Ecology and Management of Mindarus kinseyi Voegtlin (Aphidoidea: Mindaridae) on White-Fir Seedlings at a California Forest Nursery
AuthorsL. E. Ehler
M. G. Kinsey
Authors AffiliationsL. E. Ehler was Professor of Entomology &; Entomologist in the Experiment Station, Department of Entomology, University of California, Davis, CA 95616; M. G. Kinsey was Staff Research Associate IV, Department of Entomology, University of California, Davis, CA 95616.
Hilgardia 62(1):1-62. DOI:10.3733/hilg.v62n01p006. September 1995.
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.
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