Direct and indirect effects of planning density, nitrogenous fertilizer and host plant resistance on rice herbivores and their natural enemies

In rice ecosystems, seeding densities can be adjusted to compensate for lower nitrogen levels that reduce GHG emissions, or to increase farm profitability. However, density-induced changes to plant anatomy could affect herbivore-rice interactions, and alter arthropod community dynamics. We conducted an experiment that varied transplanting density (low or high), nitrogenous fertilizer (0, 60 or 150 kg added ha−1) and rice variety (resistant or susceptible to phloem-feeding insects) over two rice-growing seasons. Yields per plot increased with added nitrogen, but were not affected by variety or transplanting density. Planthopper and leafhopper densities were lower on resistant rice and in high-density field plots. Nitrogen was associated with higher densities of planthoppers, but lower densities of leafhoppers per plot. High planting densities and high nitrogen also increased rodent damage. The structure of arthropod herbivore communities was largely determined by season and transplanting density. Furthermore, two abundant planthoppers (Sogatella furcifera (Horváth) and Nilaparvata lugens (Stål)) segregated to low and high-density plots, respectively. The structure of decomposer communities was determined by season and fertilizer regime; total decomposer abundance increased in high-nitrogen plots during the dry season. Predator community structure was determined by season and total prey abundance (including decomposers) with several spider species dominating in plots with high prey abundance during the wet season. Our results indicate how rice plasticity and arthropod biodiversity promote stability and resilience in rice ecosystems. We recommend that conservation biological control, which includes a reduction or elimination of insecticides, could be promoted to attain sustainable rice production systems.info:eu-repo/semantics/publishedVersio

Brown planthopper (Nilaparvata lugens Stal.) (Delphaciedae: family) adaptation to rice resistance genes

Hoy día el Brown Planthopper (BPH), Nilaparvata lugens Stål, se ha convertido en una seria amenaza para la producción de arroz asiática. Recientemente, se han identificado 30 genes de resistencia en contra del BPH, sin embargo, únicamente se introdujeron 3 de ellos en las variedades de arroz de IRRI (International Rice Research Institute). Los genes bph1 y bph2 son actualmente ineficientes contra el BPH, pero bph3 es todavía eficaz en Filipinas. En el presente estudio, se determinó los efectos de la adaptación a IR62 (con el gen bph3), de variedades de arroz creadas por IRRI, de la variedad donante de la resistencia (Rathu Heenati) y de diferentes variedades de arroz con otros genes de resistencia (bph4, bph20 (t)) que al igual que el gen bph3, están situados en el cromosoma 6 del arroz. La colonia no adaptada que se utilizó en los bioensayos como test de melaza, supervivencia de las ninfas y desarrollo de las poblaciones de BPH, se vio reducida en IR62 comparando con la variedad susceptible TN1. Sin embargo, la aplicación de nitrógeno incremento la susceptibilidad de IR62. Después de 13 generaciones, las colonias se criaron en la variedad IR62 y se obtuvieron una tasa de alimentación y supervivencia similar en ambas variedades (IR62 y TN1) e incluso en las variedades relativas (IR60, IR66, IR68, IR70, IR72 y IR74). Las tasas fueron más rápidas en colonias adaptadas. Además, la tasa de alimentación y desarrollo de la colonia IR62 adaptada, eran significativamente mayores en las variedades de arroz, Babawee (bph4) y BPH20 (Bph20(t)). Aunque Rathu Heenati y PTB33 continuaban siendo resistentes en contra de la colonia IR62, el resultado se vio comprometido por la adaptación. Estos resultados indican que la adaptación de las variedades con el gen de resistencia bph3 puede conducir a la virulencia en contra de variedades con el mismo gen e incluso, contra variedades con diferentes genes pero que podrían estar relacionados. Las implicaciones de estos resultados discuten las estrategias actuales de manejo de resistencias.The Brown Planthopper (BPH), Nilaparvata lugens Stål, has re-emerged as a serious threat to rice production in Asia. Currently some 30 resistance genes have been identified and proposed for resistance breeding against BPH. However, to date only three resistance genes have been incorporated into IRRI (International Rice Research Institute) rice varieties. Two of these, bph1 and bph2, are now ineffective against BPH at a regional scale and the third, bph3, is still effective in the Philippines. In the present study, we determined the effects of adaptation to IR62 (containing the bph3 gene) on resistance of, related IRRI rice varieties, the resistance-donor variety (Rathu Heenati) and differential varieties with resistance genes (bph4, bph20 (t)) that are located on the same rice chromosome 6 at bph3 gene. The non-adapted colonies that were used in the honeydew test, nymphal survival and population build up test, were reduced on IR62 compared to the susceptible standard TN1. However, nitrogen application increased the susceptibility of IR62. After 13 generations without introgression of wild caught individuals, BPH reared on IR62 had similar feeding rates and survival on both IR62 and TN1, and on related varieties (IR60, IR66, IR68, IR70, IR72 and IR74). Rates were generally faster than for non-adapted BPH. Furthermore, feeding and development rates on Babawee (bph4) and BPH20 (Bph20(t)) were also significantly higher for IR62- adapted BPH. Although Rathu Heenati and PTB33 remained relatively resistance against IR62-adapted BPH, resistance was compromised by adaptation. These results indicate that adaptation to varieties with bph3 resistance gene can lead to virulence against varieties with the same gene, as well as virulence against varieties with different, but possibly related genes. The implications of these results are discussed the current strategies for resistance management.Ingeniería AgronómicaNekazaritza Ingeniaritz

Ervi.morphoj

Data for the scientific article of "Morphological variation of <i>Aphidius ervi</i> Haliday (Hymenoptera: Braconidae) associated with different aphid hosts"

Interactions between Rice Resistance to Planthoppers and Honeydew-Related Egg Parasitism under Varying Levels of Nitrogenous Fertilizer

International audienceHost plant resistance is the most researched method for the management of planthoppers and leafhoppers in tropical rice. For optimal effects, resistance should be resilient to fertilizer inputs and work in synergy with natural enemies. In field plot experiments, we examined how rice resistance and fertilizer inputs affect mortality of planthopper and leafhopper eggs by hymenopteran parasitoids. We used IR62 as a variety with resistance to Nilaparvata lugens (Stål) [BPH], Sogatella furcifera (Horváth) [WBPH] and Nephotettix virescens (Distant) [GLH], and IR64 as a susceptible control. The herbivores were more abundant during wet season sampling in low-nitrogen plots. During this study, parasitoids killed between 31 and 38% of BPH eggs and 24 and 52% of WBPH eggs during four days of field exposure. Parasitism, mainly due to Oligosita spp., was generally higher in high-nitrogen and IR64 plots. Similar densities of eggs in exposed plants suggest that these trends were mediated by semiochemicals and therefore support the Optimal Defense Hypothesis. Honeydew from BPH on IR62 had more xylem-derived wastes than honeydew on IR64. We applied honeydew from both varieties to sentinel plants. Parasitism by Anagrus spp. was higher on plants of either variety treated with honeydew derived from IR62; however, the effect was only apparent in high-nitrogen plots. Results suggest that Anagrus spp., by responding to honeydew, will counter the nitrogen-induced enhancement of planthopper fitness on resistant rice

Compatibility of Insecticides with Rice Resistance to Planthoppers as Influenced by the Timing and Frequency of Applications

International audienceThe brown planthopper, Nilaparvata lugens (Stål)(BPH) is a pest of rice in Asia. We examined the effects of seven insecticides combined with host resistance against BPH. In a screenhouse environment, we treated BPH-infested and non-infested resistant (IR62) and susceptible (IR64) rice with buprofezin, carbofuran, cartap hydrochloride, cypermethrin, deltamethrin, fipronil, or thiamethoxam + chlorantraniliprole. In one experiment, plants received one, two or three applications. In a second experiment, plants received one early or late insecticide application. Carbofuran and fipronil reduced planthopper biomass densities but resistance did not contribute to these effects (i.e., resistance was redundant). Single applications of cartap hydrochloride (at 20 or 50 days after sowing (DAS)), cypermethrin (20 DAS), or buprofezin (50 DAS) reduced BPH biomass densities on IR62 (i.e., synergies); other insecticides and application times, and multiple applications of all insecticides did not reduce BPH biomass densities on IR62 more than on IR64 (i.e., either resistance or insecticides were redundant). Deltamethrin (three applications) was antagonistic to resistance, but host resistance tended to buffer against the negative effects of single deltamethrin applications. Yields of infested IR62 were not statistically improved by insecticide applications. Late applications reduced yields of non-infested rice. We discuss how prophylactic insecticide applications could destabilize BPH populations and reduce the productivity and profitability of resistant rice

The Host-Plant Origin Affects the Morphological Traits and the Reproductive Behavior of the Aphid Parasitoid Aphelinus mali

International audienceDiversifying agroecosystems through habitat management inside or outside production fields can provide alternative hosts and/or prey for natural enemies. In semi-natural habitats, parasitoids may find alternative host-plant complexes (HPC) that could allow their development when pest hosts are scarce in the field. However, morphological and physiological differences between alternative and targeted HPCs could affect the preference and fitness of the parasitoids, possibly altering their efficacy in regulating pests. In the present study, we examined two Aphelinus mali parasitoid populations developing on Eriosoma lanigerum from two host plants (Malus domestica-apple trees and Pyracantha coccinea). We hypothesized that A. mali from both HPCs will show different life history traits and behaviors because primary and alternative host-plants are known to induce variations in parasitoid biological performance. Our findings indicate that A. mali originating from E. lanigerum on P. coccinea parasitized more aphids and are smaller than those originating from E. lanigerum on apple. Furthermore, these parasitoids did not significantly vary their ability to attack and oviposit apple E. lanigerum, suggesting that P. coccinea could function as a suitable banker plant for A. mali. We discuss the potential use of P. coccinea in conservation biological control of E. lanigerum in apple orchards

Honeydew Is a Food Source and a Contact Kairomone for Aphelinus mali

International audienceMany parasitoids need to feed on sugar sources at the adult stage. Although nectar has been proven to be a source of higher nutritional quality compared to honeydew excreted by phloem feeders, the latter can provide the necessary carbohydrates for parasitoids and increase their longevity, fecundity and host searching time. Honeydew is not only a trophic resource for parasitoids, but it can also constitute an olfactory stimulus involved in host searching. In this study, we combined longevity measurements in the laboratory, olfactometry and feeding history inference of individuals caught in the field to test the hypothesis that honeydew excreted by the aphid Eriosoma lanigerum could serve as a trophic resource for its parasitoid Aphelinus mali as well as a kairomone used by the parasitoid to discover its hosts. Results indicate that honeydew increased longevity of A. mali females if water was provided. Water could be necessary to feed on this food source because of its viscosity and its coating by wax. The presence of honeydew allowed longer stinging events by A. mali on E. lanigerum. However, no preference towards honeydew was observed, when given the choice. The role of honeydew excreted by E. lanigerum on A. mali feeding and searching behavior to increase its efficiency as a biological control agent is discussed. © 2023 by the authors

Aspects of brown planthopper adaptation to resistant rice varieties with the Bph3 gene

Despite over 30 years of deployment, varieties with the Bph3 gene for resistance to the brown planthopper (BPH), Nilaparvata lugens (Stål) (Hemiptera: Delphacidae), are still effective in much of the Philippines. In the present study, we determined the effects of adaptation to one resistant variety, IR62 – assumed to possess the Bph3 gene – on (1) resistance against a series of varieties with similar biotypical responses (presumed to contain the same major resistance genes), and (2) a differential variety with the bph4 gene that occurs at the same chromosome position as Bph3. We also examined the effects of high soil nitrogen on the effectiveness of Bph3. Feeding, planthopper biomass, and development times were reduced in a wild BPH population when reared on IR62 compared with the susceptible standard variety TN1. However, nitrogen application increased the susceptibility of IR62. After 13 generations on IR62, BPH had adapted to the plant’s resistance. Virulence of the adapted BPH against the variety ‘Rathu Heenati’ supports the idea that Bph3 is present in IR62. Across similar IR varieties (IR60, IR66, IR68, IR70, IR72, and IR74), feeding, planthopper biomass, and development rates were generally higher for IR62-adapted than for non-adapted BPH; however, contrary to expectations, many of these varieties were already susceptible to wild BPH. Fitness was also higher for IR62-adapted BPH on the variety ‘Babawee’ indicating a close relation between Bph3 and bph4. The results indicate that the conventional understanding of the genetics behind resistance in IR varieties needs to be readdressed to develop and improve deployment strategies for resistance management