Ips sexdentatus (Boerner) Screening Aid

(Subfamily Scolytinae, Tribe Ipini)

From: Cavey, J., Passoa, S. and Kucera D. 1994, Screening Aids for Exotic Bark Beetles in the Northeastern United States. NA-TP-11-94. Northeastern Area: U.S. Department of Agriculture, Forest Service.

General Appearance in a Survey Sample. At 5.5-8.2 mm in length, I. sexdentatus would be one of the largest scolytids found in a survey sample from the northeastern U.S. This brown species has an excavated elytral declivity armed laterally with spines. Viewed from above, erect yellow hairs protrude from the body perimeter.

Recognizing the Genus. In general, Ips differs from other North American scolytids in having the following combination of characters (from Wood 1982, 1986):

• Elytral declivity widely excavated and armed laterally with 3 or more teeth, the teeth arising from the summit (ridge) of the lateral margins.
• Pronotum asperate on the anterior half.
• Antennal funicle 5-segmented.
• Antennal club strongly flattened, with two sutures on the anterior face bisinuate or procurved (curved forward).

Members of the most similar genera, Orthotomicus and Acanthotomicus, are much smaller in size than I. sexdentatus.

Recognizing I. sexdentatus. This species is named for the six spines or teeth found on each lateral margin of the elytral declivity (Fig. 3). Of the U.S. Ips that have more than four spines on the declivity, only grandicollis (with 5 spines, the 3^rd spine largest) and calligraphus (with 6 spines) occur in the NER (Wood 1982, Lanier 1987, Lanier et al. 1991). Both species could be present in numbers in survey samples.

The following will separate the target exotic species from I. calligraphus:

I. sexdentatus larger 5.5-8.2 mm (Grune 1979) 4th declivital spine largest (Fig. 3) (Grune 1979) frons with a short, transverse raised line above median tubercle (Fig. 1)	I. calligraphus smaller 3.8-5.9 mm (Wood 1982) 3rd declivital spine largest (Fig. 4) (Wood 1982) frons without a raised line above median tubercle (Fig. 2) (Wood 1982)
		Figure 1. Ips sexdentatus, frontal view of head (modified from Wood 1982).	Figure 2. Ips calligraphus, frontal view of head (from Wood 1982).
In addition to those cited above, other characters were noted from a limited study of 60 or more specimens of I. sexdentatus and about 175 I. calligraphus from the U.S. National Museum and Baltimore PPQ insect collections. Most useful is the frontal ridge shown in Figure 1 and described above. Also unlike I. calligraphus, I. sexdentatus has a series of setate granules in line near the suture on each elytron, but restricted to the basal half of the declivity; and the antebasal area of the pronotum is usually impunctate near the middle. On I. calligraphus, the setate granules near the suture are numerous and continuous to the declivital apex, so that the midline of the declivity appears entirely fuzzy. (However, be careful, because hairs can be abraded.) On I. calligraphus, the antebasal area of the pronotum is sparsely, finely punctate near the middle.
		Figure 3. Ips sexdentatus, lateral view of elytral declivity.	Figure 4. Ips calligraphus, lateral view of elytral declivity with teeth numbered (from Wood 1982).

adult beetle
Photo by Steve Passoa

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