Balsam Twig Aphid Research Articles

Embryonic stage of obligatory diapause and effects of abiotic conditions on egg hatching in the balsam twig aphid, Mindarus abietinus

AbstractDiapause‐mediated dormancy in overwintering insect eggs has rarely been studied with regard to the ecological factors controlling postdiapause development. In insects of temperate latitudes, water availability at the end of winter, in interaction with temperature, could control the resumption of development for insect stages in postdiapause quiescence. The balsam twig aphid, Mindarus abietinus Koch (Hemiptera: Aphididae), overwinters as eggs in southern Québec, Canada, on balsam fir, Abies balsamea (L.) Miller (Pinaceae), in Christmas tree plantations, where it is known as a pest. Previous work has shown that eggs of this aphid maintain low water content during winter, presumably to survive sub‐zero temperatures. Conversely, in late winter and early spring, they passively or actively absorb surrounding moisture, which is accompanied by notable changes in size, shape, and fresh mass. The primary objective here was to determine the embryonic stage at which winter diapause starts and is maintained in M. abietinus, a relatively primitive aphid. Secondly, we tested the hypothesis that free water availability to postdiapause eggs, in combination with temperatures above developmental threshold, is essential for embryonic development and hatching, by experimentally soaking field‐collected eggs in water at controlled frequencies. We observed that embryogenesis starts at the time of egg laying and stops after a few days, before the anatrepsis stage of blastokinesis is complete, when the germ band has not yet entirely immersed itself into the yolk. We also found that water surrounding overwintered eggs on fir shoots, in interaction with temperature regime, significantly increases M. abietinus egg hatching rates. Potential impacts of environmental factors such as precipitation are discussed in relation to M. abietinus egg hatching rates and potential for population growth in spring.

Novel Temperature-Dependent Development Rate Models for Postdiapause Egg Eclosion of Three Important Arthropod Pests Found in Commercial Christmas Tree Plantations of Southern Québec, Canada.

The balsam twig aphid Mindarus abietinus Koch (Hemiptera: Aphididae), the spruce spider mite Oligonychus ununguis (Jacobi) (Acari: Tetranychidae), and the pine needle scale Chionaspis pinifoliae (Fitch) (Hemiptera: Diaspididae) are three important pests for the Christmas tree industry of Québec, Canada. Temperature-dependent development rates for postdiapause overwintering eggs of these species have never been studied for populations of southern Québec, where the vast majority of Christmas trees are grown. The accumulation of physiological time in growing degree days (GDD) is a standard tool to predict egg eclosion dates for pests, when first generation immatures are most vulnerable to insecticidal control. Development rates for postdiapause eggs were tested at four or five constant temperatures in the 11-23°C range under controlled conditions, based on time before hatching for eggs collected in a balsam fir plantation in late winter. The standard linear model and three published nonlinear models were fitted to the data and compared for their ability to estimate key biological temperature parameters and to predict development rates of postdiapause eggs. Validation of model predictions of egg eclosion time on balsam fir in the field was reasonably accurate using the classical linear model where field-accumulated GDD were calculated with a particular interpretation of the average method based on daily maximum and minimum temperatures. The linear model could predict mean egg eclosion within around 5 d of eclosion dates observed in the field.

Early springtime water absorption by overwintering eggs of Mindarus abietinus (Hemiptera: Aphididae): possible implications for cold hardiness and diapause termination

AbstractEggs of the balsam twig aphid Mindarus abietinus Koch (Hemiptera: Aphididae) overwinter for several months in obligate diapause, which terminates in early springtime when embryogenesis of the stem mother supposedly resumes. Important shape and size changes were observed on eggs collected at regular intervals during late winter and early spring. These observations led to the visual classification of eggs into three shape categories: flat eggs (C1), semi-flat eggs (C2), and round and turgid eggs (C3). Egg mass significantly increased with time during late winter and early spring, which coincided with the noticeable changes in morphological composition (i.e., from C2 to C3). Our observations suggest that free water surrounding eggs on fir (Abies balsamea (Linnaeus) Miller; Pinaceae) shoots is essential for M. abietinus normal embryonic development during snowmelt. Also, reduced egg water content during winter could modify its supercooling point, and the renewed availability of water in springtime may signal diapause termination and/or initiate embryogenesis of the stem mother.

Seasonal natural history of aphidophagous Syrphidae (Diptera) attacking the balsam twig aphid in balsam fir (Pinaceae) Christmas tree plantations

AbstractThe balsam twig aphid, Mindarus abietinus Koch (Hemiptera: Aphididae), is one of the most important pests of balsam fir (Abies balsamea (Linnaeus) Miller; Pinaceae) grown as Christmas trees in eastern North America. Aphid feeding on the current-year shoots results in needle distortion and shoots stunting, which reduces the aesthetic value of balsam fir trees and can have substantial economic impact. Syrphidae (Diptera) fly predators attacking this aphid are poorly known. We identified four species attacking the balsam twig aphid. Syrphus torvus Osten Sacken (Diptera: Syrphidae) was the most abundant species followed by Eupeodes lapponicus (Zetterstedt) (Diptera: Syrphidae) and Eupeodes americanus (Wiedemann) (Diptera: Syrphidae). We described the seasonal natural history of the two most abundant syrphids feeding on this aphid and we studied their synchrony with their prey. Syrphid larval density on balsam fir shoots increased rapidly and closely followed density of the balsam twig aphid. We also reported heavy parasitism of syrphid pupae by two Hymenoptera on tree foliage but lower parasitism on pupae in the soil under trees. Several cases of multiple parasitism and hyperparasitism were observed in syrphid pupae under trees. Abundance of predaceous syrphid species was higher in untreated balsam fir plantations compared with treated plantations. More research is needed to understand the role and the impact of these predators on balsam twig aphid population dynamics.

Genetically-based resistance of balsam fir (Pinaceae) to damage from the balsam twig aphid (Hemiptera: Aphididae)

AbstractWe evaluated the effect of tree genotype on the resistance of balsam fir,Abies balsamea(Linnaeus) Miller (Pinaceae), to damage from the balsam twig aphid,Mindarus abietinusKoch (Hemiptera: Aphididae), by visually assessing aphid damage in clonal seed orchards located in New Brunswick and Nova Scotia, Canada, during four consecutive years. Estimates of clone mean heritability were moderate, suggesting that heritability of resistance is influenced by genetic factors. In New Brunswick, positive phenotypic and genetic correlations of clone-mean damage among years indicate that clones rank similarly each year. Our results suggest that selectively breeding for increased resistance could result in genetic gains.

Wing Morphometry Helps Diagnose Cryptic Species and ResurrectMindarus pinicolus(Hemiptera: Aphididae)

AbstractWing venation, two-dimensional and with easily recognized reference points at vein junctions, presents an opportunity for the development of automated insect identification. Using a suite of continuous characters, I investigated the use of wing morphometry for computerized insect identification of cryptic species of the aphid genus Mindarus. A priori groups were determined using cytochrome oxidase 1 DNA barcodes. Discriminant function analysis of 24 wing measurements consistently grouped individuals of unknown taxonomic affinity with the correct a priori groups. The results suggest that diagnostic signal is present in wing morphometry, but the signal is considerably stronger with the addition of morphometry from other aphid appendages, namely, 10 leg and antennal segments. Almost all Mindarus collected in eastern North America have been determined as the balsam twig aphid, Mindarus abietinus Koch (Hemiptera: Aphididae), but molecular diagnostics reveals that the Palearctic species is not present in the Western Hemisphere. Schizoneura pinicola Thomas has been considered a North American synonym of M. abietinus. Morphometric discriminant function analysis suggests that the Abies-feeding eastern North American population is M. pinicolus. The species is here reinstated with a new combination and redescribed.

Conservation through utilization: a case study of the Vulnerable Abies guatemalensis in Guatemala

Conservation through utilization is a controversial strategy that deserves more attention from researchers and practitioners. This case study focuses on Abies guatemalensis, a Vulnerable Mesoamerican conifer that is illegally used for timber, shingles, charcoal and Christmas tree production. Conservation of the remnant populations would preserve some unique montane forests, with concomitant benefits for local water supplies and prevention of landslides. As a conservation tool we suggest establishment of additional A. guatemalensis Christmas tree plantations. These could generate income for local farmers and help halt poaching from natural stands. So far, 51 such plantations have been established in Guatemala but practical knowledge of cultivation is limited and production dominated by a few large plantations. Seed for Christmas tree plantations needs to be carefully selected because there are marked differences among populations in germination, seedling height increment and greenery quality. Insect pests such as the balsam twig aphid Mindarus sp. could limit cultivation. A market study showed that c. 23% of households in the major Guatemalan cities buy A. guatemalensis Christmas trees but currently only 2.3% of these are plantation-grown. The prices of illegal and certified Christmas trees are, however, converging, making plantation trees more competitive. Because of the market characteristics and the potential for establishment of plantations, we are moderately optimistic that the conservation through utilization strategy may be successful for this species in Guatemala.

Insect Predators and Augmentative Biological Control of Balsam Twig Aphid (<I>Mindarus abietinus</I> Koch) (Homoptera: Aphididae) on Christmas Tree Plantations

Abstract The balsam twig aphid (Mindarus abietinus Koch) (Homoptera: Aphididae) is a major insect pest of balsam and Fraser firs grown for Christmas trees. Few control methods other than chemical insecticides have been evaluated. In this study, we identified insect predators associated with M. abietinus in three fir Christmas tree fields in Michigan. We also conducted laboratory and field studies to assess the effectiveness of augmentative releases of Chrysoperla rufilabris Burmeister (Neuroptera: Chrysopidae) for M. abietinus control. A diverse complex of predators, primarily generalists including syrphids, coccinellids, and lacewings, was observed on infested trees. Predator abundance was generally low early in spring when M. abietinus fundatrices were present, but predators became more common as sexuparae and later aphid stages appeared. In controlled laboratory tests, C. rufilabris were capable of consuming at least 35 M. abietinus per day, but were able to develop on 10 aphids per day. Average adult ...

Phenology and density of balsam twig aphid, Mindarus abietinus Koch (Homoptera: Aphididae) in relation to bud break, shoot damage, and value of fir Christmas trees.

The balsam twig aphid, Mindarus abietinus Koch (Homoptera: Aphididae), is a major insect pest of balsam and Fraser fir grown for Christmas trees. Our objectives in this study were to 1) monitor the phenology of A. abietinus in fir plantations; 2) assess relationships among M. abietinus density, tree phenology, and damage to tree foliage; and 3) develop an esthetic injury level for M. abietinus on Christmas trees. We monitored phenology of M. abietinus and fir trees on three commercial Christmas tree plantations in central and northern Lower Michigan for 3 yr (1999-2001). Phenology of M. abietinus fundatrices and sexuparae was strongly correlated with accumulated degree-days (DD) base 10 degrees C. Fundatrices matured by approximately 83 DD(10 degrees C) and sexuparae were first observed at approximately 83-111 DD(10 degrees C). Trees that broke bud approximately 1 wk later than other trees in the same field escaped M. abietinus damage and shoot expansion rate in spring was generally positively correlated with M. abietinus damage. Retail customers surveyed at a choose-and-cut Christmas plantation in 2 yr did not consistently differentiate between similarly sized trees with no, light, and moderate M. abietinus damage, but heavy damage (>50% damaged shoots) did affect customer perception. Similarly, when wholesale grades were assigned, the high quality Grade 1 trees had up to 40% shoot damage, whereas Grade 2 trees had 32-62% shoot damage. Two trees ranked as unsaleable had sparse canopies and distorted needles on 42% to almost 100% of the shoots.

Podabrus rugosulus (Coleoptera: Cantharidae), an opportunist predator of Mindarus abietinus (Hemiptera: Aphididae) in Christmas tree plantations

The balsam twig aphid, Mindarus abietinus Koch, is a major pest of balsam fir, Abies balsamea (L.) Mill. (Pinaceae), grown as Christmas trees in eastern Canada and the United States (Nettleton and Hain 1982; Kleintjes 1997). This aphid has three or four generations from April to July, and overwinters as eggs on fir shoots. Mature fundatrices deposit progeny on new shoots in late May. Infested shoots develop into pseudogalls characterised by stunting and needle distortion, thus reducing the aesthetic value of trees.

Predation on Mindarus abietinus infestingbalsam fir grown as Christmas trees: the impact ofcoccinellid larval predation with emphasis on Anatis mali

The impact of natural coccinellid larvalpredation on the balsam twig aphid was evaluated bysystematically removing coccinellid egg masses in a6–8 year-old balsam fir (Abies balsamea)Christmas tree plantation in southwesternQuebec. Among coccinellid species hunting on firfoliage during development of Mindarus abietinusfundatrices in May, the indigenous Anatis mali was by far the most abundant and themain one to oviposit on trees. Comparison of trees onwhich coccinellid larval predation was excluded withcontrol trees showed that A. mali had a markedimpact both during and after the phase of rapid M. abietinus population growth that followedfundatrix maturation. On trees where coccinellidlarvae were allowed, aphid colonies became inactive(i.e. no live aphids in the colony) about two weeksearlier than on controls. A strong dampening effect onaphid density was also observed in those colonies thatremained active until the end of the aphid life cycle.Predation on aphid colonies reduced sexualsproduction, as the density of M. abietinusoverwintering eggs per shoot subsequently was reducedby 32%. Predation by coccinellid larvae occurred toolate to prevent needle damage to current year shoots,which affects the aesthetic value of Christmas trees.However, current year shoots measured in the mid-crownof trees late in the season were 19% longer on treeswhere aphid predation by coccinellid larvae wasallowed, compared with trees where they were excluded.Rearing all larval stages of A. mali on 4thinstar and adult sexuparae of M. abietinusindicated an average consumption of 269 aphids tocomplete larval development and pupate, which wasequivalent to at least seven colonies of M.abietinus at maximum aphid density at theexperimental site. Anatis mali is an importantnatural control factor of balsam twig aphid inChristmas tree plantations, hence its activity shouldbe protected and possibly stimulated by favourablepest management practices.

Comparison of Methods for Monitoring Mindarus abietinus (Homoptera: Aphididae) and Their Potential Damage in Christmas Tree Plantations

The balsam twig aphid, Mindarus abietinus Koch, causes distortion, loss, or both, of needles on balsam fir Christmas trees. Insecticides are often applied for control of twig aphids with little monitoring of population levels or their subsequent damage. This study compared the utility of 2 techniques (beating discs and visual counts of infested shoots) that could easily be used by Christmas tree growers to monitor aphids. A beating technique was better than visual counts for detecting numbers of fundatrices before and during budbreak, whereas visual counts of midcrown infested shoots were more feasible for estimating aphid abundance after budbreak. Sample size analysis indicated that a minimum of 15 trees could be used for either method to estimate mean numbers of fundatrices or mean proportions of potentially infested shoots. Correlation analyses between mean numbers of aphids or proportions of infested shoots and resulting proportions of undamaged shoots were variable with a significant and negative correlation between infested shoots and subsequent undamaged shoots ( r = −0.83). Paired comparisons were also made between selected and nonselected Choose-and-Cut Christmas trees to evaluate public perception of aphid damage. The public did not differentiate between aphid-damaged and undamaged trees, but they did show a preference for larger trees. Our results indicate that growers need to monitor aphids before budbreak and limit insecticide applications to trees with predictable levels of infestation (e.g., 2 or more fundatrices per disc results in ≈50% infested shoots) that will be harvested for shipment rather than grown for Choose-and-Cut.

Midseason Insecticide Treatment of Balsam Twig Aphids (Homoptera: Aphididae) and their Aphidophagous Predators in a Wisconsin Christmas Tree Plantation

The balsam twig aphid, Mindarus abietinus Koch, is a pest of balsam fir, Abies balsamea (L.) Mill., and Fraser fir, Abies fraseri (Pursh) Poir., Christmas trees. This study evaluated the impact of a growers' application of an insecticide (Phosphamidon-8) upon populations of aphids and their arthropod predators (Coccinellidae larvae and adults, Syrphidae larvae, Chrysopidae and Hemerobiidae larvae) in a plantation in western Wisconsin. Spraying occurred on 27 May 1994 as a result of aphids (fundatrigenia and sexuparae) visibly damaging Christmas trees targeted for December 1994 sales. Aphids and predators were sampled by visual counts of infested shoots before and after insecticide treatment. Percentages of treated aphid-infested shoots significantly decreased from 86% prespray to 3% postspray, whereas percentages of untreated infested shoots increased from 75-88%. Two weeks postspray, percentages of both sprayed and unsprayed infested shoots were 5%. Numbers of aphidophagous predators significantly decreased on sprayed trees and significantly increased on unsprayed trees. Spiders increased on all trees. Assessment of needle damage 9 mo after treatment revealed no significant differences in the mean number of damaged shoots between sprayed and unsprayed trees. However, during the following growing season, treated trees contained significantly less numbers of aphids and predators than did unsprayed trees. This indicates that insecticide treatment of the shoot-feeding stages (fundatrigenia and sexuparae) can reduce numbers of aphids and their predators in the current and subsequent year, but will not necessarily reduce needle damage.

Ecology and Management ofMindarus kinseyiVoegtlin (Aphidoidea: Mindaridae) on White-Fir Seedlings at a California Forest Nursery

In recent years, an aphid identified as balsam twig aphid, Mindarus abietinus Koch, was observed on seedlings of white fir (Abies concolor [Gord. &; Glend.] Lindl.) at the USDA—Forest Service Nursery near Placerville, California. Both first- and second-year seedlings were infested and aphid-induced stunting of seedlings was observed. Investigations during 1989-92 revealed that the aphid had a life cycle that differed from that reported for M. abietinus. The following stages were detected: egg, fundatrix, vivipara (apterous and alate), sexupara (apterous and alate), and sexualis (male and ovipara). Third and subsequent generations of apterous viviparae were observed; these, plus the alate viviparae and the apterous sexuparae, have not been recorded for other Mindarus species. Aphid populations first appeared in spring, but persisted throughout the summer, fall, and well into winter. The aphid was recently described as Mindarus kinseyi Voegtlin. Ecological studies of M. kinseyi revealed that initial infestation of first-year seedlings was coincident with the discrete flight period of alate viviparae. Alates presumably originated in nearby plantings of second-year seedlings, or in white fir growing at other nearby sites. Alate colonization generally led to an aphid population that was distributed in patches in first-year seedlings. Mean aphid density peaked at replacecodegt25 per seedling (replacecodegt100 per infested seedling), and up to 21% of the first-year seedlings were infested. Initial infestation of second-year seedlings was due to either overwintering eggs (deposited on first-year seedlings), alate viviparae, or both. Early infestations were also patchily distributed, and in some cases, over 50% of the seedlings were eventually infested. Aphid eggs were also present on about 20% of the harvested seedlings destined for outplanting. Naturally occurring predators and parasites were not able to maintain aphid populations at low levels. The aphid’s major enemies at the nursery were aphidophagous predators, primarily larvae of syrphid flies. Survival of marked seedlings from emergence to harvest was very high (97.3%). However, cull-rate at harvest was independent of previous aphid infestation. Mean height, stem diameter, and dry weight of marked seedlings at harvest were not significantly reduced by aphid infestation. However, for marked seedlings infested early during the first season, both final height and dry weight were significantly reduced. Thus, aphid infestations can have a significant impact on growth of seedlings, but this does not necessarily lead to an increase in cull-rate at harvest. However, aphid caused mortality of first-year seedlings must also be considered. Additional seedlings were monitored at outplantings in the Eldorado and Stanislaus National Forests during 1991 and 1992. Seedlings were infested with aphids during the first year; however, seedling mortality was independent of aphid infestation during the season. A management program for M. kinseyi was developed and evaluated at the nursery. The program was based on careful monitoring, particularly during the aphid flight season, and spot treatment with compatible suppressive measures. The use of reflective lath fencing (placed horizontally over first-year seedlings) was not effective in reducing alate colonization. Larvae of the lacewings Chrysoperla carnea (Stephens) and C. rufilabris (Burmeister) were released in infested patches and provided good aphid suppression in most cases. Safer® insecticidal soap was also successfully employed as a spot treatment. In a management demonstration, about 10% of the first-year seedlings in the control group (without treatment) were infested by the end of the season compared to only about 1% in the management plot; all infestations in the latter were treated with either larvae of C. rufilabris, Safer® soap, or both. During the second season, all infested patches in the management plot were treated with Safer® soap; by the end of the season, about 20% of the seedlings in the control showed aphid damage compared to approximately 3% in the management plot. At harvest, the cull rate for both plots was relatively high, but independent of aphid infestation. The management program was evaluated again in 1992 with similar results. The pest status of M. kinseyi should be evaluated on a case-by-case basis and the management program implemented as needed. The primary aphid-suppression tactics (soap sprays, lacewing larvae) that were effective in a nursery setting could also be employed against M. kinseyi at Christmas-tree farms.

Control of Balsam Twig Aphid with Penncap M, 1992

Abstract Penncap M was applied at 2 rates to determine the efficacy against BTA. The experiment was conducted in a Christmas tree plantation in Westmoreland, NH. The experimental design was a RCB with 4 replicates, 5 trees per replicate. Trees were 5-7 ft tall. Applications were made 21 May when new growth was 1-1.5 inches long, and aphids were readily visible. Applications were made with a Solo backpack sprayer. At a rate of 100 gal water/acre, new growth was adequately covered. Conditions at the time of application: air temperature, 86.4°F; soil temperature at 2 inches, 73.7°F; sky clear, no rain for several days. The experiment was rated 2 Jun. Damage was rated by counting the percent of curled twigs per 20 randomly selected twigs per tree and converting to percent. The number of infested twigs was determined by counting the number of twigs with aphids on 10 twigs/tree.

DO BALSAM TWIG APHIDS (HOMOPTERA: APHIDIDAE) LOWER TREE SUSCEPTIBILITY TO SPRUCE BUDWORM?

AbstractThe balsam twig aphid, Mindarus abietinus Koch, infested nearly all trees in a range-wide provenance plantation of balsam fir, Abies balsamea (L.) Mill., in Michigan. Infestation levels were highest on eastern and lowest on western seed sources of fir. Large populations of the aphid were correlated with low survival and reduced developmental rates of the spruce budworm, Choristoneura fumiferana (Clemens). We propose that chronic, high susceptibility of trees to aphids could reduce concomitant susceptibility to budworm through direct (competition) and indirect (host and community-level) effects.

Spruce Budworm (Lepidoptera: Tortricidae): Role of Adult Imbibing in Reproduction

Laboratory-caged bud worm adults readily imbibed water droplets adhering to balsam fir foliage, as well as honey-sweetened and nonsweetened water in foam-latex sponges. Performance in six aspects of reproduction improved 27 to 108% when adults imbibed water compared with nothing, and 15 to 72% when they imbibed sweetened water compared with nonsweetened water. Respective gains in total fecundity including unlaid eggs were 27 and 20%; in number of eggs laid, 56 and 64%. Imbibing water increased oocyte maturation after eclosion, and imbibing sweetened water both increased oocyte production and further increased oocyte maturation after eclosion, phenomena not previously documented for tortricines. Precipitation provides water for natural imbibing, and a possible sweetener is honeydew of the balsam twig aphid, Mindarus abietinus Koch.

Balsam Twig Aphid Control, 1981

Abstract A study was conducted in April, 1981 to determine the efficacy of insecticidal soap for Balsam Twig Aphid control. Two locations in Ashe County, NC and 1 location in Waynesville, NC were selected as test sites. At each site, 100 Fraser fir trees were sprayed with Safer’s Insecticidal Soap (1.5 oz/gal) using a Solo backpack mist blower. A second block of 100 trees was left as a control. Twenty, 15-cm twig samples were taken from the center of each block before treatment and 1, 2 and 4 wk after treatment. The samples were analyzed for Balsam Twig Aphid eggs and motiles.

Genetic variation in susceptibility of Abiesbalsamea to Mindarusabietinus

A northern Vermont provenance test containing 1 Fraser fir (Abiesfraseri (Pursh) Poir.) and 21 balsam fir (Abiesbalsamea (L.) Mill.) provenances was attacked by the balsam twig aphid (Mindarusabietinus Koch.) during 1977 and 1978. Balsam fir from eastern provenances had 15–60% greater incidence of attack and averaged nearly twice the crown injury than did that from western provenances. Trees from an Indian Lake, NY, provenance were injured most with an average of 27 and 62% of current-year shoots injured during the 1977 and 1978 infestations. Trees from an Isle, MN, provenance were injured least with an average of 2 and 9% of current year shoots injured during the 2 years. The relative distribution of injury among provenances was similar from year to year. Fraser fir suffered little or no injury and appears to avoid twig aphid attack when planted in the north because it begins growth after the aphid population has peaked. The concentration of β-phellandrene in twigs was strongly correlated with twig aphid injury in balsam fir, whereas height, date of budbreak, needle length, and concentrations of other monoterpenes were weakly or only indirectly correlated with twig aphid injury.

Occurrence and Control of the Balsam Twig Aphid on Abies grandis and A. concolor12

The balsam twig aphid, Mindarus abietinus Koch, attacked A. grandis (Douglas) Lindley and A. concolor (Gordon and Glend.) Lindley and caused severe stunting, needle fall, and twig distortion of Christmas trees in westem Washington. Ultra-low-volume application of 0.25 g oxydemetonmethyl per 4- to 6-ft-tall tree gave effective seasonal control. Oxydemetonmethyl, dimethoate, and Azodrin® (3-hydroxy-N-methyl- cis -crotonamide dimethyl phosphate) applied to the trunk at 2.5 g per tree in water alone or with the adjuvants Estab® (Velsicol Chemical Co.) or Roplex® (Rohm &Haas Co.) gave excellent control, but this high rate and application expense is economically impractical except for high-value trees.