Favorable Host Plants Research Articles

Comparison of gut transcriptome and bacterial composition of the yellow peach moth, Conogethes punctiferalis larvae associated with host plants adaptation

The yellow peach moth, Conogethes punctiferalis, is one of the most destructive polyphagous pests to corn crops in the Huang-Huai-Hai summer corn region of China. However, little is known about the host plant adaptation mechanism of C. punctiferalis. In this study, we analyzed the performance of C. punctiferalis on two of its favorable host plants (corn and sorghum). Then, we used RNA-seq and 16S rRNA sequencing to explore the potential adaptation mechanism of C. punctiferalis on these two host plants. Results showed that C. punctiferalis gained more fresh weight on sorghum while its total lipid and triglyceride content was significantly lower than on corn. In total, 2155 genes weredifferentially expressed (DEGs) between corn and sorghum reared C. punctiferalis. Most of the DEGs were involved in nutritional biosynthesis and metabolism including amino acid biosynthesis, protein digestion and absorption, and glycolysis. Enzymatic analyses revealed that C. punctiferalis reared on corn had higher trypsin activity but lower P450 activity than that reared on sorghum. Meanwhile, C. punctiferalis reared on corn harbored more gut bacteria, while its diversity is lower than that reared on sorghum. The potential functional prediction of the gut bacteria revealed that nutritional metabolism functions were differently enriched between two host plants of C. punctiferalis. Taken together, these findings clarify the impact of host plants on the gene expression and gut bacteria in C. punctiferalis. They also suggest that the plasticity of gene expression and gut bacteria cooperatively contribute to insect host adaptation of insects.

Ecology and management of the invasive land snail Bulimulus bonariensis (Rafinesque, 1833) (Stylommatophora: Bulimulidae) in row crops.

Solutions for managing the growing populations of the snail Bulimulus bonariensis (Rafinesque, 1833) in row crops, notably peanut (Arachis hypogaea L.), are urgently needed in the United States. This species has become a concern to the economy and food security for infesting commercial crops in U.S. southern states. In the present study, sampling, trapping, and management strategies were investigated to support a management program for B. bonariensis in row crops. In addition, the preference of B. bonariensis for species of row crops and weeds, used as a shelter, and snail dispersal capacity were documented. The results indicated that the ideal tools for monitoring and capturing snails are beat cloth and cardboard trap, respectively. Metaldehyde 4% bait produced effective control. Tillage was tested as an alternative cultural management tactic and produced the most promising outcomes in lowering snail populations. According to snail ecological studies, peanut and soybean are the preferred crops used as shelter over cotton and corn. Among eight common winter-growing weeds, the favored non-crop host plants are cutleaf primrose (Oenothera laciniata) and dandelion (Taraxacum officinale). The snail field population tends to increase as early spring temperatures rise, with more snails becoming trapped in warm, humid conditions but not through heavy precipitation. This study provides ecology information on B. bonariensis and validates tactics to manage this invasive species in row crops, in an IPM approach.

Medfly Phenotypic Plasticity as A Prerequisite for Invasiveness and Adaptation

The hypothesis of this study was that different plant hosts of the medfly Ceratitis capitata may cause variability as a prerequisite for its invasiveness. The main objective was to determine population variability based on medfly wing shape in three favorable medfly host plants (peach, fig and mandarin) from different agroecological growing areas with different pest management practices, and to evaluate phenotypic plasticity as a basis for future expansion into new areas and new hosts. Using geometric morphometric methods across 14 specific landmarks on the medfly wings, 10 populations were tested from infested peach, fig and mandarin fruits, as well as laboratory-grown sterile populations. The studies led to the following main findings: (1) all of the medfly populations that were studied exhibited sexual dimorphism in wing shape; (2) the hosts in which the medfly develops influence wing shape and condition its variability; (3) there is significant variability between laboratory mass-reared sterile and wild individuals in male and female populations; (4) a high phenotypic plasticity of medfly populations was observed along the study sites. Even the low but clearly detected variability between different agroecological conditions and localized variability indicate genotypic stability and high phenotypic plasticity, which can be considered as a prerequisite for medfly invasiveness and dispersal to new areas.

Brassica carinata: New Reproductive Host Plant of Bemisia tabaci (Hemiptera: Aleyrodidae)

A laboratory experiment was conducted on two potential reproductive host plant species of the whitefly Bemisia tabaci (Gennadius). The two plant species, Brassica carinata A. Braun (carinata or Ethiopian mustard) and Myrica cerifera L. (southern wax myrtle), were considered for study as potential overwintering host species for B. tabaci because of their presence with green foliage in the southeastern United States agricultural community from the fall through spring season. The Middle-East-Asia Minor 1 of the cryptic whitefly species group of B. tabaci survives the mild winters in the southeastern United States. In this study, B. carinata was demonstrated to be a favorable host plant for B. tabaci. Based on a no-choice experiment, oviposition, egg hatch, and survival to the adult stage were similar for whiteflies on B. carinata as compared with collard (B. oleracea var. acephala de Condolle), a known favorable host for B. tabaci. However, results from a dual choice experiment indicated that the whiteflies preferred B. carinata to B. oleracea for feeding and oviposition. Conversely, although southern wax myrtle served as an ovipositional host, the ovipositional performance of B. tabaci in a no-choice assay was over eight-fold less than on B. carinata, and nymphal survival was not successful beyond the second instar on southern wax myrtle in a laboratory experiment. However, a few nymphs survived to the fourth instar on intact plants of southern wax myrtle in the landscape. The results of this study have implications on whitefly population dynamics. Winter populations of B. tabaci are suppressed in the field, but plant species, such as carinata or collard, that are present during the mild winter may help support a buildup of whiteflies during the spring.

Long-term decline in the parasitism rate of passionvine hopper eggs (Scolypopa australis)

Passionvine hopper, Scolypopa australis (Walker) (Hemiptera: Ricaniidae), (PVH) is an introduced pest of kiwifruit grown in New Zealand. Two aphelinid egg parasitoids, Centrodora scolypopae Valentine and Ablerus sp., are thought to be its most important natural enemies. Rates of egg parasitism measured during 2010–2015 in the Bay of Plenty region and in a wider survey of the North Island of New Zealand in 2015 were ≤ 10% compared with medians of about 30–50% for historical estimates. PVH eggs laid in bracken, a favored host plant, in 2015 and 2019 were parasitized at about half the rate or less than indicated by measurements made 20, 35–38 and 57 years ago. The apparent decline may have been the result of asynchrony between one or both egg parasitoids and PVH associated with warmer summer and autumn temperatures. Further work is needed to clarify the role of each parasitoid in PVH population dynamics.

Investigation of Varietal Characteristics of Tomato Plants for Determining the Diverse Preferences of Bemisia Tabaci (Aleyrodidea: Hemiptera)

The whitefly (Bemisia tabaci) is a well-known pest of vegetables and ornamental cash crops including tomato plant. Tomato plant disorders, in many instances, are related mostly with the silver leaf whitefly (Bemisia tabaci) feeding. It is well thought out that tomato plant is one of the most favorable host plants for the whitefly. Thus we aimed to study distinctive morphological characteristics of the leaves in seven selected tomato varieties including trichome density, trichome length, leaf lamina thickness and RGB value (red, green, blue) and HSB value (hue, saturation, brightness). Seven hybrid F1 tomato varieties such as TO-1057, TAI-1757, T‑1359, Advanta-1247, New Super, Sultan and Super were tested for the whitefly preferences. Our study suggests that T‑1359 is the highly preferred variety for the whitefly adults (5.32 ± 0.81) and nymphs (6.30 ± 1.13) population. In contrast, Advanta-1247 exhibits the lowest population of whitefly adults (2.71 ± 0.70) and nymphs (1.88 ± 0.43). This study systematically identifies the morphological characters of the tomato plants alongside the whitefly population. The study can be potentially extended to other crops as well.

Migratory Helicoverpa armigera (Lepidoptera: Noctuidae) Exhibits Marked Seasonal Variation in Morphology and Fitness.

Many insects adopt seasonal, trans-latitudinal migration in response to altering climatic conditions, resource availability or reproductive requirements. Though the migration behavior of the cotton bollworm, Helicoverpa armigera (Hübner)(Lepidoptera: Noctuidae), has been well-studied, little is known about the extent of intra-specific variation between northward- and southward-migrating individuals. In this study, we captured H. armigera adults along the species' migration route during 2017-2018 to determine seasonal variability in their morphology, flight capability, and reproductive performance. Northward migrants have broader, longer bodies and are 1.33 times heavier than southward migrants, hinting at a comparatively higher allocation of resources in the abdomen. Accordingly, the former migrants engaged in longer flights, had greater reproductive capacity and a longer lifespan than southward ones. As northward migrants originate from favorable environmental conditions, their fitness is higher than that of the southward cohorts that develop on less favorable host plants and in perhaps more adverse climatic or ecological conditions. Northward H. armigera migrants thus possess an advantageous morphology that benefits habitat colonization and resource exploitation. Our work offers a novel perspective on the ecological and reproductive benefits of long-distance migration and can aid the development of population monitoring and forecasting methods for this globally important agricultural pest.

Linden trees are favourable host plants for phytoseiid generalists in urban environment

The assemblages of phytoseiid mites on the leaves of Tilia cordata and T. platyphyllos planted in heterogeneous urban habitats were studied. Six phytoseiid species, namely, Euseius finlandicus, E. gallicus, Neoseiulella tiliarum, N. aceri, Paraseiulus talbii, and Typhlodromus (Typhlodromus) pyri, were found on the studied linden leaves. The results indicate that both T. cordata and T. platyphyllos may serve as favourable host plants for the generalists E. finlandicus and N. tiliarum in urban environments. Both generalist predatory species preferred sheltered leaf microhabitats. The first record of E. gallicus in central Europe and the consistent occurrence of other phytoseiid species on the surveyed linden trees confirm the important role of urban greenery in landscape biodiversity.

Laboratory Studies on the Host Preference of Cotton Mealybug ‘Phenacoccussolenopsis’ Tinsely (Hemiptera: Pseudococcidae) in Khartoum State, Sudan

Cotton mealybug (Phenacoccussolenopsis) is a serious devastating pest which goes on a wide array of plant families. The pest spread all over the world from cool to dry hot regions. The main objective of this study was to investigate the food preference and behavior of P. solenopsis Tinseley (Hemiptera:Pseudococcidae) towards selected host plants in Khartoum State, Sudan, where a multi-choice experiment under laboratory conditions was adopted. Eight plant species were screened for attractiveness and food preference to Cotton mealybug. Where the proportions of the 1st, 2nd and 3rd nymphal instars and the adult females were recorded at 2, 8 and 24 hours after release, and compared with Chinese rose (Rosa chinensis) the control. The result revealed that the proportions of the 1st, 2nd and 3rd nymphal instars and adult females were maximum on plants of family Malvaceae, particularly the Okra (Hibiscus esculentus) followed by Cotton (Gossypium sp.) and Hambouk (Abutilon pannosum) as compared with the control. However, in contrast, the proportions were very low on unpalatable plants like Zaleya (Locally known as Raba) (Zaleyapentandra) and Eggplant (Solanum melongenaL.). However, in contrast, the proportions were very low on unpalatable plants like Zaleya (Locally known as Raba) (Zaleya pentandra) and Eggplant (SolanummelongenaL.). In conclusion, the most favorable host plants of the Cotton mealybug belonging to the family Malvaceae, while the families of Solanaceae [Egg plant (SolanummelongenaL.)] and Aizoaceae (Raba) were found to be the least preferred host plants.

Host utilization and fitness of the larval parasitoid Tetrastichus planipennisi are influenced by emerald ash borer’s food plants: Implications for biological control

Emerald ash borer (Agrilus planipennis) is one of the most destructive, invasive forest pests in North America and is responsible for the death of hundreds of millions of ash trees (Fraxinus spp.) in its introduced host range. Recently, this invasive beetle was also discovered attacking the white fringetree (Chionanthus virginicus) in North America. In response to emerald ash borer’s lack of evolutionary history with this host plant, we hypothesize that this host range expansion will result in enemy free space from the introduced larval parasitoid Tetrastichus planipennisi. Here we conducted both No Choice and Choice assays to evaluate the parasitism response of T. planipennisi to the emerald ash borer larvae reared or inserted in white fringetree sticks vs sticks of the favored host plant, green ash (F. pennsylvanica). Additionally, we observed the host-finding behavior of T. planipennisi when given a choice with the two host plants infested with emerald ash borer larvae. The No Choice assay demonstrates that T. planipennisi is able to parasitize and successfully develop on emerald ash borer larvae reared in white fringetree sticks. Choice assays further show that T. planipennisi is capable of parasitizing suitable stages of emerald ash borer larvae inserted in white fringetree even with the presence of emerald ash borer infested green ash in the same assay arena. However, rates of the host larval parasitism by T. planipennisi were significantly lower in white fringetree sticks than in green ash sticks and T. planipennisi spent less time on white fringetree sticks than green ash. These findings suggest that emerald ash borer may experience partial enemy free space through the utilization of white fringetree as an alternative host to ash, and thus biological control of emerald ash borer in white fringetrees with T. planipennisi may be less effective than in ash trees.

Canola Nutrition and Variety Affect Oviposition and Offspring Performance in the Generalist Herbivore, Mamestra configurata (Lepidoptera: Noctuidae).

Bertha armyworm Mamestra configurata Walker (Lepidoptera: Noctuidae) is a generalist herbivore that feeds on several crops in different plant families. Canola Brassica napus L. (Capparales: Brassicaceae) is one of the most favored host plants making the bertha armyworm a significant insect pest in the Canadian Prairie Provinces. The performance of the bertha armyworm on canola may vary with the quality of the canola plant. We tested the impact of plant nutrition and canola variety on oviposition and subsequent larval development of the bertha armyworm. A range of fertilization levels (0.0, 1.0, 3.0, and 5.0 g/pot) were applied to three different canola varieties: Clearfield 5535 CL, Roundup Ready hybrid 6060RR, and Q2. The total number of eggs laid on plants in a no-choice experiment increased with fertilizer level but a similar number of eggs were laid on plants that received moderate and high fertilizer treatments. Larvae reared on plants that received the moderate fertilizer application yielded heavier pupae than those reared on plants with low and high fertilizer treatments. Most eggs were laid on the Q2 variety when compared to Clearfield 5535 CL and Roundup Ready 6060 RR. Bertha armyworm females preferred to lay eggs on plants that received moderate or high fertilization over plants with the low fertilizer treatment. Plant leaf tissue nutrient content and plant growth were highest in plants that received moderate and high fertilizer treatment. We conclude that bertha armyworm oviposition behavior and larval performance are influenced by fertilizer treatment and canola variety.

Leaf Morphological Characters Can Be a Factor for Intra-Varietal Preference of Whitefly Bemisia tabaci (Hemiptera: Aleyrodidae) among Eggplant Varieties.

The sweetpotato whitefly, Bemisia tabaci (Hemiptera: Aleyrodidae) MEAM1, is considered a serious pest of horticultural and many other crops. While eggplant (Solanum melongena) is one of the most favored host plants, the whiteflies exhibit preferences among different varieties. We hypothesized that certain morphological leaf characteristics of different varieties, like leaf trichome density, trichome length, leaf lamina thickness and leaf color, may affect whitefly landing, feeding and oviposition. In this study, we investigated the variation in leaf morphological characters among selected eggplant varieties and evaluated the effect of these leaf characteristics in rendering eggplant varieties either susceptible or resistant to B. tabaci. We evaluated eight eggplant varieties in choice feeding tests, and we found that the varieties JinSheng Zilongchangqie (JSZ) and H149 were the highly preferred varieties with the highest numbers of whitefly adults and eggs. Significantly lower numbers of whitefly adult eggs were found on the resistant variety Tuo Lu Bamu (TLB). The varieties JinGuangbo Luqie (JGL), JinGuangbo Ziquanqie (JGZ), DaYang Ziguanqie (DYZ), QinXing Ziguanqie (QXZ), and QinXing Niuxinqie (QXN) were moderately favored by B. tabaci. Leaf trichome density, trichome length and leaf lamina thickness were positively correlated with numbers of whitefly adults and eggs. B. tabaci was less attracted to the leaves that reflect long and middle wavelength light (higher R and G values) than to the bright green leaves (medium G value), but the short wavelength light (higher B value) had no significant effect on whitefly preference. The degree of hue had a positive effect, and saturation and brightness had a negative effect on whitefly attraction.

BIOLOGI DAN NERACA HAYATI KUTU PUTIH PEPAYA PARACOCCUS MARGINATUS WILLIAMS & GRANARA DE WILLINK (HEMIPTERA: PSEUDOCOCCIDAE) PADA TIGA JENIS TUMBUHAN INANG

Biology and life table of papaya mealybug Paracoccus marginatus Williams & Granara de Willink (Hemiptera: Pseudococcidae) on three host plant species. The papaya mealybug, Paracoccus marginatus Williams & Granara de Willink (Hemiptera: Pseudococcidae), has been considered as a new invasive pest causing heavy damage on papaya in Indonesia since 2008. The pest is polyphagous with more than 55 host plant species. Study was conducted in laboratory with the objectives to determine developmental biology and life table parameters of the mealybug feeding on papaya, physic nut, and cassava leaves. Host plant species affected papaya mealybug performances. Egg stage lasted 7.25, 8.09, and 9.86 d on papaya, physic nut, and cassava, respectively. The shortest female nymphal developmental time was on papaya (18.91 d) and the longest on cassava (32.45 d). Longevity of adult males ranged from 1.09-2.85 d while females 12.29-14.93 d. When the mealybugs were reared on a seedling, the fecundity was higher on papaya (324.6) than those on physic nut (186.6) and cassava (157.5). No egg production occurred in virgin females. The sex ratio of P. marginatus favoured females, which comprised about 90% of population on papaya and cassava. The intrinsic rate of increase (rm) was significantly different among hosts, with the highest rate (0.117 female offspring/female/d) on papaya, followed by physic nut (0.079) and cassava (0.057). The maximum values of rmalong with net reproductive rate (Ro) and finite rate of increase(λ), and the shortest mean generation time (T) and doubling time (Dt) on papaya, indicating that papaya was the more favorable host plant for P.marginatus.

Repellency of selected Psidium guajava cultivars to the Asian citrus psyllid, Diaphorina citri

Huanglongbing (HLB) is the most devastating disease of citrus worldwide. It is caused by bacteria of the genus ‘Candidatus Liberibacter’ and transmitted by two psyllid species, the Asian citrus psyllid (ACP) Diaphorina citri, and the African citrus psyllid Trioza erytreae. Considerable research has been conducted toward developing and implementing HLB and ACP management strategies. With respect to ACP control, of interest is that reports indicate guava, Psidium guajava, can be repellent to ACP. We conducted research to further evaluate repellency of guava to ACP. In one set of experiments, guava oil from five Brazilian guava cultivars (‘J3’, ‘Pedro Sato’, ‘Século XXI’, ‘Thailand’ and ‘Paluma’) was extracted from leaves (immature and mature) by hydro-distillation in a Clevenger-type apparatus and evaluated for psyllid repellency. In a second set of experiments, repellency of guava leaves to ACP was investigated using leaves (immature and mature) from two guava cultivars in Florida, ‘Pink’ and ‘Thai White’. In each set of experiments, repellency was evaluated by releasing ACP adults into a cage with two large vials, one containing a young flush shoot (= immature leaves) of Murraya exotica (a favored host plant of the psyllid, the flush of which is highly attractive to ACP) and one with M. exotica flush and the test material of interest (guava oil, immature guava leaf or mature guava leaf). The adults were free to move throughout the cage and into the vials, and the number of psyllids in each vial was counted after 24 h. The results showed that all guava materials tested had at least some repellency to ACP. Mature leaves tended to have a greater repellent effect than immature leaves. Each of the five oils exhibited repellency. A report in the literature suggested that sulfur compounds associated with guava may be responsible for ACP repellency. Interestingly, the five guava oil extracts we studied were repellent to ACP but none contained any sulfur compounds. Identification of the constituents responsible for repellency could lead to new ACP management tactics.

Edge Effects Influence the Abundance of the Invasive Halyomorpha halys (Hemiptera: Pentatomidae) in Woody Plant Nurseries.

The invasive brown marmorated stink bug, Halyomorpha halys (Stål), has caused severe economic losses in the United States and is also a major nuisance pest invading homes. In diverse woody plant nurseries, favored host plants may be attacked at different times of the season and in different locations in the field. Knowledge of factors influencing H. halys abundance and simple methods to predict where H. halys are found and cause damage are needed to develop effective management strategies. In this study, we examined H. halys abundance on plants in tree nurseries as a function of distance from field edges (edge and core samples) and documented the abundance in tree nurseries adjoining different habitat types (corn, soybean, residential areas, and production sod). We conducted timed counts for H. halys on 2,016 individual trees belonging to 146 unique woody plant cultivars at two commercial tree nurseries in Maryland. Across three years of sampling, we found that H. halys nymphs and adults were more abundant at field edges (0-5 m from edges) than in the core of fields (15-20 m from edges). Proximity of soybean fields was associated with high nymph and adult abundance. Results indicate that monitoring efforts and intervention tactics for this invasive pest could be restricted to field edges, especially those close to soybean fields. We show clearly that spatial factors, especially distance from edge, strongly influence H. halys abundance in nurseries. This information may greatly simplify the development of any future management strategies.

Novel synthetic compounds enhance the attractiveness of host-plant volatiles: An opportunity to boost detection and monitoring of Asian citrus psyllid?

Author(s): Patt, J.; Woods, D.; Dimitratos, S.; Meikle, W.; Stockton, D.; Lapointe, S.; Mafra-Neto, A. | Abstract: In the absence of pheromone attractants, host-plant volatiles offer the most likely means of improving capture levels of ACP with sticky cards and other types of visual traps. However, developing scent lures that can compete with the attractiveness of actual host-plants, especially those in flush, is challenging. We are developing a new class of synthetic scent lures that may enhance the attractiveness of naturally-occurring host-plant volatiles. These compounds are synthetic ligands that bind to chemosensory proteins (CSPs) found in the olfactory sensilla of target insects. These ligands may mimic naturally-occurring odorants and function as super-stimuli because of their strong affinity to CSPs. In our study, CSPs from ACP antennae were identified based on their reactivity to petitgrain oil (an essential oil extracted from sour orange leaves), an ACP attractant. Two behavioral assays were used to assess the biological activity of several candidate ligands. One assay measured ACP probing frequency into a line of emulsified wax (SPLAT®, ISCA Technologies) containing a test ligand, the other assay measured the retention time of psyllids in an airstream carrying the ligand. One ligand, nicknamed ‘Titan’, was more stimulatory than limonene, a common citrus volatile, while a mixture of Titan and limonene was significantly more stimulatory than either alone. Subsequent assays showed that Titan was as stimulatory to ACP as the odor emitted by flushing sprigs of orange jasmine, a favored host-plant. These results indicate that CSP ligands may synergize the attractiveness of naturally-occurring citrus volatiles and boost their effectiveness as scent lures for ACP.

Spider mites adaptively learn recognizing mycorrhiza-induced changes in host plant volatiles.

Symbiotic root micro-organisms such as arbuscular mycorrhizal fungi commonly change morphological, physiological and biochemical traits of their host plants and may thus influence the interaction of aboveground plant parts with herbivores and their natural enemies. While quite a few studies tested the effects of mycorrhiza on life history traits, such as growth, development and reproduction, of aboveground herbivores, information on possible effects of mycorrhiza on host plant choice of herbivores via constitutive and/or induced plant volatiles is lacking. Here we assessed whether symbiosis of the mycorrhizal fungus Glomus mosseae with common bean plants Phaseolus vulgaris influences the response of the two-spotted spider mite Tetranychus urticae to volatiles of plants that were clean or infested with spider mites. Mycorrhiza-naïve and -experienced spider mites, reared on mycorrhizal or non-mycorrhizal bean plants for several days before the experiments, were subjected to Y-tube olfactometer choice tests. Experienced but not naïve spider mites distinguished between constitutive volatiles of clean non-mycorrhizal and mycorrhizal plants, preferring the latter. Neither naïve nor experienced spider mites distinguished between spider mite-induced volatiles of mycorrhizal and non-mycorrhizal plants. Learning the odor of clean mycorrhizal plants, resulting in a subsequent preference for these odors, is adaptive because mycorrhizal plants are more favorable host plants for fitness of the spider mites than are non-mycorrhizal plants.

Comparison of the potential rate of population increase of brown and green color morphs of Sitobion avenae (Homoptera: Aphididae) on barley infected and uninfected with Barley yellow dwarf virus

Life tables of brown and green color morphs of the English grain aphid, Sitobion avenae (Fabricius) reared on barley under laboratory conditions at 20 ± 1°C, 65% ± 5% relative humidity and a photoperiod of 16 : 8 h (L : D) were compared. The plants were either: (i) infected with the Barley yellow dwarf virus (BYDV); (ii) not infected with virus but previously infested with aphids; or (iii) healthy barley plants, which were not previously infested with aphids. Generally, both color morphs of S. avenae performed significantly better when fed on BYDV-infected plants than on plants that were virus free but had either not been or had been previously infested with aphids. Furthermore, when fed on BYDV-infected plants, green S. avenae developed significantly faster and had a significantly shorter reproductive period than the brown color morph. There were no significant differences in this respect between the two color morphs of S. avenae when they were reared on virus-free plants that either had been or not been previously infested with aphids. These results indicate that barley infected with BYDV is a more favorable host plant than uninfected barley for both the color morphs of S. avenae tested, particularly the green color morph.

Evaluation of Management Programs for Protecting Young Citrus Plantings from Huanglongbing

Asiatic huanglongbing (HLB) is a devastating disease of citrus associated in North America with the bacterium ‘Candidatus Liberibacter asiaticus’ (LAS) vectored by the Asian citrus psyllid (ACP), Diaphorina citri Kuwayama. ACP management is considered a vital component of a program aimed at reducing the incidence and spread of HLB. Considerable research has been published comparing the efficacy of different insecticides for ACP control as well as on seasonal strategies for applying ACP insecticides. However, published information was largely lacking for even the most intense insecticide programs on their effectiveness for keeping HLB out of a new citrus planting in Florida citrus. We therefore conducted two replicated (individual plots 0.2 to 0.4 ha in size) experiments on protecting young citrus from HLB using different ACP management programs. An intensive insecticide program was evaluated in each experiment: eight annual calendar applications of traditional insecticides (hereafter referred to as the “complete” program). In one experiment, citrus was either planted alone and subjected to the complete program or citrus was interplanted with orange jasmine, Murraya exotica L. (a favored ACP host plant) and subjected to a reduced insecticide program (four calendar sprays of traditional insecticides). There was one set of plots in which both jasmine and citrus were treated with insecticides and one set in which jasmine was not treated at all. In the second experiment, citrus was either subjected to the complete program or to one of two other programs: a reduced insecticide program consisting of five calendar applications of traditional insecticides or a mineral oil program (oil applications every 3 weeks plus one dormant insecticide spray). The results of the two experiments were similar. Relatively good ACP control was achieved under each ACP management program during the first year but, as the experiments progressed and trees increased in size, ACP outbreaks occurred regardless of the psyllid management program. Little HLB developed under any ACP management program during the first year, but thereafter HLB increased and large percentages of the trees in each experiment became LAS-infected in less than two to three years. The combined results of the experiments indicated that up to eight monthly pesticide treatments per year applied on a calendar schedule were ineffective for preventing young citrus from becoming diseased. Of important significance is that the orchard within which the two experiments were conducted was subjected to a minimal psyllid management program and contained many older trees known to be infected by the HLB pathogen, a challenging situation for getting young trees into production without contracting the disease. Thus, the ACP management programs we evaluated might have been more effective if ACP in the surrounding areas had been more aggressively controlled and diseased trees in the surrounding areas removed to reduce inoculum loads. Also, the programs might have been more effective for slowing the spread of HLB if our research plots had been larger.

Analysis of morphological traits in different host plants associated with resistance to Phenacoccus solenopsis- an invasive pest in Pakistan

Phenacoccus solenopsis Tinsley (Pseudococcidae: Hemiptera) is a sucking insect pest and is polyphagous in nature. Twenty five (25) different host plants were screened against P. solenopsis and their physicomorphic traits were determined to correlate their role against pest population. Among the tested plant species, most favorable host plants of mealy bug on the basis of population were Gossypium hirsutum (69.74±10.5), Solamum melongena (62.41±10.0), Helianthus annuus (61.83±10.0), Hibiscus rosa-sinensis (61.1±10.0) and Lantana camara (55.83±9.75), but the least preferred plants were tandla Digera arvensis (1.57±1.00) and Conyza bonariensis (3.83±1.75). Significant variations were observed in all the morphological plant characters recorded from different plant species. The maximum leaf thickness per plant was 2.04±0.23 im in plant species S. melongena while minimum thickness of leaf was recorded from lehli (0.25±0.02 im). Maximum trichome density per plant was 444±72.4 in sunflower followed by 411.6±19.6, 399±52, 391.6±22.0, in C. bonariensis, Abelmoschus esculentus and Withania somnifera respectively but minimum were 2.33±1.45 in Chinopodium morale , followed by 2.66±1.4, and 3±2.08 in Portulaca oleracea and Trianthema portulacastrum respectively. The maximum hair length per plant (2.62±0.07 mm) was of sunflower followed by 2.55±0.03 mm in okra, 2.53±0.06 mm in both S. melongena and G. hirsutum . It was concluded that plant characters including trichome density and hair length favor mealy bug population showing r-values of 0.357* and 0.190 respectively but leaf size and leaf width (leaf area and leaf thickness) exerted negative effect on pest population showing r-values of -0.172 and -0.285 respectively. Key words : Phenacoccus solenopsis , invasive species, physicomorphic traits, resistance.