The reproductive behaviour of Metopolophium festucae (Theobald) at different temperatures and on different host plants

Metopolophium festucae is a cold-hardy species: on young oat seedlings nymphs are produced from apterae at temperatures below 6 °C. Alatae are less well adapted to low temperatures: in a laboratory experiment the average daily production of nymphs from apterae was 0·96 at 10·2 °C and 2·71 at 22·8 °C; the corresponding figures for alatae were 0·42 and 1·81. Aphids on oats, wheat and Italian ryegrass have a slightly higher progeny production than on barley, timothy and cocksfoot: the adults produced on the cereals are heavier than those on the grasses. It is postulated that the aphids require a perennial crop on which to overwinter as nymphs or parthenogenetic adults; consequently successful colonization of cereal crops is rare.     

The effect of plant phenology on the induction of alatae and the development of populations of Metopolophium dirhodum (Walker), the rose-grain aphid, on winter wheat

In field experiments apterous Metopolophium dirhodum produced significantly more alatae when reared on mature plants (milky ripe stage) than on young plants. Nymphal and adult survival and relative growth rate were little affected by the developmental stage of the host plant. Relative growth rate and fecundity were strongly related to temperature. Laboratory experiments confirmed that the developmental stage of wheat had no significant effect on survival or relative growth rate of the aphids. However, laboratory grown plants did not produce the levels of alate production seen in field crops and in the field experiments. It is suggested that in investigations into the effects of the host plant on cereal aphids field grown plants should be used whenever possible. Alate production is proposed as the major plant induced factor affecting the development of M. dirhodum populations on wheat in the field. Alatae developed on mature plants even when the number of aphids was very low.     

四种十字花科蔬菜上小菜蛾自然种群连续世代生命表

利用作用因子生命表技术,组建芥菜、芥蓝、小白菜和菜心4种十字花科蔬菜上小菜蛾自然种群连续世代生命表,分析寄主植物和生物因子对小菜蛾种群数量的控制作用。结果表明：在4种十字花科蔬菜的一造菜上,小菜蛾均能完成两个世代。虽然小菜蛾在芥菜上的初始卵量最高,但害虫种群总增长倍数在芥蓝上最高,其次为小白菜,菜心和芥菜,分别为17．64、11．90、11．43和3．76。这说明尽管芥菜对小菜蛾成虫的产卵有一定的吸引作用,但不适合小菜蛾生长发育。芥蓝是最适宜小菜蛾种群增长的寄主。生物因子在小菜蛾自然种群控制中起着重要的作用,但是在不同种类十字花科蔬菜上,天敌类群对小菜蛾控制作用存在一定差异。除芥菜之外,寄生性天敌对芥蓝、菜心和小白菜上的小菜蛾种群控制作用最大,其次为“捕食及其它”,病原微生物的控制作用最小。“捕食及其它”对芥菜上小菜蛾种群的作用非常明显,如果排除此因子作用,小菜蛾种群两代后将增长126．03倍。该因子是导致芥菜小菜蛾自然种群增长趋势指数低的主要原因。因此在制定小菜蛾防治策略时,应考虑蔬菜的种类和布局,加大对芥蓝小菜蛾种群的防治力度;芥菜可作为一种诱杀植物种植,以吸引小菜蛾产卵,并集中防治。这些防治策略在小菜蛾综合治理中具有重要的实际意义。     

A Possible Role for Rhizobacteria in Water Treatment by Plant Roots

By accumulating Cd from solution, roots of hydroponically grown Indian mustard (Brassica juncea L.), a high biomass crop plant, were able to cause substantial reductions in the concentration of Cd in solution. The removal of Cd from solution was linearly correlated with Cd accumulation by roots. Screening of 300 different rhizobacterial isolates identified several that, when inoculated onto roots of Indian mustard, significantly enhanced the total amount of Cd removed from solution. Further investigations revealed that this enhancement was because of an overall increase in root biomass in the rhizobacterial-treated plants. Rhizobacteria were found to accumulate Cd from solution, and ultrastructural observations suggested that rhizobacteria promote the precipitation of Cd on the root surface. By precipitating Cd at the root surface, rhizobacteria reduce the amount of Cd taken up into roots, thereby protecting the plants, and in particular the roots, from the toxic effects of Cd. This reduced Cd toxicity allows for the increased proliferation of roots observed when plants are inoculated with certain rhizobacteria.     

Comparative transmission of bean leaf roll and pea enation mosaic viruses by aphids

Acyrthosiphon pisum was a more efficient vector than Myzus persicae of bean leaf roll virus (BLRV), but the two species transmitted pea enation mosaic virus (PEMV) equally well and much more often than Megoura viciae. M. viciae did not transmit BLRV, and Aphis fabae did not transmit BLRV or PEMV. BLRV and PEMV were transmitted more often by nymphs of A. pisum than by adult apterae or alatae that fed on infected plants only as adults, but both viruses were readily transmitted by adults that had developed on infected plants. The shortest time in which nymphs acquired BLRV was 2 h, and 50 % transmitted after an acquisition period of 4 days. Some nymphs acquired PEMV in 30 min and 50% in 8 h. The shortest time for inoculation of BLRV by adults was 15 min, but some transmitted PEMV in probes lasting less than 1 min. The median latent periods of BLRV and PEMV in aphids fed for 12 h on infected plants were, respectively, 105 and 44 h. Clones of A. pisum differed in their ability to transmit BLRV and PEMV, and efficiency in transmitting the two viruses seemed to be unrelated. Some aphids that fed successively on plants infected with each virus transmitted both viruses, and infectivity with one virus did not seem to affect transmission of the other.     

Transgenic Bt maize and Rhopalosiphum padi (Hom., Aphididae) performance

Abstract.  1. The population abundance and age structure of Rhopalosiphum padi , one of the most common maize aphid species, on transgenic Bt (expressing the Cry1Ab protein) and non-Bt isogenic maize was studied in commercial plots during three crop seasons.
2. A higher density of aphids, particularly alates and young nymphs, occurred in Bt plots at very young maize development stages, corresponding to the settlement period, in the 3 years studied. Possible causes are discussed. After this period, there were no differences between Bt and non-Bt maize.
3. Mortality, development, and reproduction of the offspring of alate forms of R. padi and the offspring of different generations of apterous forms fed with Bt maize were evaluated in the laboratory under controlled conditions.
4. The developmental and pre-reproductive times of the offspring of the first generation of alatae were shorter and the intrinsic rate of natural increase ( r _m ) higher when aphids fed on Bt maize. The opposite occurs with the offspring of the first generation of apterous mothers, which have lower nymphal and adult mortality, shorter developmental and pre-reproductive times, a higher effective fecundity rate, and greater r _m , when fed on non-Bt maize. The differences in aphid development on the two cultivars may be linked to changes in host-plant quality due to pleiotropic effects of the genetic modification.
5. No differences on aphid mortality, developmental and pre-reproductive times, fecundity, and r _m were found between the offspring of apterous aphids maintained on Bt or non-Bt maize for several generations.     

Resistance to the aphid Metopolophium festucae cerealium: effects of the host plant on flight and reproduction

The levels of resistance present in two cereal and four grass hosts of M. f. cerealium were assessed in terms of the percentage of alatae flying from the host and reproductive rates of alatae. Festuca rubra and F. arundinacea exhibited highest levels of resistance, inducing a greater proportion of the alatae to fly (94% and 84% respectively) after producing only a few nymphs. Although between 38% and 64% of alatae flew from L. multiflorum, oats, L. perenne and wheat these alatae deposited more nymphs on the hosts before flight than occurred on Festuca. The weight of alatae did not influence the flight response. The differences in the flight/reproductive response of M. festucae to various host plants are discussed in relation to possible host selection strategies of this species and to antixenotic/antibiotic host resistance experiments in general.     

Aphid colonization of spring cereals

In 1970-1, Metopolophium dirhodum, Rhopalosiphum padi and Sitobion avenae were the commonest alatae trapped from April/May to August, with most in July and early August. The first alatae appeared in the Rothamsted survey suction trap 0–34 days before aphids were found on the cereals, but during May and June no relationship was found between the numbers trapped and the number on the crop. Most species occurred first near the sheltered edge of the crop, but M. dirhodum was widespread over the field. Most infestations were quickly dispersed by the movements of older morphs; adults only stayed in one place for about 2 days. Alate M. dirhodum moved more often than apterae, but both morphs of S. avenae moved equally often and more frequently between larvipositions than did those of M. dirhodum. Apterae deposited more nymphs in a ‘group’ than alatae, and M. dirhodum deposited more than S. avenae. Few ‘groups’ persisted for more than a week. Although M. dirhodum occupied the crop area faster than S. avenae, all 0–3 m lengths of row sampled being infested within 2–5 wk of their first appearance, most or all of the tillers were colonized only in late July 1970.     

Influence of prey on developmental performance, reproduction and prey consumption of Neoseiulus californicus (Acari: Phytoseiidae)

The Spical strain of the predatory mite Neoseiulus californicus (McGregor) is used as a biological control agent, but little is known about its preferred prey and host plants in Japan. Here we studied the development, reproduction and prey consumption of the Spical strain when fed on eggs of five different spider mite species deposited on both their laboratory-rearing plant and cherry, on which all five spider mite species developed well. The developmental periods of immature N. californicus females and males were significantly affected by the prey species they fed on, but not by the plants. No difference was found between males and females. The developmental period was shorter on eggs of two Tetranychus species than on eggs of Panonychus ulmi. Immature females had a higher predation rate than immature males. Preoviposition period, oviposition period and the number of eggs laid per female were not significantly affected by either the plants or the type of prey eggs. The postoviposition period and total adult longevity were shorter on eggs of P. ulmi than of the other four prey species, but there was no effect of plant substrate. The postoviposition period of the Spical strain was much longer than that of other N. californicus strains or other predatory mite species: the postoviposition period of the Spical strain was more than three times longer than the oviposition period, accounting for more than 75% of the total adult longevity. This suggests that the females need multiple mating to reach full egg load, but this remains to be tested. Total consumption by N. californicus adults was lower for eggs of P. ulmi than for eggs of the other four species, apparently because of the shorter postoviposition period when fed on eggs of P. ulmi. The intrinsic rates of natural increase (r _m) on the rearing plant did not differ among prey species, whereas those on cherry were significantly different: the value was higher on Tetranychus urticae eggs than on eggs of other species. Only when N. californicus fed on T. urticae eggs, the r _m-values were significantly different between the rearing plant and cherry (higher on cherry). Thus, the Spical strain of N. californicus could feed on eggs of all five spider mite species, deposited on a variety of plants with similar r _m-values, suggesting that it could be successfully used to control spider mites in orchards and various crop fields of Japan.     

Efficiency of food utilization by Dichroplus maculipennis (Orthoptera: Acrididae: Melanoplinae) on four crop plants under controlled conditions

The aim of this study was to analyze the food utilization efficiencies and the relative growth and consumption rates of different developmental stages and sexes of D. maculipennis under controlled conditions on wheat, oat, corn, and soybean plants, important crops in the Pampas region of Argentina. As expected from a polyphagous species, D. maculipennis was observed to consume all four of the plant species offered. Nevertheless, the consumption of both nymphs and adults was differentiated. Oat and wheat were more consumed than corn and soybean. Females presented higher consumption rates (384.6 ± 30.64 mg/individual/day) than males (278.71 ± 24.26 mg/individual/day). Adult females had the highest growth rate, followed by nymphs of the same sex, and then adult males. The highest values of ECI and ECD were obtained in soybean; females had higher values of food efficiencies than males, and nymphs had greater values than adults. In relation to this, soybean was the highest quality food; the amount of nitrogen present in soybean was approximately twice that found in the other species. The nutritional needs of D. maculipennis might have been satisfied by feeding on low quantities of soybean, which is, among the food offered, the most “nutritionally balanced food”.     

Relative preference of Lygus hesperus (Hemiptera: Miridae) to selected host plants in the field

Abstract Information on host plant preference of agriculturally important insect pests, such as Lygus hesperus (Knight), can be helpful in predicting its occurrence and future movement among crop and non-crop host plants. A field study was conducted during 2005 and 2006 to evaluate the host preference of Lygus to cotton and four other host plants in the Texas High Plains, including alfalfa (Medicago sativa L.), wild sunflower (Helianthus annuus L.), Russian thistle (Salsola iberica L.) and pigweed (Amaranthus palmeri L.). Sampling for both nymphs and adults during 2005 (July to November) and 2006 (June to November) showed that alfalfa and Russian thistle were the two most preferred hosts out of the five hosts evaluated. Abundance of nymphs (numbers per 50 sweeps per host plant) during the sampling period also indicated the superior reproductive suitability of alfalfa and Russian thistle. Cotton appeared to be the least attractive host plant for Lygus when Russian thistle and alfalfa were available in the host mosaic. Seasonal abundance of Lygus was found to be lower during 2006 compared to 2005, which may be explained by the difference in rainfall patterns during these two years. In terms of species dominance, L. hesperus was the most dominant species in the sampled population followed by an inconsiderable fraction of L. elisus and L. lineolaris.     

Evaluation of the local population of Eretmocerus mundus (Hymenoptera: Aphelinidae) for biological control of Bemisia tabaci biotype B (Hemiptera: Aleyrodidae) in greenhouse peppers in Argentina

Bemisia tabaci biotype B is a key pest in pepper crops in Argentina. The parasitoid Eretmocerus mundus is frequently found parasitizing this whitefly in greenhouses without pesticide applications. The present studies were carried out with the objective of evaluating control obtained with different rate and number of parasitoid releases under experimental conditions. Release rate: cages with pepper pots were positioned in an experimental greenhouse and randomly assigned to the release rate treatments (0, 1 and 3 pairs of E. mundus/plant/week with a total of three introductions). Number of releases: similar cages were assigned to the number of parasitoid introduction treatments (0, 1, 2 and 3) with the best release rate obtained in the previous trial. In both assays whitefly (adults and nymphs) and parasitoid (parasitized nymphs) population sizes in each cage were monitored weekly for a period of 10 weeks. Results suggested that the introduction of 2 E. mundus/plant/week was enough to suppress host population compared to control treatment (peaks of 7.75 adults and 58.75 nymphs/cage and 643.75 adults and 1598 nymphs/cage, respectively) (p < 0.05), with 85% of parasitism. E. mundus had to be introduced three times to achieve the best pest control (peaks of 1.17 adults and 20.33 nymphs/cage vs. 55.67 adults and 75 nymphs/cage in control treatment) with 84% of parasitism (p < 0.05). These results were then validated in a pepper crop under experimental greenhouse conditions. Whitefly population was lower in those greenhouses where E. mundus was released compared to control greenhouses (0.15 adults and 0.71 nymphs/4 leaves and 0.73 adults and 1.64 nymphs/4 leaves, respectively), with a peak of 54% of parasitism (p < 0.05). We concluded that good suppression of B. tabaci could be achieved using E. mundus under spring conditions in Argentina.     

Intra-specific mechanisms in relation to the natural regulation of numbers of Aphis fabae Scop

Parthenogenetic virginoparous apterae of Aphis fabae Scop. on field beans (Vicia faba) reproduced faster initially in populations of eight colonizing apterae than in those with 2–4 or 16–32 per plant. The aphids were at first mutually benefited but were quickly affected by competition as numbers rose above the critical density represented by about eight apterae and their first progeny. This is because the aphids remained densely aggregated and seemingly created a local shortage despite abundant food and space elsewhere on the plant. Such self-induced competition provides the basis for self-regulation of numbers of A. fabae in relation to (1) food and space provided by the growing plant and (2) mortality from natural enemies and from other causes including insecticides. As competition increased, the multiplication of A. fabae populations slowed, newly formed adult apterae emigrated and increasing numbers of alatae were formed. The mean weights of apterae decreased from about 1·8 mg. to 0·3 mg. and of alatae from 0·9 to 0·2 mg. Such decrease probably favours production of many adults that might otherwise fail to mature. Experiments in a glasshouse and in field cages indicated the success with which an A. fabae population adapts to and exploits a growing plant. Field bean plants sown in mid-March and infested as in the field produced an average of 15,000–17,000 A. fabae emigrants per plant of which 78–84% were adults (mostly alatae). This is equivalent to about 1600 million alate emigrants from 1 acre (0·4 hectare) of an infested field bean crop.     

Bottom-up Mediation of an Ant-Membracid Mutualism: Effects from Different Host Plants

The relationship between the membracid, Publilia modesta, and the tending ant, Formica obscuripes, was either a mutualism or commensalism depending on the host plant species. Experimental manipulation of the presence of ants in two different years indicated that the presence of ants had a positive effect on nymph numbers on both host plants, Chrysothamnus viscidiflorus and Wyethia spp. However, Wyethia spp. senesced before membracid nymphs reached adulthood, causing extensive mortality of membracids. In contrast, C. viscidiflorus plants senesced after nymphs had developed into adults. The increased number of nymphs in the presence of ants translated into more new adults on C. viscidiflorus, but not on Wyethia spp. Poor host plant choices may render the presence of ants irrelevant for such insects on some host plants. Being a host plant generalist may lead to significant variability in the outcomes of mutualistic interactions. Co-ordinating editor: N. Yamamura     

Biology of Tupiocoris cucurbitaceus (Hemiptera: Miridae), a predator of the greenhouse whitefly Trialeurodes vaporariorum (Hemiptera: Aleyrodidae) in tomato crops in Argentina

The predator Tupiocoris cucurbitaceus is frequently found attacking Trialeurodes vaporariorum in greenhouses without pesticide applications in Argentina. The objective of these studies was to evaluate some biological characteristics of this species fed on three types of diet (whitefly nymphs, Sitotroga cerealella eggs and a mix of both) and on two host plants (tomato and tobacco), under controlled experimental conditions. Preimaginal developmental time for female and male bugs was shorter in the presence of whiteflies than with only moth eggs. Females lived longer when they ate only whitefly nymphs compared to a mixed diet or only moth eggs. The amount of adult descendants was greater when bugs could eat whiteflies, regardless of the presence of S. cerealella. Embryonic development time, male longevity and sex proportion were not affected by the diet or the host plant. Prey consumption was evaluated for three T. cucurbitaceus life history stages (fourth/fifth instar nymphs, female and male adults) on two types of prey (whitefly nymphs and S. cerealella eggs). On tomato, females were more voracious than males and nymphs. On tobacco, adults and nymphs consumed more S. cerealella than T.vaporariorum nymphs, but again, bug females preyed more than males and nymphs. Results demonstrate that T. cucurbitaceus can survive, develop and reproduce normally using both T. vaporariorum and S. cerealella eggs as prey on tobacco or tomato plants. This information can be useful for managing this predator against T. vaporariorum through conservative or augmentative biological control strategies.     

Gene dispersal from transgenic crops

The risk of release of genetically modified oilseed rape (Brassica napus) was investigated in relation to interspecific gene flow with hoary mustard (Hirschfeldia incana). Microscopic studies showed polymorphism within the population of hoary mustard for pollen germination on oilseed rape flowers. The transgenic herbicide-resistant and a commercial cultivar of oilseed rape were not different for pollen behaviour and ovule fertilization. Pollen tube growth was slow and erratic in interspecific crosses. Fertilization efficiency of oilseed rape and hoary mustard pollen in interspecific crosses was 15% and 1.3%, respectively, of that in intraspecific crosses. This unequal efficiency in reciprocal crosses was confirmed by hybrid seed set in pods. There was no post-zygotic barrier to the development of hybrid embryos in hoary mustard pods. Up to 26 spontaneous hybrids per male sterile oilseed rape plant, and one per hoary mustard plant, were obtained in field experiments. Hybrids were identified by isozyme electrophoresis, morphology and cytology. All hybrids were triploid with 26 chromosomes, and had low fertility. They produced 0.5 seeds per plant after spontaneous backcrossing with hoary mustard. Some of these descendants were produced from unreduced gametes. Our results suggest that gene flow is likely to occur, but its actual frequency under crop growing conditions remains to be estimated.     

The effect of host quality and crowding on the settling and take-off of cereal aphids

Settling and take-off behaviour of Sitobion avenae was studied in the laboratory using infested and uninfested wheat at a range of developmental stages. Of the later developmental stages of wheat alate S. avenae preferred to settle on and gave birth to relatively more offspring on flowering and watery-ripe plants. The time to take-off of alatae which matured on wheat was influenced by both the developmental stage of their host plant and the degree of crowding they experienced. All alatae flew but those isolated on flowering plants stayed longer than those crowded or isolated on any of the other developmental stages tested. Similarly the number of offspring produced before take-off was inversely related to the degree of crowding and positively to the time spent on a plant before take-off.     

The effects of nutrition and density on the production of alate Elatobium abietinum on Sitka spruce

Summary Observations over a period of 10 years showed that, in Northeastern Scotland, alatae of E. abietinum regularly appeared in mid-May, the timing being unrelated to aphid density. The peak number of alatae produced was, however, correlated with aphid density. Following an initially high level the proportion of alatae dropped to virtually nil by mid-June, whilst over the same period the aphid population density increased. Amino acid levels in spruce needles were considerably higher during the period of alate formation than they were at the termination of alate production. It is suggested that a high amino acid level was the main factor controlling the formation of alatae and that population density affected the proportions of these alatae only when nutritional levels were favourable for alate formation.     

Invasion Pattern of Herb Garlic Mustard (Alliaria petiolata) in High Quality Forests

The invasion of non-indigenous plant species poses a severe threat to native plant communities. Garlic mustard (Alliaria petiolata) is a naturalized European biennial herb that has spread rapidly through the eastern US and adjacent Canada. To determine garlic mustard rate of spread, eleven permanent plots (50×25 m) were located in seven high quality (relatively undisturbed) forests in the early stages of invasion. Garlic mustard presence was recorded within six 50×2 m permanent belt transects, and density and percent cover by age class were recorded in 36 permanent 1 m² quadrats, between 1989 and 1992, and again in 1997. Garlic mustard spread at an average rate of 5.4 m per year between 1989 and 1992, in all plots combined. Within individual plots rate of spread varied substantially, with location of the front increasing up to 36 m and decreasing as much as 18 m between years. While the front alternately advanced and retreated, over time garlic mustard consistently advanced through all forests. Rate of spread was influenced by establishment of satellite populations, and disturbance (wind-throw and flooding). The pattern of spread within plots was one of a ragged advancing front, supplemented by establishment of satellite populations 6–40 m distant from the front, which then coalesced with the main population. Garlic mustard presence between 1989 and 1997 increased significantly within all plots, and in each age class within each plot. The greatest increases occurred in plots where this plant was initially rarest. Garlic mustard cover and density varied nonsignificantly during the same time period. These results indicate that after garlic mustard invades a forest it becomes a permanent part of the community, annually increasing in presence but fluctuating in cover and density. Garlic mustard maintains a low profile under low disturbance conditions, but increases rapidly with periodic disturbance. This study monitored garlic mustard invasion in high quality relatively undisturbed forests, and may underestimate the rate of spread in low quality highly disturbed forests.     

Plant Screening for Chromium Phytoremediation

Thirty-six plant species of different agronomic importance, size, dry matter production, and tolerance to heavy metals were evaluated for Cr(III) and Cr(VI) uptake and accumulation as influenced by rate, form, source, and chelate application to a Cr-contaminated soil. There was a significant difference in the degree of tolerance, uptake, and accumulation of Cr among plant species. Sunflower (Helianthus annuus) was the least tolerant to Cr, and Bermudagrass (Cynodon dactylon) and switchgrass (Panicum virgatum) were the most tolerant. Indian mustard (Brassica juncea, cv 426308) and sunflower accumulated more Cr than other agricultural plant species. There was no inhibition of growth and little Cr accumulation in the presence of Cr(III) in soil, but most of the plant species that were treated with Cr(VI) hyperaccumulated Cr and died. EDTA chelate added to soil enhanced Cr(III) accumulation in some plants. The phytoremediation potential of the plant species tested was limited because Cr was accumulated in the plant roots and a high concentration in the shoots was toxic to plants. The difference in behavior between Cr(III) and Cr(VI) and their importance in soil and environment contamination should be the basis for remediation strategies.