Host plant phenology affects performance of an invasive weevil, Phyllobius oblongus (Coleoptera: Curculionidae), in a northern hardwood forest

We investigated how host plant phenology and plant species affected longevity, reproduction, and feeding behavior of an invasive weevil. Phyllobius oblongus L. (Coleoptera: Curculionidae) is common in northern hardwood forests of the Great Lakes Region. Adults emerge in spring, feed on foliage of woody understory plants, and oviposit in the soil. Preliminary data indicate that adults often feed on sugar maple, Acer saccharum Marshall, foliage early in the season, then feed on other species such as raspberry, Rubus spp. Whether this behavior reflects temporal changes in the quality of A. saccharum tissue or merely subsequent availability of later-season plants is unknown. We tested adult P. oblongus in laboratory assays using young (newly flushed) sugar maple foliage, old (2-3 wk postflush) sugar maple foliage, and raspberry foliage. Raspberry has indeterminate growth, thus always has young foliage available for herbivores. Survival, oviposition, and leaf consumption were recorded. In performance assays under no-choice conditions, mated pairs were provided one type of host foliage for the duration of their lives. In behavioral choice tests, all three host plants were provided simultaneously and leaf area consumption was compared. Adults survived longer on and consumed greater amounts of young maple and raspberry foliage than old maple foliage. P. oblongus preferred young maple foliage to old maple foliage early in the season, however, later in the growing season weevils showed less pronounced feeding preferences. These results suggest how leaf phenology, plant species composition, and feeding plasticity in host utilization may interact to affect P. oblongus population dynamics.     

The biology and preliminary host range of Megacopta cribraria (Heteroptera: Plataspidae) and its impact on kudzu growth

The bean plataspid, Megacopta cribraria (F.), recently was discovered in the United States feeding on kudzu, Pueraria montana Lour. (Merr.) variety lobata (Willd.), an economically important invasive vine. We studied its biology on kudzu and its impact on kudzu growth. We also tested its ability to use other common forest legumes for oviposition and development. Flight intercept traps operated from 17 May 2010 to 31 May 2011 in a kudzu field near Athens, GA showed three peaks of adult flight activity suggesting there are two generations per year on kudzu. Vine samples examined for eggs from April 2010 to April 2011 and June to October 2011 showed two periods of oviposition activity in 2010, which coincided with the peaks in adult activity. In 2011, the second period of oviposition began on or before 24 June and then egg abundance declined gradually thereafter until late August when we recovered <2 eggs/0.5 m of vine. Samples of the five nymphal instars and adults on vines did not show similar trends in abundance. Adults did not lay eggs on the various legume species tested in 2010 in a no-choice test possibly because the cages were too small. In the 2011 field host range experiments conducted in a kudzu field by using 12 legume species, M. cribraria preferentially oviposited on kudzu over soybean, Glycine max Merrill., but they still laid 320 eggs per plant on soybean. Lespedeza hirta (L.) Hornem. and Lespedeza cuneata (Dum. Cours.) G. Don had 122.2 and 108.4 eggs per plant, respectively. Kudzu and soybean were the only species M. cribraria completed development on. Plots protected from M. cribraria feeding by biweekly insecticide applications had 32.8% more kudzu biomass than unprotected plots. Our results show that M. cribraria has a significant impact on kudzu growth and could help suppress this pest weed.     

No-choice preference of cerotoma trifurcata (coleoptera: chrysomelidae) to potential host plants of bean pod mottle virus (Comoviridae) in Iowa

To better understand the naturally occurring host range of Bean pod mottle virus (family Comoviridae, genus Comovirus, BPMV) and its principal vector Cerotoma trifurcata (F?rster) (Coleoptera: Chrysomelidae), 18 field-collected perennial plant species were tested for the presence of BPMV. By using no-choice assays, we determined the preference of these plants by bean leaf beetle, by measuring their level of herbivory relative to soybean, Glycine max (L.). New food hosts for adult bean leaf beetles include Lespedeza capitata (Michaux), Lotus corniculatus L., Trifolium alexandrinum L., Trifolium ambiguum Bieberstein, and Trifolium incarnatum L. Desmodium illinoense Gray is discovered as a new naturally occurring host for BPMV.     

Factors restricting the feeding of the cabbage stem flea beetle (Psylliodes chrysocephala)

The feeding acceptability of 40 different plants to Psylliodes chrysocephala L. (Coleoptera: Chrysomelidae) was determined using leaf disc consumption tests for the adult, and stem or petiole penetration tests for the larvae. Only plants that contained glucosinolates were accepted as food, but addition of the glucosinolate sinigrin to rejected food plants did not make them acceptable to adults. Of the 34 plants that contained glucosinolates, nine were either totally or mostly rejected. Solvent extracts of the rejected plants applied to oilseed rape inhibited feeding by adults. The feeding of P. chrysocephala within the group of plants tested is influenced by the presence or absence of glucosinolates, which may act as feeding stimulants, and other, unidentified chemicals which act as feeding inhibitors.     

Insect responses to plant water deficits. I. Effect of water deficits in soybean plants on the feeding preference of Mexican bean beetle larvae

Abstract. 1. We examined the preference of larvae of the Mexican bean beetle, Epilachna varivestis Mulsant (Coleoptera: Coccinellidae), for foliage of soybean ( Glycine max [L.] Merr.) grown under several levels of water deficit. Third instar larvae were exposed simultaneously to excised foliage from plants that were either well-watered (control) or had experienced water deficits (treatment).
2. Water-deficient plants were re-watered 12 h prior to initiating feeding trials to eliminate physical differences between control and treatment foliage such as leaf water potential, diffusive resistance, relative water content, and foliage toughness.
3. Examination of the free amino acid contents of re-watered and excised foliage indicated that amino acid concentrations increased markedly in foliage grown under water deficits, and that this increase persisted during the preference tests.
4. Larvae preferred control foliage, but shifted preference to treatment foliage under mild water deficits. When the leaf water potential of water-deficient treatment foliage was lower than – 1.13 MPa or when it was more than 0.5 MPa lower than that of control foliage, larvae preferred to feed on foliage from well-watered control plants.
5. The expression of preference for well-watered control foliage was coincident with increases in the concentrations of total free amino acids and individual free amino acids in the water-deficient treatment foliage.
6. These results are inconsistent with White's (1974) hypothesis because Mexican bean beetle larvae avoid plants grown under water deficits that have increased concentrations of free amino acids.     

Companion planting – do aromatic plants disrupt host‐plant finding by the cabbage root fly and the onion fly more effectively than non‐aromatic plants?

Brassica and Allium host‐plants were each surrounded by four non‐host plants to determine how background plants affected host‐plant finding by the cabbage root fly (Delia radicum L.) and the onion fly [Delia antiqua (Meig.)] (Diptera: Anthomyiidae), respectively. The 24 non‐host plants tested in field‐cage experiments included garden ‘bedding’ plants, weeds, aromatic plants, companion plants, and one vegetable plant. Of the 20 non‐host plants that disrupted host‐plant finding by the cabbage root fly, fewest eggs (18% of check total) were laid on host plants surrounded by the weed Chenopodium album L., and most (64% of check total) on those surrounded by the weed Fumaria officinalis L. Of the 15 plants that disrupted host‐plant finding in the preliminary tests involving the onion fly, the most disruptive (8% of check total) was a green‐leaved variant of the bedding plant Pelargonium × hortorum L.H. Bail and the least disruptive (57% of check total) was the aromatic plant Mentha piperita × citrata (Ehrh.) Briq. Plant cultivars of Dahlia variabilis (Willd.) Desf. and Pelargonium×hortorum, selected for their reddish foliage, were less disruptive than comparable cultivars with green foliage. The only surrounding plants that did not disrupt oviposition by the cabbage root fly were the low‐growing scrambling plant Sallopia convolvulus L., the grey‐foliage plant Cineraria maritima L., and two plants, Lobularia maritima (L.) Desv. and Lobelia erinus L. which, from their profuse covering of small flowers, appeared to be white and blue, respectively. The leaf on which the fly landed had a considerable effect on subsequent behaviour. Flies that landed on a host plant searched the leaf surface in an excited manner, whereas those that landed on a non‐host plant remained more or less motionless. Before taking off again, the flies stayed 2–5 times as long on the leaf of a non‐host plant as on the leaf of a host plant. Host‐plant finding was affected by the size (weight, leaf area, height) of the surrounding non‐host plants. ‘Companion plants’ and aromatic plants were no more disruptive to either species of fly than the other plants tested. Disruption by all plants resulted from their green leaves, and not from their odours and/or tastes.     

Altered GAI activity of hybrid aspen has minimal effects on the performance of a polyphagous weevil,Polydrusus sericeus

Genetically modified plants can have unintended effects on herbivores, even when the transgene is not explicitly devised for pest protection. These effects may lead to altered ecological relationships in areas where transgenic plants are deployed. We tested several genetically‐modified hybrid aspen clone INRA 717‐IB4 [Populus tremula L. ×P. alba L. (Salicaceae)] lines expressing transgenic constructs with altered gibberellic acid expression for their effects on a polyphagous insect, Polydrusus sericeus (Schaller) (Coleoptera: Curculionidae). Longevity, egg production, and leaf consumption were measured in laboratory assays. Only male longevity was negatively affected by foliage from genetically modified trees, and in no case was oviposition or leaf consumption significantly altered. The importance of males in population dynamics varies among species, but we do not have evidence it is a major driver in this system. Contrary to our hypothesis of increased performance on modified foliage, adult P. sericeus were rarely affected by GM foliage, suggesting that not all genetic modifications that alter secondary metabolism in plants will necessarily have a strong effect on specific insect‐plant relations, supporting the view that evaluations continue to require case by case analysis.     

Oviposition behaviors in relation to rotation resistance in the western corn rootworm

Across a large area of the midwestern United States Corn Belt, the western corn rootworm beetle (Diabrotica virgifera virgifera LeConte, Coleoptera: Chrysomelidae) exhibits behavioral resistance to annual crop rotation. Resistant females exhibit increased locomotor activity and frequently lay eggs in soybean (Glycine max L.) fields, although they also lay eggs in fields of corn (Zea mays L.) and other locations. The goals of this study were (1) to determine whether there were any differences in ovipositional behavior and response to plant cues between individual rotation-resistant and wild-type females in the laboratory and (2) to examine the roles of, and interaction between, host volatiles, diet, and locomotor behavior as they related to oviposition. Because rootworm females lay eggs in the soil, we also examined the influence of host plant roots on behavior. In the first year of the study, rotation-resistant beetles were significantly more likely to lay eggs in the presence of soybean foliage and to feed on soybean leaf discs than wild-type females, but this difference was not observed in the second year. Oviposition by rotation-resistant females was increased in the presence of soybean roots, but soybean herbivory did not affect ovipositional choice. Conversely, ovipositional choice of wild-type females was not affected by the presence or identity of host plant roots encountered, and wild-type females consuming soybean foliage were more likely to lay eggs.     

Host plant, temperature, and photoperiod effects on ovipositional preference of Frankliniella occidentalis and Frankliniella fusca (Thysanoptera: Thripidae)

Host plant effects of tomato, Lycopersicon esculentum Mill., and chickweed, Stellaria media (L.) Vill., foliage infected and uninfected with Tomato spotted wilt virus (family Bunyaviridae, genus Tospovirus, TSWV) on the ovipositional preferences of western flower thrips, Frankliniella occidentalis (Pergande), and tobacco thrips, Frankliniella fusca (Hinds), were investigated for whole plants in the greenhouse. In addition, the preference for leaf disks from the same host plants was investigated under a range of temperatures, 15-30 degrees C at a photoperiod of 12:12 (L:D) h, and at three photoperiods, 6:18, 12:12, and 18:6, at 20 degrees C in no-choice and choice studies conducted in growth chambers. In a choice test, F. fusca oviposited significantly more eggs per whole plant foliage over a 7-d period than F. occidentalis by an average ratio of 3:1 over both tomato and chickweed. The optimum temperature for oviposition of F. occidentalis and F. fusca was 24.5 and 24.9 degrees C, respectively. Both species laid significantly more eggs under the longest daylight hours tested, 18:6, in the choice study. Temperature and photoperiod did not significantly interact in terms of thrips ovipositional preference. Ovipositional preference for chickweed or tomato foliage was different for each thrips species in the choice and no-choice tests. However, both thrips species laid significantly more eggs per square centimeter of leaf area in chickweed than in tomato in the whole plant choice test.     

Prior host feeding experience influences ovipositional but not feeding preference in a polyphagous insect herbivore

Black vine weevils, Otiorhynchus sulcatus (Fabricius) (Coleoptera: Curculionidae), are globally‐distributed polyphagous pests of many horticultural crops. We investigated how adult weevils were affected by host switching and, in particular, how host plant species nutritional and defensive chemistry affected subsequent host plant species selection and oviposition. Adults were fed one of three host plant species, blackcurrant [Ribes nigrum L. (Grossulariaceae)], raspberry [Rubus idaeus L. (Rosaceae)], or strawberry [Fragaria x ananassa Duchesne (Rosaceae)], throughout their pre‐reproductive periods and then subjected to behavioral choice assays with these plants. Foliar chemistry differed significantly among the three host plant species. Compared to raspberry and strawberry foliage, blackcurrant foliage was 13% lower in nitrogen, 3% higher in carbon, and 28% higher in phenolic compounds. Initial host plant species had a significant effect on weevil mortality, with more weevils dying when previously fed blackcurrant (12%) than strawberry (3%) or raspberry (0%) regardless of subsequent host. Initial host plant species also affected oviposition, with weevils laying only ca. two eggs per week when previously fed blackcurrant, compared to those on raspberry or strawberry (ca. 11 and 15 eggs per week, respectively). When given a choice, weevils discriminated among host plant species and tended to oviposit on plants on which they had previously fed, even when the plant was nutritionally inferior for egg production and adult survival. In contrast, feeding behavior was only affected by the current host plant species. Feeding and oviposition were related to leaf chemistry only in blackcurrant, as leaf consumption was negatively correlated with foliar carbon and zinc concentrations, and positively correlated with foliar phosphorus and potassium concentrations.     

Gallerucida bifasciata (Coleoptera: Chrysomelidae), a potential biological control agent for Japanese knotweed (Fallopia japonica)

Host specificity of foreign natural enemies are becoming more and more critical in classical biological control programs, as concerns about potential risk from introduced biocontrol agents have been increasing recently. Understanding the insect's fundamental and ecological host ranges is the first step in determining the potential for introduction of an insect to control invasive plants. Japanese knotweed, Fallopia japonica (Houttuyn) Ronse Decraene (Polygonaceae) is an invasive weed in the United States and Europe. A leaf beetle, Gallerucida bifasciata (Coleoptera: Chrysomelidae) is an important natural enemy attacking this plant in Asia. However, its host range records were ambiguous. This study examined the beetle's host specificity through a set of choice and no-choice tests in the laboratory and field in its native China. Gallerucida bifasciata larvae were able to complete development on seven of 87 plant species in larval development tests, while adults fed and oviposited on 10 plants in no-choice tests. Multiple choice tests showed adults strongly preferred Fallopia japonica, Persicaria perfoliata (L.) H. Gross and Polygonum multiflorum Thunb over all other plants. Open field tests and field surveys further revealed that these three species were in its ecological host range. The results of this study suggest that G. bifasciata is a potential promising agent for control of Japanese knotweed in the United States and Europe, although additional host specificity tests and risk assessment should be completed.     

Augmentation of soil detritus affects the spider community and herbivory in a soybean agroecosystem

If soil detritivores provide a significant prey source for predators in the vegetation, then augmentation of the soil community could affect the grazing food web. Specifically, increases in predator density could enhance any top‐down effects and reduce herbivory. We tested this hypothesis by providing detrital subsidies in the form of composted vegetable matter to 36 m² plots in soybean, Glycine max (L.) Merr. (Fabales: Fabaceae), fields that were managed using either conventional or conservation tillage practices. The foliage‐dwelling spiders, insect predators, and leaf‐chewing insects were censused and the body size of one large spider species, Argiope trifasciata (Forskål) (Araneae: Araneidae), was measured. In addition, the density and size of the plants were assessed and leaf damage was quantified. Any effects of treatments on the palatability of soybean plants to herbivores were determined in two laboratory experiments. Compost increased the density of foliage dwelling spiders and the abdomen size of A. trifasciata. We uncovered no treatment effects on insect predators, herbivorous insects, or plant characteristics except that compost addition reduced leaf damage. In addition, there was a negative correlation across plots between spider abundance and soybean leaf damage and abdomen width of A. trifasciata and weed herbivory levels across plots. These results suggest a connection between the soil community and the foliage food web, but the spiders appear to have exerted a top‐down effect without a shift in herbivore abundance. Further study of the specific seasonality of the herbivores and their behavior in the presence of spiders are needed to uncover the underlying mechanism. Nevertheless, these results provide evidence for complex linkage between the soil and grazing food webs that may be important to biological control.     

Host plant choice experiments of Colorado potato beetle (Coleoptera: Chrysomelidae) in Virginia

Field and laboratory-choice experiments were conducted to understand aspects of host plant orientation by the Colorado potato beetle, Leptinotarsa decemlineata Say (Coleoptera: Chrysomelidae), in Virginia. In laboratory bioassays, L. decemlineata oriented to volatiles emitted by potato, Solanum tuberosum L., foliage over both tomato, Lycopersicon esculentum L., and eggplant, Solanum melongena L., foliage, and eggplant over tomato foliage, all of which had been mechanically damaged. Field choice tests revealed more L. decemlineata adults, larvae, and egg masses on eggplant than on tomato. In other experiments, counts of live L. decemlineata on untreated paired plants and counts of dead beetles on imidacloprid-treated plants did not differ between potato and eggplant. L. decemlineata was significantly attracted to eggplant over both tomato and pepper. To determine whether feeding adults affected orientation to host plants, an imidacloprid-treated eggplant or potato plant was paired with an untreated eggplant or potato plant covered in a mesh bag containing two adult male beetles. Significantly more adults were attracted to eggplant with feeding male beetles paired with another eggplant than any other treatment combination. These results indicate that the presence of male L. decemlineata on plants affects host plant orientation and suggests that the male-produced aggregation pheromone may be involved.     

Plant defense elicitors fail to protect Viburnum dentatum from herbivory by viburnum leaf beetle (Coleoptera: Chrysomelidae)

Pyrrhalta viburni (Paykull) (Coleoptera: Chrysomelidae), a new landscape pest in the United States, feeds in both the larval and adult stages on foliage of plants in the genus Viburnum. A field trial was conducted from 2004 to 2006 to examine the impact of several elicitors of plant defense on ability of arrowwood viburnum (Viburnum dentatum L.) to resist attack by P. viburni in both larval and adult stages. The treatments included jasmonic acid (JA), harpin, and paclobutrazol. For comparison, imidacloprid and untreated controls were included in the trial. The soil-applied treatments (paclobutrazol and imidacloprid) were applied once during the trial (spring 2004), and the foliarly applied treatments (JA and harpin) were applied each spring. Herbivory by viburnum leaf beetle larvae and adults was measured yearly in spring and summer, respectively, and plant height was recorded at the end of each growing season. The only treatment that decreased feeding by viburnum leaf beetle was imidacloprid; these plants were virtually untouched throughout the duration of the trial. Plants treated with JA and harpin actually suffered greater feeding damage at the end of the second growing season; other than this observation, the elicitors had no impact on viburnum leaf beetle. As expected, plant height was decreased for the shrubs treated with paclobutrazol, a plant growth regulator, and unaffected by JA and harpin. Plant height was increased for the shrubs treated with imidacloprid. These shrubs also seemed to be protected from viburnum leaf beetle after residues dropped below lethal levels.     

Use of transgenic plants to measure insect herbivore movement

Use of ingested transgenic corn tissue as a marker for measuring movement of adult Diabrotica virgifera virgifera (LeConte) (Coleoptera: Chrysomelidae; western corn rootworm) was investigated. Laboratory observations of beetles feeding on corn foliage, pollen, silks, or soybean foliage provided background on feeding patterns. The interval between food consumption and its appearance in feces (gut passage time) ranged from 102.7 +/- 11 min for soybean foliage to 56.7 +/- 2.9 min for corn silks. In a laboratory assay, protein expression tests identified the presence of Cry3Bb1 protein inside 50% of adult D. virgifera for up to 16 h after they had last consumed Cry3Bb1 protein-expressing corn silks from 'YieldGard Rootworm' corn plants (Monsanto Co.). Cry3Bb1 protein could not be detected by 32 h postfeeding. The proportion of Cry3Bb1 protein-positive beetles declined linearly with increasing time since feeding on 'YieldGard Rootworm' tissue. Approximately 20% of adult D. virgifera collected near 'YieldGard Rootworm' corn plots tested positive for Cry3Bb1 protein, indicating 'YieldGard Rootworm' tissue consumption within the last 16-32 h. Based on a 16- to 32-h postfeeding detection interval for Cry3Bb1 protein and the distance between 'YieldGard Rootworm' sources and sites where Cry3Bb1-positive insects were collected, 85.3% of males and females moved < or = 4.6-9.1 m/d through R2-R3 stage corn. Among Cry3Bb1-positive adults that left corn and were captured in an adjacent soybean field, 86.4% of males and 93.1% of females moved < or = 4.6-9.1 m/d through soybean. Detection of transgenic plant tissues in mobile insect herbivores is a novel application of biotechnology to the study of insect movement.     

Host range evaluation of the leaf-feeding beetle,Zygogramma bicolorata and the stem-boring weevil,Listronotus setosipennis demonstrates their suitability for biological control of the invasive weed,Parthenium hysterophorus in Ethiopia

The invasive weed, parthenium (Parthenium hysterophorus L.) (Asteraceae: tribe Heliantheae), damages agriculture, adversely impacts biodiversity and is hazardous to human and animal health in Ethiopia. The host range of two natural enemies, a leaf-feeding beetle, Zygogramma bicolorata (Coleoptera: Chrysomelidae) and a stem-boring weevil, Listronotus setosipennis (Coleoptera: Curculionidae) was evaluated for biological control of the weed in Ethiopia. The specificity of Z. bicolorata and L. setosipennis was assessed against 29 and 31 non-target plant species, respectively. The host range of Z. bicolorata and L. setosipennis was first assessed using no-choice tests to examine their oviposition and feeding response on non-target plants. Although oviposition by Z. bicolorata occurred on six non-target species in four Asteraceae species in no-choice tests, it was significantly lower than on parthenium and no larvae developed. Zygogramma bicolorata nibbled the leaves of one of the five niger seed (Guizotia abyssinica L. – an oil seed crop closely related to parthenium) cultivars tested, but feeding and oviposition were significantly less than on parthenium. Furthermore, choice tests indicated that Z. bicolorata did not oviposit nor feed on G. abyssinica when parthenium was present. In no-choice tests, L. setosipennis did not oviposit on any of the non-target species assessed. Mean oviposition on parthenium was 39.0?±?3.4 eggs per plant whereas no eggs were laid on any of the 31 species tested. Based on these and other host range tests, permission was obtained to field release Z. bicolorata and L. setosipennis in Ethiopia.     

Effect of soybean varieties on survival and fecundity of western corn rootworm

The western corn rootworm, Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae), is a major pest of corn (Zea mays L.) in North America and has evolved resistance to crop rotation by ovipositing in alternate crops such as soybeans [Glycine max (L.) Merr.]. Through experiments with plants grown in the greenhouse and the field, we tested whether soybeans with resistance to the soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), affected survival, fecundity, and consumption of soybean for D. v. virgifera. Soybean varieties tested included those types resistant to A. glycines (Rag1 and rag1/rag3) and a susceptible near isoline of the Rag1 variety. Females were provided with a diet of corn tissue for 4 d after which they were fed a diet of tissue from one of three soybean varieties for 4 d, starved for 4 d, or fed corn tissue. When fed greenhouse grown plants, strains differed significantly in survival and consumption, but consumption did not differ by variety of soybean. Diet treatment only affected fecundity; individuals fed corn continuously had greater fecundity than those individuals fed soybeans. In the experiment with plants grown in the field, leaf consumption differed among strains and individuals fed corn continuously had greater fecundity than the other treatments. Soybean varieties with Rag1 and rag1/rag3 resistance to A. glycines did not appear to affect the fitness of D. v. virgifera. Thus, planting of these A. glycines-resistant soybean varieties should not directly affect the spread of rotation-resistant D. v. virgifera.     

Prior flea beetle herbivory affects oviposition preference and larval performance of a potato beetle on their shared host plant

Abstract 1. The herbaceous plant Solanum carolinense (L.) (Solanaceae) is host to a number of specialist insects, including the leaf-feeding beetles Epitrix fuscula (Crotch) and Leptinotarsa juncta (Germar) (Coleoptera: Chrysomelidae). Potted individuals of S. carolinense were subjected to one of two treatments: exposure to herbivory by E. fuscula or exclusion of all herbivores. The effects of E. fuscula herbivory on larval performance and oviposition preference of L. juncta were investigated.
2. Although the masses of the L. juncta pupae did not differ between the two treatments, larvae feeding on damaged plants developed more slowly than those feeding on undamaged plants.
3. In both paired leaf choice trials and whole plant choice trials, larvae of L. juncta showed no preference for undamaged versus damaged hosts.
4. In a field transplant experiment, adult L. juncta females showed slight feeding preferences and strong oviposition preferences for undamaged plants versus plants that had been fed on by E. fuscula .
5. The results are discussed with reference to their implications for plant-mediated competition among herbivores and constraints on the evolution of plant resistance.     

Plant-mediated effects on an insect–pathogen interaction vary with intraspecific genetic variation in plant defences

Baculoviruses are food-borne microbial pathogens that are ingested by insects on contaminated foliage. Oxidation of plant-derived phenolics, activated by insect feeding, can directly interfere with infections in the gut. Since phenolic oxidation is an important component of plant resistance against insects, baculoviruses are suggested to be incompatible with plant defences. However, plants among and within species invest differently in a myriad of chemical and physical defences. Therefore, we hypothesized that among eight soybean genotypes, some genotypes would be able to maintain both high resistance against an insect pest and high efficacy of a baculovirus. Soybean constitutive (non-induced) and jasmonic acid (JA)-induced (anti-herbivore response) resistance was measured against the fall armyworm Spodoptera frugiperda (weight gain, leaf consumption and utilization). Indicators of phenolic oxidation were measured as foliar phenolic content and peroxidase activity. Levels of armyworm mortality inflicted by baculovirus (SfMNPV) did not vary among soybean genotypes when the virus was ingested with non-induced foliage. Ingestion of the virus on JA-induced foliage reduced armyworm mortality, relative to non-induced foliage, on some soybean genotypes. Baculovirus efficacy was lower when ingested with foliage that contained higher phenolic content and defensive properties that reduced armyworm weight gain and leaf utilization. However, soybean genotypes that defended the plant by reducing consumption rate and strongly deterred feeding upon JA-induction did not reduce baculovirus efficacy, indicating that these defences may be more compatible with baculoviruses to maximize plant protection. Differential compatibility of defence traits with the third trophic level highlights an important cost/trade-off associated with plant defence strategies.     

Rapid preliminary characterisation of host specificity of leaf-beetles (Coleoptera: Chrysomelidae)

Rapid characterisation of host specificity is important both in biological control of weeds and studies in ecology and evolution. A means for doing this was developed and tested on four species of leaf beetles of interest for biological control of the weed Mimosa pigra (Mimosaceae). We identified the most promising for the more detailed tests necessary to obtain release approval. The impact of time-dependent effects and effects of experience were also investigated as part of this study but were not detected. Short-term host specificity tests on adult feeding accurately predicted the results of longer term trials. The long-term trial showed that survival on a plant species depended on feeding on it. Hence short-term feeding trials can predict the longer term survival of adults on other plant species. Different feeding results were obtained in cut foliage versus entire plants but no consistent pattern was shown: of the two insect species tested, one species ate more of the cut material while the opposite was demonstrated for the second species. Species in order of priority for further consideration as biocontrol agents were Syphrea bibiana, Genaphthona sp., Syphrea sp. and Paria sp. The latter three species were probably not sufficiently specific for release. The tests done here allow the identification of the most likely species upon which to conduct the more laborious and difficult larval developmental tests, saving considerable resources.