Effect Of Host Plants Research Articles

Understanding the interplay between host-specificity, environmental conditions and competition through the sound application of Joint Species Distribution Models

A recommendation of: Benoit Facon, Abir Hafsi, Maud Charlery de la Masselière, Stéphane Robin, François Massol, Maxime Dubart, Julien Chiquet, Enric Frago, Frédéric Chiroleu, Pierre-François Duyck & Virginie Ravigné Joint species distributions reveal the combined effects of host plants, abiotic factors and species competition as drivers of species abundances in fruit flies 10.1101/2020.12.07.414326

Host plant and humidity effects on phytoseiid mite, Gynaeseius liturivorus (Acari: Phytoseiidae) egg hatchability.

Gynaeseius liturivorus (Ehara) (Acari: Phytoseiidae) is a promising biological control agent for tiny arthropod pests, including Thrips tabaci Lindeman (Thysanoptera: Thripidae) known as a major pest of Welsh onion. In fields during summer, G. liturivorus is observed on soybean, but not on Welsh onion, even when numerous T. tabaci are present. To elucidate G. liturivorus's occurrence on soybean and Welsh onion in relation to relative humidity (RH), we examined its egg hatching on their seedlings under low RH conditions. Then we estimated the moisture transpiration from both plants. Egg hatching occurred only on soybean plants exhibiting greater moisture transpiration. Aiming at utilizing G. liturivorus as a biological control agent for Welsh onion production in summer, evaluation of its relative tolerance and compensation potential for drought injury is necessary. Therefore, we used five phytoseiid species including G. liturivorus and Neoseiulus californicus to estimate the RH and vapor pressure deficit (VPD) at which 50% of eggs hatch (RH50 and VPD50). Furthermore, we examined G. liturivorus and N. californicus egg hatching under different RH oscillation conditions. Results show G. liturivorus as the most drought-sensitive among the five species tested, but G. liturivorus isable to compensate for lethal low-RH effects on egg hatching in part by periodic exposure to high RH conditions, as observed for N. californicus.

Microbiomes of willow-galling sawflies: effects of host plant, gall type, and phylogeny on community structure and function.

While free-living herbivorous insects are thought to harbor microbial communities composed of transient bacteria derived from their diet, recent studies indicate that insects that induce galls on plants may be involved in more intimate host-microbe relationships. We used 16S rDNA metabarcoding to survey larval microbiomes of 20 nematine sawfly species that induce bud or leaf galls on 13 Salix species. The 391 amplicon sequence variants (ASVs) detected represented 69 bacterial genera in six phyla. Multi-variate statistical analyses showed that the structure of larval microbiomes is influenced by willow host species as well as by gall type. Nevertheless, a "core" microbiome composed of 58 ASVs is shared widely across the focal galler species. Within the core community, the presence of many abundant, related ASVs representing multiple distantly related bacterial taxa is reflected as a statistically significant effect of bacterial phylogeny on galler-microbe associations. Members of the core community have a variety of inferred functions, including degradation of phenolic compounds, nutrient supplementation, and production of plant hormones. Hence, our results support suggestions of intimate and diverse interactions between galling insects and microbes and add to a growing body of evidence that microbes may play a role in the induction of insect galls on plants.

Tree Species Richness and Neighborhood Effects on Ectomycorrhizal Fungal Richness and Community Structure in Boreal Forest.

Tree species identity is one of the key factors driving ectomycorrhizal (EcM) fungal richness and community composition in boreal and temperate forest ecosystems, but little is known about the influence of tree species combinations and their neighborhood effects on EcM communities. To advance our understanding of host plant effects on EcM fungi, the roots of silver birch, Scots pine, and Norway spruce were analyzed using high-throughput sequencing across mature boreal forest exploratory plots of monocultures and two- and three-species mixtures in Finland. Our analyses revealed that tree species identity was an important determinant of EcM fungal community composition, but tree species richness had no significant influence on EcM fungal richness and community composition. We found that EcM fungal community composition associated with spruce depends on neighboring tree species. Our study suggests that at a regional-scale tree species identity is the primary factor determining community composition of root-associated EcM fungi alongside with tree species composition effects on EcM fungal community of spruce in mixed stands.

Effect of host plant on cornucopia of mango fruit flies (Diptera: Tephritidae) and their triumphant management in context of climate change.

A study was performed to assess the preference of fourteen mango cultivars for fruit flies and their management by bagging. So the choice of Tephritid flies to mango cultivars during fruiting phase is crucial. Fourteen different cultivars of mango viz., ‘Dusehri’, ‘Malda’, ‘Langra’ early cultivars, ‘Chaunsa’, ‘Fajri Klan’, ‘Sensation’ medium whereas ‘Sanglakhi’, ‘Retaul-12’, ‘Mehmood Khan’, ‘Tukhmi’, ‘Kala Chaunsa’, ‘Chitta Chaunsa’, ‘Dai Wala’ and ‘Sobey De Ting’ late cultivars were assessed for their suitability for fruit flies. The results indicate that the population density of fruit flies was higher on late cultivars like ‘Sanglakhi’ (20.61 percent), ‘Mehmood Khan’ (20.22 percent) and ‘Reutal-12’ (19.92 percent) were proved to be highly susceptible to fruit flies. Among these the cultivar ‘Reutal-12’ was selected being commercial and future cultivar for the management of fruit flies through bagging. The results reported that the attack of tephritid fruit flies and other insect pests were zero in bagged fruits as compared with control. It was further recorded that the bagged fruits has maximum average fruit weight i.e. 203.50 and 197.83 g per fruit was noted in those treatments where butter paper bag and brown paper bag was wrapped with better coloration as compared with un-bagged fruit with 159.5 g per fruit. Similarly, on an average fruit length were more i.e. 90.17, 91.33 mm in bagged fruit and 85.33 in un-bagged fruits. Furthermore, bagged fruits have zero incidence of disease with reduced fruit crack, fruit sunburn, mechanical damage, bird damage, fruit blemished and agrochemical residues on the fruit. So, it is concluded that the special attention should be given on ‘Reutal-12’ for the management of fruit flies when devising an IPM program for the control of fruit flies. Further, bagging has proved to be the good agricultural practices for the production of quality mango.

Interactive effects of host plant and insecticide foliar application on oviposition and performance of Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) cryptic species Mediterranean (MED) and Middle East-Asia minor 1 (MEAM1) in Brazil

The Bemisia tabaci (Gennadius) cryptic species complex is composed of important pest insects, with cryptic species Mediterranean (MED) and Middle East-Asia Minor 1 (MEAM1) having caused severe yield reduction on crops worldwide. The former was reported in Brazil in 2014, while the latter was first reported in the country in the 1990s. Although farmers have highly adopted insecticide application for B. tabaci management, its efficacy may vary among host plants and cryptic species. Cyantraniliprole is a new anthranilic diamide insecticide with a mode of action that activates the insect ryanodine receptor (RyR). In this context, the purpose of this study was to investigate the effects of cyantraniliprole spraying on the oviposition and performance of MEAM1 and MED cryptic species in tomato and sweet pepper plants. Cyantraniliprole caused high adult mortality for both cryptic species on sweet pepper (> 94%), while its efficacy was moderate for MEAM1 (~ 56%) and low for MED (~ 12%) on tomato. MED laid more eggs on sweet pepper and tomato treated with water and cyantraniliprole, respectively, than MEAM1. Additionally, cyantraniliprole reduced the hatchability of MED and MEAM1 on sweet pepper and tomato, respectively. Moreover, MED showed better performance than MEAM1 regardless of the treatment and host plant, except on tomato treated with water. Our results indicate that cyantraniliprole efficacy changes according to B. tabaci cryptic species and host plant. These findings will be important for redesigning cyantraniliprole doses for B. tabaci management in Brazil.

Effects of host plants on the population parameters and activities of detoxification enzymes in Laodelphax striatellus

AbstractThe small brown planthopper (SBPH), Laodelphax striatellus (Fallén) (Hemiptera: Delphacidae), is an economically important pest of rice (Oryza sativa L.), wheat (Triticum aestivum L.), and other members of the Poaceae. The effects of host plant type on SBPH life table parameters reared on two cultivars of rice (Zixiangnuo 2315 and Wuyujing 3), wheat (Jimai 22 and Nongda 26), and one grass weed (Echinochloa crusgalli Beauv.) under laboratory conditions were determined using the age‐stage, two‐sex life table. Additionally, the corresponding activities of three detoxifying enzymes – carboxylesterase (CarE), glutathione‐S‐transferase (GST), and mixed‐function oxidase (MFO) – were also measured. The results showed that host plant species and cultivars had effects on population parameters and activities of detoxification enzymes. Rice cv. Zixiangnuo 2315 and wheat cv. Nongda 26 were shown to be more suitable than the other three hosts. The activities of the three detoxifying enzymes showed different patterns of changes on the three host plants after feeding for 0–72 h. Regardless of short‐term (72 h) or long‐term (one generation) induction on host plants, the activity levels of GST and MFO in adult SBPH reared on rice ‘Zixiangnuo 2315’ were lower and higher, respectively, than on the other four hosts. The results may help understand the host adaptability of this pest and inform the development of strategies for effective field‐based integrated pest management programs.

Effect of Different Host Plants on the Biology of Diamond-Back Moth, Plutella Xylostella Under Laboratory Conditions in Northern Punjab, Pakistan

Plutella xylostella is an oligophagous pest of several host plants belonging to the family Cruciferae (cauliflower, cabbage, canola). This is widely distributed in all those areas where its hosts exist and cause severe crop losses. The current study was conducted to check the effect of host plants such as cabbage, cauliflower and canola on the biology of P. xylostella. The effect on incubation period, growth, development time, fecundity, oviposition, % survival and % egg viability was studied on canola, cabbage and cauliflower. The developmental time from 1st instar to adult emergence was longest (18 days) on canola while shortest on cauliflower (15 days). Fecundity was recorded maximum (259 eggs) on cauliflower and minimum (159 eggs) on canola. Percentage survival of each stage was recorded maximum on cauliflower (84%) followed by cabbage (73%) and canola (69%). A significant difference was observed intheintrinsic rate of increase, rm with host plants. The intrinsic rate of increase(0.290) and finite rate of increase values (1.35) were obtained on cauliflower while 0.283, 1.30 and 0.239, 1.23 on cabbage and canola, respectively. Cauliflower was found to be the most preferable host for P. xylostella due to higher percentage of survival, higher fecundity, higher % egg viability and shorter developmental period. The study provides knowledge about the host plants that prove helpful in enhancing the P. xylostella population.

Preliminary Studies on the Humoral Immune Response of Mulberry Silkworm, Bombyx mori Larvae Fed on Different Mulberry Varieties

Diseases infecting silkworms cause 30-40% cocoon crop loss. The silkworm, Bombyx mori L. defense against pathogens is provided by open circulatory system through humoral and cellular response. Three mulberry varieties, Morus alba var. Rosa, M. alba var. Morittiana and M. alba var. Laevigata, were used to study the effect of host plant and bacterial contagious infection on the humoral immune of B. mori larvae. The specific activity of related enzymes in haemolymph of fifth instar larvae was estimated. Results indicated that mulberry varieties and bacterial contagious infection had significant effects on enzymes activity values in larval haemolymph. Moreover, M. alba var. laevigata was superior in the humoral immune response.

Effect of Different Host Plants on The Different Haemocyte Counts and Haemocyte Viability of Larvae of Spodoptera littoralis and Agrotis ipsilon

The present study aimed to investigate the effect of different six host plants namely, Cabbage, alfalfa, Jaw’s mallow, lettuce, turnip, and castor leaves on the total haemocyte count (THC), percentage of haemocyte viability, and the percentage of each type of haemocyte (differential haemocyte count, DHC) in Spodoptera littoralis and Agrotis ipsilon fourth instar larvae. There are five types of haemocytes in A. ipsilon and S. littoralis larvae; Prohaemocyte, Plasmatocyte, Granulocyte, Spherocytes, and Oenocyte. Results recorded the highest value 13.3±0.68 of Prohaemocyte at lettuce and the lowest value 9.3 for Cabbage, alfalfa and turnip. On the other hand, Prohaemocyte recorded the highest value 12.6 ± 0.9 in the case of castor feeding and 8.7 ± 0.3 for turnip for S. littoralis. Plasmatocyte recorded 45.3 ± 2.9 cells/mm3for A. ipsilon feed on turnip and 47.3 ± 1.8 cells/mm3for S. littoralis feed on lettuce as the highest value while Granulocyte recorded 33 ± 4.1 and 35 ± 0.7 for A. ipsilon feed on Jaw’s mallow, respectively. Spherocytes recoded 15.3 ± 0.9 and 12.3 ± 0.9 for A. ipsilon and S. littoralis feed on alfalfa. Finally, Oenocyte recorded 7.7 ± 1.5 and 7.3 ± 1.4 for A. ipsilon and S. littoralis feed on castor. Total haemocytic count recorded 29 ± 0.3 and 36 ± 0.75 cells/mm3 as the highest value when both A. ipsilon and S. littoralis feed on Alfalfa. Also, the haemocyte viability % recorded the highest value 91.5 ± 2.6 and 96.2 ± 0.8 % for A. ipsilon and S. littoralis feed on feed on Alfalfa. The result recorded increasing DHC level after feeding of the fourth larval instar of S. littoralis and A. ipsilon on different plant hosts such an increase in DHC gives an impression that blood cells may share in detoxifying. The most obvious activity of haemocyte is phagocytosis. In this context, the most active phagocytes are the Plasmatocyte, Plasmatocyte which was implicated in the encapsulation of necrotic tissues.

Effect of Host Plants on the Viability of Black-veined White Aporia crataegi L. at Low Natural Population Density

Patterns of interaction of an oligophagous insect, black-veined white Aporia crataegi L., with host plants in years with a low density of its natural population are analyzed. In years with low A. crataegi population abundance in the south of Sverdlovsk region (Sysertsky district), the species composition of caterpillar host plants gradually decreases from several woody rosaceous species of the genera Padus, Sorbus, Malus, and Crataegus to one species (Padus avium Mill.). It is shown that the mortality rate is higher for fifth-instar caterpillars developing on mountain ash than for those developing on bird cherry. Adult A. crataegi developing on bird cherry are not only larger but also grow faster than those developing on mountain ash, which may be an additional factor responsible for the observed chronographic variation during the emergence of A. crataegi generation in nature.

Migration and penetration of Meloidogyne enterolobii and M. incognita in soil columns with tomato and marigold

Root-knot nematodes (Meloidogyne spp.) can parasitize and reduce yields of nearly all agricultural crops. Although migration studies focus on the model species, M. incognita, there is little information about M. enterolobii, which has been a major threat for guava in Brazil. The vertical migration of second-stage juveniles (J2) of M. enterolobii and M. incognita was evaluated to determine the effect of good host and nonhost plants on nematode motility. Fourteen-cm long soil columns were constructed of PCV rings with Styrofoam cups containing a 4-week-old tomato or marigold (Tagetes patula) seedlings as plant stimuli; host-free cups were used as nontreated control. After inoculating 1000 freshly-hatched J2, the columns were placed in environmental chamber sets at 20 °C. The columns were disassembled at 3, 6, and 9 days after inoculation (DAI). The experiment was completely randomized block with four replicates. J2 were extracted from each ring and cup, while tomato and marigold roots were stained to observe J2 that penetrated roots. Data were subjected to repeated-measure MANOVA and chi-square test to compare J2 distribution along the columns. The migrations under tomato and marigold stimuli were comparable to those under host-free columns. Although both species migrated over 13 cm, M. enterolobii was more mobile than M. incognita. Juveniles of M. enterolobii infected tomato roots as early as 3 DAI, whereas marigold delayed nematode penetration. Our results show that two species of root-knot nematodes behave differently within the soil, and under the same conditions J2 of M. enterolobii migrate faster than M. incognita.

The Population Growth of Spodoptera frugiperda on Six Cash Crop Species and Implications for Its Occurrence and Damage Potential in China.

Simple SummaryThe fall armyworm Spodoptera frugiperda is an invasive pest, which can cause severe economic losses by larvae feeding on a variety of crops. To develop effective control technology, it is particularly necessary to study the basic biology and ecology of this invasive insect. This experiment investigated the development, survival, and reproduction and population growth of S. frugiperda on six cash crop species. This study indicated that S. frugiperda fed on maize and wheat had shorter preadult developmental durations, higher preadult survival, greater pupal weights and higher fecundity compared to the other four plants. Moreover, although the young larvae of S. frugiperda feeding on Chinese cabbage had a high mortality rate, the old larvae were voracious, which might still cause economic losses to Chinese cabbage. Our results showed that S. frugiperda could cause great economic losses to these cash crops, which should attract the attention of agricultural management departments.Spodoptera frugiperda is a significant migratory invasive pest, identified as a serious threat to agricultural production and food security in China. However, to our knowledge, the effects of most host plants on the biological characteristics of S. frugiperda have not been well studied. To develop effective management strategies for S. frugiperda in its new invasive habitat, basic biological and ecological knowledge of this pest are crucial requirements. Here, we examined the effects of six cash crops maize, wheat, soybean, tomato, cotton and Chinese cabbage on the development, survival, fecundity of S. frugiperda by using the age-stage, two-sex life table. The preadult stage, adult preoviposition period and total preoviposition period of S. frugiperda were shortest on maize and wheat but were longest on tomato. Fecundity was greatest on maize and wheat but smallest on tomato. The highest intrinsic rate of increase, finite rate of increase, net reproductive rate and the shortest mean generation time were recorded on maize. This present study showed that S. frugiperda could cause great economic losses to these cash crops, which should attract the attention of agricultural management departments. Our findings provide useful information in predicting population dynamics and understanding the potential damage that could be incurred by S. frugiperda invasion.

Nutritional Relationship between Bemisia tabaci and Its Primary Endosymbiont, Portiera aleyrodidarum, during Host Plant Acclimation.

Simple SummaryPlant sap-sucking insects commonly have established mutualistic relationships with bacteria that live within their bodies and often provide nutrients that are lacking in the insect’s diet. The sweet potato whitefly (Bemisia tabaci) harbors one primary and up to seven secondary endosymbiotic bacteria. The primary endosymbiont of B. tabaci is already known to play a critical role in providing necessary nutrients for B. tabaci. Our objective was to study the relationship among B. tabaci, its primary endosymbiont, and the host plant through the effects of host plant shifting and acclimation, that is, physiological adjustments as an insect becomes accustomed to a new host plant over several generations. The results showed that host shifting from Chinese kale to cotton plants led to a decrease in the fecundity of B. tabaci in the first generation, which was restored after 10 generations of acclimation, and that its developmental time was also decreased by the tenth generation. Furthermore, essential amino acid biosynthesis genes of its primary endosymbiont were differentially regulated after B. tabaci had become acclimated to cotton plants. We speculate that the primary endosymbiont has a close nutritional relationship with B. tabaci during host plant acclimation.Plant sap-sucking insects commonly have established mutualistic relationships with endosymbiotic bacteria that can provide nutrients lacking in their diet. Bemisia tabaci harbors one primary endosymbiont, Portiera aleyrodidarum, and up to seven secondary endosymbionts, including Hamiltonella defensa and Rickettsia sp. Portiera aleyrodidarum is already known to play a critical role in providing necessary nutrients for B. tabaci. In the present study, the relationship among B. tabaci, its primary endosymbiont, and the host plant were examined through the effects of host plant shifting and acclimation. Bemisia tabaci was transferred from Chinese kale to four different host plants, and the effects on both its performance and the expression levels of nutrient-related genes of P. aleyrodidarum were analyzed. The results showed that host shifting from Chinese kale to cotton plants led to a decrease in the performance of B. tabaci in the first generation, which was restored after 10 generations of acclimation. Furthermore, the expression levels of essential amino acid biosynthesis genes of P. aleyrodidarum were found to be differentially regulated after B. tabaci had acclimated to the cotton plants. Host plant shifting and acclimation to cucumber, poinsettia, and tomato plants did not affect the fecundity of B. tabaci and the expression levels of most examined genes. We speculate that P. aleyrodidarum may help B. tabaci improve its performance and acclimate to new hosts and that P. aleyrodidarum has a close nutritional relationship with its host during host plant acclimation.

Pot host and media treatments towards kayu papi’s (Exocarpus latifolius R.Br) growth

Kayu papi or shrub sandalwood (Exocarpus latifolius R.Br.) is a hemiparasitic plant, member of Santalacea family which incorporated host plant on their nutrient absorption. Kayu papi is a fragrant wood that can mimic and perhaps substitute sandalwood (Santalum album Linn.). Many studies recorded that exocarpic acid derived from kayu papi is also beneficial as a tuberculosis remedy. However, the information on silvicultural techniques has only been investigated just a few times. This study aimed to examine the effect of host plants and media combination on kayu papi’s growth under the nursery condition. Kayu papi seedlings were planted with five different hosts and control (without host plant) on six different media. The parameters are the height and diameter of the seven-month kayu papi seedlings. The result indicates that host plants significantly affected kayu papi’s growth. The interaction between the host plant (Alternanthera spp.) and media combination latosol soil and manure also significantly promoted the height of kayu papi. While kayu papi grown in grumusol with Saorupus androgynous host showed the highest diameter on average. In conclusion, kayu papi seedlings indicate that host plant presence and particular media optimized their growth.

Effect of host plant on the fitness of the spittlebug Notozulia entreriana: alternative method for rearing

AbstractAmong the species belonging to 11 genera of Neotropical spittlebugs attacking graminaceous plants, Notozulia entreriana (Berg) (Hemiptera: Cercopidae) is one of the most important pests of grasses in several countries of South America. In this study, we evaluate the influence of three economically relevant species of host plants (Poaceae) on life‐cycle traits of N. entreriana. We tested for differences in fitness responses (survival and fecundity) of insects on forage species which are frequent hosts for wild populations of spittlebugs. Comparison of life cycles on three host plants showed that only 2.5% of nymphs completed their development on Zea mays L., 22.5% on Chloris gayana Kunth, and 95% on Brachiaria decumbens Stapf. All the above suggests that C. gayana and B. decumbens are able to sustain complete development, behaving like natural hosts; the latter species is superior for artificial colonies because a shorter developmental period, higher survivorship in nymphs, and longer lifespan of adults were observed. Zea mays did not allow proper development, causing high mortality instead. We also developed a new approach for small‐scale breeding of N. entreriana, which will enable subsequent biological and behavioral studies on this important pest species.

Modulation of Reproductive Behavior of Diaphania indica (Lepidoptera: Pyralidae) by Preferred and Non-preferred Host Plants

The cucumber moth, Diaphania indica (Lepidoptera: Pyralidae), is one of the most destructive pests of cucurbitaceous plants all over the world. Previously, we showed that volatile organic compounds (VOCs) from cucumber plants play a crucial role in guiding gravid D. indica females to oviposition sites, whereas watermelon VOCs did not, and females significantly prefer cucumber over watermelon for oviposition. It remained unclear, however, whether preferred and non-preferred host plants also affect moth reproductive behaviors. In the present study we investigated the effect of preferred and non-preferred host plants on female calling, male attraction to female sex pheromone, and mating behavior in D. indica. In the presence of cucumber, virgin females engaged in significantly more calling on the first night than in either the watermelon treatment or the control. Also, we found that the mean time per bout on the first night in the cucumber plant treatment was significantly higher than that of the other two groups. The combination of cucumber foliage with female pheromone significantly increased the attraction and landing of males compared to either watermelon or the control in the wind tunnel. Furthermore, for one-day-old insects mating occurred only in the cucumber treatment. All insects in the cucumber treatment exhibited their first mating on one of the first three nights, but in the watermelon treatment only by night four had all insects mated. We also found that the duration of first mating in cucumber was significantly greater than in either watermelon or control. Overall, our study provides evidence that preferred and non-preferred host plants affect reproductive behaviors in D. indica.

Interactions of Metarhizium brunneum-7 with Phytophagous Mites Following Different Application Strategies.

Metarhizium brunneum is a generalist entomopathogenic fungus known to be virulent against Acari. We investigated Metarhizium brunneum-7 (Mb7) interactions in three systems of phytophagous mites and their respective plant hosts: Volkamer lemon (Citrus volkameriana) and the citrus rust mite Phyllocoptruta oleivora; common bean (Phaseolus vulgaris) and the two-spotted spider mite Tetranychus urticae; and spring onion (Allium cepa) and the bulb mite Rhizoglyphus robini. All three mite species were susceptible to directly applied Mb7 conidia. Results obtained using the standard method for studying endophytic colonization vs. live confocal imaging of plant tissues using the green fluorescent protein (GFP)-transformed fungus differed markedly, demonstrating that microscopy validation was more definite than the standard process of recovery from plant tissue. Endophytic colonization was observed in conidium-infiltrated citrus leaves and in roots of onion plants treated with soil-drenched conidia, but not in common bean treated by either spray or drench of conidia. Endophytic colonization of citrus leaves did not affect the citrus mite population. Drench application in common bean reduced two-spotted mite population. Similarly, drench application in onion reduced bulb mite population. This study emphasizes the importance of the host plant effects on Mb7 control efficacy of mite pests, and the merits of live-imaging techniques in studying endophytic interaction.

Host plant-related responses on the thermal fitness of Chilo partellus (Swinhoe) (Lepidoptera: Crambidae)

Diet quality influences arthropod performance under changing environments. However, little is known about how host plant species may influence the responses of polyphagous insects to climate stressors despite their exploitation of different plant species within and across seasons. Against this background, we examined the effects of host plant species (Zea mays L. and Sorghum bicolor L. Moench) on the thermal tolerance of Chilo partellus (Swinhoe) (Lepidoptera: Crambidae) measured as lower and upper thermal activity limits, chill coma recovery time and heat knockdown time. Experiments were conducted on field-collected larvae and laboratory-reared F1 larval offspring from each of the two host species. Our results showed significant host plant effects on both cold and heat tolerance. Insects from sweet sorghum showed higher thermal resilience (cold and heat) relative to those from maize as indicated by their low lower thermal activity limits (0.73 and 0.02 °C magnitude, respectively) and high upper thermal activity limits (0.5 and 0.28 °C magnitude, respectively). Both field and F1 larval populations from sweet sorghum recovered faster from chill coma and also took longer to be knocked down by acute heat stress, further affirming their superior thermal tolerance to those that fed on maize. These results therefore indicate that host plant species may potentially mediate thermal fitness of C. partellus. Despite wide adoption of sweet sorghum as a climate resilient crop owing to its drought tolerance and perennial nature, our findings suggest this may come at a cost of enhanced C. partellus performance and pest pressure under changing temperature environments.

Nutrient dilution and climate cycles underlie declines in a dominant insect herbivore.

Evidence for global insect declines mounts, increasing our need to understand underlying mechanisms. We test the nutrient dilution (ND) hypothesis-the decreasing concentration of essential dietary minerals with increasing plant productivity-that particularly targets insect herbivores. Nutrient dilution can result from increased plant biomass due to climate or CO2 enrichment. Additionally, when considering long-term trends driven by climate, one must account for large-scale oscillations including El Niño Southern Oscillation (ENSO), North Atlantic Oscillation (NAO), and Pacific Decadal Oscillation (PDO). We combine long-term datasets of grasshopper abundance, climate, plant biomass, and end-of-season foliar elemental content to examine potential drivers of abundance cycles and trends of this dominant herbivore. Annual grasshopper abundances in 16- and 22-y time series from a Kansas prairie revealed both 5-y cycles and declines of 2.1-2.7%/y. Climate cycle indices of spring ENSO, summer NAO, and winter or spring PDO accounted for 40-54% of the variation in grasshopper abundance, mediated by effects of weather and host plants. Consistent with ND, grass biomass doubled and foliar concentrations of N, P, K, and Na-nutrients which limit grasshopper abundance-declined over the same period. The decline in plant nutrients accounted for 25% of the variation in grasshopper abundance over two decades. Thus a warming, wetter, more CO2-enriched world will likely contribute to declines in insect herbivores by depleting nutrients from their already nutrient-poor diet. Unlike other potential drivers of insect declines-habitat loss, light and chemical pollution-ND may be widespread in remaining natural areas.