatoes (Ipomea Batatas. L.) Pest

Pandanus conoidus, or red fruit, is a nutrient-dense native Papuan plant, whereas Ipomea batatas are the main food for the Wamena people. Biomass from red fruit seed waste can be used as liquid smoke to control Ipomea batatas . At a temperature of between 300 - 450 °C, liquid smoke is produced through a pyrolysis process. Pyrolysis produces phenolic chemicals and aldehydes that have antioxidant and antimicrobial properties (anti-bacterial and anti-fungal). The assessment of pH, acidity, and phenol concentration characterizes the quality of liquid smoke. The potential of red fruit seed waste as a liquid smoke product for biopesticides in Ipomea batatas is explored in this study. Additionally, study development aims to determine the optimal method for pyrolyzing red fruit seed waste, its characteristics, chemical content, and the way to use liquid smoke as a biopesticide in Ipomea batatas . The results showed that the liquid smoke of grade 3 red fruit seed waste contains 7 components that can be detected using a mass spectrometer. The higher the concentration of liquid smoke produced by grade 3 red fruit seeds, the higher the possibility of Cylas formicarius mortality. Cylas formicarius had the highest mortality rate (90%) when tested at a 7% test solution concentration.

Rancangan Penyuluhan untuk Mengubah Persepsi Petani Ubi Jalar Terhadap Pengendalian Hama Lanas Menggunakan Daun Mimba dan Feromon

One of the obstacles in the sweet potato production system is the attack of the sweet potato weevil (Cylas Formicarius) that is the main pest on sweet potato plants. The efforts of farmers in Maja District to deal with these pests are still low and depend on the use of chemical pesticides. The behaviour of farmers is influenced by the perception of farmers who consider chemical pesticides to be the main solution in controlling plant-disturbing organisms. Innovations in pest control can be carried out with preventive measures such as the use of pheromone that trap and disrupt pest mating and plant-based insecticides that are more environmentally friendly. The study aims to analyze the perception of sweet potato farmers on controlling sweet potato weevil pests through the use of pheromones and neem leaf vegetable insecticides, related factors and strategies that can be done in increasing farmers' perceptions. The results of descriptive analysis of 72 sample respondents can be seen that the perception of sweet potato farmers in Maja District on the use of pheromones and neem leaf vegetable insecticides in controlling sweet potato weevil pests is in the poor category with a value of 49.9%. The results of the correlation analysis of rank spearman at a significance level of 5% (0.05) show related factors including land area, income, technical aspects and social interaction.

Effect of potassium fertilizers doses on the growth, tuber yield, and resistance to weevil infestation of sweet potato on Latosol soil

Major problems in sweet potato (Ipomoea batatas L.) cultivation are low yield and high weevil (Cylas formicarius) infestation. The effect of potassium (K) on growth and yield has been intensively reported. However, there is less information on the correlation between K and the resistance to weevil infestation. The aim of the research was to determine the optimum dose of K fertilizers for maximum tuber yield and minimum weevil infestation Sweet potato var. Ase Kapas was planted with a K dose of 0, 45, 90, 135, and 180 kg K2O ha-1. The experiment was conducted using a randomized block design with 4 replications in January – July 2020 at Latosol soil. The experimental plot was 4m x 2m which was divided into 4 ridges. Stem cuttings were planted on the center of the ridge with a 0.20 m spacing. Variables of growth, tuber yield, and level of weevil infestation were observed at 3 weeks after planting and at harvest. There were significant quadratic responses of yield variables to the K application. It is recommended the use of 125 kg K2O ha-1 can provide the highest tuber yield and a significant reduce of weevil infestation level. At the K dose of 125 kg K2O ha-1 , tuber yield increased by 179 % (357.4 g plant-1, compared to the control of 127.9 g plant-1) and the weevil infested tuber was reduced as much as 61.6 % (from 6.46, at the control dose to 2.37 tuber plant-1).

The Fungus Metarhizium sp. BCC 4849 Is an Effective and Safe Mycoinsecticide for the Management of Spider Mites and Other Insect Pests.

Simple SummaryThe spider mite is a destructive pest of various crops during warm and dry conditions in tropical countries, including Thailand. The pest is difficult to control despite synthetic acaricide use. In the field, insect populations gradually develop resistance to synthetic pesticides over long-term use. The use of entomopathogenic fungi is more human- and environmentally friendly. We searched and identified a potential fungal isolate from a culture collection, focusing on the genus Metarhizium. Metarhizium sp. BCC 4849 not only controls the spider mite but also plays a significant role as a natural regulator of other insect pests. Here, we investigated its infection process on the mite, optimized a conidial formulation for extended shelf life, and conducted toxicological assays in animals to assess its biosafety in humans. The fungal genome has been sequenced. The genomic data indicated that oxidoreduction proteins; zinc-, heme-, and iron-binding proteins; and transmembrane transporters are abundant in the genome.Five isolates of Metarhizium sp. were evaluated for their pathogenicity against the spider mite (Tetranychus truncatus Ehara) (Acari: Tetranychidae) and Metarhizium sp. BCC 4849 resulted in the highest mortality (82%) on the 5th day post-inoculation (DPI). Subsequent insect bioassay data indicated similar high virulence against five other insects: African red mites (Eutetranychus africanus Tucker) (Acari: Tetranychidae), bean aphid (Aphis craccivora Koch) (Hemiptera: Aphididae), cassava mealybug (Phenacoccus manihoti Matile-Ferrero) (Hemiptera: Pseudococcidae), sweet potato weevil (Cylas formicarius Fabricius) (Coleoptera: Brentidae), and oriental fruit fly (Bactrocera dorsalis Hendel) (Diptera: Tephritidae), at mortalities of 92–99%, on 3rd–6th DPI, and in laboratory conditions. The pathogenicity assay against E. africanus in hemp plants under greenhouse conditions indicated 85–100% insect mortality on 10th DPI using the fungus alone or in combination with synthetic acaricide. Genome sequencing of Metarhizium sp. BCC 4849 revealed the high abundance of proteins associated with zinc-, heme-, and iron-binding; oxidation-reduction; and transmembrane transport, implicating its versatile mode of interaction with the environment and adaptation to various ion homeostasis. The light and scanning electron microscopy indicated that at 24 h post inoculation (PI), adhesion and appressorial formation occurred, notably near the setae. Most infected mites had stopped moving and started dying by 48–72 h PI. Elongated hyphal bodies and oval blastospores were detected in the legs. At 96–120 h PI or longer, dense mycelia and conidial mass had colonized the interior and exterior of dead mites, primarily at the bottom than the upper part. The shelf-life study also indicated that conidial formulation combined with an oxygen-moisture absorber markedly enhanced the viability and germination after storage at 35 °C for four months. The fungus was tested as safe for humans and animals, according to our toxicological assays.

Development of efficient integrated management package against sweet potato weevil (Cylas formicarius [Fabricius, 1798

The sweet potato weevil (Cylas formicarius, 1798) is one of the most damaging sweet potato pests. To prevent an economic crop loss, it is very important to develop a suitable and efficient integrated pest management strategy. A field experiment was set up with three replications at Jamalpur to select the best integrated management package from eight different treatments against sweet potato weevil. The results showed that the lowest percentage of infestation by number (2.94 %) and mass (3.22 %) was found when the crop was planted on November 01; earthing-up for two times, Carbofuran 5G was sprayed @ 15 kg ha-1 at 60 days after planting with irrigation and tuber was harvested at 130 days after planting. The marketable yield (23.75 kg) and percent increase of yield than control (50.86 %) performed the highest in the same combination. These findings suggested an effective integration of different management strategies to reduce sweet potato weevil infestation in Bangladesh successfully.

Screening of Five Lamiaceae Essential Oils as Repellents for Sweet Potato Weevil, Cylas Formicarius (F.) (Coleoptera: Brentidae)

In this research, the repellent activity of five Lamiaceae essential oils, Agastache rugosa, Elsholtzia blanda, Elsholtzia ciliata, Elsholtzia penduliflora, and Plectranthus ovatus, was evaluated against sweet potato weevil, Cylas formicarius using a two-choice test between the essential oil-treated filter paper and the control. E. blanda and A. rugosa essential oils have some sweet potato weevil attractant properties at low dose (<47.16 nl/cm2),while N,N-diethyl-3-methylbenzamide (DEET), P. ovatus, E. penduliflora, and E.ciliata essential oils have repellent properties at doses ranging from 15.72 nl/cm2 to 196.49 nl/cm2. The effect of type of essential oil and their dose were interactively associated with repellent efficacy. There was a increase in repellent efficacy as the dose increased for all essential oils. The repellent activities of P. ovatus essential oil and E. penduliflora were higher than the others, and the repellent effects of E. ciliata essential oil and DEET were more dose-dependent than others, indicating that at low dose, P. ovatus and E. penduliflora essential oils have stronger repellent efficacy, but at higher dose DEET and E. ciliata have greater effects. Our findings clearly demonstrate that P. ovatus, E. penduliflora, and E. ciliata essential oils are candidate materials for future investigation as repellent compounds against sweet potato weevil control.

General and specific combining ability studies of yield and yield character of sweet potato weevil in predominant and non-predominant environments

Combining ability for marketable sweet potato root yield were carried out using ten sweet potato varieties and their F1 hybrids in Cylasformicarius endemic (Landmark University, Omu Aran) and free (University of Ibadan) environments during 2012 cropping season. Both general combining ability and specific combining ability play significant role on traits such as marketable root yield, non- marketable root yield, and total number of storage root/plant and marketable storage root, root size, percentage of tuber damage and weight of total roots, as well as the incidence and severity were generally low, suggesting the role of additive and dominant gene action in tolerances to Cylasformicarius. Hybrids from the parents Resisto, TIS 87/0087 displayed high performance in term of Cylasformicarius tolerance. These parents and their hybrids appeared to have gene pools for Cylasformicarius tolerance that can be manipulated for developing promising hybrids in South west, Nigeria.

First report of Sweet potato virus G in sweet potato in Italy

Sweet potato (Ipomoea batatas) is the sixth most important food crop in terms of production globally. In Italy, sweet potato is mainly cultivated in Veneto province (northeast Italy), and to a lesser extent in Lazio and Apulia provinces, on a total area of about 400 hectares. Among the sweet potato pests, viruses are the second most important constraint next to sweet potato weevil (Barkessa, 2018). In 2020, tubers of six different genotypes, with uncertain geographical origins, were sent by a grower from Veneto province to IPSP-CNR, with the aim of ascertaining their phytosanitary status. Two tubers of each genotype were grown in an insect-proof greenhouse (26/22°C, day/night) under natural light conditions and transplanted in 25 cm diameter pots containing peat bog-moss as a substrate. After about one month, leaves of only one genotype (identified as DP/578) showed light diffuse chlorotic symptoms (Figures 1, 2). Sap extracts from both plants of each of the six genotypes were tested with ELISA using broad-spectrum potyvirus antibodies (Bioreba, Switzerland). Only the symptomatic genotype DP/578 tested positive to potyvirus antibodies. Total RNA was extracted from the leaves of the two plants of DP/578 and from a healthy plant, with the Plant RNA Kit (Omega Bio-Tek, USA), and subjected to RT-PCR using the universal Potyviridae forward primer (5'-GGBAAYAAYAGYGGDCARCC-3'; Gibbs & Mackenzie, 1997) and the reverse primer SPFMV-Rv (5'-TTGCACACCCCTCATTCCYAAG-3'; Parrella et al., 2006). An amplification product of approximately 1700 bp was produced only from samples with symptoms but not from the healthy control. Sequences obtained from the two symptomatic plants were identical (GenBank Accession No. MW456564) and showed highest identity (98.2%) with the CH2-32-1 isolate of Sweet potato virus G (SPVG) from China (MK778832). SPVG alone is not considered a real threat to sweet potato production since infected plants rarely display symptoms (Rännäli et al., 2008). Significant yield losses have been recorded only when SPVG co-infects sweet potato with other potyviruses such as Sweet potato feathery mottle virus (SPFMV) (Clark & Hoy, 2006). Previously, outbreaks of SPFMV were reported in sweet potato cultivation in central Italy (Parrella et al., 2006). In the current study, attempts to amplify other sweet potato closely related potyviruses were unsuccessful using RT-PCR developed by Li et al. (2012). Based on our observation and results (symptoms recorded and serological detection of SPVG), the yield effects of SPVG may have been overlooked in sweet potato. Considering the number of existing SPVG strains and of sweet potato landraces/varieties, further investigation would be desirable to understand the real incidence of SPVG in individual sweet potato crops and its effects on production.

Laboratory and Greenhouse Evaluation of Melia volkensii Extracts for Potency against African Sweet Potato Weevil, Cylas puncticollis, and Fall Armyworm, Spodoptera frugiperda

The African sweet potato weevil, Cylas puncticollis, and fall armyworm, Spodoptera frugiperda, are insect pests of economic importance that have a negative impact on sweet potato and maize production, respectively. In this study, we aimed to evaluate the potential of Melia volkensii extracts to protect sweet potato and maize plants against damage by both insect pests. We evaluated extracts from the bark, leaves, pulp and nuts of Melia volkensii for antifeedant activity against C. puncticollis and S. exigua (used as a substitute for S. frugiperda), under laboratory conditions. Interestingly, extracts of all plant parts showed antifeedant activity. These results led us to investigate the effectiveness of nut and pulp extracts to protect sweet potato and maize crops in greenhouse conditions. Against C. puncticollis, the sweet potato plants treated with nut extracts showed the lowest tuber damage (18%) when compared to pulp extracts (30%), positive control (33%) and negative control (76%). Nut extracts, pulp extracts and positive control reduced maize leaf and whorl damage by S. frugiperda compared to the negative control. Altogether, this study highlights the potential of M. volkensii extracts and their application in integrated insect pest management

A screening of resistance to sweet potato weevil (Cylas formicarius Fab.) in a collection of sweet potato clones under laboratory conditions

Abstract. Mau YS, Wadu MN, Ndiwa ASS, Markus JER, Arsa IGBA. 2021. A screening of resistance to sweet potato weevil (Cylas formicarius Fab.) in a collection of sweet potato clones under laboratory conditions. Intl J Trop Drylands 5: 41-47. Sweet potato is a potential carbohydrate source as a rice substitute in Indonesia, especially in East Nusa Tenggara (ENT). However, the productivity of this crop is still low at the farmer level due to, among others, the use of low-yielding varieties and yield loss caused by sweet potato weevil (SPW), Cylas formicarius. The use of SPW resistant varieties is considered the most effective and eco-friendly way of controlling the pest. However, the availability of resistant varieties is currently limited. This study aimed to evaluate the SPW-induced damage intensity and SPW-resistance level in a collection of sweet potato clones. The study was conducted in the laboratory of Universitas Nusa Cendana, Kupang, Indonesia. Observed variables included the percentage of damaged roots, the intensity of root damage, the number of C. formicarius per root, the number of feeding tunnels per root, root epidermal thickness, and root latex level. Observed data were subjected to analysis of variance followed by Duncan's post hoc test of 5%, except root latex level that was subjected to descriptive analysis. A correlation analysis was also performed. The damaged root percentage ranged from 77.8% to 100%, and the intensity of root damage was from 14.0% to 76.6%. The laboratory assay categorized the tested genotypes into Moderately Resistant, Moderately Susceptible, and Susceptible levels, with the Resistant category being absent. The SPWs ranged from 1.4 to 31.9 per root, while the number of feeding tunnels ranged from 1.4 to 31.1 per root. The observed sweet potato genotypes possessed root epidermal thickness between 1 mm to 4 mm, and the root latex was low to a high level. The study revealed a strong correlation between the damaged root intensity and the number of feeding tunnels per root or SPWs per root. A highly positive correlation was also observed between the number of SPWs and the number of feeding tunnels per root. A weak and positive correlation was found between root epidermal thickness and the number of SPWs or feeding tunnels per root.

Insect Management for Sweet Potatoes

Sweet potatoes, both orange- and white-fleshed varieties, are widely grown in Florida. Foliar pests, leafminers, whiteflies and armyworms, are generally not difficult to manage; in fact insecticides should be avoided to conserve their natural enemies. More serious are those pests whose immature stages feed on roots: sweetpotato weevil, wireworms, banded cucumber beetles, pale-striped and sweetpotato flea beetles, and in south Florida, Diaprepes weevils and white grubs.

Three chemosensory proteins from the sweet potato weevil, Cylas formicarius, are involved in the perception of host plant volatiles.

Chemosensory proteins (CSPs) play important roles in chemical communication, but their precise physiological functions are still unclear. Cylas formicarius is the most serious pest attacking sweet potato around the world. At present, there is no effective way to control this pest. Our results showed that CforCSP1, 5 and 6 genes were highly expressed in the antennae of both sexes of C. formicarius. In addition, results from a fluorescence competitive binding assay showed that the CforCSP1, 5 and 6 proteins had high binding affinities for 17 plant volatiles including eight host plant volatiles. This indicated that the three proteins may be involved in the detection of host plant volatiles. Furthermore, results from four-arm olfactometer bioassays showed that there was a significant tendency for C. formicarius to be attracted to eucalyptol, β-carotene, benzaldehyde, vanillin and phenethyl alcohol, while it was repelled by β-ionone. Finally, the levels of expression of the three CforCSPs in C. formicarius were successfully inhibited by RNA interference (RNAi). Behavioral experiments showed that CforCSP1, 5 and 6-deficient C. formicarius were partly anosmic to β-cyclocitral, benzaldehyde, octyl aldehyde, and β-ionone and exhibited a reduced ability to locate the host plant volatiles β-carotene and vanillin. Our data suggest that CforCSP1, 5 and 6 likely are involved in the chemical communication between C. formicarius and host plant volatiles, which may play pivotal roles in oviposition and feeding site preferences. More importantly, these results could provide information for the development of monitoring and push-pull strategies for the control of C. formicarius. © 2021 Society of Chemical Industry.

Female Marking via Rubidium-Labeled Ejaculates in the West Indian Sweetpotato Weevil (Coleoptera: Curculionidae)

The West Indian sweetpotato weevil, Euscepes postfasciatus (Fairmaire), is one of the pests of the sweet potato, Ipomoea batatas, in tropical and subtropical countries. Although an eradication program using the sterile insect technique (SIT) for this weevil is now underway in Japan, the lack of potent attractants such as sex pheromones for this weevil species prevents effective monitoring and hampers pest control operations. New methods to monitor the performance of sterile males using trapped wild females are needed. In this study, we tested whether the ejaculate of the labeled males that were fed an artificial diet labeled with the trace element, rubidium (Rb), is detectable in the fertilized females. We fed an artificial diet treated with Rb (1.00, 0.50, 0.25, and 0.00%) to adult male weevils for 14 d after emerging and quantified the rubidium content in inseminated females. We also examined the side effects of the artificial diet on mating performance and longevity. The advantages of monitoring the spatial level of sterility using data from females labeled with ejaculate of Rb-fed males in an SIT eradication program are discussed.

Economic analysis of sweet potato (Ipomoea batata L.) farming in Lamongan regency

Sweet potato has the potential to be developed for diversified food consumption programs as a source of carbohydrates, nutrients, with a small risk of failure, low production costs, various processed products, food providers, industrial raw materials, and animal feed. This research aimed to analyze sweet potato farming economically and socially. The study was carried out quantitatively using a survey method. The research was conducted in Lamongan Regency, East Java, Indonesia. The location was chosen purposively. The sampling method was carried out using census in Kalitengah and Kedungpring Districts, in 6 villages, with 348 respondent farmers. The data analysis employed Revenue Cost (R/C) and descriptive analysis. The results revealed that 80.46% of farmers did not complete elementary school. Farmers with experience in sweet potato farming over 20 years reached 67.53%. Their income from total farm costs was IDR 5,178,296, with an R/C ratio is 1.89. Sweet potato farming is profitable and feasible to develop. The utilization of small sweet potato tubers affected by Cylas Formicarius disease as a fish feed was carried out by 19.54% of the farmers. Meanwhile, 51.72% of the farmers utilized sweet potato stalks and leaves as goat feed.

Efficacy of Fluxametamide for Control of Two Sweetpotato Weevil Species, 2019

Efficacy of Fluxametamide for Control of Two Sweetpotato Weevil Species, 2019

English

The sweet potato weevil, Cylas formicarius (Fabricius) (Coleoptera: Brentidae), is a destructive insect pest that damages sweet potatoes both in the field and during storage. To identify new environmentally friendly insecticides to control this insect pest, three assays (olfactory test, anti-feeding assay, and toxicity assay) were conducted to evaluate the efficacy and mode of action of 10 botanical insecticides against C. formicarius adults in 2015 and 2016. Of these 10 botanical insecticides, tea saponin, pyrethrins, and veratrine showed significant repellency in olfactory tests. Eight botanical insecticides showed anti-feeding effects in the feeding choice test. Five botanical insecticides had high toxicity. Among them, the lethal concentrations of rotenone were lowest followed by pyrethrins. The lethal time values of rotenone were shortest followed by nicotine. In conclusion, rotenone, pyrethrins, nicotine, and toosendanin have the potential to control C. formicarius adults. Of these, pyrethrins and toosendanin are more environmentally friendly than rotenone and nicotine and were identified as better insecticides to control C. formicarius. Key words: Toxicity, repellency, anti-feeding, Coleoptera, Brentidae, environmentally friendly insecticides.

Effects of hydroxycinnamic acid esters on sweetpotato weevil feeding and oviposition and interactions with Bacillus thuringiensis proteins

Sweetpotato weevil (SPW) pest management is challenging because the pest target is sub-terranean, so the application of pesticides is impractical and usually ineffective. Host plant resistance and the genetic transformation of sweetpotatoes to produce entomotoxic Bt proteins offer potential for environmentally benign pest control. Resistance can be conferred by naturally occurring hydroxycinnamic acids which protect against oviposition by adults, but these compounds are restricted to the root surface so do not protect against the cortex bound larvae where the greatest damage occurs. Resistance could be enhanced if combined with expression of Bt proteins in transformed plants, but interactions between hydroxycinnamic acids and Bt proteins remain unknown. Here the bioactivity of Cry7Aa1 protein and hydroxycinnamic acid esters was evaluated individually and in combination against SPW larvae and mortality determined. Low and high concentrations of hydroxycinnamic acid esters alone caused significantly higher mortality of both weevil species in all experiments compared to the control. SPW larval mortality was greater when tested as a combination of hydroxycinnamic acid esters and Bt protein, but this effect was additive not synergistic. Although we report no evidence of antagonistic interactions, the antifeedant effects of the plant compounds conferring host plant resistance could have reduced consumption of the Bt protein in our assays leading to a lower efficacy when combined. Further work is required to determine whether the toxic effects of Bt proteins function alongside host plant resistance in sweetpotato under field conditions.

Screening of sweetpotato germplasm collections for sweetpotato weevil (Cylas spp.) resistance in Tanzania

Weevil damage caused by sweetpotato weevil (Cylas spp.) is a major constraint to sweetpotato production in Tanzania due to a lack of improved varieties with durable resistance. The objective of this study was to screen sweetpotato germplasm collections for weevil resistance and to select the best parents to be used in resistance breeding. Field studies involving 96 sweetpotato genotypes were conducted at two weevil hotspot sites in Western Tanzania using a 12 x 8 lattice design with three replications at each site. Data collected included yield and yield related traits, weevil reaction and weevil damage score. The tested genotypes differed significantly (P < 0.01) for sweetpotato storage root number, root weight, root infestation and root damage score. Weevil infestation on storage roots significantly (P ≤0.05) correlated with total root number (r = 0.38) and weevil damage score (r = 0.79). Marketable root weight and total root weight were significantly correlated with infested root weight each with r = 0.45. The study identified nine sweetpotato genotypes expressing resistance and 10 genotypes with moderate resistance to weevil. Five genotypes including Magunhwa, Chuchu ya Nesi, Rugomoka, Tumauma and New Kawogo were selected with weevil resistance and desirable yield and yield-related traits. These genotypes can be used in future weevil resistance breeding programs of sweetpotato in Western Tanzania or related agro-ecologies.