Study

Effects of a biological control introduction on three nontarget native species of Saturniid moths

  • Published source details Boettner G.H., Elkinton J.S. & Boettner C.J. (2000) Effects of a biological control introduction on three nontarget native species of Saturniid moths. Conservation Biology, 14, 1798-1806.

Summary

The nontarget effects of a generalist parasitoid fly, Compsilura concinnata (Diptera: Tachinidae), introduced repeatedly to North America from 1906 to 1986 as a biological control agent against 13 pest species was examined. The effect of established populations of this fly on two native, nontarget silk moths (Lepidoptera: Saturniidae), Hyalophora cecropia and Callosamia promethea was experimentally investigated in a Massachusetts forest. An additional small scale study of Hemileuca maia maia (a threatened native species) to investigate potential parasitism by C.concinnata was also undertaken (for a summary see: www.conservationevidence.com/EditEntry.asp?ID=997).

Study area: The study was conducted in Cadwell Memorial Forest, Massachusetts (42˚22'N, 72˚25' W) northeast USA, in 1995 on C.promethea and 1997 on H.cecropia. The forest had abundant wild black cherry Prunus serotina (H.cecropia host plant) and sassafras Sassafras albidum (C.promethea host plant). The trees used in the study were understory plants (0.5–2.5 m in height) with a red oak Quercus rubra dominated canopy. An earlier study at this site indicated that C.concinnata was recently abundant.

Parasitism: H. cecropia and C. promethea eggs were obtained from The Butterfly Place, Westford, Massachusetts. To measure parasitism, larvae were reared indoors to ensure they were not parasitized, and then placed on host plants in the field. After approximately 1 week, larvae were relocated and reared in the lab. Any resultant parasitoids were collected and identified.

H.cecropia survival in the field: Two methods for studying survival of H.cecropia larvae were used.

i) 'the direct observation method' - first instar larvae were placed in the field and observed daily until pupation. Mortality factors observed were noted, but because cadavers usually disappear after predation or parasite emergence, the source of mortality often could not be determined.

ii) 'the cohort method' - groups of larvae were left in the field for only one instar, before bringing them into the lab for rearing. Fresh larvae of the next instar were deployed in the field on a new set of trees. This method allowed quantification of mortality from parasitoids and disease at each instar by bringing larvae back to the lab before they died or disappeared.

Short-term exposure of C. promethea to C.concinnata: C. promethea larvae were randomly deployed on 22 July 1995 at differing densities per plant (1, 3, 10, 30 and 100) on 115 sassafras trees (spaced 5–20 m apart along eight parallel 300 m long, transect lines in a 5-ha area) and were retrieved after 8 days. On 24 July more larvae were similarly released on 135 trees and retrieved after 6 days. A total of 1,407 larvae were deployed.

For newly hatched H. cecropia larvae (n = 500), placed five per tree in the field, no survival was found beyond the fifth instar. Observations of simultaneously deployed cohorts (n = 100) of each of the first three instars to measure the effect of parasitoids during each stage of development found that C. concinnata was responsible for 81% of H.cecropia mortality in the first three instars.

Semigregarious C.promethea released in aggregations of 1–100 larvae in the field and revealed high rates of parasitism by C.concinnata among the larvae exposed for 6 days (69.8%) and 8 days (65.6%).

Based on results of this study and an additional field study undertaken at Cape Cod, Massachusetts (for summary see: www.conservationevidence.com/EditEntry.asp?ID=997 ), the authors suggest that reported declines of silk moth populations in New England (USA) may be caused by the introduction of C.concinnata.


Note: If using or referring to this published study, please read and quote the original paper, this can be viewed at:

http://www.blackwell-synergy.com/doi/full/10.1046/j.1523-1739.2000.99193.x

 

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