Controlling the sugar beet beetle <Emphasis Type="Italic">Cassida vittata</Emphasis> with entomopathogenic nematodes

Sugar beet, Beta vulgaris L. is a strategic crop of sugar industry in Egypt. It is threatened by several insect pests among most important of them is the beet beetle Cassida vittata. This work deals with the biological control of this insect using four Egyptian and imported entomopathogenic nematodes (EPNs). The nematodes included Steinernema carpocapsae S2, Heterorhabditis bacteriophora S1, S. feltiae and H. bacteriophora (1-3). Daily mortality of larvae, pupae and adults of C. vittata were recorded after treatment with serial concentrations (from 500 to 4,000 infective juveniles/ml) of each of four studied EPNs. Development of nematodes in insect bodies was followed up. S. carpocapsae S2 was chosen for the application against different stages of the pest in a sugar beet field. In the field, single application of S. carpocapsae S2 killed 65% of the larvae, 92% of the pupae and 57.3% of the adults of C. vittata within a week. This work is the first report on using the EPNs to control sugar beet beetle.     

Evaluation of four entomopathogenic nematodes againstSpodoptera littoralis (Lepid., Noctuidae) larvae under different temperatures

The efficacies of four strains of entomopathogenic nematodes on infecting and killingSpodoptera littoralis were tested in the laboratory concerning soil temperature, nematode dose and emergence from the insect cadavers. All the tested nematodes attained almost 100% insect mortality at 4, 10 and 25 °C but at 35 °C,Heterorhabditis bacteriophora (HP88) achieved the least (64%). As soil temperature rise to 35 °C, the most adversely affected nematode in terms of recycling efficiency wasH. bacteriophora (EASD98) followed bySteinernema riobravis, H. bacteriophora (HP88) and finallyH. indicus (EAS59). Although all nematodes could infect and kill the host insects at 35 °C, those ofH. bacteriophora (EASD98) could not emerge from the cadavers. Differences in the numbers of emerging infective juveniles as related to nematode concentration and different degrees of soil temperatures were obvious and may be considered in developing a biocontrol strategy for the management of the cotton leaf-worm.With 4 tablesThis research was supported by the NARP project No. H-035 and is a part of a M. Sc. thesis by Mr. Atwa Ahmed Atwa.     

Influence of soil on the efficacy of entomopathogenic nematodes in reducing <Emphasis Type="Italic">Diabrotica virgifera virgifera</Emphasis> in maize

The use of entomopathogenic nematodes is one potential non-chemical approach to control the larvae of the invasive western corn rootworm (Diabrotica virgifera virgifera LeConte, Coleoptera: Chrysomelidae) in Europe. This study investigated the efficacy of Heterorhabditis bacteriophora Poinar (Rhabditida: Heterorhabditidae), Heterorhabditis megidis Poinar, Jackson and Klein (Rh., Heterorhabditidae) and Steinernema feltiae Filipjev (Rh., Steinernematidae) in reducing D. v. virgifera as a function of soil characteristics. A field experiment was repeated four times in southern Hungary using artificially infested maize plants potted into three different soils. Sleeve gauze cages were used to assess the number of emerging adult D. v. virgifera from the treatments and untreated controls. Results indicate that nematodes have the potential to reduce D. v. virgifera larvae in most soils; however, their efficacy can be higher in maize fields with heavy clay or silty clay soils than in sandy soils, which is in contrast to the common assumption that nematodes perform better in sandy soils than in heavy soils.     

Control of a new turf pest, <Emphasis Type="Italic">Dorcadion pseudopreissi</Emphasis> (Coleoptera: Cerambycidae), with the entomopathogenic nematode <Emphasis Type="Italic">Heterorhabditis bacteriophora</Emphasis>

The use of biological control in turf has increased to avoid possible negative effects on humans. Entomopathogenic nematodes (EPNs) belonging to the families Steinernematidae and Heterorhabditidae have control potential against many economically important insect pests. In the present study, the efficacy of Heterorhabditis bacteriophora against a new pest on turf, Dorcadion pseudopreissi, was examined in the field. Cages (1 × 1 × 1 m) with female and male D. pseudopreissi were placed on two kinds of turf: Lolium perenne and Festuca arundinacea. After beetles had deposited eggs into the moist soil surface, the cages were removed and H. bacteriophora was applied at 0.5 million infective juveniles/m² to half the plots. Application of H. bacteriophora caused a statistically significant reduction in numbers of beetle larvae in L. perenne plots and a non-significant reduction in F. arundinacea plots. The area damaged by D. pseudopreissi was significantly reduced by nematode application in both turf species. The number of nematodes declined after application, but small numbers could still be detected after 6 months.     

A laboratory study on the activity of <Emphasis Type="Italic">Steinernema feltiae</Emphasis> (Rhabditida: Steinernematidae) Rioja strain against horticultural insect pests

The potential of the entomopathogenic nematode Steinernema feltiae (Filipjev) (Rhabditida: Steinernematidae) Rioja strain was assessed under laboratory conditions. Last instar larvae of Leptinotarsa decemlineata Say (Coleptera: Chrysomelidae), Spodoptera littoralis Boisdouval (Lepidoptera: Noctuidae) and Trichoplusia ni Hübner (Lepidoptera: Noctuidae) were exposed to infective juveniles (IJs) under laboratory conditions. Larval mortality, days to larval death, infection cycle length, and reproductive potential were recorded. Efficacy was assessed performing dose–response experiments. The results indicate that control of L. decemlineata with S. feltiae Rioja strain is not economically profitable (LC₅₀ = 99.61 IJs/cm²), whereas results obtained for T. ni (LC₅₀ = 0.27 IJs/cm²) are promising. Due to the life cycle of this insect, the efficacy needs to be investigated in foliar application studies. The effects on S. littoralis (LC₅₀ = 0.69 IJs/cm²) was considered the most suitable for development of the Rioja strain as a biocontrol agent for soil application.     

Infectivity prospects of both nematodes and bacterial symbionts against cotton leafworm, Spodoptera littoralis (Biosduval) (Lepidoptera: Noctuidae)

A study was made on the susceptibility of the cotton leafworm, Spodoptera littoralis (Biosd.), to the nematode, Steinernema carpocapsae (All) and Heterorhabditis bacteriophora. Three concentrations of each nematode species were used (75, 150, and 300 infective juveniles) for each treatment. The nematode, H. bacteriophora, gave 100% mortality 96, 90, and 48 h, respectively, post-treatment of S. littoralis larvae with 75, 150, and 300 infective juveniles. On the other hand, S. carpocapsae (All) gave 100% mortality 120, 90, and 56 h post-treatment, respectively. Therefore, H. bacteriophora was more potent against cotton leafworm than S. carpocapsae. Studies on the infestation intensity of the nematode species against the cotton leafworm showed the predominance of H. bacteriophora over S. carpocapsae, while in studies of the reproductive rate those of S. carpocapsae predominate. The bacterial symbionts of each nematode species were isolated and tested alone against cotton leafworm at concentrations ranging between 1×10² and 5×10³ bacterial cells/larva. The results showed a higher activity of Photorhabdus luminescens than that of Xenorhabdu nematophilus.     

Efficacy of entomopathogenic nematodes (Rhabditida: Steinernematidae and Heterorhabditidae) against the chive gnat, Bradysia odoriphaga

Chive gnat, Bradysia odoriphaga Yang & Zhang (Diptera: Sciaridae), is the most serious pest of Chinese chive, Allium tuberosum. The present study aimed at determining the biocontrol potential of different indigenous entomopathogenic nematode (EPN) isolates for the management of chive gnat in China. The virulence of 145 EPN isolates belonging to 13 species against B. odoriphaga was evaluated in the laboratory, and then the most promising isolates (Steinernema ceratophorum HQA-87; S. hebeiense JY-82; S. feltiae JY-90, JY-17; S. litorale HXY-68; Heterorhabditis indica ZZ-68; H. bacteriophora NY-63, HQ-94; and H. megidis LFS-10) were selected for further experiments. The mortality of fourth instar B. odoriphaga was significantly affected by nematode isolates and concentrations of infective juveniles (IJ). Third and fourth instars of B. odoriphaga were generally more susceptible to the nematodes than first and second instars and pupae. Pot experiments showed no differences in B. odoriphaga population reduction at 50 and 75 IJ/cm² of different isolates; the tested isolates caused a 78–94 % reduction of the chive gnat population at an application rate of 75 IJ/cm². In a field experiment, S. feltiae JY-90 generated the strongest pest suppression 14 days after EPN application, whereas after 28 days pest densities in the plots treated with S. feltiae JY-17 and S. hebeiense JY-82 were similar to those in plots treated with phoxim and yielded significant reductions of the B. odoriphaga populations. Our findings indicate that EPN may have good potential for use in the integrated management of B. odoriphaga populations in Chinese chive.     

Entomopathogenic nematodes for the biological control of crustaceans (Porcellio scaber Latr.) and millipedes (Blaniulus guttulatus Bosc.) in greenhouse

The effect of entomopathogenic nematodesSteinernema feltiae applied in dose 80 nematodes/cm² of soil on non-insect pests: crustaceans and millipedes were assessed in greenhouse. No differences were got between number of plants damaged by these pests when nematodes were added to the soil 8 days after vegetables sowing. When the plants were sown after nematodes application number of seedlings damaged were two in case of millipedes, or three in case of crustaceans, times less than in the check withoutS. feltiae. About 50% and higher cumulative mortality of these pests was observed between 2–8 week after nematodes application. The nematodes multiplied well in the millipedes and crustaceans bodies.

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Zusammenfassung Im Gewächshaus wurde die Wirkung einer Freilassung des entomopathogenen NematodenSteinernema feltiae (80 Indiv./cm² Boden) auf Asseln und Tausendfüßer untersucht. Es ergab sich kein Unterschied hinsichtlich der Zahl geschädigter Pflanzen nach Zugabe der Nematoden 8 Tage nach Aussäen der Pflanzen. Wurden aber die Pflanzen nach dem Einbringen der Nematoden gesät, war der Schaden im Fall der Tausendfüßer 2 x, im Fall der Asseln 3 x geringer als in Kontrollparzellen ohne Nematoden. Die Mortalität dieser Schädlinge stieg 2–8 Wochen nach Einbringen der Nematoden auf 50% und mehr an. Die Nematoden vermehrten sich in den Krpern der Asseln und Tausendfüßer stark.

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With 3 tables     

Preliminary investigations on the effect of gamma irradiation on the infectivity of the entomoparasitic nematodeSteinernema feltiae (Filipjev) (Rhabditida,Steinernematidae)

The effect of different doses 5, 10, 15, 30, 40 and 50 KR of gamma irradiation on the infectivity ofSteinernema feltiae Filipjev nematode has been studied. It was found thatS. feltiae was inactivated by gamma irradiation. Motility of nematodes as well as the mortality and infestation intensity of the host decreased at the higher doses. Development of nematodes was inhibited at the highest dose. No reproduction of nematodes occurred with any of gamma irradiation doses.     

Effect of the nematodeHeterorhabditis bacteriophora and the bacteriumBacillus thuringiensis as integrated biocontrol agents of the black cutworm

The entomopathogenic nematodeHeterorhabditis bacteriophora Pionar (HP 88) and the bacteriumBacillus thuringiensis Berliner var.kurstaki were tested in the laboratory against the black cutworm, a widely distributed polyphagous insect pest of vegetables and field crops. The experiment was conducted under 15.7 °C (14 to 19 °C) to simulate the average winter temperature in Egypt. The two biocontrol agents influencedAgrotis ipsilon differently whereH. bacteriophora had a more promising control levels than that ofB. thuringiensis. Generally, nematode concentration of ca 500 infective juveniles/insect vial was highly effective (100% mortality) within nine days post nematode infection. The highest concentration of the bacteriumB. thuringiensis var.kurstaki (2,000 Intern. Units/mg) gave significant larval control after 12 days of bacterial infection. Combined effect of both the nematodes and the bacteria did not result in significantly greater control than that achieved by the nematodes used alone. The present results indicated that nematodes could be used successfully against the black cutworm,Agrotis ipsilon larvae during the winter which is the active season of this insect pest in Egypt.     

Nutrient cycling and soil leaching in eighteen pure and mixed stands of beech (Fagus sylvatica) and spruce (Picea abies)

Studies on the combined effects of beech–spruce mixtures are very rare. Hence, forest nutrition (soil, foliage) and nutrient fluxes via throughfall and soil solution were measured in adjacent stands of pure spruce, mixed spruce–beech and pure beech on three nutrient rich sites (Flysch) and three nutrient poor sites (Molasse) over a 2-year period. At low deposition rates (highest throughfall fluxes: 17 kg N ha⁻¹ year⁻¹ and 5 kg S ha⁻¹ year⁻¹) there was hardly any linkage between nutrient inputs and outputs. Element outputs were rather driven by internal N (mineralization, nitrification) and S (net mineralization of organic S compounds, desorption of historically deposited S) sources. Nitrate and sulfate seepage losses of spruce–beech mixtures were higher than expected from the corresponding single-species stands due to an unfavorable combination of spruce-similar soil solution concentrations coupled with beech-similar water fluxes on Flysch, while most processes on Molasse showed linear responses. Our data show that nutrient leaching through the soil is not simply a “wash through” but is mediated by a complex set of reactions within the plant–soil system.     

Effect of Lecanicillium muscarium on Eretmocerus sp. nr. furuhashii (Hymenoptera: Aphelinidae), a parasitoid of Bemisia tabaci (Hemiptera: Aleyrodidae)

Pathogenicity of Lecanicillium muscarium, against Eretmocerus sp. nr. furuhashii (Hymenoptera: Aphelinidae), was investigated under laboratory conditions to determine if the fungal infection of the whitefly host can effect the survival, longevity and fecundity of female parasitoid. The results indicated that the number of parasitized larvae surviving a L. muscarium treatment after 6 days of oviposition decreased with increasing concentrations of L. muscarium and in later stages of development (12 days post oviposition) were not affected by fungal application. There were no significant differences on adult parasitoid survivorship after 7 days among all treatments. Maximum survivorship (73.33%) was observed for control and it was minimum (60%) at 1 × 10⁸ conidia/ml. L. muscarium showed a non significant effect on longevity and next offsprings of female parasitoids. The percentage emergence of parasitoids from the whitefly nymphs produced by the females emerged from treated pupae was almost similar. Maximum emergence (69.77%) was observed at 1 × 10⁶ conidia/ml and it was lowest (61.02%) at conidial concentration of 1 × 10⁸ conidia/ml. Maximum longevity of adult Eretmocerus sp. emerging from whitefly nymphs when treated after 12 days of postoviposition was observed for 1 × 10⁵ conidia/ml having a mean value of 5 days whereas the lowest longevity was 4.9 days observed at 1 × 10⁸ conidia/ml. The results mentioned above indicate that the interaction among biocontrol agents is positive to a greater extent with minimum risk hazards.     

Distribution and persistence ofSteinernema spp. andHeterorhabditis spp. (Nematodes) under different field conditions

The vertical and horizontal distribution, as well as the persistence ofSteinernema glaseri, S. carpocapsae (1192, I 100 and Mexican strains),Heterorhabditis bacteriophora, H. heliothidis andHeterorhabditis sp. were studied in three different soil types under field conditions. The presence of infective juveniles in soil samples taken at various depths was assessed usingGalleria mellonella larvae as baits for the nematodes. Results show that all tested nematodes had a similar pattern of vertical distribution. On the other hand,Heterorhabditis spp. were significantly more persistent thanSteinernema spp. in all soil types. As for the horizontal dispersal, none of the nematodes were ever found outside the treated plots, indicating that most of the juveniles remained near the point of application.     

地形因子对思茅松人工林土壤有机碳储量的影响

[目的]以思茅松人工中龄林为研究对象,探讨不同坡向、坡度和坡位对思茅松人工林SOC储量的影响,为精确评估思茅松人工林碳储量提供科学依据。[方法]对不同坡向、坡度和坡位不同土壤层次的SOC含量、全氮、土壤密度、C:N和SOC储量进行T检验和单因素方差分析,对不同土层的SOC储量和全氮、土壤密度、C:N之间进行Pearson相关分析。[结果]思茅松人工中龄林,SOC含量、全氮和C:N随着土层加深而减少,土壤密度随着土层加深而增加。不同的坡向和坡度显著影响SOC储量大小,阳坡的SOC储量要显著高于阴坡,坡度为20 30°的SOC储量要显著低于10 20°和0 10°,坡位对SOC储量大小无显著影响。在0 100 cm土层中,随着土层深度的增加,不同立地条件的思茅松人工中龄林的SOC储量呈减小趋势,不同坡向、坡位和坡度0 20 cm土层SOC储量均显著高于其它土层。坡向和坡度显著影响0 20 cm土层的SOC储量(P0.05);坡位对各层SOC储量均无显著影响(P0.05)。0 20 cm土层中SOC储量和土壤密度呈极显著负相关,和坡向、坡度呈显著负相关关系;除2040 cm土层外,其它土层的SOC储量与全氮之间呈极显著正相关;SOC储量和坡位与C:N在任一土层均无显著相关关系。[结论]立地条件差异影响SOC储量的大小与分布,尤其是坡向和坡度的不同会造成思茅松人工中龄林SOC储量的差异。     

伊氏杀线真菌与苏云金芽孢杆菌对松材线虫的联合毒力研究

[目的]探究伊氏杀线真菌与苏云金芽孢杆菌(Bacillus thuringiensis,Bt)对松材线虫的联合毒力。[方法]使用Esteya vermicola孢子悬浮液与Bt发酵液处理松材线虫,通过线虫的形态变化、死亡率及死亡速度3个方面测定E.vermicola与Bt联合对松材线虫的影响。[结果]经过E.vermicola孢子悬浮液处理过的线虫会出现内容物渗漏,体腔收缩、弯曲、断裂的现象;高浓度的E.vermicola孢子悬浮液与Bt发酵液联合处理松材线虫可以明显地提高线虫的死亡率,最高可以达到100%;联合处理的线虫死亡速度较快,随着处理时间的延长,死亡率会一直呈上升的趋势。[结论]应用这两种生防微生物在合适的浓度下混配能够在较短时间内提高松材线虫的死亡率。     

Evict or infect? Managing populations of the large pine weevil, Hylobius abietis, using a bottom–up and top–down approach

Hylobius abietis is the most important pest of replanted coniferous sites in Northern Europe, where feeding by adult weevils can result in up to 100% mortality of seedlings. Field trials were conducted with the aim of reducing H. abietis populations developing in Sitka spruce stumps by increasing pressure from natural enemies (top–down pressure), and reducing the quality of stumps for development (bottom–up pressure). Top–down pressure was applied through inundative treatment of stumps with entomopathogenic nematodes (Heterorhabditis downesi or Steinernema carpocapsae). Bottom–up pressure was applied by treating stumps with the wood colonising fungus Trichodermakoningii. Natural levels of parasitism of H. abietis by the parasitoid Bracon hylobii and the effect of applied agents on B. hylobii were also investigated. Heterorhabditis downesi parasitised more immature weevils than S. carpocapsae, and significantly reduced numbers of adults emerging from stumps compared to controls. Entomopathogenic nematodes did not significantly impact on populations of B. hylobii, and over three sites the effects of both agents were additive. Stumps modified by application of the fungus (bottom–up pressure) did not have fewer H. abietis developing in, or emerging from them; however, development of H. abietis was more advanced in these stumps, and the success of natural enemies was differentially affected. T.koningii facilitated B. hylobii while having the opposite effect on entomopathogenic nematodes, suggesting that it affected the outcome of competition between the nematodes and the parasitoid.     

Development and population growth of <Emphasis Type="Italic">Stephanitis pyri</Emphasis> (F.) (Heteroptera: Tingidae) at five temperatures

Pear lace bug, Stephanitis pyri (F.) (Heteroptera: Tingidae) is a pest of apple and pear trees and ornamental Rosaceae plants in Mediterranean countries and palearctic region. The aim of this study is to determine the effects of temperatures on S. pyri in the laboratory. Development and fecundity of S. pyri reared on apple leaves (Pyrus malus L.) were investigated at five constant temperatures (20, 23, 26, 29 and 32 ± 1°C) and a 16L:8D photoperiod. Longevity was determined to be 12.6 days at 32°C and 58.7 days at 20°C for females, and 9.7 and 37.7 days for males. Females laid 186.9 eggs per female with the highest number achieved during 28.5 days of oviposition period at 26°C. Female lifetime fecundity was reduced at 32°C (40.0 eggs per female). While the net reproductive rate (R ₀) was highest at 26°C, the intrinsic rate of natural increase (r _m ) was highest at both 26 and 32°C. The mean generation time (G) was estimated to be 27.2–78.4 days at 20 and 32°C, respectively. The longest development times for egg and total nymph stages were obtained as 22.0 and 24.9 days, respectively, at 20°C. S. pyri developed fastest from egg to egg in 24.3 days at 32°C. The lower developmental threshold (T ₀) was 9.7°C and the thermal constant (K) was 517.3 degree-days for S. pyri. Thus, S. pyri is calculated to have 3.8 theoretical generations in Tekirdag. The optimum developmental temperature for S. pyri was 26°C.     

Potential of Nepalese entomopathogenic nematodes as biocontrol agents against <Emphasis Type="Italic">Holotrichia longipennis</Emphasis> Blanch. (Coleoptera: Scarabaeidae)

Holotrichia longipennis Blanch. (Coleoptera: Scarabaeidae) is a serious pest of commercial crops in Siduwa, Dhankuta, Nepal. Seven indigenous isolates of entomopathogenic nematodes (Steinernema lamjungense LMT5, S. lamjungense SS4, S. everestense DKP4, S. abbasi CS1, S. sp. KL1, Heterorhabditis indica CK2 and H. indica CK6) were used in a series of bioassays against the insect. All isolates showed an increased dispersal in response to H. longipennis. Nematodes were more attracted towards third instar larvae than to second instars. Differences in penetration and multiplication in the insect were observed amongst the seven isolates. Steinernema lamjungense LMT5, S. everestense DKP4 and S. abbasi CS1 caused greater mortality than other isolates to different developmental stages. Pupae and second instar larvae were more susceptible than third instar larvae. Significant differences were observed in LT₅₀ values of the isolates against different stages of H. longipennis. Three isolates (S. lamjungense LMT5, S. everestense DKP4 and S. abbasi CS1) along with a commonly used insecticide (chlorpyrifos) were tested against this insect in pot and field experiments. In pot experiments using maize and cabbage as a host crop, S. lamjungense LMT5 and S. everestense DKP4 performed better than S. abbasi CS1 and yielded a mortality comparable with chlorpyrifos. Similar results were observed in field experiments 3 weeks after nematode application. These experiments overall suggest S. lamjungense LMT5 to be a promising biocontrol agent against H. longipennis followed by S. everestense DKP4 and S. abbasi CS1.     

淡紫拟青霉航天诱变菌株对南方根结线虫的致病力

[目的]为筛选对南方根结线虫具有高致病力的淡紫拟青霉航天诱变菌株,通过淡紫拟青霉山东寿光菌株搭载神舟八号获得10个淡紫拟青霉航天诱变菌株.[方法]以这10个航天诱变菌株对南方根结线虫卵进行寄生试实验,观察了其发酵液对南方根结线虫卵及二龄幼虫的作用,并对与毒力相关的胞外酶几丁质酶和蛋白酶活性进行了测定.在此基础上,通过盆钵试验方法, 检验菌株Sd-m-9、Sd-m-16和Sd-m-26对花椒南方根结线虫的防治效果.[结果]结果表明:10个诱变菌株对南方根结线虫卵的寄生率与原始菌株存在分化,其中有3个诱变菌株的寄生率增强,即Sd-m-9、Sd-m-16和Sd-m-26;这10个诱变菌株的几丁质酶和蛋白质酶的活性与对南方根结线虫卵的寄生率之间呈正相关.在盆钵试验中,菌株Sd-m-9、Sd-m-16和Sd-m-26对南方根结线虫的根结指数较原始菌株下降88.34%~89.70%.[结论]因此,航天诱变菌株Sd-m-9、Sd-m-16和Sd-m-26可用于对南方根结线虫的防治.     

Sustainability of extraction and production of copaiba (Copaifera multijuga Hayne) oleoresin in Manaus, AM, Brazil

We evaluate the ecological sustainability of extracting the oleoresin of Copaifera multijuga Hayne and some factors influential in its production. We monitored oleoresin production after initial extraction in 43 mother trees in the Adolpho Ducke Forest Reserve, near Manaus, Brazil (2°57′43″ S, 59°55′38″ W). We evaluated production relative to tree diameter (DBH), collection interval, soil clay content, competition intensity, and termite infestation. 57% of productive trees had DBH ≥ 41 cm and were responsible for 95% of total production. Although these trees had the highest initial production, after one year only 28% of initial oleoresin production was recuperated, much slower than in trees with DBH < 41 cm. Production was positively correlated with DBH and dominance within mother tree. Oleoresin production varied slightly with season. Trees that never produced oleoresin did not have termite infestations.