Responses of Heterodera glycines Populations to a Postemergence Herbicide Mixture and Simulated Insect Defoliation.

Effects of a mixture of the postemergence herbicides acifluorfen and bentazon, and simulated defoliation expected from green cloverworm on population densities of Heterodera glycines were determined in field plots in Iowa. The herbicide mixture and defoliation each suppressed soybean growth. Population densities of H. glycines were generally lower in herbicide-treated than untreated plots. Population densities of the nematode were unaffected by defoliation in 1988 and 1990-91, but were increased by the treatment in 1989.

Maternal and nutritional contributions to infant rats' activational responses to ingestion.

Infant rats deprived of food, maternal care, and the opportunity to suckle display a dramatic behavioral activation and vigorously ingest when provided milk through oral cannulas. These experiments assessed which components of deprivation are important in producing these responses to milk. Nutritional deprivation alone, with or without the presence of an active maternal female, appears to be sufficient to produce ingestion. Behavioral activation, on the other hand, appears to require both nutritional deprivation and deprivation from a maternal female. The effect of maternal stimulation on later behavioral reactivity was not a function of the pups' opportunity to suckle. However, active maternal stimulation was more effective in preventing activation than was passive maternal stimulation (e.g., thermotactile and olfactory stimulation). Stimulation provided by an active, nonlactating mother was effective in preventing behavioral activation, but the effect was short-lived, lasting only 2 hr after the pup was removed from the mother's care. This series of studies thus reveals that identified components of maternal separation have dissociable effects on appetitively motivated behaviors in infant rats.

Ontogeny of glucose inhibition of independent ingestion in preweanling rats.

Rat pups that have been maternally and nutritionally deprived will vigorously ingest diet infused directly into the mouth. The development of nutritive controls in this form of ingestion was examined by administering nutritive and non-nutritive gastric preloads to 6- and 15-day-old pups. In 6 day-old pups, nutritive gastric preloads (0.6 M glucose in distilled H2O or saline) and vehicle preloads were followed by similar intakes; only the change in hydrational state caused by distilled H2O loads appeared to affect intake. By 15 days of age, intake following nutritive preloads was less than intake following non-nutritive preloads. Also, at 15 days, stomach volume at the termination of intake was less following nutritive preloads. In a separate experiment with 6-day-old pups, gastric preloads of an alternative energy source, the ketone beta-hydroxybutyrate, also failed to inhibit intake when given at a dose that did not cause excessive gastric distension. These results indicate that a nutritive control of intake termination in rats is not present at 6 days of age but develops by 15 days of age.

The ontogeny of independent ingestion in mice: or, why won't infant mice feed?

Unlike infant rats, which show deprivation-related ingestion in several different test situations, infant mice appeared to be relatively unwilling to feed independently of suckling until 12 days of age. We tested mouse pups that were deprived (of food, water, suckling, and maternal care) for 1, 7, or 24 hr in ingestive tests in which a milk diet was spread on the floor of their test container (Experiment 1). Pups at 3, 6, and 9 days of age consumed small amounts of the diet and showed little increase in intake when deprivation was increased. In contrast (and like rat pups of all ages), mouse pups 12 and 15 days of age actively ingested the diet and increased their intake with increased deprivation. Six-day-old mouse pups were similarly unwilling to ingest a 5% sucrose solution, though 12-day-old pups showed deprivation-related intake (Experiment 2). Cellular dehydration (produced by hypertonic saline injection), a potent stimulus for ingestion in infant rats, did not stimulate ingestion in mice younger than 12 days of age (Experiment 3). Finally, when ingestion was tested with diet infusions made through oral cannulas, mouse pups at 6 and 9 days of age showed only a slight increase in intake with increased deprivation. However, by 12 days of age, pups' ingestion increased markedly with deprivation (Experiment 4). Thus, mouse pups seem to be very different from rat pups with respect to the early existence of ingestive systems. The neural substrates for the ingestive responses that subserve independent ingestion are only minimally present in infant mice or are somehow inhibited.