Performance of bean bruchids Callosobruchus maculatus and Zabrotes subfasciatus (Coleoptera: Bruchidae) reared on resistant (IT81D-1045) and susceptible (Epace 10) Vigna unguiculata seeds: Relationship with trypsin inhibitor and vicilin excretion

Seeds of nonhost species as sources of toxic compounds for the cowpea weevil Callosobruchus maculatus (F.)

Cowpea weevil, Callosobruchus maculatus, is the primary pest of stored cowpea seeds. The management of this infestation currently relies on insecticides, resulting in environmental pollution and selection of insecticide-resistant pests. Consequently, research efforts are being devoted to identify natural insecticides as sustainable and environment friendly alternatives for the control of C. maculatus. In this study, we explore the toxic effects of the nonhost seeds Parkia multijuga, Copaifera langsdorffii, Ormosia arborea, Amburana cearensis, Lonchocarpus guilleminianus, Sapindus saponaria, and Myroxylon peruiferum, on the cowpea weevil C. maculatus. Notably, all nonhost seeds led to reductions between 60 and 100% in oviposition by C. maculatus females. Additionally, the larvae were unable to penetrate the nonhost seeds. Artificial seeds containing 0.05% to 10% of cotyledon flour were toxic to C. maculatus larvae. Approximately 40% of larvae that consumed seeds containing 0.05% of O. arborea failed to develop, in contrast to control larvae. Proteomic analysis of A. cearensis and O. arborea seeds identify revealed a total of 371 proteins. From those, 237 are present in both seeds, 91 were exclusive to O. arborea seeds, and 43 were specific to A. cearensis seeds. Some of these proteins are related to defense, such as proteins containing the cupin domain and 11S seed storage protein. The in silico docking of cupin domain-containing proteins and 11S storage protein with N-acetylglucosamine (NAG)4 showed negative values of affinity energy, indicating spontaneous binding. These results showed that nonhost seeds have natural insecticide compounds with potential to control C. maculatus infestation.

Oviposition preference and life-history parameters of Callosobruchus maculatus (Coleoptera: Chrysomelidae) on different soybean (Glycine max) cultivars

BACKGROUND

Callosobruchus maculatus (F.) (Coleoptera: Chrysomelidae) is one of the most destructive pests of stored legume seeds in many regions of the world. Evaluation of varietal resistance of host seeds to C. maculatus infestation can be useful in preventing severe damage. We studied the susceptibility and resistance of eight conventional soybean cultivars (Caspian, Kosar, L17, Nekador, Sari, Tapour, Williams and Zane) based on the oviposition preference (choice and no-choice tests) and population growth parameters of the pest.

RESULTS

Compared with other cultivars tested, oviposition preference of C. maculatus was the lowest on Nekador. The developmental time of C. maculatus differed from 40.34 days on Nekador to 48.35 days on L17, and was negatively correlated with the seed protein content. Other performance measures of C. maculatus did not match the oviposition preference. Immature survival and female longevity were highest on Caspian. The intrinsic rate of increase (r_m ) was higher on Tapour, Nekador and Caspian than on Zane, Williams, and Kosar. A positive correlation was observed between the r_m value of the pest and moisture content of the cultivars. Cluster analysis showed that cvs Nekador, Sari, Tapour, and Caspian were relatively susceptible, and cvs Kosar, Zane, Williams and L17 were partially resistant to this pest.

CONCLUSION

Protein and moisture contents of soybean cultivars play an important role in the development and population growth of C. maculatus, and these traits could be used to develop safe and effective management strategies for this pest on stored soybean seeds. © 2022 Society of Chemical Industry.

The resistance of the cowpea cv. BRS Xiquexique to infestation by cowpea weevil is related to the presence of toxic chitin-binding proteins

The cowpea weevil (Callosobruchus maculatus) is the main pest that attacks cowpea (Vigna unguiculata) seeds during storage, causing nutritional and economic losses in the cowpea crop. Thus, studies aiming to identify resistant cowpea cultivars have been developed. Chitin-binding proteins (CBP), such vicilins and chitinases, have been detected in seeds and related with the toxicity to insects. In this work, we investigated the presence of chitin-binding proteins in the partially resistant cowpea cv. BRS Xiquexique and evaluated their toxicity towards cowpea weevil. The CBP fraction was isolated by chitin affinity chromatography. CBP fraction showed, through 15% SDS PAGE, protein bands with varying molecular masses, mainly below 55 kDa. Proteins present in CBP fraction were identified by Western blotting and mass spectrometry analysis, as vicilins and chitinases. CBP fraction, at 5%, was able to interfere with the development of cowpea weevil, decreasing larval mass and length. A CBV (chitin-binding vicilin) fraction isolated from CBP fraction was toxic, at 2.0%, to C. maculatus, decreasing larval mass and length in 64.3% and 33.23%, respectively. These results suggest that chitin binding proteins, such vicilins and chitinases, may be related to the resistance of cowpea cv. BRS Xiquexique to the infestation by C. maculatus.

Efficacy of bioactive compounds and their association with different cowpea cultivars against their major stored pest

BACKGROUND

Stored grain insects are controlled with fumigant insecticides which can select resistant insect populations and cause environmental and applicator contamination. Thus, resistant cultivars and chemical constituents of essential oils are an alternative to the almost exclusive use of these insecticides. The effects of the combination of cowpea cultivars Vigna unguiculata (L.) Walp. with chemical constituents of essential oils against Callosobruchus maculatus were determined. Four cowpea cultivars: BRS Tracuateua, BR 17 Gurgueia, Epace 10 and Sempre Verde (insect rearing) untreated were used in the experiments and combined with chemical constituents of essential oil: eugenol, geraniol and trans-anethole. The biological parameters observed were: total egg number and eggs per grain, egg viability (%), insects emerged and insects per grain, immature stage viability (%), instantaneous rate of growth (ri), insect dry weight (mg), grain weight loss (%) and egg-adult period.

RESULTS

When comparing all biological parameters, the cultivars BRS Tracuateua and BR 17 Gurgueia were harmful to C. maculatus. In the toxicity tests, the results showed that LC₃₀ and LC₅₀ of the chemical constituents ranged from 54.77 to 103.48 ppm and 60.99 to 125.18 ppm, respectively. In most of the biological parameters, LC₅₀ had adverse effects significantly higher than LC₃₀ and BR 17 Gurgueia treated were harmful to C. maculatus.

CONCLUSIONS

Overall, the findings showed that BR 17 Gurgueia combined with eugenol and geraniol more significantly affected the biological parameters of C. maculatus than when associated with trans-anethole, reducing egg number, insects emerged and egg viability. © 2020 Society of Chemical Industry.

Purification of legumin-like proteins from Coffea arabica and Coffea racemosa seeds and their insecticidal properties toward cowpea weevil ( Callosobruchus maculatus ) (Coleoptera: Bruchidae)

Legumin-like proteins from seeds of Coffea arabica (CaL-1 and CaL-2) and Coffea racemosa (CrL-1 and CrL-2) were characterized and isolated by gel filtration and reverse-phase chromatography. The insecticidal properties of the purified proteins were tested against Callosobruchus maculatus using artificial diets. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analyses indicated that CaL-1 is composed of two subunits of 33 and 24 kDa, while CaL-2, CrL-1, and CrL-2 were monomeric with a single band of 14 kDa. The LD(50) values were 0.5% (w/w) for CaL-1 and 0.3% (w/w) for CaL-2, CrL-1, and CrL-2. ED(50) at 0.3% was assessed for all protein concentrations. The legumin-like proteins were not digested by midgut homogenates of C. maculatus until 8 h of incubation. CaL-1 and CaL-2 ( C. arabica ) and CrL-1 and CrL-2 ( C. racemosa ) are chitin-binding proteins, and their insecticidal properties toward C. maculatus larvae might be related to their capacity to bind chitin present in the larval gut and their associated low digestibility.

Molecular identification of four different alpha-amylase inhibitors from baru (Dipteryx alata) seeds with activity toward insect enzymes

The endophytic bruchid pest Callosobruchus maculatus causes severe damage to storage cowpea seeds, leading to economical losses. For this reason the use of alpha-amylase inhibitors to interfere with the pest digestion process has been an interesting alternative to control bruchids. With this aim, alpha-amylase inhibitors from baru seeds (Dipteryx alata) were isolated by affinity chromatographic procedures, causing enhanced inhibition of C. maculatus and Anthonomus grandis alpha-amylases. To attempt further purification, this fraction was applied onto a reversed-phase HPLC column, generating four peaks with remarkable inhibition toward C. maculatus alpha-amylases. SDS-PAGE and MALDI-ToF analysis identified major proteins of approximately 5.0, 11.0, 20.0 and 55 kDa that showed alpha-amylase inhibition. Results of in vivo bioassays using artificial seeds containing 1.0% (w/w) of baru crude extract revealed 40% cowpea weevil larvae mortality. These results provide evidence that several alpha-amylase inhibitors classes, with biotechnological potential, can be isolated from a single plant species.