Performance of Colorado potato beetle larvae, Leptinotarsa decemlineata (Say), reared on synthetic diets supplemented with Solanum glycoalkaloids

Glycoalkaloids are a class of secondary compounds (nitrogenous, steroidal g lycosides), ubiquitously distributed throughout the Solanaceae. Numerous st udies (in planta) have shown that certain glycoalkaloids, e.g., alpha-tomat ine, solanocardenine, and leptine, have a negative impact on performance of the Colorado potato beetle, Leptinotarsa decemlineata (Say). However, the presence of other secondary compounds, as well as the nutritional status of the plants used, are additional variables in such experiments. By rearing Colorado potato beetle, from egg to prepupal stage, on a synthetic diet sup plemented with the glycoalkaloids alpha-tomatine, alpha-chaconine, alpha-so lanine, leptine I and the steroidal aglycone solanidine, we have been able to further establish the effects (ex planta) of these compounds on the Colo rado potato beetle. Leptine I displayed a dose-dependent negative activity against the Colorado potato beetle (as measured by larval weight gain and t ime to molt), when assayed at 0.31, 0.62 and 1.23 mM concentrations; howeve r, by the fourth stadium no effect was found. When Colorado potato beetle w ere fed a higher concentration of leptine I (2.4 mM), there was a sustained effect in all stadia. At 2.4 mM, leptine I displayed a greater negative im pact on Colorado potato beetle growth and development than did alpha-tomati ne. alpha-Chaconine at 2.4 mM did not impair Colorado potato beetle perform ance relative to Colorado potato beetle reared on control diets. alpha-Chac onine plus alpha-solanine, at concentrations commonly found in Solanum tube rosum L. foliage (0.6 and 0.3 mM respectively), did not impair Colorado pot ato beetle performance. The steroidal aglycone solanidine (2.4 mM) had a si gnificant negative impact on Colorado potato beetle performance. Results ar e discussed in the context of host-plant resistance and insect-plant intera ctions.