Decoding phenotypic signatures of Cylas formicarius Fab. resistance in a global sweetpotato (Ipomoea batatas [L.] Lam.) germplasm collection

Sweet potato (Ipomoea batatas L.) is a major root crop worldwide. Sweet potato weevils (SPWs) pose one of the most significant challenges to sweet potato production in tropical and subtropical regions, causing deleterious economic and environmental effects. Characterizing the mechanisms underlying natural resistance to SPWs is therefore crucial; however, the genetic basis of host SPW resistance (SPWR) remains unclear. Here we obtained two sweet potato germplasm with high SPWR and, by map-based cloning, revealed two major SPW-resistant genes-SPWR1 and SPWR2-that are important regulators of natural defence against SPWs. The SPW-induced WRKY transcriptional factor SPWR1 directly activates the expression of SPWR2, and SPWR2, the conserved dehydroquinate synthase, promotes the accumulation of quinate derivative metabolites that confer SPWR in sweet potato. Generally, our results provide new insights into the molecular mechanism underlying sweet potato-SPW interactions and will aid future efforts to achieve eco-friendly SPW management.

Intraspecific competition is shared in the insect world, especially under the condition of limited food and space resources. To avoid intraspecific competition and increase offspring survival, insects have evolved various effective strategies. A widely-accepted tactic is employing chemical cues, which are frequently utilized as indicators of conspecific colonization. The sweet potato weevil (SPW), Cylas formicarius, is a destructive pest of sweet potatoes. Its larvae bore into sweet potatoes and alter the emission of odors. The present study aimed to investigate whether volatiles associated with SPW larvae feeding influence the behavioral preference of conspecific adults. Volatiles from SPW larvae-infested sweet potatoes were collected by a head-space method and analyzed using gas chromatography-electroantennogram detector (GC-EAD) and gas chromatography-mass spectrometry (GC-MS). Five compounds eliciting EAD responses from the antennae of both male and female adult SPW were identified from sweet potatoes with the third-instar larvae, including linalool, citronellol, nerol, geraniol, and ipomeamarone. Four monoterpene alcohols significantly repelled SPW adults from feeding and oviposition at higher doses in the behavioral preference bioassays. Among them, geraniol displayed the strongest repellent activities for SPW feeding and oviposition. These results suggested that SPW larvae could reduce colonization of adult SPWs by inducing monoterpene alcohols, thereby avoiding intraspecific competition. The present study demonstrated that volatile monoterpene alcohols induced by SPW larvae are chemical cues of larvae occupation for SPW adults to change their behavioral preference. Unveiling factors that mediate avoidance of intraspecific competition could help develop repellents or oviposition deterrents for SPW control. © 2023 Society of Chemical Industry.

Sweetpotato weevil, Cylas formicarius (Fabricius), is the most limiting factor of sweet potato, Ipomoea batatas (L.) Lam., production worldwide (Jansson & Raman 1991). Feeding and oviposition damage in roots and vines can cause severe cosmetic and economic damage. In response to tissue damage, sweet potato roots produce foul tasting terpenoids (Uritani et al. 1975) rendering them unpalatable for human consumption. Thus, commercial growers can tolerate very little sweetpotato weevil damage. Historically, weevil management has relied heavily on cultural and chemical control (Sutherland 1986, Chalfant et al. 1990). However, chemical control provides little protection once an egg is laid because immatures develop within roots and vines (Chalfant et al. 1990). Cultural controls, such as sanitation, crop rotation, planting away from weevilinfested fields, removal of alternate hosts, hilling plants, etc., can help to reduce damage (Talekar 1991); however, they require considerable labor and have not been universally adopted. Recent studies indicate that entomopathogenic nematodes and sex pheromones may provide new means to control the sweetpotato weevil (Jansson 1991, Jansson et al. 1991). Pheromones have typically been used three ways: (1) monitoring insect populations using pheromone-baited traps; (2) mass-trapping, where large numbers of traps are used to reduce the insect population; and (3) mating disruption, in which the pheromone is used at high dosages to permeate the atmosphere so as to disrupt communication between the sexes, thus reducing mating (Kydonieus & Beroza 1982, Campion 1984). Mating disruption has been examined in many insect systems (McLaughlin et al. 1972, Shorey et al. 1972, Landolt et al. 1982, Sower 1982, Schwalbe & Mastro 1988, for reviews see Kydonieus & Beroza 1982, Campion 1984), and in general, some success has been achieved. The objective of our study was to examine the potential of sweetpotato weevil synthetic sex pheromone as a mating disruptant by examining male confusion (i.e. communication disruption) in a large commercial field plot.

The sweetpotato weevil (SPW), Cylas formicarius elegantulus (Summers) is the most economically important insect pest of sweet potato, Ipomoea batatas (L.) Lam., worldwide. Low level infestations reduce quality and marketable yield (Proshold 1983). Terpenoids that are produced by sweet potato in response to SPW feeding may make even slightly damaged roots unfit for human consumption (Uritani et al. 1975, Akazawa et al. 1960). Yield losses of up to 60-80% have been attributed to SPW (Hua 1970, Subramaniam et al. 1977, Mullen 1984). Economically effective control measures for SPW in regions with large resident populations are lacking. There are no insecticides that will adequately control weevils in an infested field (Stall et al. 1984) because SPW immature stages are spent within vines and/or roots. For this reason, other SPW management approaches, such as host plant resistance, have been explored (Waddill & Conover 1978, Mullen et al. 1980a,b, 1981, 1982, 1985). With one exception (Waddill & Conover 1978), resistant cultivars have not been field tested in regions with high SPW population pressure. The present study was conducted to evaluate SPW resistance in four sweet potato cultivars in southern Florida, a region with a dense SPW population. Also, we determined the -impact of a mechanical barrier (polyethylene mulch) on field plant protection from SPW. Lastly, we compiled preliminary data on the within-vine distribution of SPW in sweet potato. The experiment was conducted in 1986 at the Tropical Research and Education Center in Homestead, Florida. Four sweet potato cultivars, I. batatas cv. Resisto, Regal, Sumor, and NC1135, were planted in a split-plot design with three replications. Plastic polyethylene mulch (white/black, 38 microns thick covering a 0.9-m bed width) was the whole-plot factor and cultivar was the split-plot factor. Cultivars were handplanted on 22 April in raised beds with 1.8 m centers. Slips (0.3-m long) of each cultivar were planted 0.3 m apart in one row per bed. Replicate plots consisted of 40 slips

Diurnal emission of herbivore-induced (Z)-3-hexenyl acetate and allo-ocimene activates sweet potato defense responses to sweet potato weevils

Piecemeal versus one-time harvesting of sweet potato in north-eastern Uganda with special reference to pest damage

The sweet potato weevil (Cylas formicarius) is an important pest in the growing and storage of sweet potatoes. It is a common pest in the sweet potato production areas of southern China, causing serious harm to the development of the sweet potato industry. For the existing cultivars in China and abroad, there is no sweet potato variety with complete resistance to the sweet potato weevil. Thus, understanding the regulation mechanisms of sweet potato weevil resistance is the prerequisite for cultivating sweet potato varieties that are resistant to the sweet potato weevil. However, very little progress has been made in this field. In this study, we inoculated adult sweet potato weevils into sweet potato tubers. The infected sweet potato tubers were collected at 0, 24, 48, and 72 h. Then, a miRNA library was constructed for Eshu 6 and Guang 87 sweet potato tubers infected for different lengths of time. A total of 407 known miRNAs and 298 novel miRNAs were identified. A total of 174 differentially expressed miRNAs were screened out from the known miRNAs, and 247 differentially expressed miRNAs were screened out from the new miRNAs. Moreover, the targets of the differentially expressed miRNAs were predicted and their network was further investigated through GO analysis and KEGG analysis using our previous transcriptome data. More importantly, we screened 15 miRNAs and their target genes for qRT-PCR verification to confirm the reliability of the high-throughput sequencing data, which indicated that these miRNAs were detected and most of the expression results were consistent with the sequencing results. These results provide theoretical and data-based resources for the identification of miRNAs in response to sweet potato weevil infection and an analysis of the molecular regulatory mechanisms involved in insect resistance.

Sweet potato is an important food crop, grown commonly in tropical and subtropical regions, but production has been subjected to less research worldwide, compared to the major staple crops. Sweet potato weevils are the major destructive pest causing drastic yield decline and resulting in a decrease in millions of dollar annually. A wide range of management strategies in controlling sweet potato weevils includes; cultural method, chemical method, biological method, Sterile Insect Technique, soil management, Sterile Insect Release, pheromone traps, Host Plant Resistance and Integrated Pest Management. However, the chemical method is limited by larvae internal feeding, whilst the biological approach has been constraints to some point. The pheromone method has enhanced for monitoring of sweet potato weevils, but adapting to integrated pest management is most highly effective and environmentally safe to growers. This paper reviews the factors that contribute to the infestation of weevils, mode of infestation, and various control management strategies towards decreasing the infestation of weevils in the plantation of sweet potato.

Sweet potato is an important food crop, grown commonly in tropical and subtropical regions, but production has been subjected to less research worldwide, compared to the major staple crops. Sweet potato weevils are the major destructive pest causing drastic yield decline and resulting in a decrease in millions of dollar annually. A wide range of management strategies in controlling sweet potato weevils includes; cultural method, chemical method, biological method, Sterile Insect Technique, soil management, Sterile Insect Release, pheromone traps, Host Plant Resistance and Integrated Pest Management. However, the chemical method is limited by larvae internal feeding, whilst the biological approach has been constraints to some point. The pheromone method has enhanced for monitoring of sweet potato weevils, but adapting to integrated pest management is most highly effective and environmentally safe to growers. This paper reviews the factors that contribute to the infestation of weevils, mode of infestation, and various control management strategies towards decreasing the infestation of weevils in the plantation of sweet potato.

The sweet potato weevil (Cyclas formicarius Fabr.) remains a serious threat to sweet potato (Ipomoea batatas Poir.) production and is considered the most destructive pest of sweet potatoes in the field and storagein the Philippines. Chemical control of the weevil is seldom practiced by farmers because they find it too costly, it may increase the chance for pesticide resistance, and because of public concern of its effectson non-target organisms. The use of biological controls such as entomopathogenic nematodes (EPN) could offer an effective, economical, and environmentally-friendly alternative management of the weevil. This study determined the occurrence and distribution of entomopathogenic nematodes in selected sweet potato growing areas in the Philippines. Using soil from 13 sweet potato growing areas, EPNs were recovered using the insect baiting method. Morbid insect larvae were suspended in sterile water for 48 h, and the suspension was examined under a stereomicroscope for the presence of EPN. Out of 47 samples collected from the 13 sweet potato production areas, 39 (82%) were positive for the presence of EPNs. Preliminary identification of the EPNs through morphological characters showed that they belonged to Rhaditida: Heterorhabditidae and Steinernematidae. This is the first report on the occurrence of EPNs in sweet potato fields in the Philippines, and their distribution strongly supports the possibility of utilizing them in an IPM management approach as biological agents against the sweet potato weevil. Morphometric and molecular-based identification and pathogenicity studies are underway.

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.

Sweetpotato storage roots are subjected to several forms of post harvest spoilage in the tropical climate during transportation from farmers' field to market and in storage. These are due to mechanical injury, weight loss, sprouting, and pests and diseases. Sweetpotato weevil is the single most important storage pest in tropical regions for which no control measures or resistant variety are yet available. Several microorganisms (mostly fungi) have been found to induce spoilage in stored sweetpotatoes. The most important among them are Botryodiplodia theobromae, Ceratocystis fimbriata, Fusarium spp., and Rhizopus oryzae. The other less frequently occurring spoilage microorganisms include Cochliobolus lunatus (Curvularia lunata), Macrophomina phaseolina, Sclerotium rolfsii, Rhizoctonia solani, Plenodomus destruens. Microbial spoilage of sweetpotato is found associated with decrease in starch, total sugar, organic acid (ascorbic acid and oxalic acid) contents with concomitant increase in polyphenols, ethylene, and in some instances phytoalexins. Several methods are used to control microbial spoilage. Curing to promote wound healing is found as the most suitable method to control microbial spoilage. Curing naturally occurs in tropical climates where mean day temperature during sweetpotato harvesting season (February–April) invariably remains at 32–35°C and relative humidity at 80–95%. Sweetpotato varieties varied in their root dry matter content, and low root dry matter content attributed for their high curing efficiency. Curing efficiency of varieties also differed in response to curing periods. Fungicide treatment, bio-control, gamma irradiation, hydro warming, and storage in sand and saw dust were found to have intermediate impacts in controlling spoilage and enhancing shelf life of sweetpotato roots. Breeding program has to be chalked out to develop new varieties suitable to curing under tropical conditions in addition to developing varieties having multi-spectrum resistance to major post harvest rot pathogens and sweet potato weevils.

Nineteen sweet potato genotypes were screened for tolerance against sweet potato weevils and viruses at different locations of Eastern Hararge. Disease incidence and weevil population was assessed using standard procedures. Results of this study revealed that sweet potato weevils (SPW) and sweet potato virus diseases (SPVD) were present in studied area varied among sweet potato genotypes. Genotypes; Awassa-83, Bekale-A, Bekale-B, CN-1752-9, Cuba-2, Korojo, TIS-70357-5 and TIS-9465-2 had least load of SPW while, Bekale-A, TIS-8250-7 and TIS-9465-2 genotypes were free of virus diseases. Genotypes showing resistance to sweet potato can be used in varietal improvement program. The present studies concluded that the resistant sweet potato genotypes identified for SPW and SPVD could be utilized in integrated sweet potato production for the locations where the pests are major production bottleneck, like in Eastern Hararge.   Key words: Resistant, tolerance, Integrated pest management (IPM), sweet potato viruses, Oromiya, Hararge.

This study aims to evaluate the potential of the entomopathogenic fungus Metarhizium anisopliae as a biological control agent against sweet potato weevil. Sweet potato weevil (Cylas formicarius) is a major pest of sweet potato crops, causing severe economic losses due to its ability to infest both storage roots and vines. Concerns regarding the ecological health risks posed by chemical insecticides in sweet potato farming, a natural approach were tested as an alternative method for controlling this pest. This study evaluates the potential of the entomopathogenic fungus Metarhizium anisopliae as a biological control agent against sweet potato weevil. Laboratory experiments were conducted to compare the effectiveness of different strains of M. anisopliae and other entomopathogens, using two application techniques: "dipping" and "ingestion." Results demonstrated that M. anisopliae significantly increased Sweet potato weevil (SPW) mortality, with the "ingestion" method rather than "dipping" method across all treatments. Among the tested strains, M. anisopliae (MR) showed the highest mortality rate (62.47%) when applied through ingestion. The findings highlight that both the choice of fungal strain and application technique are critical for optimizing pest control outcomes. The study also underscores the advantages of M. anisopliae as an eco-friendly alternative to chemical pesticides, with potential to reduce environmental impact while maintaining effective pest management. Furthermore, the results emphasize the importance of integrating biological control agents with precise application methods to enhance pest control efficacy. This research contributes to sustainable agriculture by promoting the use of entomopathogenic fungi as part of integrated pest management strategies. Further research is suggested to assess the field-level use of M. anisopliae under varying environmental conditions, aiming to establish its effectiveness in large-scale sweet potato cultivation in order to reduce reliance on chemical pesticides. However, field studies are needed to reach a good conclusions and practical applications.

Sweet potato (Ipomoea batatas (L.) Lam. is an important food crop adaptable to a broad range of agro-ecological conditions. The knowledge of the performance of the available varieties under a specific ecological condition is important to improve the production. A field experiment was carried out at the University of Ghana farm during the major and minor rainy seasons of 2015 to determine the yield performance of seven improved Ghanaian sweet potato varieties (CRI-Apomuden, CRI-Ligri, Faara, CRI-Bohye, CRI-Dadanyuie, Okumkom, Sauti) and their susceptibility to the sweet potato weevil, Cylas spp. (Coleoptera: Brentidae). Significant difference was found in the storage root yield among the varieties, with CRI-Ligri having the highest in both major (23.11 t/ha) and minor (22.49 t/ha) rainy seasons. CRI-Apomuden and CRI-Ligri scored the highest levels of infestation by sweet potato weevil in the major and minor seasons (1.94 and 2.00, 1.84 and 1.96, respectively) and yield loss (44.44 % and 42.80 %, 23.84 % and 23.87 %, respectively). While the lowest infestation levels in the major rainy season were recorded on Faara and Okumkom (1.18 and 1.31, respectively) with yield losses of 10.32 % and 9.09 %, respectively. However, in the minor rainy season, there was no significant difference among Faraa, Okumkom, CRI-Bohye and CRI-Dadanyuie in terms of infestation level and yield losses. Significant difference was found in all measured root characteristics including the shortest weevil distance, root neck length, root length, root girth and root size index. The storage root infestation had a strong negative correlation with the shortest weevil distance, a strong positive correlation with the root size index and a weak negative correlation with root neck length. In this study, Okumkom appeared to be less susceptible to sweet potato weevil infestation with relatively acceptable yield performance and therefore can be recommended for use by farmers to improve sweet potato production.