Impact of reflective mulch on yield of strawberry plants and incidence of damage by tarnished plant bug (Heteroptera: Miridae).

The current study investigated the impact of reflective mulch on yield of strawberry plants and incidence of damage by tarnished plant bugs, Lygus lineolaris (Palisot de Beauvois), for three strawberry cultivars: 'Honeoye', 'Earliglow', and two sibling Dayneutrals ('Tribute' and 'Tristar', herein considered as one cultivar). Of all cultivars tested, Honeoye was the most productive and least susceptible to tarnished plant bug. For Earliglow and Honeoye, reflective mulch enhanced productivity of strawberry plants and suppressed density of nymphs per flower cluster and proportion of damaged fruits, but did not significantly impact numbers of nymphs or damaged fruits per hectare, Results with Dayneutrals were not consistently significant. Both in the presence or absence of reflective mulch, proportion of damaged fruits increased with increasing density of nymphs per flower cluster and with decreasing number of fruits harvested per row section, suggesting that planting productive strawberry cultivars or maintaining cultural practices that promote high yield may provide an effective line of defense against tarnished plant bug. These results also suggest that reflective mulch may suppress incidence of damage by tarnished plant bug both directly, by reducing number of nymphs per flower cluster, and indirectly, by enhancing productivity of strawberry plants. Economic analyses evaluating costs and benefits of using reflective mulch, as well as studies investigating mechanisms that underlie the impact of reflective mulch on yield and incidence of damage by tarnished plant bug, are still needed before reflective mulch can be implemented as a management strategy in commercial strawberry fields.     

Effect of plant structure on oviposition behavior of Anopheles minimus s.l.

Knowledge of factors that influence oviposition behavior of malaria mosquitoes is critical to vector control measures aimed at larval habitat modifications and source reduction. Anopheles minimus s.l., an important malaria vector in Southeast Asia, generally breeds in clear, unpolluted water along shaded grassy edges of slow-moving streams. The objective of this study was to determine the influence of vegetation and plant structure on An. minimus s.l. ovipositing females. Twenty gravid female mosquitoes per replication were given a choice to lay eggs in bowls surrounded by different combinations of bare soil, grasses, small-leaved plants, and large-leaved plants. An. minimus s.l. females generally preferred to lay eggs in bowls with vegetation. A significantly higher number of eggs were found in bowls with small-leaved plants compared to bowls with grasses (P<0.05). The results suggest that gravid females preferred oviposition habitats in the following order: small-leaved plants > large-leaved plants > grasses > soil. Further studies are needed to determine the possible roles of plant structure and factors such as semiochemicals in the different species of the An. minimus species complex. Knowledge of female oviposition behavior is essential for the development of locally adapted vector control approaches.     

Testing the resource concentration hypothesis with tarnished plant bug on strawberry: density of hosts and patch size influence the interaction between abundance of nymphs and incidence of damage

Abstract. 1. Attributes of patches with strawberry plants were manipulated experimentally to assess the impact of patch size and host density on the abundance of tarnished plant bug (Hemiptera: Miridae) and incidence of fruit damage.
2. The density of nymphs per inflorescence increased with patch size and host density for some but not all generations of plant bug, providing partial support for the resource concentration hypothesis, while emphasising the importance of replicating experiments across several generations of herbivore.
3. Increasing density of nymphs with increasing patch size and host density did not translate into a high incidence of damage, which may be due to the relatively low feeding impact of nymphs in patches with numerous fruits and to the relatively high perimeter-to-area ratio in small patches resulting in a relatively high proportion of damaged fruits.
4. The decreasing proportion of damaged fruits with increasing density of fruits per patch suggests that nymphs exhibit a saturating functional response to density of strawberry fruits. Functional responses of herbivores may be a critical yet overlooked component that influences interactions between insects and their host plant. In particular, concentrated plant resources may result in increased numbers of herbivores yet sill have a negligible influence on plant damage and/or fitness.     

Comparison of economic and plant phenology-based thresholds for management of Lygus lineolaris (Hemiptera: Miridae) in Minnesota strawberries

Field studies were conducted in southeastern Minnesota, 2000-2002, to assess damage potential and management options for adult Lygus lineolaris (Palisot de Beauvois) in June-bearing strawberries (Fragaria x ananassa). The first study was designed to assess the efficacy of a published economic threshold for L. lineolaris nymphs compared with a plant phenology-based threshold management program, targeted at L. lineolaris adults. L. lineolaris nymphs were sampled using the standard white pan beat method; adults were sampled using yellow sticky traps. In the second study, during 2001-2002, caged strawberries were artificially infested with adult L. lineolaris at specific plant growth stages (i.e., vegetative, green bud, white bud, first blossom, peak blossom, first green fruit, and first ripe fruit) to determine the most susceptible growth stages of strawberry. The phenology-based thresholds proved to be more effective in managing L. lineolaris than the current economic threshold based on nymphs. Results from the infestation timing study indicate that early-growth stages (i.e., green and white bud) are most susceptible to adult L. lineolaris feeding damage. During the early-growth stages, only L. lineolaris adults were present; infestations of nymphs occurred primarily from first blossom to green berry. Results from both studies indicate that (1) management of adult L. lineolaris during the early strawberry growth stages is recommended for maximizing marketable yield and (2) the use of plant phenology-based thresholds, when adults are present, will significantly improve insecticide spray timing, and thus minimize the number of insecticide sprays.     

Ovipositional preferences, damage thresholds, and detection of the tomato-potato psyllid Bactericera cockerelli (Homoptera: Psyllidae) on selected tomato accessions

The tomato-potato psyllid Bactericera [Paratrioza] cockerelli (Sulc) has recently caused losses exceeding 50% on fresh market tomatoes in California and Baja, Mexico by injecting a toxin that results in a condition known as 'psyllid yellows'. The objectives of this study were to: (i) document oviposition preferences on a range of tomato cultivars; (ii) determine threshold levels for psyllid densities that would cause psyllid yellows on tomatoes within the first three weeks following transplanting; and (iii) identify the most important 'psyllid yellows' symptoms that might be used in surveying and monitoring for this pest. Plant lines tested included the commonly-planted commercial cultivars 'Shady Lady' and 'QualiT 21', an older, previously commercial cultivar '7718 VFN', a common cultivar planted by consumers 'Yellow Pear', and a wild type plant accession, PI 134417. When given a choice, psyllids significantly preferred 'Yellow Pear' and avoided PI 134417 for oviposition. Under no-choice conditions psyllids laid significantly fewer eggs on PI 134417, but all the other plant lines were equally good substrates for laying eggs. Thus, oviposition preference is not likely to provide a functional management strategy in large plantings. On 'Shady Lady', psyllids preferred to oviposit on plants already infested with adults. On both 'Shady Lady' and '7718 VFN' oviposition was significantly greater on plants previously infested by nymphs as compared to uninfested control plants. This suggests that, at least for some cultivars, there is a physiological change in plant attractiveness following psyllid feeding. 'Yellow Pear' and 'QualiT 21' were relatively tolerant of psyllids, requiring 18 nymphs per plant to produce the disease symptoms. Only eight nymphs per plant were needed on 'Shady Lady' and '7718 VFN'. For all cultivars, the pest density showed strong correlations with measurements such as the number of yellowing leaves and leaflets and distorted leaves, which were as good as or better than the first factor extracted from principal component analysis. Therefore, such measurements have the potential to simplify field surveys.     

Possible Age-Dependent Variation in Egg-Loaded Host Selectivity of the Pierid Butterfly, Anthocharis scolymus (Lepidoptera: Pieridae): A Field Observation

To understand better the effects of age on host selection through conspecific egg detection by Anthocharis scolymus females, field observations were performed at a graveyard where the insect population was isolated and the host plant was limited to the cruciferous plant, Turritis glabra. We chased females and recorded their oviposition behaviors and the conditions of plants which females approached. Older females tended to avoid ovipositing on egg-loaded host plants and selectively laid eggs on nonloaded host plants. This result was not confounded by other factors such as seasonality, air temperature, plant height, plant phenological stage, surrounding vegetation, host plant density, and extent of plant damage. We discuss the possibility that females make an oviposition decision on how to lay their limited number of eggs during their remaining lifetime.     

Induction of plant responses to oviposition and feeding by herbivorous arthropods: a comparison

Plants may respond both to feeding and oviposition by herbivorous insects. While responses of plants to feeding damage by herbivores have been studied intensively during the past decades, only a few, but growing number of studies consider the reactions of plants towards egg deposition by herbivorous insects. Plants showing defensive response to oviposition by herbivores do not `wait' until being damaged by feeding, but may instead react towards one of the initial steps of herbivore attack, the egg deposition. Direct plant defensive responses to feeding act directly against the feeding stages of the herbivores. However, a plant may also show direct defensive responses to egg deposition by (a) formation of neoplasms, (b) formation of necrotic tissue (= hypersensitive response), and (c) production of oviposition deterrents. All these plant reactions have directly negative effects on the eggs, hatching larvae, or on the ovipositing females. Indirect plant defensive responses to feeding result in the emission of volatiles (= synomones) that attract predators or parasitoids of the feeding stages. A few recent studies have shown that plants are able to emit volatiles also in response to egg deposition and that these volatiles attract egg parasitoids. Studies on the mechanisms of induction of synomones by egg deposition show several parallels to the mechanisms of induction of plant responses by feeding damage. When considering induced plant defence against herbivores from an evolutionary point of view, the question arises whether herbivores evolved the ability to circumvent or even to exploit the plant's defensive responses. The reactions of herbivores to oviposition induced plant responses are compared with their reactions to feeding induced plant responses.     

The effects of feeding damage in ragweed Ambrosia artemisiifolia (Asteraceae) on populations of Zygogramma suturalis (Coleoptera,Chrysomelidae)

Summary Field sampling indicated that the number of eggs laid by a Zygogramma suturalis female within a sampling plot correlated inversely with the mean degree of ragweed damage. Feeding on extensively damaged ragweed in the laboratory caused a drop in oviposition intensity, and a considerable proportion of females completely stopped oviposition. Feeding on slightly damaged ragweed had no significant effect on oviposition intensity. Ovipositing females preferred to feed on the intact ragweed and lay their eggs close to it. The locomotory activity of ovipositing females was significantly higher on highly damaged ragweed whereas non-ovipositing (diapausing) females and males were behaviourally indifferent to the extent of ragweed damage. Under natural conditions, ovipositing females more frequently left damaged host plants for less damaged one. If the degree of ragweed damage is high over a large area, the insects that were unable to find undamaged plants for several days oviposited less and some females entered diapause. The adaptive effect of these reactions is a decrease of population density in advance, before it might drop as a result of starvation. These results are in agreement with the second model of insect reaction to the damage-induced changes in a host plant (Edwards and Wratten 1987).     

Field evaluation of efficacy and persistence of an insect vacuum device against the tarnished plant bug (Hemiptera: Miridae) in a day-neutral strawberry field

The efficacy of a vacuuming device to reduce Lygus lineolaris (Palisot de Beauvois) populations was evaluated over 3 yr in a day-neutral strawberry field. Immediately after treatments, a significant reduction of population estimates (by tapping of flower clusters) was observed for adults (75% of the time) and nymphs (50% of the time). Under the same conditions, control (i.e., vacuum turbine off) treatments significantly reduced adult population estimates 25% of the time. Lygus lineolaris tapping samples taken from strawberry plants adjacent to the treated zone did not show significant variations over sampling time, suggesting that no escape behavior occurred. This was supported by adult catches on sticky traps located in zones adjacent to the treated one. Our results suggest that vacuuming had inconsistent effect on tarnished plant bug populations and that L. lineolaris mobility plays a marginal role in the use of this control method.     

Genetic variation in chrysanthemum for resistance toFrankliniella occidentalis

In a choice-experiment, 42 chrysanthemum cultivars were screened for resistance toFrankliniella occidentalis (Pergande). Oviposition preference, two types of feeding damage and thrips numbers per flower were recorded as measures of resistance. A large genetic variation in thrips resistance was found among the cultivars screened. The amount of feeding damage was strongly determined by oviposition preference. Besides, a positive correlation was found between the oviposition preference in non-flowering chrysanthemums (number of eggs) and flowering chrysanthemums (number of thrips per flower). Thrips feeding on young, developing tissues, causes growth damage because affected cells are unable to expand and leaves become distorted. Thrips feeding on older, expanded leaves causes cells to become filled with air, resulting in ‘silver’ damage. The amounts of growth-and ‘silver’ damage were negatively correlated suggesting that thrips chose either young or older leaves to feed on. The order of resistance among cultivars did not change during the experiment. In order to get more insight in resistance mechanisms the influence of some plant- and flower characters on resistance was examined. The plant characters height, number of leaves, flower production and flower weight were all negatively correlated with resistance. It is suggested that tall chrysanthemum cultivars with many and large flowers may invest less in defence than smaller cultivars, and therefore are more damaged by thrips.     

Host plant conspicuousness and the distribution of eggs and larvae in the butterfly,Anthocharis scolymus (Lepidoptera: Pieridae)

We investigated how the distribution pattern of eggs and larval on the host plant, Turritus glabra, was influenced by the oviposition behavior of the pierid butterfly Anthocharis scolymus. Females searched for the host plants visually and they frequently approached taller host plants with sparse surrounding vegetation. After encountering host plants, oviposition behavior of females was independent of host plant characteristics such as height, density, and type of surrounding vegetation. A female laid eggs singly on a host plants. Most females appeared to lay their eggs regardless of the presense of eggs on the host plant. Consequently egg and larva tended to be abundant on conspicuous host plants as measured by height or relative isolation from other plants. However, overcrowding of eggs on an individual host decreased the survival rate of larvae.     

Cotton plants expressing a hemipteran-active Bacillus thuringiensis crystal protein impact the development and survival of Lygus hesperus (Hemiptera: Miridae) nymphs

The plant bugs Lygus hesperus Knight (Hemiptera: Miridae) and L. lineolaris (Palisot de Beauvois) have emerged as economic pests of cotton in the United States. These hemipteran species are refractory to the insect control traits found in genetically modified commercial varieties of cotton. In this article, we report the isolation and characterization of a 35 kDa crystal protein from Bacillus thuringiensis, designated TIC807, which causes reduced mass gain and mortality of L. hesperus and L. lineolaris nymphs when presented in an artificial diet feeding assay. Cotton plants expressing the TIC807 protein were observed to impact the survival and development of L. hesperus nymphs in a concentration-dependent manner. These results, demonstrating in planta activity of a Lygus insecticidal protein, represent an important milestone in the development of cotton varieties protected from Lygus feeding damage.     

How discriminating are cabbage butterflies?

The egg-laying responses of cabbage butterflies Pieris rapae L. to differences in the size, quality and spatial distribution of available oviposition sites, were studied in the laboratory (Australia) and the field (Australia and Canada). Differences on three scales were investigated: between leaves within the same plant, between plants within a patch, and between patches of plants. The butterflies lay most eggs on the larger, older leaves of plants, though the oldest are sometimes avoided. Larger plants also receive more eggs than smaller ones of the same cultivar, but cultivar preferences may override the response to size. The butterflies do not discriminate against plants already bearing eggs or larvae, unless larval feeding damage to the plant is severe. They lay more eggs on young plants than old ones of the same size; plants grown in the lower of two light intensities also received more eggs. Australian butterflies discriminate not only between different species of crucifers, but also between varieties of the same species. This discrimination against less acceptable varieties is just as strong when plants of preferred varieties are not present, as when both varieties occur in the same patch. The observed responses are discussed in relation to the butterflies’ host-finding behaviour and the adaptive significance of the lack of a response to eggs and larvae is considered.     

A study on common bean cultivars to identify sources of resistance against the black bean aphid,Aphis fabae Scopoli (Hemiptera: Aphididae)

Black bean aphid is an important common bean pest in the world. Aphids damage crops both directly by their feeding and by spreading viruses. Also, they indirectly damages with excretion honeydew and smokes moulds growth through some physiological processes and transmission of viruses. Resistant cultivars application is the main strategy to control Aphis fabae Scopoli. In this experiment, different lines and cultivars were infested with five wingless adult aphids. After 7 and 14?days, plants were evaluated and aphid population was counted and recorded. After 45?days when plants reached to the flowering stage, test was repeated. Result showed that there was a significant difference among cultivars in number of adult aphid in two-leaf stage. Most of the number of adult at the first week in two-leaf stage observed on Goynok cultivar that had significant difference to other lines and cultivars. Number of adults and nymphs among the line and cultivar at flowering stage did not show significant difference. Number of deployed aphids after two weeks was significantly higher than the first week that observed in all cultivars. Totally, the most resistant cultivar was Sayad and the most susceptible cultivar was Goynok.     

Effects of cultivar on oviposition preference, larval feeding and development time of diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), on some Brassica oleracea vegetables in Victoria

Abstract We studied oviposition preference of Plutella xylostella for four cultivars of cabbage, broccoli and cauliflower in the field. There were no differences in the number of eggs found on the various cultivars of broccoli or cauliflower. Significantly more eggs were laid on cultivar Savoy King than any of the other cabbage cultivars tested. We then compared the development time and feeding damage of larvae reared on Savoy King and Green Coronet cabbages. Larvae developed more rapidly and fed more and for longer on Green Coronet than Savoy King. Thus, while Savoy King is more attractive to oviposition in the field, net impacts on the crop may be lessened to some degree through lower feeding proficiency of the larvae on that cultivar.     

Behavior and Activity Pattern of Cephalonomia stephanoderis (Hymenoptera: Bethylidae) Attacking the Coffee Berry Borer,Hypothenemus hampei (Coleoptera: Scolytidae)

We describe behavioral sequences and daily activities of pre-ovipositing and ovipositing females of Cephalonomia stephanoderis (Hymenoptera: Bethylidae), an ectoparasitoid of the coffee berry borer, Hypothenemus hampei (Coleoptera: Scolytidae). Noticeable behavioral differences among preovipositing and ovipositing females include host examination, host stinging—probing, host feeding, and the oviposition per se. The female of C. stephanoderis feeds primarily on host eggs, but pupae are also exploited, mainly by pre-ovipositing females. After the onset of the oviposition period, C. stephanoderis examines the pupae repeatedly, stings them at frequent intervals, and spends more time feeding than during the pre-oviposition period. Host paralysis is linked both to host feeding and oviposition. It induces irreversible developmental arrest, which presumably allows preservation of the host until subsequent utilization, and contributes to successful offspring development, particularly by reducing host motility. Oviposition consists in a host selection process, a prolonged period of preparation of the potential host, and the egg-laying phase itself. Under our experimental conditions, pre-ovipositing and ovipositing females are active 17% and 36% of the day, respectively. Host handling time averages 6% and 23% in pre-ovipositing and ovipositing females, respectively. All coffee berry borer developmental stages are exploited by C. stephanoderis females, either for host feeding and/or oviposition activities. Such flexible behavior is advantageous given that host availability is limited inside the coffee berries.     

Oviposition choice by the Onopordum capitulum weevil Larinus latus (Coleoptera: Curculionidae) and its effect on the survival of immature stages

Female Larinus latus lay eggs into the capitula of their Onopordum spp. host plants from the onset of capitulum development until the completion of flowering. This tight linkage between insect life-history and plant development optimised larval survival, apart from some initial asynchrony between the readiness of the females to oviposit and the suitability of the very small capitula to physically support eggs. Eggs were laid on bracts and stems of capitula or directly in the florets, when these became available. Both the location of the egg and time of oviposition influenced mortality factors such as egg and larval parasitism, egg desiccation and larval establishment. Overall, survival of eggs laid later in the season into florets was higher, although the adults that emerged were smaller. The change in choice of oviposition site that occurs at the onset of flowering, not only favours survival, but ensures more efficient resource use by the larvae. This occurs because sequential flowering of Onopordum spp. drives a sequential oviposition pattern and spreads the egg load more evenly over the available capitula, reversing a trend earlier in the season to clump eggs that were laid directly on the bracts. Other potential constraints, such as capitulum size, absolute egg density and previous egg-laying do not play a major role in determining the oviposition pattern of L. latus. Larval survival was positively correlated with capitulum size and not strongly influenced by egg density. Competition for resources only appeared to play a role in smaller capitula, and manifested itself in a reduction in the size of emerging adults rather than the death of immatures. In the absence of strong interspecific competition, the oviposition behavior of L. latus has become geared to maximising resource use for larvae (i.e. its own potential competitiveness) rather than minimising interactions with other members of the capitulum endophage guild.     

Cultivar and insecticide applications affect the physiological development of the brown planthopper, Nilaparvata lugens (Stål) (Hemiptera: Delphacidae)

Nilaparvata lugens (St?l) (Hemiptera:Delphacidae) is a serious migratory pest of rice in Asia. Pest resurgence often occurs because of insecticide overuse. Using both susceptible (TN1) and moderately resistant (Xieyou 963) cultivars, we studied the effect of foliar insecticides on the percentage of brachypterous adults, female reproductive rate, and crude fat and soluble sugar contents in third- and fifth-instar nymphs and adults. The percentage of brachypterous adults and reproductive rate of adult females developed from nymphs that fed on insecticide-treated plants varied significantly with rice cultivar, type of insecticide, and its concentration. Feeding on susceptible plants increased the percentage of brachypterous adults and reproductive rate of adult females. Also, deltamethrin increased brachypterous production relative to imidacloprid and triazophos. The highest reproductive rate was on plants treated with triazophos. All insecticide treatments in both cultivars resulted in increase of soluble sugar contents in third- and fifth-instar nymphs and adults developed from nymphs feeding on insecticide-treated rice plants. This effect was stronger on the susceptible cultivar. Changes of crude fat content after N. lugens feeding on insecticide-treated plants were related to its feeding duration. Crude fat content in adult developed from nymphs feeding on treated plants was significantly higher that on control plants. These studies showed that plant and insecticide influences on physiological ecology of this planthopper will influence its population dynamics under commercial production of rice in Asia.     

Intraspecific Variation in Chemical Attraction of Rice to Insect Predators

The olfactory response of predators of the brown planthopper,Nilaparvata lugensStål, to different genotypes of rice (14 cultivars and breeding lines ofOryza sativaL. and 1 wild species,Oryza nivaraSharma et Shastry) was measured in an airflow olfactometer. Odor from rice plants attracted more females of the mirid predatorCyrtorhinus lividipennisReuter than plain air (control) on only 6 of the 15 rice genotypes. Orientation ofC. lividipennistoward volatiles of certain rice genotypes was apparent even when the plants were free of the brown planthopper. However, the predator distinguished between prey-infested and uninfested plants and preferred plants with eggs over plants with nymphs. The predator did not distinguish different stages of plant growth (vegetative, booting, or flowering). Plants artificially injured to simulate brown planthopper oviposition wounds were not as attractive to the predator as plants on which the planthopper had oviposited. The preassay preconditioning on the cultivar TN1 did not produce a predator bias for this genotype. This suggests that rearing effects or chemically mediated associative learning reported for some natural enemies did not influenceC. lividipennis'host response. Results with another predator, the coccinellidMicraspis hirashimaiSasaji, produced less consistent behavior. Planthopper-infested plants attracted more females ofM. hirashimaithan unifested plants in only 1 of the 12 rice genotypes evaluated. Implications for augmenting predators by rice cultivar selection and modification are discussed.     

Utilization of early soybeans for food and reproduction by the tarnished plant bug (Hemiptera: Miridae) in the delta of Mississippi

Commercially produced maturity group (MG) IV soybeans, Glycine max L., were sampled during bloom for tarnished plant bugs, Lygus lineolaris (Palisot de Beauvois), during May and June 1999 (3 fields) and 2001 (18 fields). The adults and nymphs were found primarily in single population peaks in both years, indicating a single new generation was produced during each year. The peak mean numbers of nymphs were 0.61 and 0.84 per drop cloth sample in 1999 and 2001, respectively. Adults peaked at 3.96 (1999) and 3.76 (2001) per sweep net sample (25 sweeps). Tests using laboratory-reared and field-collected tarnished plant bugs resulted in very poor survival of nymphs on 16 different soybean varieties (MG III, one; IV, four; V, nine; VI, two). A large cage (0.06 ha) field test found that the number of nymphs produced on eight soybean varieties after mated adults were released into the cages was lower than could be expected on a suitable host. These results indicated that soybean was a marginal host for tarnished plant bugs. However, the numbers of adults and nymphs found in the commercially produced fields sampled in the study may have been high enough to cause feeding damage to the flowering soybeans. The nature of the damage and its possible economic importance were not determined. Reproduction of tarnished plant bugs in the commercially produced early soybean fields showed that the early soybeans provided tarnished plant bugs with a very abundant host at a time when only wild hosts were previously available.