Summary Hyphae formed in soil by the vesicular‐arbuscular (VA) mycorrhizal fungus, Glomusfasciculatum (Thaxter sensu Gerd.) Gerd. and Trappe were extracted using the membrane filter techniqe and their length was estimated by the grid intersection method. The effect of phosphorus on the formation of this external mycelium was assessed after sampling procedures had been investigated. Phosphorus supply was varied from amounts severely deficient to those adequate for the growth of subterranean clover. After 6 weeks, the alleviation of severe phosphorus deficiency increased both the length of infected root and the length of external hyphae per centimetre of infected root. Further additions of phosphorus decreased both of these measurements. However, the level of added phosphorus at which the most external hyphae was formed per centimetre of infected root was higher than the level of phosphorus which gave the greatest length of infected root. The increase in phosphorus supply which gave the greatest increase in the length of external hyphae per centimetre of infected root also decreased the formation of vesicles within infected roots. At phosphate levels adequate for growth of mycorrhizal plants, there was little development of either external hyphae in soil or vesicles within the mycorrhizal roots.
Ten host plant (Solanaceae) and twelve non‐host plant species were tested as foodplants for first instar larvae of the tobacco hornworm, Manduca sexta. Only nine host and three non‐host plant species elicited feeding and supported growth up to fifth instar. The range of acceptability suggested that plants be divided into hosts, acceptable non‐hosts, and unacceptable non‐hosts. Using the two‐choice feeding preference test we found that the initial preference for hosts was preserved when larvae were reared on hosts, but was less strong or absent for larvae reared on acceptable non‐hosts. Thus oligophagy in the tobacco hornworm is not induced, but must be inherited. Newly‐hatched first instar larvae and fifth instar larvae showed a preference hierarchy among both hosts and non‐hosts. Fifth instar larvae reared separately on two different host species showed slightly different preference hierarchies among hosts. The preference for the rearing plant was increased and also two other host species changed positions in hierarchies. Feeding preferences of larvae reared on hosts or acceptable non‐hosts were determined using plant combinations of host vs. host, host vs. acceptable non‐host, and acceptable non‐host vs. acceptable non‐host. Induction of feeding preference was found in all three of these categories. This shows that induction of feeding preference in the tobacco hornworm is not restricted to host plant species. The degree to which feeding preferences were induced ranged from very strong to undetectable and dependend on the plant species paired. The strength of induction in the tobacco hornworm was found to correlate inversely with taxonomic relatedness of the plant species paired. Analysis of induction data from the literature revealed a similar correlation for other lepidopteran species. RÉSUMÉ Sélection des plantes consommées et induction d'un choix alimentaire entre plantes hǒtes ou non chez les chenilles de Manduca sexta Vingt‐deux espèces de plantes, dont 10 plantes‐hǒtes (Solanées), ont été testés comme plantes alimentaires pour des chenilles de ler stade de Manduca sexta. Sur cet ensemble, seulement 12 plantes (dont 9 plantes hǒtes) induisaient la prise de nourriture et permettaient la croissance jusqu'au 5ème stade. La diversité des résultats suggère que les plantes pouvaient ětre classées en hǒtes, non‐hǒtes acceptables et non‐hǒtes refusés. En utilisant le test du choix alimentaire préférentiel entre deux rondelles de feuilles, les chenilles néonates de ler stade ont préféré nettement les plantes‐hǒtes aux autres. Cette préférence initiale pour les plantes‐hǒtes était préservée quand les cheniles étaient élevées sur plantes‐hǒtes, mais devenait moins nette ou disparaissait pour des chenilles élevées sur d'autres plantes acceptées. Ainsi l'oligophagie ches M. sexta n'est pas induite, mais doit ětre héritée. Les chenilles néonates, aussi bien que celles de 5ème s...
The objective was to develop a method for estimating intestinal availability of rumen undegradable protein. One-gram samples of six feedstuffs were placed into small (3.5 X 5.5 cm) nylon bags (pore size 48 micron). Bags were heat sealed and ruminally incubated in a polyester mesh (lingerie) bag in quadruplicate for each of six time periods (0, 2, 4, 8, 12, 24 h). Two bags from each rumen incubation time were inserted into the small intestine via a duodenal cannula at the rate of one bag per 45 min. Bags were mechanically washed either upon removal from the rumen--for determination of rumen degradability, or when recovered from the feces--for estimation of intestinal availability. Dried bags plus contents were digested intact for nitrogen analysis. Rumen degradable protein and apparent intestinal availability of undegradable protein (based on 8 h of rumen incubation) for corn gluten meal, fish meal, meat and bone meal, soybean meal, canola meal, and alfalfa hay, respectively, were 11.8, 95.0; 28.5, 82.8; 46.7, 73.0; 55.1, 99.3; 69.7, 79.2; and 68.8, 71.2. Results support the use of this technique as a rapid method for estimating both ruminal degradability, and intestinal availability of rumen undegradable protein.
The contributions of olfactory and gustatory organs in food plant discrimination were examined in larvae of Manducu sexta (Johan.) (Lepidoptera, Sphingidae) . Larvae, from which various chemosensory
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