The cotton boll weevil, Anthonomus grandis grandis Boheman (Coleoptera: Curculionidae), is one of the most important insect pests of cotton, causing significant yield losses. This insect completes ...its life cycle only on the flower structures of some Malvaceae species, with cotton being its preferred host. However, during the cotton off‐season, the boll weevil enters a reproductive dormancy state, in tropical regions, with important alterations in their reproduction organs. During this period, a remaining insect population survives feeding on a variety of other food sources, but the insects do not reproduce. We hypothesized that these alterations in the insect's reproductive organs are associated with the nutritional levels provided by alternative food sources during the cotton off‐season. To test our hypothesis, we first investigated food sources that sustain insect survival for long periods, such as weed species and fruits of cultivated crops. Then, we evaluated how various food sources affect the reproductive organs and reproductive capacity of the boll weevil. Among the alternative food sources tested, insect longevity was highest on banana (Musa paradisiaca L.), mango (Mangifera indica L.), papaya (Carica papaya L.), milkweed (Euphorbia heterophylla L.), and lilac tasselflower (Emilia sonchifolia L.). However, only banana and mango resulted in greater longevity than cotton squares. Banana was the preferred food and resulted in the highest levels of nutrients in the insects. Additionally, insects previously fed on banana made more oviposition punctures on cotton squares than those fed only on cotton squares, which resulted in a significantly higher number of emerged adults. Histological analysis of the insects' reproductive organs showed that feeding on papaya resulted in morphological changes and testicle degradation. In conclusion, we present evidence that boll weevils fed on alternative food sources (other than cotton squares or similar‐quality food) display a nutritional imbalance, associated with substantial alterations in the reproductive tissues of this insect, which may trigger the reproductive dormancy state.
Anthonomus grandis (Coleoptera: Curculionidae) feeds preferentially on cotton and completes its cycle only on a few plants of the Malvaceae family. However, this insect survives the cotton off‐season period feeding on other plant species, such as cultivated fruits or weed flowers. These insects survived longer and preferred banana over cotton squares. When they fed on low‐nutritional food (e.g., papaya fruit), their reproductive organs (testicles and oocytes) showed an abnormal morphology, which impaired their ability to lay viable eggs.
Common bean (
Phaseolus vulgaris
L.) is a staple food in Brazil with both nutritional and socioeconomic importance. As an orphan crop, it has not received as much research attention as the commodity ...crops. Crop losses are strongly related to virus diseases transmitted by the whitefly
Bemisia tabaci
, one of the most important agricultural pests in the world. The main method of managing whitefly-transmitted viruses has been the application of insecticides to reduce vector populations. Compared to chemical vector control, a more sustainable strategy for managing insect-borne viruses is the development of resistant/tolerant cultivars. RNA interference has been applied to develop plant lines resistant to the whitefly in other species, such as tomato, lettuce and tobacco. Still, no whitefly-resistant plant has been made commercially available to date. Common bean is a recalcitrant species to
in vitro
regeneration; therefore, stable genetic transformation of this plant has been achieved only at low frequencies (<1%) using particle bombardment. In the present work, two transgenic common bean lines were obtained with an intron-hairpin construct to induce post-transcriptional gene silencing against the
B. tabaci vATPase
(Bt-
vATPase
) gene, with stable expression of siRNA. Northern blot analysis revealed the presence of bands of expected size for siRNA in leaf samples of the line Bt-22.5, while in the other line (11.5), the amount of siRNA produced was significantly smaller. Bioassays were conducted with both lines, but only the line Bt-22.5 was associated with significant mortality of adult insects (97% when insects were fed on detached leaves and 59% on the whole plant). The expression of the Bt-
vATPase
gene was 50% lower (
p
< 0.05) in insects that fed on the transgenic line Bt-22.5, when compared to non-transgenic controls. The transgenic line did not affect the virus transmission ability of the insects. Moreover, no effect was observed on the reproduction of non-target organisms, such as the black aphid
Aphis craccivora
, the leafminer
Liriomyza
sp. and the whitefly parasitoid
Encarsia formosa
. The results presented here serve as a basis for the development of whitefly-tolerant transgenic elite common bean cultivars, with potential to contribute to the management of the whitefly and virus diseases.
Tritrophic interactions mediated by semiochemicals have been intensively studied from the viewpoint of ecological relationships with Nearctic tritrophic organisms. However, there are few studies ...involving interactions with different herbivores on the same host plant in Neotropical systems. The objective of the current study was to investigate the effects of herbivory by two species of stink bugs (Heteroptera: Pentatomidae) with the same feeding habit – Tibraca limbativentris Stål and Glyphepomis spinosa Campos & Grazia – on indirect and direct defence strategies of rice plants. The responses of each stink bug species (virgin and mated females) and of their main natural enemy, the egg parasitoid Telenomus podisi Ashmead (Hymenoptera: Platygastridae; mated females), to volatiles from undamaged and herbivore‐damaged rice plants were evaluated using a Y‐tube olfactometer. The results showed that rice plants responded differently to T. limbativentris or G. spinosa herbivory, enhancing the production of a different blend of volatile compounds, which reduced the attraction for conspecific stink bugs and elicited the foraging behaviour of T. podisi.
Rice plants responded differently to the herbivory damage provoked by Tibraca limbativentris or Glyphepomis spinosa (both Heteroptera: Pentatomidae), enhancing the production of different blends of volatile compounds, mainly monoterpenes and sesquiterpenes. In a Y‐tube olfactometer, the volatile blends reduced the attraction of conspecific stink bugs and stimulated the attraction of their main natural enemy, the egg parasitoid Telenomus podisi (Hymenoptera: Platygastridae).
Abstract
The stink bug Glyphepomis spinosa Campos & Grazia (Hemiptera: Pentatomidae) is a potential rice pest in Brazil. This study evaluates the interaction between silicon sources and 3 rice ...cultivars (BRS Esmeralda, Canela de Ferro, and IRGA 417) and examines how increasing silicon levels affect the stylet probing behavior of G. spinosa. The experiment was set up in a completely randomized design with a 3 × 3 factorial scheme (silicon sources: calcium silicate, potassium silicate, a control, and 3 rice cultivars). Fertilizing rice plants with Si altered the probing behavior of the stink bug G. spinosa. The cultivar interaction by Si source was significant in a few variables. This was evidenced by longer periods without ingestion, prolonged time to the first stylet probe (initial probing), and less time spent in cellular maceration. This result supports the use of electropenetrography as a tool to evaluate resistance inducers in plants.
Bioassays using an olfactometer showed that Oebalus poecilus males produce the sexual pheromone, and the chemical analysis demonstrated that this compound is zingiberenol. Two groups of isomers, each ...containing four diastereoisomers, (1RS,4RS,1′S)- and (1RS,4RS,1′R)-zingiberenol, were prepared. These diastereoisomers were not separated on a chiral GC column. Therefore, to determine the absolute configuration of the carbon 1, 4, and 1′ of zingiberenol produced by males, the following strategies were conducted. The extract containing males volatiles was submitted to dehydration microchemistry to produce zingiberene, in which the isomers are separated by chiral GC analysis, and by comparison with the natural zingiberene from ginger oil, the absolute stereochemistry of the carbons 4 and 1′ was determined to be R and S, respectively, and the carbon 1 was determined as R from the 13C NMR spectra of quercivorol. Finally, the bioassays showed that O. poecilus females responded to racemic mixture and to (1RS,4RS,1′S)-zingiberenol.
ABSTRACT The fall armyworm, Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae), is an important rice pest which consumes leaf area during all phases of plant development. The objective of ...this study was to identify rice genotypes that provide antixenosis and antibiosis to fall armyworm. Antixenosis was investigated by measuring non-preference in free-choice and no-choice tests while antibiosis was determined by measuring biological parameters and nutritional indices of S. frugiperda in twelve rice genotypes. The genotype Miúdo Branco showed antixenosis to S. frugiperda, whereas the genotypes IR 64 and Bacaba Branco showed antibiosis to S. frugiperda by affecting insect development and prolonging insect life cycle. Insects that fed on Bacaba Branco genotype demonstrated the lowest nutritional indices. Since Miúdo Branco, IR 64 and Bacaba Branco showed moderate resistance, rice producers could use these genotypes as part of a control strategy for S. frugiperda.
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•Adults of Tibraca limbativentris are more susceptible to thiamethoxam than to lambda-cyhalothrin.•T. Limbativentris exhibited a natural resistance to Metarhizium anisopliae.•Subdoses ...of chemical insecticides enhanced susceptibility of T. limbativentris to M. anisopliae.
This study investigated the interaction of the fungus Metarhizium anisopliae (Metsch.) Sorok. with sublethal doses of synthetic chemical insecticides thiamethoxam and lambda-cyhalothrin for the control of Tibraca limbativentris adults under laboratory and field conditions. Median lethal time (LT50) was reduced significantly when M. anisopliae (5×106–5×108 conidia/mL) was combined with a sublethal dose (0.77ppm AI) of thiamethoxam compared with fungus only. A similar response on host mortality was observed for M. anisopliae at 5×107 conidia/mL in combination with sublethal dose of lambda-cyhalothrin at 9.33ppm (AI). Additionally, the thiamethoxam-fungus combination increased overall mortality and percent mycosed insects in comparison to their counterparts alone. Increasing fungus concentration did not increase insect susceptibility when combined with thiamethoxam either at 0.77 or 0.38ppm (AI). In a field experiment, the combination of M. anisopliae at 1×1012 viable conidia/ha with thiamethoxam at 12.5g (AI)/ha (¼ full dose) synergistically increased mortality and mycosis of adults of T. limbativentris. Therefore, enhanced T. limbativentris control could potentially be achieved within label rates of fungus (5×106 conidia/mL) and sublethal thiamethoxam (0.77ppm). The strategy of using sublethal doses of chemical insecticides in combination with entomopathogenic fungi is a promising approach to battle the rice stalk stink bug in rice fields.
The development of the stink bug Cyptocephala alvarengai Rolston (Hemiptera: Pentatomidae) was studied on rice panicles under laboratory conditions. Adults were collected in rice fields in Goianira, ...Goiás, Brazil. The number of eggs per egg mass ranged from 6 to 20, with a mean of 11.8 ± 0.8. The egg to adult developmental time was 33.2 d. Adult longevity ranged from 16 to 46 d. The pre-oviposition, oviposition, and post-oviposition periods were 7.0, 22.3, and 6.3 d, respectively. Fertility was 82.3%. Cyptocephala alvarengai presents biological similarities to other stink bugs that feed on rice panicles, and has potential as a rice pest.
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 stem bug, Tibraca limbativentris Stal (Hem.: Pentatomidae), is one of the main insect pests in Brazilian rice crops. Knowledge of its spatiotemporal distribution can support the development ...of an effective sampling system and improve IPM strategies. This study aimed to map the spatiotemporal distribution of rice stem bug in flooded rice crop in Southern Brazil. Flooded rice crop was scouted for two seasons to estimate insect densities. Four occurrence categories were observed: no insect, only adults, only nymphs, and both phases. The relationship between phenological stages and insect categories was established. Interpolation (mapping) of occurrence categories of T. limbativentris was performed by multiquadric equations. In two seasons during the rice cycle, the results indicate that rice stem bug “adults” were the most abundant category until the mid-vegetative phase of the rice; “nymphs” were the most abundant from the end of vegetative phase; “adults+nymphs” occurred from the beginning of reproductive phase; there were no rice stem bugs in more than 66% of the area, as they were most concentrated near the edge of the crop. The information presented here provides further knowledge about T. limbativentris spatiotemporal dynamics that can be applied to improve IPM strategies, such as developing sampling plans and localized control measures at the edge of rice fields.
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