Forest stand preference of Sirex nigricornis, and Sirex noctilio hazard in the Southeastern United States

In 2005, a non-native woodboring pest, Sirex noctilio F. , was found established in North America. Sirex noctilio has an extensive history as an economically important pest in pine plantations throughout the Southern Hemisphere. The United States has a rich fauna of native Siricidae and associated parasitoids, but they are rarely studied due to their status as economically inconsequential organisms. With the introduction of S. noctilio, interest in the ecology of native siricid populations has increased. A study was conducted in Fall 2011 to investigate the effects of forest stand characteristics and stand types on native Siricidae abundance, and the flight phenology of Siricidae . A newly developed method was used to collect wood wasps; the pairing of Lindgren funnels with fresh pine material. A total of 609 native Siricidae were captured, consisting of 608 Sirex nigricornis F. and 1 Urocerus cressoni Norton. The flight period of Siricidae captured in our study was similar to that of studies from Arkansas, (October December) but differed other studies across the U.S (June or July October). Unthinned pine plantations had significantly more Siricidae than thinned pine plantations, mixed pine-hardwood and old growth forests. It appears that proper silvicultural management of pine plantations may 40 reduce stand hazard to native Siricidae in the southeastern U.S. as it does to S. noctilio in the Southern Hemisphere. We propose that silvicultural models used for the southern pine beetle be implemented and encouraged for prevention of infestations from S. noctilio and other pine pests. Introduction Siricids, commonly called wood wasps or horntails (Hymenoptera: Siricidae), are xylophagous insects that help decompose woody material in temperate forest ecosystems (Hall 1968, Spradberry & Kirk 1978). Worldwide there are 122 species of Siricidae in 10 extant genera; the Americas contain 33 species in 7 genera (Schiff et al. 2012). The family Siricidae is composed of two subfamilies. The subfamily Siricinae oviposit into gymnosperms and harbor fungus in the genus Amylostereum, whereas the subfamily Tremicinae utilize angiosperms as hosts and harbor Cerrena fungus (Tabata & Abe 1995, Schiff et al. 2006). Siricids are rarely studied in their natural habitat because of their economically inconsequential status. However, global interest in Siricidae have increased as the European woodwasp, Sirex noctilio Fabricius, has been introduced throughout the Southern Hemisphere and most recently in North America (Hoebeke et al. 2005, Carnegie et al. 2006). Sirex noctilio was detected in Oswego County, New York (2004) and the following summer in Ontario, Canada (2005) (Hoebeke et al. 2005, de Groot 2006). Sirex noctilio has caused significant damage (up to 90% mortality) to pine plantations throughout the Southern Hemisphere, travelling via solid wood packing materials (Neumann et al. 1987, Morgan 1989, Tribe & Cillie 2004). In North America, Sirex noctilio is not currently a serious pest (Dodds et al. 2010). However, S. noctilio is 41 predicted to cause economical loss if it becomes established in Southeastern and northwestern North America (Haugen 1990, Hoebeke et al. 2005, Yemshanov et al. 2009 , Ryan et al. 2012). One way of improving our predictions of how S. noctilio will behave in North America is to better understand the ecology and biology of the native siricid fauna and what factors prevent these populations from reaching outbreak status. The introduction of S. noctilio has spurred a great deal of research in North America concerning taxonomy (Schiff et al. 2006, Schiff et al. 2012), the native siricid parasitoid complex (Eager et al. 2011, Coyle & Gandhi 2012, Standley et al. 2012), silvicultural control efforts (Dodds et al. 2007, Dodds et al. 2010, Zylstra et al. 2010) and the composition of native Siricidae and woodboring insect competitors in North America (Ryan et al. 2011, Coyle et al. 2012, Ryan et al. 2012, Dodds et al. 2012). The effect of management schemes on S. noctilio or native Siricidae abundance has yet to be determined in North America. Because S. noctilio is not currently present in the Southeast, it is unknown how stand characteristics and management practices might impact its distribution, abundance, and behavior. However, S. nigricornis F. is a species whose ecosystem function is very similar to that of S. noctilio in its native range. By understanding how S. nigricornis populations are affected by management practices, better inferences can be made on how S. noctilio might behave if introduced into the Southeastern U.S. forests. The objectives of this study were three-fold: 1) to examine siricid flight activity in northern Mississippi and compare results to other studies performed throughout the United States (Coyle et al. 2012, Keeler 2012, Schiff et al. 2012); 2) to investigate what affect forest stand type and management practice have on native Siricidae abundance; and 42 3) to determine what forest stand characteristics (i.e. tree diameter, age and height) are correlated with native Siricidae abundance. Methods Forest Stand Types This study was conducted in four forest stand types: unthinned pine plantation, thinned pine plantation, mixed hardwood-pine forest, and old growth forest (Table 3.1). The age of each forest was determined from known planting dates for each forest stand except for the mixed stand at Longview Road, which was unknown (estimated to be 45 years of age in analysis). Sixteen stands (each stand type having four locations) were selected in northern Mississippi (Figure 3.1) based on the definitions in Table 3.1. Pine plantations consisted of Pinus taeda L. (loblolly pine), which was also the dominant pine species found in mixed and old growth forests. Pinus echinata Mill. (shortleaf pine) was sparsely found throughout mixed and old growth forests. Insect Trapping Three Lindgren® funnel traps with wet collection cups (Lindgren 1983) (Synergy Semiochemical Corp., Burnaby, BC, Canada) were dispersed at each of the 16 sites (48 traps total). Each trap location was arbitrarily selected within the stand and traps were hung at breast height (≈ 1.7 m) Traps were separated by a distance of at least 150 m. Traps were placed on the week 28 September 2011 and removed the week of 21 December 2011. Collection cups contained a mixture of 50/50 Prestone® Low Tox® Antifreeze/Coolant and water. A recent study found that standard Sirex lures (comprised of a 70:30 α/β-pinene blend) were relatively ineffective attractants for native Siricidae in