BUSCADOR RECOLECTA

Hyposoter didymator (Thunberg) (Hymenoptera: Ichneumonidae) and baculovirus (BV) might be used jointly to provide effective control of the Spodoptera genus. The literature has mostly covered the safe compatibility between natural enemies and BV-based insecticides, but research on the potential dispersal of BV by natural enemies is lacking. Thus, the goal of this manuscript was to ascertain if H. didymator was able to disperse the broad host range of Autographa californica nucleopolyhedrovirus (AcMNPV) to Spodoptera littoralis and Spodoptera exigua in choice and non-choice conditions and whether the preference of the parasitoid by one of these noctuids could mediate this dispersion. It was previously needed to improve the rearing of the parasitoid in the laboratory, concerning the optimal host age and length of parasitization, parasitoid competition, and influence of parasitization on the longevity of females. The best rearing conditions for S. littoralis are collective parasitization of mature L3 larvae for 24 h, after at least one day of copulation. Hyposoter didymator transmits AcMNPV to both lepidopterans, but its efficiency is mediated by host preference and the pathogenicity of the BV in each host. In this particular case, H. didymator as well as AcMNPV showed a clear preference towards S. exigua., This research was funded by MCIN/AEI/10.13039/501100011033, grants AGL2017-83498-C2-2-R, PID2020-117062RB-C22 and IJC2018-035042-I, and by Ministerio de Hacienda de Paraguay/Programa nacional de becas de postgrado en el exterior D. Carlos Antonio López, grant 01/2019.

Background: Alphabaculoviruses are Lepidoptera-specific virulent pathogens that infect numerous pests, including the Spodoptera complex. Due to their low environmental persistence, the traditional use of Alphabaculoviruses as bioinsecticides consist in high-rate spray applications with repeated treatments. Several abiotic and biotic factors can foster its dispersion,
promoting their persistence in the agroecosystem. Amongst biotic factors, predatory arthropods can disperse the viruses by
excretion after preying on infected individuals. Therefore, this study focused on promoting predator's ingestion of nucleopolyhedrovirus (NPV)-treated diets, and the later exposition of the insect host to leaf surfaces contaminated with predator
excreta. The virus–host–predator system studied was Spodoptera littoralis nucleopolyhedrovirus (SpliNPV), Spodoptera littoralis (Boisduval) and Nesidiocoris tenuis (Reuter). The infective potential of N. tenuis feces and the retention time of SpliNPV were
assessed under laboratory conditions after feeding on treated diets (sucrose solution and Ephestia kuehniella eggs).
Results: Mortality of S. littoralis larvae was lower via N. tenuis excretion than in positive control (spray application) in the first
infection cycle, together with a delay in host death. In the second infection cycle, both SpliNPV-treated diets triggered 100%
mortality. Both diets allowed the transmission of SpliNPV, with a faster excretion via sucrose solution compared to
E. kuehniella eggs. SpliNPV remained in N. tenuis digestive tract and was viable after excretion at least for 9 days for both diets.
Conclusions: This study demonstrated the potential of the predator N. tenuis as inoculative agent of baculoviruses, representing a new alternative that, along with inundative applications, might contribute to improve pest management strategies., This study was funded by the Spanish Ministry of Science and Innovation through the State Research Agency with the projects entitled: AGL2017-83498-C2-2-RB ‘Development of effective baculovirus-based insecticides with a broad spectrum of hosts and advances towards its integration in IPM programs’ and PID2020-117062RB-C22 ‘Exploiting entomophagous insects to enhance the control of Spodoptera spp through the use of baculovirus’. OG Gutiérrez-Cárdenas acknowledges the Government of Mexico and the National Council of Humanities, Science and Technology (CONAHCYT) for the PhD research grant number 717840-2018.

We are currently facing a world in constant and rapid change, largely caused by anthropogenic activities. A sustainable agriculture should be achieved in order to contribute simultaneously to eradicate hunger and to stabilize the global climate. Climate change effects can alter pest and disease pressure, undermine biological control and therefore, impact food security. Thus, it is critical to investigate the compatibility of new environmentally friendly strategies in plant protection, such as the use of activators of plant defences, with biocontrol strategies, and subsequently, their combined effects on integrated pest management (IPM) programs. Furthermore, it is necessary to understand how climate change affects multitrophic interactions in order to be prepared for the future challenges in agriculture. Therefore, this thesis aims to face two main questions. Firstly, if it is compatible the use of plant activators with the biological control of aphids, as important agricultural pests. Secondly, how climate change could impact multitrophic interactions involved in biological control. The salicylic acid analogue BTH (benzo-(1,2,3)-thiadiazole-7-carbothioic-acid S-methyl ester) was chosen to be evaluated in this thesis because it induces systemic acquired resistance by promoting plant resistance against numerous plant pathogens and some insect pests. Specifically, we assessed the activation of plant defences by BTH on melon (Cucumis melo L., Cucurbitaceae) and its effects on the herbivore Aphis gossypii Glover (Hemiptera: Aphididae) and on its predator Chrysoperla carnea (Stephens) (Neuroptera: Chrysopidae). Under laboratory conditions, plants were sprayed with BTH (50 g/ha) zero (B0), four (B4), and seven (B7) days prior exposure to insects. B0 treatment resulted in 100 % mortality of aphid nymphs and disrupted adult feeding behaviour (recorded by electrical-penetration-graphs technique), by prolonging the time to reach the phloem, requiring more probes to first salivation and reducing ingestion activities. There were no effects on feeding behaviour of A. gossypii fed on B4 plants but on its life history because fewer nymphs were born, intrinsic rate of natural growth decreased and mortality increased. There were no effects on biological parameters of aphids reared on B7 plants. Prey consumption by C. carnea larvae when predated A. gossypii fed on BTH-treated plants was not different among treatments. Therefore, BTH enhances the suppression of A. gossypii in the short term, without negative effects on the predatory larva C. carnea, which makes this plant activator a useful tool to be considered in IPM programs. The herbivore-induced plant volatiles (HIPVs) are released when a plant is damaged by any herbivore, and have an important role in tritrophic interactions and plant-plant communication. Application of exogenous chemical elicitors could induce plant defence and be partially analogous to HIPVs. However, there is a lack of information about the effect of BTH on volatiles emission and its possible attractiveness to aphid parasitoids. In this sense, the second line of research of the thesis aimed to evaluate the blend of volatiles emitted by melon treated with BTH at different periods. Volatiles were collected via dynamic headspace technique and further analysed by gas chromatography mass spectrometry. The electroantennogram technique was used to evaluate the physiological response of the parasitoid Aphidius colemani Vierick (Hymenoptera: Braconidae) to some selected volatiles. Hydrocarbons were the majority compounds emitted by BTH-treated and control plants (unsprayed). Independently of the application time, BTH-treated melon plants did not emit green leaf volatiles, important compounds in herbivore defence by attracting natural enemies; but emit nonanal, which is related to the expression of resistance genes. Within another important group of HIPVs, limonene was the unique terpene emitted by BTH-treated plants (four and seven days before volatiles extraction). Neither females nor males of A. colemani had a positive response to the individual volatiles tested or those from a BTH-treated plant. Further research should be needed to conclude if HIPVs induction by BTH could be an interesting mean to enhance biocontrol in the trophic system studied. Elevated carbon dioxide (eCO2) concentration directly affects plant growth, physiology and biochemistry, indirectly influencing herbivore insects due to changes in its nutritional requirements, and likewise, higher trophic levels. Not many studies have analysed the impact of climate change on plant-insect interactions in horticultural crops. Therefore, the third line of research in this thesis was focused to examine the effect of eCO2 on the individual fitness of A. gossypii and on the performance of its parasitoid A. colemani, both reared for two successive generations on melon plants, previous acclimated during two or six weeks to different CO2 levels, eCO2 (700 ppm) or ambient CO2 (400 ppm). Under eCO2, melon plants decreased nitrogen foliar concentration and increased carbon to nitrogen ratio (C:N), independently of acclimation period, significantly reducing the content of some amino acids (alanine, asparagine, glycine, isoleucine, lysine, serine, threonine, and valine) and increasing the carbohydrate (sucrose) content in melon leaves. The dilution in some essential amino acids for aphid nutrition could have reduced A. gossypii body mass and negatively impaired aphid individual fitness, prolonging its development time and decreasing its fecundity, negatively affecting the intrinsic rate of natural increase of two successive generations of A. gossypii grown under eCO2. Furthermore, eCO2 also reduced A. gossypii population growth reared on melon previously acclimated two weeks to eCO2. There was lower proportion of parasitoids emergence (i.e. pupal survivorship) in first generation A. colemani grown under eCO2. However, parasitism rate, emergence percentages by sex and the overall development time, remained unchanged due to the effect of eCO2 for the two generations of A. colemani. Our research suggests that the effects of eCO2 on the tritrophic interaction studied could reduce herbivore infestation by decreasing its growth rate. Despite the parasitism efficiency is maintained, in the long term A. colemani will not easily find A. gossypii for parasitism and their populations could be compromised, although less than other parasitoids with greater host specificity. The effects of climate change on trophic systems could be intensified, modified or even mitigated because of the interrelation of different climate change factors, and the impact of the combination could be different to the impact of the abiotic factors analysed separately. Thus, the combination of climate and atmospheric variables is the better approach to predict how multitrophic systems will respond in the future: (1) to better understand the effects of climate change on pathosystems and on insect vector-borne diseases dynamics, (2) to ascertain the impacts of climate change on the ecosystem service of insect pest control by natural enemies and subsequently, (3) to improve biological control programs as part of IPM in agricultural crops. However, studies evaluating the potential impacts of combined abiotic stresses, such as elevated CO2 and temperature, on the interactions among natural enemies, vectors, diseases and crops, are limited. Therefore, the fourth line of research in the thesis was to investigate the effects of the simultaneous increase in CO2 and temperature on the performance of the parasitoid A. colemani when its aphid host Rhopalosiphum padi L. (Hemiptera: Aphididae) was grown on non-infected or Barley yellow dwarf virus species PAV (BYDV-PAV)-infected wheat (Triticum aestivum L., Poaceae). Using controlled environment chambers, plant parameters, aphid individual fitness and parasitoid performance were examined under two scenarios, current (ambient CO2 and temperature = 400 ppm and 20 °C), and future predicted (elevated CO2 and temperature (+2°C) = 800 ppm and 22 °C). Combined elevated CO2 and temperature increased plant growth, biomass, and C:N ratio, which in turn significantly decreased aphid fecundity and development time. However, virus infection reduced chlorophyll content, biomass, wheat growth and C:N ratio, significantly increased R. padi fecundity and development time. Regardless of virus infection, aphid growth rates remained unchanged under simulated future conditions. Therefore, as R. padi is currently a principal pest in temperate cereal crops worldwide, mainly due to its role as a plant virus vector, it will likely continue to have significant economic importance. Development time from oviposition to adult emergence of A. colemani significantly decreased under elevated CO2 and temperature, on virus-infected and non-infected plants. However, parasitism rate, sex ratio and pupal survivorship remained unchanged under future predicted conditions, regardless of BYDV-PAV infection. Therefore, we incline to suggest that the biocontrol of R. padi by A. colemani will continue being effective in a future climate with similar conditions as studied here. Furthermore, an earlier and more distinct virus symptomatology was highlighted under the future predicted scenario, with consequences on virus transmission, disease epidemiology and, thus, wheat yield and quality. This study provides empirical data on a particular tritrophic system (plant-pest-parasitoid) affected by plant virus and simultaneous increase in CO2 and temperature, essential to complement scientific knowledge about the impact of climate change on complex interactions of agro-ecosystems. ----------RESUMEN---------- En la actualidad el mundo se enfrenta a un constante y rápido cambio, en gran parte provocado por las actividades antropogénicas. Lograr una agricultura sostenible es fundamental para contribuir a erradicar el hambre a la vez que estabilizar el clima global. Los efectos del cambio climático pueden alterar la presión ejercida por las plagas y enfermedades en agricultura, socavar el control biológico y, por consiguiente, afectar la seguridad alimentaria. Por lo tanto, es fundamental investigar la compatibilidad de estrategias de control biológico con nuevas estrategias de protección vegetal, como por ejemplo el uso de activadores de defensas de las plantas, en los programas de manejo integrado de plagas (MIP). Además, es necesario comprender cómo el cambio climático afecta a las interacciones entre los distintos niveles tróficos, con el fin de estar preparados para los desafíos a los que se enfrentará la agricultura. Por tanto, esta tesis pretende afrontar dos cuestiones principales. En primer lugar, si es compatible el uso de activadores de plantas con el control biológico de plagas agrícolas. En segundo lugar, cómo el cambio climático puede afectar a las interacciones entre los distintos niveles tróficos involucrados en el control biológico. El compuesto análogo del ácido salicílico BTH (benzo[1,2,3]tiadiazol-7-carbotioato de S-metilo) fue elegido para ser evaluado en esta tesis por su papel como inductor de resistencia sistémica adquirida que activa las defensas de las plantas contra numerosos patógenos vegetales y algunas plagas de insectos. En concreto, se examinó la activación de las defensas vegetales por BTH en melón (Cucumis melo L., Cucurbitaceae) y sus efectos sobre el herbívoro Aphis gossypii Glover (Hemiptera: Aphididae) y sobre su depredador Chrysoperla carnea (Stephens) (Neuroptera: Chrysopidae). En condiciones de laboratorio, se pulverizaron las plantas con BTH (50 g/ha) cero (B0), cuatro (B4) y siete (B7) días antes del contacto con los insectos. El tratamiento B0 resultó en una mortalidad del 100% de las ninfas de pulgón y dificultó el comportamiento de alimentación de los adultos registrado mediante la técnica de gráficos de penetración eléctrica, al prolongar el tiempo para alcanzar el floema, requiriendo mayor número de pruebas hasta la primera salivación y reduciendo las actividades de ingestión. No hubo efectos sobre el comportamiento alimentario de A. gossypii en plantas B4, pero en este tratamiento se redujo la fecundidad, la tasa intrínseca de crecimiento natural disminuyó y la mortalidad aumentó. No hubo efectos sobre los parámetros biológicos de los pulgones criados en plantas B7. El consumo de presas por las larvas de C. carnea cuando depredaron pulgones que se habían alimentado con plantas tratadas con BTH no difirió entre tratamientos. Por tanto, el BTH potenció la supresión de A. gossypii a corto plazo, sin tener efectos negativos sobre la larva depredadora de C. carnea, lo que convierte a este activador de las defensas de las plantas en una herramienta útil a considerar en los programas de MIP. Los volátiles de plantas inducidos por herbívoros (HIPVs, por sus siglas en inglés) se liberan cuando una planta es atacada por cualquier herbívoro y tienen un papel importante en las interacciones tritróficas y la comunicación planta-planta. La aplicación de elicitores químicos exógenos podría inducir las defensas de las plantas y actuar de manera análoga a los HIPVs. Sin embargo, apenas existe información sobre el efecto del elicitor BTH sobre la emisión de volátiles en melón y su posible atracción para parasitoides de pulgones. En este sentido, la segunda línea de investigación de la tesis tuvo como objetivo evaluar la mezcla de volátiles emitidos por melón tratado con BTH a diferentes períodos. Los volátiles se recogieron mediante la técnica de espacio de cabeza dinámico y se analizaron posteriormente mediante espectrometría de masas acoplada a cromatografía de gases. Se utilizó la técnica del electroantenograma para evaluar la respuesta fisiológica del parasitoide Aphidius colemani Vierick (Hymenoptera: Braconidae) a algunos volátiles. Los hidrocarburos fueron los compuestos mayoritarios emitidos por las plantas tratadas con BTH y las plantas control (sin pulverizar). Independientemente del tiempo de aplicación, las plantas de melón tratadas con BTH no emitieron volátiles de hojas verdes, compuestos importantes en la defensa contra herbívoros al atraer enemigos naturales; pero emitieron nonanal, aldehído relacionado con la expresión de genes de resistencia. Dentro de otro grupo importante de HIPVs, el limoneno fue el único terpeno emitido por las plantas tratadas con BTH (cuatro y siete días antes de la extracción de volátiles). Ni las hembras ni los machos de A. colemani tuvieron una respuesta positiva a los volátiles individuales analizados, ni a la mezcla emitida por una planta tratada con BTH. Es necesario realizar más investigaciones para poder concluir si la inducción de HIPVs por BTH podría ser una herramienta interesante para mejorar el control biológico en el sistema trófico estudiado. Los niveles elevados de dióxido de carbono (eCO2) atmosférico afectan directamente el crecimiento, la fisiología y la bioquímica de las plantas, influyendo indirectamente en los insectos herbívoros debido a los cambios en sus requerimientos nutricionales y, del mismo modo, en los niveles tróficos superiores. No se han realizado muchos estudios sobre el impacto del cambio climático en las interacciones planta-insecto en cultivos hortícolas. Por tanto, la tercera línea de investigación de la tesis se centró en examinar el efecto del eCO2 sobre la eficacia biológica de A. gossypii y sobre el comportamiento de su parasitoide A. colemani, ambos desarrollados durante dos generaciones sucesivas en plantas de melón previamente aclimatadas durante dos o seis semanas a diferentes concentraciones de CO2, eCO2 (700 ppm) o CO2 ambiental (400 ppm). Bajo eCO2, las plantas de melón disminuyeron la concentración foliar de nitrógeno y aumentaron la relación carbono/nitrógeno (C/N), independientemente del período de aclimatación, reduciendo significativamente el contenido de algunos aminoácidos (alanina, asparagina, glicina, isoleucina, lisina, serina, treonina y valina) y aumentando el contenido de carbohidratos (sacarosa) en las hojas de melón. La dilución de algunos aminoácidos esenciales para la nutrición de los pulgones podría ser la causa de la reducción de la masa corporal de A. gossypii y el impacto negativo en la eficacia biológica del pulgón, prolongando su tiempo de desarrollo y disminuyendo su fecundidad, afectando negativamente a la tasa intrínseca de incremento natural de las dos generaciones sucesivas de A. gossypii desarrolladas bajo eCO2. Además, el eCO2 también redujo el crecimiento de la población de A. gossypii desarrollada en melón previamente aclimatado dos semanas a eCO2. También se redujo la proporción de emergencia de parasitoides (es decir, la supervivencia de pupas) en la primera generación de A. colemani desarrollada bajo eCO2. Sin embargo, la tasa de parasitismo, los porcentajes de emergencia por sexo y el tiempo de desarrollo general, permanecieron sin cambios debido al efecto de eCO2 para las dos generaciones de A. colemani. Nuestra investigación sugiere que los efectos del eCO2 en la interacción tritrófica estudiada podrían reducir la infestación del pulgón al disminuir su tasa de crecimiento. En el caso del parasitoide, a pesar de que se mantiene la eficacia del parasitismo, puede que a largo plazo A. colemani no encuentre fácilmente A. gossypii para parasitar y sus poblaciones podrían verse comprometidas, aunque menos que las de otros parasitoides con mayor especificidad. Los efectos del cambio climático en los sistemas tróficos podrían intensificarse, modificarse o incluso mitigarse debido a la interrelación de los diferentes factores involucrados en el cambio climático, y el impacto de la combinación podría ser diferente al impacto de los factores abióticos analizados por separado. Por consiguiente, la combinación de distintas variables climáticas es el mejor enfoque para predecir cómo responderán los sistemas tróficos en el futuro: (1) para comprender mejor los efectos del cambio climático en los patosistemas y en la dinámica de las enfermedades transmitidas por insectos vectores, (2) para determinar los impactos del cambio climático sobre el servicio ecosistémico del control de plagas de insectos por parte de enemigos naturales y, posteriormente, (3) para mejorar los programas de control biológico como parte del MIP en cultivos agrícolas. Sin embargo, los estudios que evalúan los impactos potenciales de factores abióticos combinados, como el incremento de los niveles de CO2 y temperatura, sobre las interacciones entre enemigos naturales, vectores, enfermedades y cultivos, son limitados. Por lo tanto, la cuarta línea de investigación de la tesis fue investigar los efectos del aumento simultáneo de CO2 y temperatura sobre el desempeño del parasitoide A. colemani cuando su pulgón huésped Rhopalosiphum padi L. (Hemiptera: Aphididae) se desarrolló en plantas de trigo (Triticum aestivum L., Poaceae) infectadas o no con el virus del enanismo amarillo de la cebada, especie PAV (BYDV-PAV). Utilizando cámaras climáticas, se examinaron diferentes parámetros de la planta y la eficacia biológica de los pulgones y de los parasitoides en dos escenarios climáticos, el actual (condiciones ambientales de CO2 y temperatura = 400 ppm y 20 °C) y uno de los previstos para el futuro (condiciones elevadas de CO2 y temperatura (+2°C) = 800 ppm y 22 °C). La combinación de condiciones elevadas de CO2 y temperatura aumentó el crecimiento de las plantas, la biomasa y la relación C/N, lo que a su vez disminuyó significativamente la fecundidad de los pulgones y su tiempo de desarrollo. Sin embargo, la infección por virus redujo el contenido de clorofila, la biomasa, el crecimiento y la relación C/N en el trigo, y aumentó significativamente la fecundidad y el tiempo de desarrollo de R. padi. Independientemente de la infección por virus, las tasas de crecimiento de pulgones se mantuvieron sin cambios en las condiciones futuras simuladas. Por lo tanto, dado que R. padi es actualmente una importante plaga en los cultivos cerealistas de zonas templadas en todo el mundo, principalmente debido a su función como vector de virus vegetales, es probable que continúe teniendo una importancia económica significativa. El tiempo de desarrollo desde la oviposición hasta la emergencia adulta de A. colemani disminuyó significativamente bajo CO2 y temperatura elevados, en plantas infectadas y no infectadas por virus. Sin embargo, la tasa de parasitismo, la proporción por sexo y la supervivencia de pupas se mantuvieron sin cambios en las condiciones futuras previstas, independientemente de la infección por BYDV-PAV. Por consiguiente, nos inclinamos a sugerir que el control biológico de R. padi por A. colemani seguirá siendo efectivo en un clima futuro con condiciones similares a las aquí estudiadas. Además, se observó una sintomatología del virus más precoz y perceptible en el escenario futuro predicho, lo cual podría tener consecuencias en la transmisión del virus, la epidemiología de la enfermedad y, finalmente, en el rendimiento y la calidad del trigo. Este estudio aporta datos empíricos sobre un sistema tritrófico particular (planta-plaga-parasitoide) afectado además por un virus vegetal, bajo el aumento simultáneo de CO2 y temperatura, fundamental para complementar el conocimiento científico sobre el impacto del cambio climático en las interacciones complejas de los agroecosistemas.

Spodoptera littoralis (Boisduval, 1833) and Spodoptera exigua (Hübner, 1808) are two noctuid pests whose marked polyphagy makes them especially harmful to agriculture in southeastern Spain, sometimes appearing individually and on other occasions in coexistence. Currently they are basically controlled by chemical control, giving rise to resistance phenomena, which is why various control strategies have been investigated and applied, including biological control.

Hyposoter didymator (Thunberg, 1822) and Chelonus inanitus (Linnaeus, 1767) are two koinobiont endoparasitoids, larval and ovolarval respectively, whose females oviposit in the host, where the larva develops and feeds on its tissues, exits the host before spinning a silk cocoon, and emerge as an adult. Both parasitoids can be used to control species of the genus Spodoptera, especially S. exigua. On the other hand, another type of biological control against noctuids is baculoviruses, entomopathogens that are marketed as microbial insecticides.

In this Thesis, we have worked with the broad-spectrum baculovirus AcMNPV-Autographa californica multiple nuclear polyhedrosis virus, and those specific to S. exigua (SeMNPV-Spodoptera exigua nuclear polyhedrosis virus) and S. littoralis (SpliMNPV-Spodoptera littoralis multiple nuclear polyhedrosis virus), with the main objective of studying, under laboratory conditions, their dispersal by the parasitoids H. didymator and C. inanitus, also analyzing their interactions.

First, the development of C. inanitus was studied, both in its natural host S. littoralis and in the alternative host Ephestia kuehniella (Zeller, 1879), with the aim of improving its breeding in the laboratory. It was observed that the longevity of C. inanitus adults was significantly shorter in the presence of eggs from each of the hosts compared to the absence of eggs. Regarding reproduction, it was shown that the reproduction of the parasitoid C. inanitus was much less efficient when raised on its natural host S. littoralis since its intrinsic growth rate turned out to be negative, which would indicate that the offspring would be lost after several generations.

Second, tests were carried out to evaluate the effect of egg age on the parasitization of C. inanitus on S. littoralis, proving that the parasitization of 48-hour-old eggs provided a higher number of females in the offspring. The effect of parasitization time on the progeny was also studied and, in this case, C. inanitus was more effective in terms of adult production by parasitizing 6 and 24 hours than at shorter times (1 and 3 hours), although no statistically significant differences were found.

Next, choice assays were performed to evaluate the ability of C. inanitus to discriminate between eggs treated or not with the specific baculoviruses of S. exigua and S. littoralis, as well as the preference between parasitizing S. exigua and S. littoralis when both species were treated with the broad-spectrum baculovirus AcMNPV. It was observed that C. inanitus preferred to attack S. exigua eggs treated with SeMNPV. However, it did not distinguish between SpliMNPV-treated or untreated eggs. No preference for any host was observed when both eggs were treated with AcMNPV.

The dispersion of the specific baculoviruses SpliMNPV and SeMNPV by C. inanitus females was also investigated, demonstrating that the parasitoid can disperse both viruses. The mortality caused by SeMNPV was much higher than that of SpliMNPV. The dispersion of baculovirus was more efficient when C. inanitus females were in contact with pepper leaves sprayed with the virus compared to eggs treated with the same virus, thus evidencing that contact is the main route of dispersion.

Finally, the parasitization preference in a S. exigua-S. littoralis multihost system and the transmission of a broad-spectrum baculovirus under these conditions were studied. Hyposoter didymator was observed to transmit AcMNPV to both lepidopterans, but its efficiency was mediated by host preference and baculovirus pathogenicity in each host. In this particular case, both H. didymator and AcMNPV showed a clear preference towards S. exigua. It was also studied whether H. didymator was capable of discriminating between S. exigua larvae infected and not infected with SeMNPV and it was shown that it equally parasitized larvae from both treatments.

RESUMEN

Spodoptera littoralis (Boisduval, 1833) y Spodoptera exigua (Hübner, 1808) son dos plagas de noctuidos cuya marcada polifagia las hace especialmente dañinas para la agricultura del sureste español, apareciendo a veces de forma individual y otras, en coexistencia. Actualmente se controlan básicamente por lucha química, dando lugar a fenómenos de resistencia, por lo que se han investigado y aplicado diversas estrategias de control, entre las que se incluye el control biológico.

Hyposoter didymator (Thunberg, 1822) y Chelonus inanitus (Linnaeus, 1767) son dos endoparasitoides koinobiontes, larvario y ovolarvario respectivamente, cuyas hembras ovipositan en el huésped, donde la larva se desarrolla y se alimenta de sus tejidos antes de tejer un capullo de seda y emerger como adulto. Ambos parasitoides pueden ser útiles para controlar especies del género Spodoptera, sobre todo S. exigua. Por otro lado, otro tipo de control biológico contra noctuidos son los baculovirus, entomopatógenos que se comercializan como insecticidas microbianos.

En la presente tesis se ha trabajado con el baculovirus de amplio espectro AcMNPV-virus de la poliedrosis nuclear de Autographa californica y los específicos de S. exigua (SeMNPV-virus de la poliedrosis nuclear de Spodoptera exigua) y S. littoralis (SpliMNPV-virus de la poliedrosis nuclear de Spodoptera littoralis), con el objetivo principal de estudiar, en condiciones de laboratorio, la dispersión de los mismos por medio de los parasitoides H. didymator y C. inanitus, analizando, además, sus interacciones.

En primer lugar, se estudió el desarrollo de C. inanitus, tanto en su huésped natural S. littoralis como en un huésped alternativo, como Ephestia kuehniella (Zeller, 1879), con la finalidad de mejorar su cría en laboratorio. Se observó que la longevidad de los adultos de C. inanitus fue significativamente más corta cuando estuvo en presencia de huevos de cada uno de los huéspedes en comparación con la ausencia de huevos. En cuanto a la reproducción, se ha demostrado que la reproducción del parasitoide C. inanitus es mucho menos eficiente cuando se cría en su huésped natural S. littoralis. ya que al calcular su tasa intrínseca de crecimiento resultó ser negativa en S. littoralis, lo cual indicaría que la cría se perdería tras varias generaciones.

En segundo lugar, se realizaron ensayos para evaluar el efecto de la edad del huevo en la parasitación de C. inanitus sobre huevos de S. littoralis, comprobándose que la parasitación de los huevos de 48 h de edad es la que proporciona un número más elevado de hembras en la descendencia. También se estudió el efecto del tiempo de parasitación sobre la progenie y, en este caso, C. inanitus es más efectivo en términos de producción de adultos parasitando 6 y 24 horas que cuando lo hace a menores tiempos (1 y 3 horas), aunque no se encontraran diferencias estadísticamente significativas.

A continuación, se realizaron ensayos de elección para evaluar la capacidad de C. inanitus de discriminar entre huevos tratados o no con los baculovirus específicos de S. exigua y S. littoralis, así como la preferencia entre parasitar S. exigua y S. littoralis cuando ambas especies han sido tratadas con el baculovirus de amplio espectro AcMNPV. Se observó que C. inanitus prefirió atacar los huevos de S. exigua tratados con SeMNPV. Sin embargo, no distinguió entre huevos tratados con SpliMNPV o no tratados y no se observó preferencia por huevos de un huésped cuando se trataron ambos plastones con AcMNPV.

También se investigó la dispersión de los baculovirus específicos SpliMNPV y SeMNPV por parte de las hembras de C. inanitus, demostrándose que el parasitoide puede dispersar ambos virus, siendo la mortalidad causada por SeMNPV mucho más elevada que la de SpliMNPV. Se comprobó que la dispersión de baculovirus fue más eficiente cuando las hembras de C. inanitus estuvieron en contacto con hojas de pimiento pulverizadas con el virus en comparación con los huevos tratados con el mismo virus, demostrándose así que el contacto es la principal via de dispersión.

Por último, se estudió la preferencia de parasitación en un sistema multihuésped S. exigua- S. littoralis y la transmisión de un baculovirus de amplio espectro en dichas condiciones. Se observó que H. didymator transmite AcMNPV a ambos lepidópteros, pero su eficiencia está mediada por la preferencia por el huésped y la patogenicidad del baculovirus en cada huésped. En este caso particular, tanto H. didymator como AcMNPV mostraron una clara preferencia hacia S. exigua. Se determinó, además, si H. didymator es capaz de discriminar entre larvas de S. exigua infectadas y no infectadas con SeMNPV y se demostró que parasita igualmente unas larvas que otras.

© 2020 by the authors., Climate change impacts crop production, pest and disease pressure, yield stability, and, therefore, food security. In order to understand how climate and atmospheric change factors affect trophic interactions in agriculture, we evaluated the combined effect of elevated carbon dioxide (CO2) and temperature on the interactions among wheat (Triticum aestivum L.), Barley yellow dwarf virus species PAV (BYDV-PAV) and its vector, the bird cherry-oat aphid (Rhopalosiphum padi L.). Plant traits and aphid biological parameters were examined under two climate and atmospheric scenarios, current (ambient CO2 and temperature = 400 ppm and 20 °C), and future predicted (elevated CO2 and temperature = 800 ppm and 22 °C), on non-infected and BYDV-PAV-infected plants. Our results show that combined elevated CO2 and temperature increased plant growth, biomass, and carbon to nitrogen (C:N) ratio, which in turn significantly decreased aphid fecundity and development time. However, virus infection reduced chlorophyll content, biomass, wheat growth and C:N ratio, significantly increased R. padi fecundity and development time. Regardless of virus infection, aphid growth rates remained unchanged under simulated future conditions. Therefore, as R. padi is currently a principal pest in temperate cereal crops worldwide, mainly due to its role as a plant virus vector, it will likely continue to have significant economic importance. Furthermore, an earlier and more distinct virus symptomatology was highlighted under the future predicted scenario, with consequences on virus transmission, disease epidemiology and, thus, wheat yield and quality. These research findings emphasize the complexity of plant–vector–virus interactions expected under future climate and their implications for plant disease and pest incidence in food crops., This project was supported by Agriculture Victoria Research, Department of Jobs, Precincts and Regions, Australia, and by Ministerio de Economía, Industria y Competitividad, Gobierno de España (Research Grants Nos. AGL2013-47603-C2-1-R and AGL2017-83498-c2-2-R). A.M. was supported by Ministerio de Educación, Cultura y Deporte (Fellowship No. FPU2015-05173) and by Consejo Social UPM (International research fellowship), Spain., Peer reviewed

© 2020 by the authors., The salicylic acid analog BTH (benzo-(1,2,3)-thiadiazole-7-carbothioic-acid S-methyl ester) induces systemic acquired resistance by promoting plant resistance against numerous plant pathogens and some insect pests. The objective of the research was to evaluate the activation of plant defenses with BTH on melon (Cucumis melo L., Cucurbitaceae) and its effects on the herbivore Aphis gossypii Glover, 1877 (Hemiptera: Aphididae) and on the aphid predator Chrysoperla carnea (Stephens, 1836) (Neuroptera: Chrysopidae). Under laboratory conditions, plants were sprayed with BTH (50 g/ha) zero (B0), four (B4), and seven (B7) days prior exposure to insects. B0 treatment resulted in 100% mortality of aphid nymphs and disrupted adult feeding behavior (recorded by electrical-penetration-graphs technique), by prolonging the time to reach the phloem, requiring more probes to first salivation and reducing ingestion activities. There were no effects on feeding behavior of A. gossypii fed on B4 plants but on its life history because fewer nymphs were born, intrinsic rate of natural growth decreased, and mortality increased. There were no effects on biological parameters of aphids reared on B7 plants. Prey consumption by C. carnea larvae when predated A. gossypii fed on BTH-treated plants was not different among treatments. Therefore, BTH enhances the suppression of A. gossypii in the short term, without negative effects on the predatory larva C. carnea, which makes this plant strengthener a useful tool to be considered in integrated pest management programs., This work was supported by Ministerio de Economía, Industria y Competitividad, Gobierno de España
(Research Grants Numbers AGL2013-47603-C2, AGL2017-83498-C2-2-R) and by a PhD grant to A.M.-D. by
Ministerio de Educación, Cultura y Deporte (Fellowship Number FPU2015-05173)., Peer reviewed

13 Pág., Chelonus inanitus L. (Hymenoptera: Braconidae) is an egg-larval parasitoid of Lepidoptera, with the potential for biological control of noctuids. The lack of information merits research on its reproductive and developmental biology. We studied the reproduction of mated parasitoid pairs during female lifetime and the development of the progeny on two hosts, the factitious Ephestia kuehniella Zeller (Lepidoptera: Pyralidae) and the natural Spodoptera littoralis Boisduval (Lepidoptera: Noctuidae). The longevity of pairs subjected or not to parasitism was compared. Development of the progeny after parasitization and growth rates were studied. Reproduction decreased the longevity of both sexes in every host. The similar survival patterns proved that sex was not a factor influencing longevity. Females parasitized immediately after emergence and offspring production peaked at 2–2.5 days. Low parasitization rates (3–12%) were generally observed. Reproduction on S. littoralis was fourfold less efficient, probably due to failure of immature stages leading to poor progeny. Sex ratio of the progeny was mostly male-biased. Males developed faster in both hosts. Development was 20 days shorter in the natural host. Strikingly, the parasitoid performed successfully better on the factitious host. Inbreeding, poor understanding of host preference, and inadequate rearing and handling practices are discussed as possible causes of the worse parasitoid performance on S. littoralis., Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature. This work was supported by MCIN/AEI/https://doi.org/10.13039/501100011033 [grants AGL2017-83498-C2-2-R, PID2020-117062RB-C22 and IJC2018-035042-I]. Ariel Morel has received fellowship from Ministerio de Hacienda de Paraguay, Programa nacional de becas de postgrado D. Carlos Antonio López [grant 01/2019]., Peer reviewed