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Glycoalkaloids are found throughout the genera Solanum (potato) and Lycopersicon (tomato). Certain glycoalkaloids, i.e., α-tomatine, solanocardenine, and leptine, have been implicated as resistance factors to the Colorado potato beetle, Leptinotarsa decemlineata Say. The allelochemical properties of these glycoalkaloids have primarily been demonstrated by studies in planta, correlating Colorado potato beetle resistance with high levels of foliar glycoalkaloids: solanocardenine in S. neocardenasii, α-tomatine in S. pinnatisectum, and leptine in S. chacoense. Although the evidence that these glycoalkaloids mediate resistance is compelling, controlled analyses of Colorado potato beetle response to purified glycoalkaloids, fed to insects in synthetic diets, are necessary to characterize the allelochemic nature of these compounds. In this study, Colorado potato beetle reared on a meridic, synthetic diet supplemented with increasing concentrations of α-tomatine exhibit retarded growth and delayed development. These effects were evident throughout the insects' development, from egg to prepupal stage. Tomatidine (the aglycone of α-tomatine) has no effect on Colorado potato beetle, suggesting that the tetrasaccharide moiety of the glycoalkaloid is essential for insecticidal activity, consistent with a membrane-lytic mechanism of action.

Glycoalkaloids are a class of secondary compounds (nitrogenous, steroidal glycosides), ubiquitously distributed throughout the Solanaceae. Numerous studies (in planta) have shown that certain glycoalkaloids, e.g., α-tomatine, 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 supplemented with the glycoalkaloids α-tomatine, α-chaconine, α-solanine, leptine I and the steroidal aglycone solanidine, we have been able to further establish the effects (ex planta) of these compounds on the Colorado potato beetle. Leptine I displayed a dose-dependent negative activity against the Colorado potato beetle (as measured by larval weight gain and tune to molt), when assayed at 0.31, 0.62 and 1.23 mM concentrations; however, by the fourth stadium no effect was found. When Colorado potato beetle were 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 impact on Colorado potato beetle growth and development than did α-tomatine. α-Chaconine at 2.4 mM did not impair Colorado potato beetle performance relative to Colorado potato beetle reared on control diets. α-Chaconine plus α-solanine, at concentrations commonly found inSolanum tuberosum L. foliage (0.6 and 0.3 mM respectively), did not impair Colorado potato beetle performance. The steroidal aglycone solanidine (2.4 mM) had a significant negative impact on Colorado potato beetle performance. Results are discussed in the context of host-plant resistance and insect-plant interactions.

Foliage of the potato, Solanum tuberosum (L.), was analyzed previously to determine its nutritional content. This information was used to help develop a meridic diet for rearing the Colorado potato beetle, Leptinotarsa decemlineata Say. Various test diets were prepared, and types and concentrations of proteins, amino acids, carbohydrates, and ascorbic acid were tested for their influence on growth and weight gain of larvae reared from the egg stage on diet. At 2.8% protein or less, neither egg albumin nor casein produced adult beetles. Adults were reared with casein concentrations of 3.0 and 4.2%, but not at 5% casein. An abbreviated list of foliar amino acids was as effective as the complete foliar complement in the rearing of adults. Oat flour or potato flakes were suitable carbohydrate sources for rearing to the adult stage. The composition of a meridic diet is presented which was used for rearing the Colorado potato beetle from the egg to the adult stage, in the absence of host plant material.

A method is described that allows the rate of oxygen consumption to be monitored in plant cell suspensions. The method utilized oxygen electrodes placed in beakers of plant cells subjected to various treatments. The voltage readings from calibrated electrodes were converted to % oxygen (100% equals air equilibration) and the rate of oxygen consumption was estimated by calibration graphs made with no cells present. This system simultaneously monitors one to sixteen or more samples, allowing comparison of treatments on identically treated cells. We have used this method to study the respiratory burst of plant cells produced in response to viable or heat-killed bacteria. Because the system was computer-monitored and open to the atmosphere, data could be collected over several hours. Various factors that affected the measurement of dissolved oxygen concentration with this technique were explored and considered.

The foliage of the potato Solanum tuberosum (L.)was analyzed to gain understanding of the within-plant distribution of the Colorado potato beetle, Leptinotarsa decemlineata Say, and to develop a synthetic diet useful for rearing of this insect for experimental purposes. Foliage from three age classes was analyzed for protein, amino acid composition of protein, free amino acids, sugar, starch, nonstarch polysaccharides, dietary fiber, and trace elements. Concentrations of the amino acids glutamine, serine, asparagine, glutamic acid, proline, histidine, and arginine were higher in the youngest foliage than in the two older categories. Protein content was highest in the youngest foliage. With the exceptions of copper and phosphorus, the oldest foliage had the highest mineral levels. Concentrations of sugars were highest in the oldest foliage. The concentrations ofnonstarch polysaccharides tended to be lowest in the youngest foliage.

A laboratory rearing experiment was conducted to determine the effect of food intake and mating on longevity and egg production of the female adult green June beetle, Cotinis nitida (L.). A positive relationship existed between the number of eggs laid per beetle and beetle longevity (r = 0.37; P < 0.0001), where apple-fed beetles laid 2.2 eggs per day during a lifespan of 23.0 days and the water-fed beetles laid 1.87 eggs per day during a significantly shorter lifespan of 14.8 days (P < 0.0001). After mean adjustments for the effects of beetle longevity (by the LSMEANS procedure), the apple-fed beetles laid an average of 50.8 eggs which was significantly higher than the 26.9 eggs laid by the water-fed beetles (P < 0.0002). The number of matings had no effect on the numbers of eggs produced nor on beetle longevity. The treatment effects on percentage egg hatch by mating and feeding were insignificant. However, the effect of mating on the percentage of egg hatch differed depending on feeding. These differences were presumed to be due to soil differences between egg rearing containers and not to the effects of mating or feeding. These results suggest that feeding beetles live longer and produce more offspring than beetles that do not feed.