The role of <Emphasis Type="Italic">Euwallacea</Emphasis> nr. <Emphasis Type="Italic">fornicatus</Emphasis> (Coleoptera: Scolytinae) in the wilt syndrome of avocado trees in Israel

The polyphagous shot hole borer (PSHB), Euwallacea nr. fornicatus (Coleoptera; Scolytinae) has become a serious threat to the avocado industry and several shade tree species in Israel. Branch wilting and tree mortality is the outcome of PSHB galleries. Understanding the relationship between avocado trees and the PSHB is required for considering management strategies. In Israel, 52 tree species from 26 botanical families were attacked by the PSHB, but only 12 species were suitable for beetle reproduction. All examined avocado cultivars were attacked, but ‘Hass’ most severely. Large and medium diameter avocado branches were more resistant to PSHB, compared to thin branches. Effectively, gallery density increased as branch diameter decreased. Concomitantly, in large and medium diameter branches, extensive sugar exudation occurred and beetle attack rarely progressed to the formation of natal galleries, whereas minimal sugar exudation was observed in thin branches. This was more evident in those that were weakened by repeated attacks followed by successful beetle colonization. PSHB prefers and successfully colonized branches that had been previously attacked by its conspecifics, and reproduction was much higher in these branches, as opposed to initial attacks. Lesion frequencies increased from late spring (April) until late summer (September). Avocado branches at the early stages of beetle colonization may be identified by sugar exudation at the base of the thin branches. The main approach for reducing damage caused by the PSHB is sanitation, achieved by the removal of colonized branches and intact infested pruned slash.     

Susceptibility of avocado varieties to the long-tailed mealybug,Pseudococcus longispinus (Targioni Tozzetti) (Homoptera: pseudococcidae), and a survey of its host plants in Israel

The common avocado varieties grown in Israel can be graded in descending order of susceptibility to the long-tailed mealybug,Pseudococcus longispinus (Targioni Tozzetti), as follows: Hass, Nabal, Fuerte, Ettinger. The long-tailed mealybug was recorded in Israel on 36 host-plants belonging to 29 different botanical families.     

Overwintering of the Japanese bayberry whitefly,parabemisia myricae,in Israel

The Japanese bayberry whitefly,Parabemisia myricae (Kuwana), was discovered in Israel on citrus and avocado trees in 1978. In order to clarify its mode of overwintering, observations and counts were carried out during the winters of 1979/80, 1982/83 and 1983/84, with the following findings. Larvae and adults were detected on citrus and avocado trees throughout the winter; only females were found. The oviposition rate ofP. myricae in winter was low, and rose steeply in spring. The density of larvae on the lower side of leaves was higher than on the upper side. Substantial numbers of larvae survived the winter on avocado trees. Emergence of adults became intensified at the end of February, reached a peak in early March, and ceased at the end of March or beginning of April.     

A list of arthropod pests of avocado and pecan trees in Israel

Lists are given of arthropod pests of avocado and pecan trees in Israel. These include ten new pests of avocado and three of pecan. The pests of economic importance on avocado includeBoarmia (Ascotis) selenaria (Schiff.) (Geometridae, Lepidoptera) andHeliothrips haemorrhoidalis (Bouché) (Thrypidae, Thysanoptera). The pests of importance on pecans includeEmpoasca decedens (Paoli) (Jassidae, Homoptera),Zeuzera pyrina L. (Cossidae, Lepidoptera), andMonellia costalis (Fitch) (Aphididae, Homoptera).     

Characterization of Glomerella cingulata isolates from almond fruit using VCG,molecular, fungicide sensitivity and pathogenicity tests 1

Almond anthracnose caused by Glomerella cingulata is a major disease of this crop in Israel. The pathogen infects young fruit resulting in fruit rot. Leaf wilting and shoot dieback accompany fruit rot, even though the pathogen cannot be isolated from leaves or twigs. Isolates of G. cingulata from diseased almond fruit were compared using vegetative compatibility grouping (VCG), molecular methods, fungicide sensitivity and pathogenicity assays in order to determine the genetic diversity and host specificity among different populations. Polymerase chain reaction amplification of genomic DNA, using four primers produced uniform banding patterns for all the almond isolates from different geographic locations in Israel. HaeIII digestion patterns of A + T-rich DNA, and Southern hybridization of the repetitive nuclear DNA element (GcpR1) to PstI-digested genomic DNA of almond isolates also revealed no polymorphism. Chlorate-resistant nitrate-nonutilizing (nit) mutants were generated and used in heterokaryon tests. Complementary heterokaryons formed between the mutants of different isolates indicated a single VCG. Isolates of G. cingulata from almond had optimal growth temperatures of 20–22°C as opposed to 26–28°C for avocado isolates. In addition, almond isolates of G. cingulata are insensitive to benzimidazole fungicides in contrast to sensitivity of isolates from avocado. In artificial inoculations, almond isolates infected almond, avocado, apple, mango and nectarine fruit at a slower rate than G. cingulata isolates from avocado, apple and mango. Only the anamorph Colletotrichum gloeosporioides has been detected on almond in Israel, whereas isolates of G. cingulata from other hosts produce ascocarps.     

Attraction ofOrthotomicus erosus andPityogenes calcaratus to a synthetic aggregation pheromone ofIps typographus

Funnel traps baited with a synthetic aggregation pheromone ofIps typographus L. (Pheroprax) or with methyl-butenol were tested for mass-trapping ofOrthotomicus erosus (Woll.) andPityogenes calcaratus Eichh. (Coleoptera: Scolytidae), the major bark beetle pests of pine forests in Israel. The traps were operated during three periods in the years 1985–1986 in five pine forests. More than 170 individuals ofO. erosus and 180P. calcaratus per trap per day were caught in Pheroprax-baited traps in the warm season; the latter species was trapped in large numbers also during the winter. Traps baited with methyl-butenol did not attract significant numbers ofO. erosus orP. calcaratus. Sixteen species of insect associates and predators of pine scolytids were trapped, but onlyHylurgus micklitzi Wachtl (Scolytidae),Eremotes porcatus Germ. (Curculionidae) (first record in Israel) andAulonium ruflcorne Oliv. (Colydiidae) were caught in considerable numbers (a total of several hundred). The mass catches of the target beetles and the very small number of predators trapped, suggest that Pheroprax-baited traps may be useful for bark beetle management in Israeli pine forests.     

Lateral transfer of a phytopathogenic symbiont among native and exotic ambrosia beetles

Different ambrosia beetle species can coexist in tree trunks, where their immature stages feed upon symbiotic fungi. Although most ambrosia beetles are not primary pests and their fungal symbionts are not pathogenic to the host tree, exceptional situations exist. Notably, Xyleborus glabratus carries a phytopathogenic symbiont, Raffaelea lauricola, which causes laurel wilt, a lethal disease of some Lauraceae species. Both X. glabratus and R. lauricola are natives of Asia that recently invaded much of the coastal plain of the southeastern USA. This study examined ambrosia beetles that breed in susceptible trees in Florida (USA), including avocado (Persea americana), redbay (P. borbonia) and swampbay (P. palustris). Raffaelea lauricola was recovered from six of eight ambrosia beetle species that emerged from laurel wilt‐affected swampbay trees, in addition to X. glabratus. Controlled infestations with cohorts of the six species other than X. glabratus revealed that each could transmit the pathogen to healthy redbay trees and two could transmit the pathogen to healthy avocado trees; laurel wilt developed in five and one of the respective beetle × host interactions. These results indicate flexibility in the lateral transfer of a non‐native ambrosial fungus to other ambrosia beetles, and for the first time documents the transmission of a laterally transferred phytopathogenic symbiont by new ambrosia beetle species. Additional work is needed to determine whether, or to what extent, the new beetle × R. lauricola combinations play a role in spreading laurel wilt.     

Note: The malvastrum mealybugFerrisia malvastra (Hemiptera: Coccoidea: Pseudococcidae): Distribution, host plants and pest status in Israel

The malvastrum mealybugFerrisia malvastra (McDaniel) (Hemiptera: Coccoidea: Pseudococcidae) is widely distributed in Israel, recorded so far from 30 species of host plants belonging to 18 families. Its occurrence on herbal plants and on avocado should be considered by farmers in Israel.     

Fusarium oxysporum schlecht. in Israel

Out of 208 isolates ofF. oxysporum, 158 produced toxic reactions when applied to rabbit skin. This fungus, ubiquitous in the soils of Israel, was the most prevalent component of theFusarium flora in the unirrigated (but not in the irrigated) soils sampled.F. oxysporum var.redolens was common only on unfertilized plots of heavy, unirrigated soils.F. oxysporum was a major constituent of theFusarium flora isolated from most of the 450 samples of 20 field and garden crops, but less common in 98 samples of citrus, avocado and mango fruits. It ranks among the most destructive pathogens of cucurbits (exceptCucurbita pepo), tomatoes, onions, and gladioli in Israel, but causes almost no damage to Brassicae, peas or cotton. In pathogenicity tests with 207 isolates from nine field and two fruit crops, numerous isolates caused seedling mortality, with watermelon, onion, cucumber, tomato and eggplant being the most susceptible. Spore measurements on 160 isolates from plants and 355 from soils, showed that spore size was not markedly affected by plant source or by irrigation, but did differ between soil samples taken at 5 and 20 cm depth, and from manured or unfertilized soils.     

Biological control of avocado white root rot with combined applications of Trichoderma spp. and rhizobacteria

This study tested the effectiveness of single and combined applications of Trichoderma and rhizobacterial strains to control white root rot (WRR) caused by Rosellinia necatrix in avocado plants. Three Trichoderma, two T. atroviride and one T. virens monoconidal strains and four bacterial strains (Bacillus subtilis, Pseudomonas pseudoalcaligenes and two P. chlororaphis) were assayed to determine their compatibilities in vitro. In addition, the effects of the bacterial filtrates were evaluated against the Trichoderma strains and reciprocally; these filtrates were applied alone or in combination to determine their effectiveness against R. necatrix. Individual control agents or combinations of them were applied to avocado plants that were artificially inoculated with a virulent R. necatrix strain. Compatibility between the combined Trichoderma applications and the bacterial strains was observed and these combinations significantly improved the control of R. necatrix during the in vitro experiments. A relative protective effect of some Trichoderma and bacteria was observed on the control of avocado WRR when they were applied singly. The combinations of T. atroviride strains with bacterial strains P. chlororaphis and P. pseudoalcaligenes showed a better control of avocado WRR, whereas the rest of Trichoderma and bacteria combinations also reduced significantly the level of disease and induced a delay at the onset of disease with respect to avocado plants inoculated either with Trichoderma or bacteria.     

Distribution and characteristics of the damage of the Syrian woodpecker,Dendrocopos syriacus (HEMP. & EHR.) (Aves: picidae), in polyethylene irrigation pipes in fruit orchards

The Syrian woodpecker,Dendrocopos syriacus (Hemp. & Ehr.), was found to attack black polyethylene pipes of both sprinkler and drip irrigation systems in Israel. Nut crops and deciduous fruits are preferred by the woodpecker, and trees infested by boring insects are favored. Damage to pipes is frequent in plots of avocado, citrus and grapevine bordered by rows of windbreakers, with the pipes near the windbreaker being the most severely attacked. In orchards without windbreakers the distribution of damage seems to be random, or concentrated near trees infected by boring insects, or near other attractive objects (e.g. electric poles).     

Contribution of <Emphasis Type="Italic">Rosellinia necatrix</Emphasis> toxins to avocado white root rot

By transversely cutting infected avocado plant stems and using PCR techniques on avocado leaves, two experiments were carried out to determine whether Rosellinia necatrix can invade avocado vascular tissues. We were unable to detect the pathogen in either stems or leaves in either experiment, so we concluded that R. necatrix does not invade the vascular system of the plant. Additionally, the toxins produced by the pathogen were also studied to determine whether such toxins could contribute to the wilting and death of avocado plants infected by R. necatrix, having an effect on avocado leaves, where they can hinder the photosynthetic process. First, we isolated and identified the toxins cytochalasin E and rosnecatrone from filtrates of six R. necatrix isolates. Second, we tried to detect cytochalasin E in sap and leaves from infected avocado plants, and it was not detected at the minimum level of 50 μg/kg in leaves or 25 μg/kg on sap. Finally, we observed changes in fluorescence emitted by the avocado leaf surface (to detect photosynthetic efficiency) after inoculating avocado plants with this toxin. Fluorescence was higher in the leaves of plants immersed in toxin solution after 4 and 8 days, but not after longer periods of time. In this work, we demonstrated that although R. necatrix is not a fungus that invades the vascular system, its toxins are probably involved in the wilting and death of infected avocado plants, decreasing the efficiency of photosynthesis.     

Management of laurel wilt of avocado,caused by <Emphasis Type="Italic">Raffaelea lauricola</Emphasis>

Laurel wilt is caused by Raffaelea lauricola, a nutritional symbiont of an Asian ambrosia beetle, Xyleborus glabratus. American members of the Lauraceae plant family are most susceptible and 300 million trees have been killed by the disease in the southeastern USA since 2003. Recently, commercial production of an important crop in the laurel family, avocado (Persea americana), has been affected in southern Florida. We summarize studies in which diverse measures were tested for managing the disease. In all studies, trees were treated with potential laurel wilt control measures and subsequently inoculated with R. lauricola. On potted plants in greenhouse experiments, commercial nutritional products (Greenstim and Keyplex 350) and SAR products (Agri-Fos and Nutri-Phite), when applied as soil drenches or foliar sprays, had either no impact on, or increased laurel wilt symptom development compared to non-treated control treatments. Bark applications of Tilt (a propiconazole fungicide for which emergency registration had been obtained in 2010) in a surfactant (Pentrabark) enabled significant laurel wilt protection in greenhouse studies on small potted plants, but Pentrabark and other surfactants moved little propiconazole into the xylem of fruit-bearing trees in field studies. In efficacy studies in the field, Propiconazole Pro (an injectable formulation of propiconazole), Tilt, and two experimental formulations of another triazole fungicide, tebuconazole, decreased the development of laurel wilt compared to nontreated control trees when applied as undiluted injections into branches and scaffold limbs (microinjection), or injection of dilute fungicide into tree flare roots (macroinfusion). However, symptoms developed in all treated trees by 10–11 months after inoculation with R. lauricola, indicating that trees would need to be re-treated at least on an annual basis. Regardless of how fungicides were applied, insignificant levels of different active ingredients entered fruit. Although fungicide treatment of fruit-bearing avocado trees is not a concern for food safety and several triazole and DMI fungicides can protect avocado trees from laurel wilt, cost-effective measures with which the xylem could be loaded with and protected by these products remains a challenge. Management of laurel wilt in commercial avocado production areas is discussed.     

The elm bark beetle Scolytus kirschi and its control in Israel1

Scolytus kirschi, a bark beetle new to Israel, was found in 1983 near Lake Kinneret affecting and killing young elm trees under stress. The main cause of the stress was water deficiency. Phytosanitation, seasonal irrigation and exposure of trap logs all slowed down the spread of the beetle and prevented further damage.     

Biological data onApanteles cerialis Nixon (Hymenoptera: Braconidae), a parasite ofBoarmia (Ascotis) selenaria Schiff. (Lepidoptera: Geometridae)

Apanteles cerialis Nixon, a thelytokous braconid parasitoid ofBoarmia (Ascotis) selenaria Schiff., attacks young caterpillars (preferably 2–5 days old) of this pest in avocado plantations of Israel. At 27±1°C, oviposition rate is 2.04 progeny per day and 18.3 progeny over the entire life span. The development time of preimaginal stages is 16.1 and 15.2 days at 25° and 30°C, respectively, and increases to 37.3 days at 17°C. The pupal stage averages 4.4 days at 30°C and 13.5 days at 17°C. The average longevity of adults is 24.2 and 7.9 days at 30° and 17°C, respectively. In avocado orchardsA. cerialis appeared in considerable numbers in late summer and autumn; it was slightly hyperparasitized by the ichneumonid waspStictopisthus sp. (1 and 2% of the samples at one site).

     

Diurnal and seasonal occurrence,feeding habits and mating behavior ofMaladera matrida adults in Israel

Adult populations ofMaladera matrida Argaman (Coleoptera: Scarabaeidae), a beetle highly injurious to agricultural crops, were studied in the coastal plain of Israel from 1985 to 1988. There were two generations annually. Adults emerged in March, April or May and disappeared in October or November. The beetles are on the wing, mate, and feed at twilight and in the dark. Feeding and mating behavior, sex ratio, and preferred food plants were studied.     

Effect of metabolites from different Trichoderma strains on the growth of Rosellinia necatrix,the causal agent of avocado white root rot

Seven different strains of Trichoderma isolated from avocado roots showed antagonism to Rosellinia necatrix, which is the causal agent of white root rot. We studied these Trichoderma strains on the basis of the secondary metabolites produced in liquid culture. Five different compounds, namely, 6PP (6-pentyl-α-pyrone), Harzianolide (4-hexa-2,4-dienyl-3-(2-hydroxy-propyl)-5H-furan-2-one), T39butenolide (4-hexa-2,4-dienyl-3-(2-oxo-propyl)-5H-furan-2-one), Dehydroharzianolide (4-hexa-2,4-dienyl-3-propenyl-5H-furan-2-one) and Cerinolactone [(3-hydroxy-5-(6-isopropyl-3-methylene-3, 4, 4a, 5, 6, 7, 8, 8a-octahydronaphthalen-2-yl) dihydrofuran-2-one); a recently discovered novel metabolite], were obtained. In vitro studies of the effects of these compounds on different R. necatrix strains isolated from avocado roots and with different virulence demonstrated that 6PP had the strongest effect even at a low concentration. Although unstable, Cerinolactone and T39butenolide also had large effects on R. necatrix, mainly at a concentration of 200 μg. Harzianolide and Dehydroharzianolide exhibited the lowest effects on the pathogen. In vivo studies of Trichoderma metabolites on Lupinus luteus plants demonstrated the delay of white root rot epidemic through preventive application of 6PP or Harzianolide to seeds or plantlets by immersion in solutions of these metabolites at 1 mg l^?1 (minimum effective dosage). In contrast, Cerinolactone only was effective at 10 mg l^?1 when applied by plantlet immersion. Thus, this study reports the role that these metabolites could play for controlling avocado white root rot caused by R. necatrix.     

Potency and effect ofBacillus thuringiensis preparations against larvae ofSpodoptera littoralis andBoarmia (Ascotis) selenaria

The potency of two newBacillus thuringiensis (B.t.) preparations (coded ABG 6104 and ABG 6105) and of Dipel (B. thuringiensis var.kurstaki) was determined againstSpodoptera littoralis (Boisd.) 5th-instar larvae on a calcium-alginate diet. With this bioassay, the newB.t. products were more than twice as potent as Dipel. They were also 2–3 times more active than Dipel on alfalfa and cotton leaves in the laboratory. When applied in an alfalfa field at the rate of 312 mg/m², ABG 6104 and ABG 6105 caused 40% mortality of 5th-instar larvae and reduced the weight of the survivors to 30–40% of the control; only half of this activity was obtained with Dipel. On cotton, the activity of all theB. t. products was low. NeonateS. littoralis larvae were effectively controlled on avocado seedlings; however, there was high mortality also in the untreated controls. All threeB. t. preparations had a similar effect onBoarmia (Ascotis) selenaria Schiff. on avocado leaves in the laboratory. Addition of a chitinase enzyme did not increase the pathogenicity of the microbial preparations in the latter tests.     

An evaluation of the role of oxidative enzymes in Colorado potato beetle resistance to carbamate insecticides

Carbofuran and carbaryl LD₅₀ values were determined with and without piperonyl butoxide pretreatment for a resistant (New Jersey) and two susceptible (Utah and Netherland) populations of Colorado potato beetle larvae. Similar bioassays were conducted with carbofuran for resistant (Rutgers) and susceptible (NAIDM) adult house flies. The degree of resistance development by New Jersey Colorado potato beetles (RR = 848) was greater than that of the laboratory-selected colony of Rutgers house flies (RR = 583). Comparisons of synergist difference calculations including “percentage synergism” (%S), “log percentage synergism” (L%S), and “relative percentage synergism (R%S) for the resistant (R) and the susceptible (S) populations indicated the possibility that monooxygenases and other resistance mechanisms may be involved in Colorado potato beetle resistance to these carbamates. Monooxygenase involvement in resistance of Rutgers house flies was demonstrated in vitro by a 4-fold enhancement of p-nitroanisole O-demethylation over that of NAIDM house flies. O-demethylation of p-nitroanisole could not be demonstrated for potato beetle larvae. Colorado potato beetle resistance was associated with increases in microsomal levels of NADPH-cytochrome c reductase (ca. 2-fold) and NADPH oxidation (1.2-fold). The inability to measure O-demethylation in Colorado potato beetles may have been due to the solubilization of NADPH-cytochrome c reductase during microsomal preparation. Significant differences between resistant and susceptible Colorado potato beetle larvae were not observed in the penetration of [¹⁴C]carbaryl. Excretion of the radiocarbon may have been significantly greater in the resistant New Jersey population, but some of the insecticide may have also rubbed off the cuticle. This increased capacity for excretion, combined with increased levels of monooxygenase enzymes, could account for the high resistance level of this population.