Effect of the California red scale Aonidiella aurantii sex pheromone on the natural parasitism by Aphytis spp. in Mediterranean citrus

Mating disruption has proved successful against California red scale (CRS), Aonidiella aurantii Maskell (Hemiptera: Diaspididae) in Mediterranean citrus. Although mating disruption does not affect negatively the parasitism by Aphytis melinus DeBach (Hymenoptera: Aphelinidae), a CRS parasitoid introduced to the Mediterranean, there is no information regarding its potential effect on the native Aphytis species. In the present study, the effect of CRS mating disruption on the field parasitism inflicted by Aphytis spp. has been assessed and compared to a mineral oil and a control treatment. In order to confirm the effectiveness of the mating disruption we also evaluated its effect on the captures of the CRS males and on fruit infestation. Moreover, the potential role of the CRS sex pheromone as kairomone for the Aphytis species was also evaluated by comparing captures of parasitoids on sticky traps with or without pheromone. Significantly lower CRS male captures and fruit damage were registered in the mating disruption respect to the control or oil treatments indicating that mating disruption was effective. In September, when compared to the control, parasitism by Aphytis spp. was significantly lower in the mating disruption and mineral oil treatments and crucially no Aphytis chrysomphali Mercet were registered in the mating disruption treatment. Finally, while the captures of both A. melinus and Aphytis lepidosaphes (Mercet) were not significantly different between traps with or without pheromone, A. chrysomphali captures were significantly higher in traps baited with CRS pheromone. These results suggest a possible kairomonal effect of the CRS pheromone on A. chrysomphali.     

Biological control: lessons from a study of California red scale

A 20-year study of suppression of California red scale, a world-wide pest of citrus, by the parasitoid Aphytis melinus has established that the interaction is dynamically stable and that the mechanisms leading to control and stability operate at a local scale: spatial processes are not important. Key features appear to be an invulnerable class in the pest and rapid development of the parasitoid compared with the pest, as well as the fact that the parasitoid is an in situ specialist on the pest. Although another parasitoid species and two predator species are also present, they play at most a negligible role in pest control. These features—long-term persistence, suppression by a single natural enemy, an invulnerable stage in the pest and rapid development in the natural enemy—appear to be common in other coccid pest systems. By contrast, in temporary crops where the pest and enemy populations are open (i.e., sustained over the long run mainly by immigration) and non-persistent locally, as is frequently found in aphid pests, we expect that multiple generalist enemies are required for control and, of course, that spatial processes are important. There are very few well-studied examples of such systems, but these support our expectations. In these cases, it also appears that neither rapid enemy development nor an invulnerable pest stage is important for successful control.     

Mode of action of a novel nonchemical method of insect control: atmospheric pressure plasma discharge

Atmospheric pressure plasma discharge (APPD) has been applied to a number of industrial applications, including the bacterial sterilization of medical equipment of bacteria. APPD may also have applications in insect control. A positive correlation was found between exposure time to APPD and mortality of western flower thrips, Frankliniella occidentalis (Pergande); tobacco thrips, Frankliniella fusca (Hinds); Asian tiger mosquito, Aedes albopictus (Skuse); twospotted spider mite, Tetranychus urticae Koch; and German cockroach, Blattella germanica (L.), with the level of mortality also increasing with time after treatment. Cockroaches exposed to APPD for 60, 90, 120, and 180 s lost on average 7.5 +/- 0.8, 8.1 +/- 0.6, 8.7 +/- 0.4, and 10.1 +/- 1.1 (+/-1 SEM) mg of water weight, respectively, which was an increase over that of the controls. The metabolic rate of cockroaches exposed to plasma for 180 s increased from 0.79 +/- 0.03 to 1.07 +/- 0.04 ml of oxygen consumed mg-cockroach(-1) h(-1) at standard temperature and pressure. The level of cuticular hydrocarbons identified by electron impact gas chromatography-mass spectrometry were not significantly affected by plasma exposure in the green peach aphid, Myzus persicae (Sulzer), German cockroach, and citrus mealybug, Planococcus citri (Risso), except for a reduction in n-tritriacontane in the latter. However, changes in the behavior of cockroaches after plasma exposure, including the loss of photo-, vibro-, and thigmotropic responses, inability to right themselves, and hyperexcitatory symptoms, suggest that the site of action of APPD in insects is the nervous and/or neuromuscular system.     

Responses of male California red scale to sex pheromone isomers

The California red scale, Aonidiella aurantii (Maskell), sex pheromone components were previously identified as two independently attractive norsesquiterpenes. The four possible optical isomers of one and the four possible geometric and optical isomers of the other were synthesized and tested for male California red scale attractiveness in field tests and greenhouse bioassays. The results showed that there was enantiomeric and geometric specificity and only 1 isomer of each component was significantly more active than the others. The active isomers were (3S,6R)-3-methyl-6-isopropenyl-9 decen-1-yl acetate and (3Z,6R)-3-methyl-6-isopropenyl-3,9-decadien-1-yl acetate. The presence of other isomers, including the synthetic analogue 3-methyl-6-isopropylidene-9-decen-1-yl acetate, had no effect on trap catch.     

Effects of pyriproxyfen on California red scale (Hemiptera: Diaspididae) development and reproduction

Two life stages of a laboratory colony of California red scale, Aonidiella aurantii (Maskell) (Hemiptera: Diaspididae), were exposed to 10 concentrations of pyriproxyfen to evaluate the effect of this insect growth regulator (IGR) on scale development and fecundity. First instars exposed to pyriproxyfen responded with mortality during the first and second molts. Second instars were more tolerant of pyriproxyfen than were first instars, indicating that growers should treat California red scale in the field before the first molt to achieve maximum efficacy. Male scales responded with an LC50 12-fold lower and an LC90 47-fold lower than was observed for female scales. Female scales that survived first instar exposure to pyriproxyfen experienced reduced fecundity with increasing pyriproxyfen concentration. Reduced fecundity was due to reduced survival of the females rather than sterility. Results from this study provide baseline California red scale susceptibility data for pyriproxyfen, and they suggest that 1 ppm pyriproxyfen can be used as a concentration that would discriminate between susceptible and resistant populations of scales. Field monitoring for incipient pyriproxyfen resistance in California red scale should be implemented in the San Joaquin Valley of California, and if resistance is detected, integrated resistance management strategies should be used to slow the progression of resistance.     

指状青霉Penicillium digitatum侵染柑橘果实的细胞学研究

采用电子显微镜技术系统研究了指状青霉Penicillium digitatum对柑橘果实的侵染过程及超微结构特征。结果表明室温条件下,接种12h后,伤口附近的分生孢子开始萌发产生芽管;然后从伤口处直接侵入果实表皮细胞内;接种24h后,受侵染果实细胞中的菌丝向相邻细胞扩展蔓延,寄主细胞壁开始消解,质壁分离,细胞内含物及各类细胞器凝集,颜色加深,最后完全消解,伤口部位的果皮开始变软,伤口处的菌丝向外生长;84h后伤口处病斑软化,部分长出白色的霉层;96h后病斑软化面积直径达3cm,白色霉层面积逐渐扩大;120h后白色霉层中间伤口处霉层颜色加深变为灰绿色;144h后整个果实变软腐烂。果胶质标记结果表明,菌丝侵入果实后产生果胶酶并降解柑橘细胞壁中的果胶,使得细胞壁松弛,软化腐烂。     

Development of a biological control method against postharvest diseases of citrus fruits

Candida oleophila strain O was previously selected for its high and reliable antagonistic activity against Botrytis cinerea and Penicillium expansum, two important wound pathogens on post-harvest apples. The application of these antagonistic strains on wound pathogens of Citrus was more recently undertaken. The efficacy of yeast (applied at several concentrations from 10(5) to 10(8) CFU/ml) was assessed against P. digitatum and P. italicum inoculated after one hours (at a concentration of 10(5), 106 and 10(7) spores/ml) on 'Clementine' and 'Valencia late' varieties. The protective levels were positively correlated with high concentration of antagonist and low concentration of pathogen. The antagonistic activity of this strain was also dependent on the incubation time before pathogen inoculation. The protective level increased with time between application of the antagonist and inoculation of fungal spores. Finally, the efficacy of biomass of C. oleophila strain O (produced at an industrial scale), and two different formulations of that biomass was assessed in comparison with fungicidal treatment (Thiabendazole) under semi-practical conditions against P. digitatum. This efficacy of strain O (whatever its formulation) was statistically comparable to that for TBZ at commercial dose, indicating that both formulations could be used as an alternative for conventional fungicide in postharvest treatments.     

A novel method to scale up fungal endophyte isolations

Studies involving fungal endophytes very often rely on surface-sterilisation of plant samples to enable endophyte isolations. However, surface-sterilisation can be very time-consuming, potentially limiting the number of samples processed. To overcome this limitation, a novel method was developed to bulk surface-sterilise multiple plant tissue samples simultaneously and separately. The method relies on 24 perforated Falcon? tubes, each containing a sample, sequentially transferred through a series of containers holding the sterilants. The samples that can be surface-sterilised using this method include roots, stems and leaves or entire seedlings. This method increased our throughput by a factor of 24 relative to conventional surface-sterilisation methods.     

Survey of brown soft scale Coccus hesperidum L. parasitoids in southern California citrus

The parasitoid complex of brown soft scale, Coccus hesperidum L., a multivoltine soft scale, was determined in southern California citrus over the period February 2004–March 2006. The survey was conducted by placing brown soft scale-infested yucca leaves in the canopy of citrus trees and subsequently rearing individually isolated parasitized scales in the laboratory. A total of 14 species parasitized brown soft scale in the field, the most abundant ones belonging to the genus Metaphycus Mercet (75%). The most abundant parasitoid species was Metaphycus angustifrons Compere (38% parasitism), and this is a new record of establishment for this species in California. Coccophagus species accounted for only 11% parasitism. There were important spatio-temporal differences across the parasitoid complex survey locations. We also found that the five most abundant encyrtid parasitoid species showed preferences for scales of different sizes. Our results have implications for biological control of citricola scale, Coccus pseudomagnoliarum (Kuwana), an important pest of citrus in the San Joaquin Valley of central California. Notably, this species is nearly absent in southern California. Brown soft scale is considered to be an alternate host for parasitoids of citricola scale, a univoltine soft scale, at times when the latter species is unavailable for parasitism.     

Effect of temperature and parasite density on three species ofAphytis (Hymenoptera: Aphelinidae), parasitising California red scale

Summary Three species ofAphytis parasites of California red scale,Aonidiella aurantii (Maskell) were each confined at different densities with approximately equal numbers of scale insects at several constant temperatures to determine the effect of these factors on progeny production and distribution and the search rate. Egg location on the host body by the parasites was unaffected by temperature or parasite density.A. melinus laid its eggs both dorsally and ventrally in equal proportions whileA. lingnanensis andA. chrysomphali laid their eggs ventrally. Progeny production byA. melinus andA. lingnanensis increased at the higher temperature; that ofA. chrysomphali did not. Unlike the other species,A. chrysomphali failed to oviposit at 32°C. Although increasing parasite density reduced progeny production in bothA. melinus andA. lingnanensis, they were able to maintain an almonst constant search rate. This was due to their ability to distribute their eggs among the hosts more regularly at the higher parasite densities. While the mechanism of this process is easy to understand forA. melinus which behaved as a gregarious parasite, it is unclear forA. lingnanensis, which is almost a solitary parasite. The progeny production and the search rate ofA. chrysomphali dropped significantly with increasing parasite density.     

A novel method for sampling bacteria on plant root and soil surfaces at the microhabitat scale

This study reports the first method for sampling bacteria at a spatial scale approximating a microhabitat. At the core of this method is the use of tungsten rods with laser-cut tips of known surface area (0.013 mm(2)). Exposed plant root or soil surfaces were viewed with a dissecting microscope and micro-sampling rods were guided to sample sites using a micro-manipulator. Bacteria that adhered to the sampling tips were then recovered for microbiological analyses. The efficiency of this method for removing bacteria from root surfaces was similar to that with which bacteria are recovered from dissected root segments using the conventional technique of washing. However, as the surface area of the micro-sampling tips was known, the new method has the advantage of eliminating inaccuracy in estimates of bacterial densities due to inaccurate estimation of the root or soil surface sampled. When used to investigate spatial distributions of rhizoplane bacteria, the new technique revealed trends that were consistent with those reported with existing methods, while providing access to additional information about community structure at a much smaller spatial scale. The spatial scale of this new method is ca. 1000-times smaller than other sampling methods involving swabbing. This novel technique represents an important methodological step facilitating microbial ecological investigations at a microhabitat scale.     

A history of the biological and integrated control of red scale,Aonidiella aurantii on citrus in the lower Murray valley of Australia

In the lower Murray valley of Australia, the major insect pest of citrus, California red scaleAonidiella aurantii (Maskell), is controlled by a number of introduced hymenopterous parasites. Parasite introductions began in 1943, and continued until 1979. Eight species, especially in the Encyrtid genusAphytis, were introduced and mass released. The only species to become permanently established wereAphytis chrysomphali Mercet,Comperiella bifasciata (Howard),A. melinus DeBach, andProspaltella perniciosi (Tower).A. melinus, introduced in 1961, has become widely established throughout the region, is the dominant and most important parasite, and now appears to have completely displacedA. chrysomphali (1954) in all areas.C. bifasciata (1943) is also an important parasite and is distributed throughout the area.P. perniciosi (1970) is established on a few orchards near Mildura. Most of the work on the biological and integrated control of red scale began with the establishment of laboratory and insectary facilities at Mildura in 1967 and Loxton in 1968. A commercial insectary was also established at Loxton in 1971. Biological methods of insect control were first used commercially during 1944 (war period) by a few citrus growers at Merbein in Sunraysia. However, the adoption of biological and integrated methods for the control of red scale and other citrus pests, began on a large scale in the late 1960's. The use of organophosphate insecticides on citrus has declined since that time and has been close to zero since about 1977. Parasites and petroleum oil sprays have been used together in an integrated approach to the control of California red scale on some orchards. The biological control of this key pest has led to a decline in the incidence of secondary pests to the point where all insect pests of citrus are now regarded as being under effective biological control. The incidence of red scale, and other pests, has been less under biological and integrated control than it ever was when chemical control measures were widely used in the 1960's. Factors which have contributed to the success of the programme are discussed.     

Volatile cues used by the parasitoid, Aphytis melinus, for host location: California red scale revisited

Aphytis melinus DeBach (Hymenoptera: Aphelinidae) is a biological control agent of diaspidid scale insects. The parasitoid has a narrow host range but its hosts are polyphagous. We determined the source of volatile cues the wasp uses to locate its few host species when those hosts occur on more than one host plant species. We addressed four questions in regard to the use of volatile cues in host location of California red scale, Aonidiella aurantii (Maskell) (Homoptera: Diaspididae): (1) Does A. melinus use volatile cues to assist in host location? (2) Are these cues innately recognized or learned? (3) Are cues produced by female California red scale, or from other sources? (4) Are the cues specific to the host or host plant? These questions were tested through the use of a Y-tube olfactometer. Female A. melinus used volatile cues to orient toward both infested and uninfested host plant material. Wasps learned these cues by associating odors from the host plant with host presence. They had no innate preferences for scale insect or host plant volatile stimuli. Contrary to previous studies, we found no evidence of orientation toward the female-produced sex pheromone of California red scale, nor to volatile cues from the attacked host stage. Wasps given experience with scale insects growing on lemon fruit subsequently oriented toward lemon and orange fruit and leaves. The scale species with which the wasp was given experience did not affect this preference. Wasps given experience with California red scale growing on squash did not orient toward infested lemon fruit. The host ranges of the parasitoid and its hosts are used to explain the adaptive value for the evolution of learned rather than fixed responses to cues used in foraging behavior.     

Distribution and management of citrus in California: implications for management of glassy-winged sharpshooter

The epidemiology of Pierce's disease of grape (Vitis spp.) in California has changed over the past 10 yr due to the introduction of an exotic vector, Homalodisca vitripennis (Germar), the glassy-winged sharpshooter. Although this insect is highly polyphagous, citrus (Citrus spp.) is considered a preferred host and proximity to citrus has been implicated as a significant risk factor in recent epidemics of Pierce's disease in southern California. Consequently, a detailed knowledge of the distribution and management of citrus in relation to grape is needed to improve insect and disease management. Analysis of data on the area planted to these two commodities indicates that only five counties in California concomitantly grow >1,000 ha of grape and >1,000 ha of citrus: Riverside, Kern, Tulare, Fresno, and Madera counties. Comparison of the distribution of grape and citrus within each of these counties indicates that the percentage of grape that is in proximity to citrus is greatest for Riverside County, but the total area of grape that is in proximity to citrus is greater for Fresno, Kern, and Tulare counties. The use of carbamates, neonicotinoids, organophosphates, and pyrethroids as part of the citrus pest management program for control of key insect pests was compared among the same five counties plus Ventura County from 1995 to 2006. Ventura County was included in this analysis as this county grows >10,000 ha of citrus and has established glassy-winged sharpshooter populations. The use of these broad-spectrum insecticides was lowest in Riverside and Ventura counties compared with the other four counties. Analysis of historical trapping data at the county scale indicates a negative association of broad-spectrum insecticide use with glassy-winged sharpshooter abundance. These results are used to retrospectively analyze the Pierce's disease outbreaks in Kern and Riverside counties.     

A novel method for the identification of conserved structural patterns in RNA: From small scale to high-throughput applications

Functional RNA regions are often related to recurrent secondary structure patterns (or motifs), which can exert their role in several different ways, particularly in dictating the interaction with RNA-binding proteins, and acting in the regulation of a large number of cellular processes. Among the available motif-finding tools, the majority focuses on sequence patterns, sometimes including secondary structure as additional constraints to improve their performance. Nonetheless, secondary structures motifs may be concurrent to their sequence counterparts or even encode a stronger functional signal. Current methods for searching structural motifs generally require long pipelines and/or high computational efforts or previously aligned sequences. Here, we present BEAM (BEAr Motif finder), a novel method for structural motif discovery from a set of unaligned RNAs, taking advantage of a recently developed encoding for RNA secondary structure named BEAR (Brand nEw Alphabet for RNAs) and of evolutionary substitution rates of secondary structure elements. Tested in a varied set of scenarios, from small- to large-scale, BEAM is successful in retrieving structural motifs even in highly noisy data sets, such as those that can arise in CLIP-Seq or other high-throughput experiments.     

A method for pre-harvest assessment of latent infections in fruits

A method was developed for the assessment of latent infections of Alternaria alternata in mango fruits. Fruit discs were sampled and assayed for fungal contamination under suitable growth conditions. By this method it was possible to evaluate the percentage of infections and the relative surface infected by Alternaria in mango fruits before harvest. The percentage of infections increased during the growing season but fungicide treatments prevented this increase. A significant positive correlation was found between the relative surface infected by latent Alternaria at harvest time and the incidence of black spots that developed on the fruit during storage.     

Studies onAphytis coheni,a parasite of the California red scale,Aonidiella aurantii in Israel

Studies on the development, fecundity, nutrition and the influence of temperature and humidity onAphytis coheni DeBach, an ectoparasite of the California red scale,Aonidiella aurantii (Maskell) were conducted in an effort to explain the current distribution ofA. coheni in citrus groves in Israel.