Effect of larval predators Thanasimus dubius (Coleoptera: Cleridae), reared on an improved diet, against the southern pine beetle Dendroctonus frontalis (Coleoptera: Curculionidae)

Arnaud Costa *1, John Reeve 2

1 Department of Primary Industries, Biosciences Division, Rutherglen, 3685 Victoria, Australia
2 Southern Illinois University, Department of Zoology, Carbondale, 62901 IL, USA

The clerid Thanasimus dubius is a predator of bark beetles that occurs in North America and Australia and could play an important role on bark beetle dynamics. The southern pine beetle, Dendroctonus frontalis (Coleoptera: Scolytidae) (SPB), is a major pest of pines throughout the southeastern United States. Evaluations of T. dubius against SPB have been limited by rearing methods. We first present an improvement of the rearing system that has previously developed a meridic artificial diet to feed larval T. dubius. Increasing feeding time interval and using preservatives such as sorbic acid could help to enhance the efficiency of the rearing system. We evaluated the effects on predator performance of: (i) adding sorbic acid at different concentrations (0, 0.1 and 0. 2%) in the larval diet; and (ii) increasing the feeding time intervals (2-3 vs. 5 days). Sorbic acid in the diet reduced female fecundity (by 20-40 %), but did not affect adult T. dubius size or longevity. However, using this preservative had no effect on the overall efficiency of the rearing system. Refreshing the larval diet every five days did improve the efficiency. In a second part, we conducted an experimental test where newly hatched T. dubius larvae were released at four densities (0, 50, 100, and 200 per log) on pine logs infested by SPB. The release of larval T. dubius resulted in a significant and negative effect on the SPB ratio of increase, but the initial SPB attack density also had  an effect on SPB ratio of increase.

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