Assessing Megastigmus specularis (Hymenoptera: Megastigmidae) infestations in a Fraser fir (Abies fraseri (Pursh) Poir.) clonal seed orchard of the southern Appalachians

ABSTRACT

The Christmas tree industry is mainly supplied with seeds from natural stands and genetically improved germplasm from clonal seed orchards (CSOs). Chalcid wasps (Megastigmus spp.) have a negative effect on the value of seedlots by reducing the quantity of viable seeds and represent a risk for national and international seed trade. Seed radiographies, field observations and seed-dissections from 25 Fraser fir (Abies fraseri (Pursh) Poir.) clones were used to determine chalcid infestation in a CSO of the southern Appalachians. We provided direct evidence that Mesopolobus cf. pinus is an ectoparasitoid of M. specularis, proposed a model that linked different aspects of the biology of these species and discussed host–insect phenological relationships. Infestation of seeds in some clones across surveys, suggested a potential genetic component to chalcid wasp's prevalence. Cold and dark rearing regimens were used to identify changes in adult insect emergence after variation of overwinter conditions. Both the frequency and the time of emerging M. specularis adults from seeds were affected by the duration of the treatments but not statistical differences were found for Mesopolobus cf. pinus. We present evidence for the efficiency of a gravity-seed cleaning method eliminating upwards of 95% of chalcid-infested seeds.

KEYWORDS:

• Megastigmus
• Mesopolobus
• chalcids
• Christmas trees
• orchards
• Abies

Acknowledgments

This work was supported by the North Carolina Christmas Trees Association; and the Provost's Professional Experience Program (PEP). Special thanks to Mistletoe Meadows, Avery Farm, Anne Margaret Braham, and Nick Moore at NCSU, for their invaluable support in field work. Victor Vancus (National Seed Laboratory) for x-radiography analysis. NCSU Plant Disease and Insect Clinic for first taxonomical characterization and preservation of specimens. Special thanks to Dr. Germán Plata (Elanco) and Dr. Ross Whetten (NCSU) who provided insight and expertise that greatly assisted the research.

Author Contributions

J.F., L.P.M.R., and R.J. conceived and designed the experiments; L.P.M.R. and K.G. performed the experiments. L.P.M.R analyzed the data and prepared the figures. M.B. P.J and R.A.B provided expert taxonomic identification and consultation. L.P.M.R wrote the paper with contributions from all authors.

Disclosure statement

No potential conflict of interest was reported by the author(s).