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.     

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.     

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.     

Survey and distribution of lady beetles [Coccinellidae] in citrus groves in Israel

The importance ofCoccinellidae species found in the citrus groves of Israel was evaluated according to their prey, frequency and distribution. Dense populations of aphidophagous coccinellids were found very often, feeding on scale insects in citrus groves where none of their usual prey was present; these may therefore also be important as scale predators. A few species were distributed equally in all areas, some were more frequent in the Coastal Plain and others in the warmer parts of the country.     

Ecological effects of multi‐species,ant–hemipteran mutualisms in citrus

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Competitive displacement betweenAphytis spp. [Hym. Aphelinidae] parasites of the California red scale in cyprus

In Cyprus,Aphytis chrysomphali (Mercet) andAphytis melinus DeBach are the only significant parasites of the California red scale,Aonidiella aurantii (Maskell).A. chrysomphali, presumably native, has been virtually displaced byA. melinus from the interior dry areas of the island after the importation of the latter in 1961. Presently the former parasite dominates only in some of the coastal areas with a mild and rather humid climate.Aphytis ? coheni DeBach that initially displacedA. chrysomphali in the release areas, was replaced by the latter parasite and was occasionally found in small numbers only in one location. Traces ofAphytis ?lingnanensis Compere were also found in some locations. Two otherAphytis spp., imported from California, were released and recovered but it is too early to determine their permanent establishment and significance.     

Priming Aphytis: behavioral modification of host selection by exposure to a synthetic contact kairomone

The introduced parasitoid, Aphytis melinus DeBach (Hymenoptera: Aphelinidae), utilizes a kairomone, O-caffeoyltyrosine, to recognize California red scale, Aonidiella aurantii (Maskell) (Homoptera: Diaspididae). Wasps used in augmentative release programs for California red scale on California citrus are reared on oleander scale, Aspidiotus nerii Bouché (Homoptera: Diaspididae), themselves reared on squash. The goals of this study were: 1) to determine if long-term rearing on oleander scale had caused A. melinus to develop a preference for oleander scale, and 2) to determine if the preference of oleander-reared A. melinus for California red scale might be enhanced by exposing them to synthetic O-caffeoyltyrosine prior to release. Wasps that were removed from their hosts as pupae and allowed to emerge as adults isolated from their hosts retained a strong preference for California red scale regardless of rearing host. This preference was reduced if wasps were allowed to emerge from oleander scale, thus acquiring early adult experience with oleander scale. The preference for California red scale was restored, however, by exposing wasps reared on oleander scale to synthetic O-caffeoyltyrosine prior to bioassay. Exposure of A. melinus reared in commercial insectaries to O-caffeoyltyrosine prior to release may be a means to improve the effectiveness of such wasps in augmentative release programs to control California red scale.     

Distribution ofGeotrichum candidum citrus race in citrus groves and non-citrus fields in Japan

The presence ofGeotrichum candidum citrus race, the citrus sour rot pathogen, was examined in soils of citrus groves and non-citrus fields of Japan. Soil samples were collected from 223 sites (118 sites in citrus groves, and 105 sites in fields cultivated with 33 species of non-citrus plants and in evergreen broad-leaved forest) in 11 main citrus-growing prefectures, and Hokkaido, a non-citrus-growing area. Of 236 soil samples from citrus groves, 95.76% containedG. candidum citrus race and 0.42% contained the non-citrus race; while of 210 samples from non-citrus fields, 62.85% and 4.76% contained the citrus race and the non-citrus race respectively. All of the citrus race isolates obtained either from citrus groves or non-citrus fields were pathogenic on lemon (Citrus limon) and satsuma mandarin (Citrus unshiu), but some of these isolates failed to infect orange (Citrus sinensis). The non-citrus races were pathogenic on ripe tomato fruit (Lycopersicon esculentum) and ripe muskmelon fruit (Cucumis melo var.reticulatus). Results indicated that citrus sour rot pathogen is widely distributed in citrus groves and non-citrus fields of diverse plant species in Japan.     

Parasitoeds (Hym.: Aphelinidae) of three scale insects (Hom.: Diaspididae) in a citrus grove in valencia,spain

The parasitoids ofAonidiella aurantii (Maskell),Lepidosaphes beckii (Newman) andParlatoria pergandii Comstock were studied in a Navel orange grove in Valencia, Spain during three years. Four species ofAphytis were identified on yellow sticky traps,Aphytis chrysomphali (Mercet),Aphytis melinus Debach,Aphytis lepidosaphes Compere andAphytis hispanicus (Mercet). No consistent annual pattern was observed in the flight of adults.A. melinus, introduced some years earlier in the grove, was found in very low numbers and showed no signs of increasing and displacingA. chrysomphali as a parasitoid ofA. aurantii. On female scales of the three species sampled at regular intervals from leaves, twigs and fruit, the mean annual rate of active parasitism was similar and ranged from 3.5% to 8%.P. pergandii males were not parasitized, inL. beckii parasitism was usually much lower in male than in female scales, and inA. aurantii it was higher in the males. Scales of the three species were less parasitized on twigs than on leaves, and so wereL. beckii on fruit. The annual trend of parasitism byAphytis on scales fluctuated without a definite pattern. Parasitism byEncarsia inquirenda (Silvestri), an endoparasitoid ofP. pergandii, was more stable throughout the year and increased steadily from year to year.     

Increased parasitization of California red scale in the field after exposing its parasitoid, Aphytis melinus, to a synthetic kairomone

The introduced parasitoid, Aphytis melinus DeBach (Hymenoptera: Aphelinidae), utilizes a kairomone, O-caffeoyltyrosine, to recognize California red scale, Aonidiella aurantii (Maskell) (Homoptera: Diaspididae). Wasps used in augmentative release programs for California red scale on California citrus are reared on oleander scale, Aspidiotus nerii Bouché (Homoptera: Diaspididae), themselves reared on squash. Previous laboratory studies demonstrated that wasps reared on oleander scale but exposed to O-caffeoyltyrosine before bioassay more readily accepted California red scale covers for probing than wasps reared similarly but not exposed to O-caffeoyltyrosine. The goal of this study was to determine if wasps reared on oleander scale but exposed to O-caffeoyltyrosine actually parasitized a greater number of field-reared California red scale than unconditioned wasps. In order to distinguish between progeny of conditioned and unconditioned wasps in the field, we utilized two A.melinus strains that carried different electrophoretically distinguishable alleles. In half of the releases, Strain A was conditioned to O-caffeoyltyrosine and Strain B served as the control, while this pattern of conditioning was reversed for the remaining releases. Although there were differences in the rates of population growth of the two strains, whichever strain was the conditioned strain left a greater than expected number of progeny compared to the control strain in all comparisons. Exposure of A. melinus reared in commercial insectaries to O-caffeoyltyrosine prior to release may be a means to improve the effectiveness of such wasps in augmentative release programs to control California red scale.     

Competition, resource partitioning and coexistence of an endoparasitoid Encarsia perniciosi and an ectoparasitoid Aphytis melinus of the California red scale

Abstract. 1. Laboratory experiments and field studies were conducted to explain the coexistence of an endoparasitoid, Encarsia perniciosi Tower, and an ectoparasitoid, Aphytis melinus DeBach, both of which were introduced into California to control the California red scale, Aonidiella aurantii (Mask.).
2. Encarsia parasitized all scale stages but it preferred first and second instar scales. This is in contrast to Aphytis melinus , in which previous studies have shown that it parasitizes second and third instar females and second instar males but prefers third instar female scales. Encarsia developed most rapidly when it parasitized an early second instar and slowest when it parasitized the mature female scale. However, on early second instar scales it was about 80% as fecund as a wasp that emerged from a mature female scale.
3. Second instar scales parasitized by Encarsia were accepted by Aphytis as readily as unparasitized scales.
4. Encarsia did not distinguish between unparasitized hosts and those previously parasitized by Aphytis.
5. Encarsia always outcompeted by Aphytis when both species parasitize the same host.
6. Encarsia prefers scale on stems whereas Aphytis prefers those on leaves and fruits. This, too, may be a result of interspecific competition with Aphytis.
7. The partitioning of the scale resource by the two species explains why they coexist in coastal southern California but it does not explain why Encarsia disappeared from citrus groves in the inland valleys coincident with the introduction of Aphytis melinus into southern California.     

Testing intraguild predation theory in a field system: does numerical dominance shift along a gradient of productivity?

Although ecological theory exists to predict dynamics in communities with intraguild predation (IGP), few empirical tests have examined this theory. IGP theory, in particular, predicts that when two competitors interact via IGP, with increasing resource productivity: (1) the IG predator will increase in abundance as the IG prey declines, and (2) increasing dominance of the IG predator will cause resource density to increase. Here, we provide a first test of these predictions in a field community consisting of a scale insect and its two specialist parasitoids, Aphytis melinus (the IG predator) and Encarsia perniciosi (the IG prey). The shared resource, California red scale, is a pest of citrus, and its productivity varies across a threefold range among citrus cultivars. We examined both absolute and relative densities of parasitoids along this natural gradient of scale productivity in three citrus cultivars (orange, grapefruit and lemon). Although both parasitoid species were found in all three cultivars, their abundances reflected those predicted by IGP theory: the IG prey species dominated at low productivity and the IG predator dominated at high productivity. This relationship was caused by an increase in Aphytis density with productivity. In addition, the density of scale increased with the dominance of the IG predator. These results from a field system demonstrate the important dynamic outcomes for food webs with IGP.     

Gene Flow in the Exotic Colonizing LadybeetleHarmonia axyridisin North America

The introduced parasitoid,Aphytis melinusDeBach (Hymenoptera: Aphelinidae), is used for augmentative biological control of California red scale,Aonidiella aurantii(Maskell) (Homoptera: Diaspididae). Commercially reared wasps are reared on oleander scale,Aspidiotus neriiBouché (Homoptera: Diaspididae). Oleander scale covers lack the chemical,O-caffeoyltyrosine, a kairomone mediating host selection byA. melinus.Wasps reared on oleander scale but individually exposed, or primed, toO-caffeoyltyrosine more readily accepted California red scale for probing in laboratory bioassays and parasitized a greater proportion of available California red scale in the field than wasps reared similarly but not exposed toO-caffeoyltyrosine. Thus, it may be possible to improve host recognition of commercial, insectary-rearedA. melinusby exposing them toO-caffeoyltyrosine prior to release. The goal of this study was to develop an inexpensive but effective means of priming thousands of wasps simultaneously toO-caffeoyltyrosine. The most effective method, but potentially the most expensive, was simply to spray parasitized oleander scale on their host plant with diluteO-caffeoyltyrosine prior to wasp emergence. In additional experiments, using controlled doses of syntheticO-caffeoyltyrosine applied to scale covers, we showed that primed wasps require both a lower minimum dose ofO-caffeoyltyrosine for recognition and also respond to measuredO-caffeoyltyrosine doses more consistently than unprimed wasps. The ability to mass-prime thousands of wasps prior to release is a crucial step toward realizing the concept of behavioral improvement of host selection of parasitoids on a commercial scale.     

Biological control of citrus whiteflyDialeurodes citri ashmead [Hom.: Aleyrodidae] usingEncarsia lahorensis howard [Hym.: Apheunidae] in countries of the former ussr

The citrus whiteflyDialeurodes citri Ashmead is one of the most important insect pests of citrus groves on the Black Sea coast of the Caucasus and on the Caspian Sea coast of the Talysh Mountains; it is the most important citrus pest of trench cultivation in Central Asia and in glasshouses. The parasitoidEncarsia lahorensis Howard was introduced in 1983 into Russia (Moscow) from Pakistan. It was reared in a laboratory of the All-Russian Plant Quarantine Institute. The parasitoid was released as follows: in 1985 in Adzharia (Batumi); in 1987 in a glasshouse in Russia (near Moscow) and in 1988-1990 in Central Asia - Uzbekistan (Namangan) and other regions. It established well in all places of release. The rate of parasitization ofD. citri byE. lahorensis reached 50–52% in the orchard in Batumi five years after the first release, 56–60% in the glasshouse in Moscow three years after the first release, and 50% in trenches in Namangan two years after the first release. Levels of the pest populations decreased dramatically in the glasshouse and trenches. The efficiency of the additional feeding ofE. lahorensis adults on the host larvae was evaluated to 26 to 60%. The differences between populations of the parasitoid in the three different areas are discussed.     

Occurrence of the exotic predatory ladybird Platynaspidius maculosus (Coleoptera: Coccinellidae) in citrus groves in Shizuoka City, Central Japan: seasonal prevalence of adults captured on sticky traps

Platynaspidius maculosus (Weise, 1910) (Coleoptera: Coccinellidae) is a ladybird beetle that preys on aphids and is distributed in China, Taiwan, and Vietnam. Recently, P. maculosus has invaded the southern parts of Japan; it was recorded on Okinawa Island in 1998, in Kagoshima Prefecture in 2006, and in Fukuoka Prefecture in 2010. In citrus groves in Shizuoka City, Central Japan in 2009–2012, the exotic ladybird was monitored by use of yellow sticky traps set inside citrus tree canopies. Adults of P. maculosus were captured in three out of the eight groves in 2010. This capture might be the first record of the ladybird from Honshu Island. Adults were trapped in three consecutive years, 2010–2012, in two groves; this suggests the possibility that the ladybird has become established in Shizuoka City. Adults were almost continuously caught on the traps from late April through October, being more abundant in early autumn (early September to early October), late spring (late April to mid-June), and mid-summer (early July to early August). During these periods, citrus shoots are growing and aphids are abundant. This finding suggests that the exotic ladybird might prey on citrus-infesting aphids, thereby reproducing in citrus groves. Based on the results obtained, potential impacts of the exotic ladybird on native aphidophagous ladybirds are also discussed.     

Effect of wind-borne pollens on the population dynamics ofAmblyseius hibisci [Acarina: Phytoseiidae]

Populations ofAmblyseius hibisci (Chant), an important predator of citrus red mite,Panonychus citri (McGregor) exhibited varying responses to field applications of cat-tail,Typha latifolia L., pollen in San Joaquin Valley citrus groves. Predator densities increased to significantly higher levels after pollen treatments during the fall months, and to a limited extent after late winter treatments, but not after early spring treatments. The amount of response appeared to be inversely related to the levels of natural foods present during the various seasons. Results of the wind-borne pollen monitoring studies indicated that population growth inA. hibisci was correlated with the seasonal pattern of pollen fallout. Population growth was slowest in years when pollen catches were low during the late winter and early spring, and fastest in years when peak pollen catches occurred in late winter or early spring. Population growth inA. hibisci did not appear to be markedly responsive toP. citri populations although suppression of prey densities was indicated in ca. 50% of the cases. In laboratory tests,A. hibisci reproduced through 3 generations on 11 of 23 pollens tested.     

The involvement of acetylcholinesterase in resistance of the California red scale shape Aonidiella aurantii to organophosphorus pesticides

Laboratory toxicity bioassays using chlorpyrifos (Dursban) confirmed the notion that development of resistance is responsible for widespread failures to control the California red scale, Aonidiella aurantii (Mask.) by applying organophosphorus (OP) compounds in citrus groves in Israel. Higher Vmax values of acetylcholinesterase (AChE) activity (9–13 fold) were measured in resistant strains collected from the field as compared to a susceptible line. No differences were found with respect to Km values using acetylthiocholine iodide as a substrate, or degree of inhibition (expressed by IC₅₀ values) by the OP compounds chlorpyrifos-oxon and paraoxon and the carbamate pirimicarb. We suggest that resistance of the California red scale is caused by excess of AChE molecules able to bind and thus scavenge inhibitory OP compounds. This scavenging mechanism related to AChE may be similar in other insect species where elevated levels of detoxifying esterases were implicated in conferring OP resistance.     

Aphytis riyadhi n. sp. [Hym.: Aphelinidae], a parasite ofAonidiella spp. [Hom.: Diaspididae]

A new species ofAphytis reared fromAonidiella orientalis collected from citrus in Saudi Arabia is described and compared morphologically with four other closely relatedAphytis species.

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Résumé Aphytis riyahdi n. sp., parasite deAonidiella orientalis (Newst.) en Arabie Saoudite a été importé en Californie pour procéder à des lachers contreAonidiella aurantii (Maskell) afin d'améliorer la lutte biologique contre cette cochenille dans une zone de vaste superficie et de climats variés.

     

Perspectives nouvelles dans la lutte contreAonidiella aurantii au Maroc [Hom. diaspididae]

Summary After a short introduction to place the present problem ofA. aurantii in Morocco, the authors mention importation of twoAphytis species (A. lingnanensis andA. melinus), the efficient parasites of the California Red Scale in several countries. Mass-breeding method used to build upAphytis production was this of the Californian workers, but numerous difficulties during 1966 have forbidden to raise a big production. Field colonization has been realized and good results has been obtained with low host densities, in several orchards. Now, the settlement of this problem should be searched out the ?Integrated Control? and new export patterns for Citrus from Morocco.      

Characterization,pathogenicity, and fungicide sensitivity of Alternaria isolates associated with preharvest fruit drop in California citrus

Alternaria rot has been recently described as an emerging fungal disease of citrus causing significant damage in California groves. A survey was conducted to determine latent infections on fruits, twigs, and leaves and investigate their seasonal patterns during 2019 and 2020. On fruits, latent infections were more associated with the stem end than with the stylar end, except during spring when a significantly high percentage of flowers (86%) had latent infections. Latent infections on twigs varied markedly between years (28% in 2019 and 9.5% in 2020), while Alternaria spp. were also recovered from citrus leaves. Alternaria isolates collected during the survey were identified based on multigene sequence analysis, confirming that Alternaria alternata and Alternaria arborescens are the two species associated with infections of citrus fruits. Of the 23 isolates, 19 were identified as A. alternata and demonstrated the dominance of this species over A. arborescens. Isolates representing populations of these two species were selected as representative isolates for physiological and morphological studies. A. alternata and A. arborescens showed similar conidial dimensions but differed in the number of conidia produced. Growth rates demonstrated that A. alternata grows faster than A. arborescens at all the temperatures evaluated, except at 25 and 35 °C. The growth patterns were similar for both species. The sporulation rate of the Alternaria isolates was influenced differently by temperature. This parameter also influenced conidial germination and appressorium formation, and no significant differences were observed between Alternaria species. Pathogenicity and aggressiveness tests on detached fruit demonstrated the ability of A. alternata and A. arborescens to cause internal lesions and produce fruit drop in the orchards with no quantitative differences between them (disease severity indexes of 58 and 68%, respectively). The fungicide sensitivity tests showed that DMI fungicides are the most effective fungicides in reducing mycelial growth. The SDHI fungicides had intermediate activity against the mycelial growth but also suppressed spore germination. The spore germination assay suggested that some of the isolates included in this study might have some level of resistance to QoI and SDHI fungicides. The findings of this study provide new information about the pathogens associated with the excessive fruit drop recently observed in some California citrus groves.