Effect of the flavonoid rutin on the biology of Spodoptera frugiperda (Lepidoptera: Noctuidae)

The tobacco budworm, Heliothis virescens (F.) (Lepidoptera: Noctuidae), damages soybean crops by feeding on the leaves, pods, and terminal buds. The purpose of this study was to evaluate antibiosis resistance to H. virescens by different soybean cultivars. Soybean cultivars evaluated were P 98Y30 RR, NA 7337 RR, SYN 1163 RR, NK 7059 RR, ANTA 82 RR, M 7110 IPRO, BRS 8160 RR, BRSGO Jataí, and IAC 100. The variables analyzed were duration of the larval stage, percentage of larval survival, larval weight at 10 d, duration of the prepupal stage, percentage of prepupae survival, duration of the pupal stage, percentage of pupal survival, pupal weight at 24 h, total duration of the life cycle, overall survival, and adult longevity. The cultivars BRS 8160 RR, BRSGO Jataí, and P 98Y30 RR were highly susceptible to tobacco budworm, whereas IAC 100 and M 7110 IPRO showed antibiosis resistance to H. virescens. Resumo A lagarta-da-maçã do algodoeiro Heliothis virescens (F.) (Lepidoptera: Noctuidae) pode causar prejuízos na cultura da soja alimentando-se de folhas, vagens e brotos terminais. Objetiva-se com este trabalho avaliar a resistência do tipo antibiose em diferentes cultivares de soja a H. virescens. Foram utilizadas sementes de soja das cultivares P 98Y30 RR, NA 7337 RR, SYN 1163 RR, NK 7059 RR, ANTA 82 RR, M 7110 IPRO, BRS 8160 RR, BRSGO Jataí e IAC 100. As variáveis avaliadas foram: período, e % de sobrevivência do estágio larval e peso de lagartas aos dez dias de idade, período e sobrevivência pré-pupal, período, sobrevivência e peso pupal com 24 horas de idade, ciclo e sobrevivência total e longevidade de adultos. As cultivares BRS 8160 RR, BRSGO Jataí, P 98Y30 RR foram altamente suscetíveis e as cultivares IAC 100 e M 7110 IPRO apresentaram resistência do tipo antibiose à H. virescens.

Tibraca limbativentris Stål (Hemiptera: Pentatomidae) is a major pest causing economic losses to rice cultivation in Brazil. The objectives of this work were to assess different sources of silicon in the induction of plant resistance, to examine the interaction of rice varieties with silicon-based resistance, and to determine the effects of varieties and silicon on stink bug biology. The interaction of rice cultivars BRS Esmeralda, IRGA 429 (widely cultivated in Brazil), and Canela de Ferro (a resistant cultivar), and 2 sources of silicon (K silicate, and Ca + Mg silicate) were studied. Plant parameters measured were percentage of damaged stems, chlorophyll content at 50 and 65 d after emergence, and silicon content. Insect biological parameters measured were the number of live insects, total dry mass, individual insect dry mass, total body surface area, and individual insect body surface area. The interaction between BRS Esmeralda with K silicate and Ca + Mg silicate provided greater plant silicon content and resulted in a lower level of stink bug-damaged stems. These results show that it is possible to increase resistance in rice plants susceptible to T. limbativentris by increasing silicon content.

The rice stalk stink bug, Tibraca limbativentris Stål, damages plant stalks while feeding, making it one of the most important rice pests in South America. Because the feeding behavior of T. limbativentris has not yet been studied in rice, we investigated T. limbativentris stylet penetration (probing) in rice stalks. A waveform library was created using the new AC-DC EPG monitor with different levels of input resistance (Ri). Six different waveforms were recorded and correlated via histological studies and grouped into three phases: non-probing waveforms (Z and Np), pathway waveforms (Tl1), and ingestion waveforms (Tl2 and Tl3). The Z waveform was observed when the stink bug was standing still on the plant surface, Np when the stink bug was walking on plant surface, Tl1 was associated with stylet insertion and deep penetration into the plant tissue, and Tl2 when the stink bug was feeding on xylem vessels. The Tl3 waveform was associated with the rupture of stalk cells and was divided into two subtypes (Tl3a and Tl3b). The Tl3a waveform probably represents cell laceration with combined enzymatic maceration of stalk tissues, while Tl3b represents a short ingestion period of macerated tissues. Tibraca limbativentris uses two strategies to feed on rice stalks: a salivary sheath for feeding on xylem vessels and cell rupture (laceration and maceration) for feeding on parenchyma cells. Our study provides crucial benchmark definitions of waveforms. Future studies can now compare effects of treatments on stink bug feeding, to ultimately improve management of this pest in rice.

The fungus Metarhizium anisopliae is under development as a bioinsecticide for Euschistus heros. To further elucidate the effect of this fungus on E. heros behavior, we monitored the feeding activities of adults treated with the fungus at 1 × 10⁸ conidia mL⁻¹ on soybean in the pod-filling stage (R5) through electropenetrography (EPG) AC-DC. We also determined the virulence of M. anisopliae to adults and its damage to soybean seeds. M. anisopliae displayed high levels of virulence to adults even at low concentrations of 5 × 10⁶ conidia mL⁻¹ (98% mortality). E. heros females were more susceptible to M. anisopliae than males, exhibiting a lower LT₅₀ for mycosed adults (7.1 and 9.7 days, respectively). The EPG experiment showed that fungus-treated adults spent significantly less time on probing activities (reduced by 86% at day four and ceased at day five) than untreated insects, and the number of waveform events per insect significantly decreased. This information is valuable for managing stink bugs at the field level, as it shows that even though the insect is alive, its feeding is compromised, consequently minimizing the damage inflicted to the crop. This study paves the way for further research employing entomopathogenic fungi in pest control.