The ambrosia beetle Xyhsandrus germanus (Blanford) (Coleoptera: Curculionidae) is among the most important exotic pests of orchards and nurseries in the United States. It attacks a wide range of hosts and is difficult to control using conventional insecticides. As part of our studies on the biology and control of X. germanus, we are trying to optimize conditions for rearing beetle progeny to adulthood in the laboratory. In this study we tested the brood production by X. germanus reared on artificial diet based on sawdust from American beech (Fagus americana L.), black walnut (Juglans nigra. L.), European buckthorn (Rhamnus cathartica L.), and red oak (Quercus rubra L.). We also tested the growth of different strains of the beetle fungal symbiont, Ambrosiella hartigii Batra, on these sawdust diets. Among the sawdust types tested, we found significantly higher average number of progeny produced on diet made with sawdust from European buckthorn (43.9 ± 1.6) compared with those made with American beech (29.2 ± 1.7), black walnut (25.5 ± 1.9), or red oak (26.3 ± 1.8). The percentage of females producing brood and the brood sex ratio (females:males) were not affected by sawdust type. Sex ratio, however, was correlated with progeny size, with fewer males produced as the number of progeny increased. In smaller broods the ratio observed was ≈4:1; in larger broods it approached 20:1. Growth of the fungal symbiont varied with strain and with sawdust. Comparison of progeny production on sawdust-based diet with symbiont growth in vitro suggests that variables other than speed of symbiont growth may be more critical in optimizing brood production.
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Vol. 41 • No. 4