The preference of the nabid, Reduviolus americoferus (L.), for potato leafhopper nymphs, Empoasca fabae (Harris), and pea aphids, Acyrthosiphon pisum (Harris), was examined using functional response models. The nabid exhibited a type-II functional response to each prey. Handling time was much higher for the aphid than for the leafhopper (3.623 vs. 0.211 h). Instantaneous search rates were also higher for the aphid (0.096 vs. 0.020 h−1). A preference index was calculated using the ratio of the instantaneous search rates. The nabid exhibited strong preference for the aphid; when both prey were present in equal numbers, the nabid consumed 3 times as many aphids. The predator did not switch to leafhopper nymphs as the proportion of leafhoppers was increased.

The commercial release of several cultivars of perennial, glandular‐haired alfalfa (Medicago sativa L.) for control of the potato leafhopper, Empoasca fabae (Harris), has increased the need to identify the causal mechanism of resistance. The objectives of this experiment were to examine the morphology and exudate of the glandular trichomes found on the perennial alfalfa clone FGplh13, in addition to comparing their density and distribution. Light, scanning, and transmission electron microscopy were utilized to characterize the morphology of the glandular trichomes and their associated exudate. Two distinct trichome morphologies, erect and procumbent glandular trichomes, occurred. The erect glandular trichomes consisted of multicellular stalks (5–11 cells) and gland heads, with the cells being arranged in distinct tiers. The procumbent glandular trichomes were composed of a stalk (1–2 cells) bent almost parallel to the plant surface. The procumbent gland head contained 8 to 12 cells, which were distinctly arranged in two to three tiers. Both types of trichomes released exudates that appeared to accumulate in a subcuticular space within a distal extrusion. Exudate from the procumbent glandular trichome became attached to the tibia of a potato leafhopper nymph. Entrapment of first instar potato leafhoppers by the glandular trichomes was also observed for the first time on a perennial glandular‐haired alfalfa clone. The erect glandular trichome was the most dense morphology on the stem, petiole, and leaf midvein.

The reproductive tract of the parasitoid Microctonus hyperodae was found to comprise 6.1 + 0.2 ovarioles containing a total of 40-60 o(Scytes. After oviposition into its host Listronotus bonariensis, the parasitoid's egg volume increased by 205 times prior to hatching. At 19.1 ~ ovipositing M. hyperodae survived for a mean 21 + 4 days and laid a mean of 48 + 8 eggs. M. hyperodae collected from Colonia, Uruguay laid a mean of 62 + 15 eggs which was significantly more than the other ecotypes. Under caging conditions with an ample supply of hosts, M.hyperodae laid 51% of its eggs in the first 72 hours and on average 41% of the species' life-span occurred after the exhaustion of its egg supply. Minimum temperature for M. hyperodae oviposition was found to be c. 5 ~ beyond this the rate of increase in egg-laying was approximately linear until 30 ~ whereafter the rate fell abruptly. There was effectively no egg-laying at 39 ~ The parasitoid showed no preference for one host sex or the other either in the laboratory or under field conditions. Compared to other Microctonus spp., M. hyperodae appeared to show low fecundity and high longevity. The adaptive implications of this are discussed.

ABSTRACT. The effects of food resources on populations of larvae of Sitona hispidulus (F.), a root and nodule herbivore of Medicago sativa L., were investigated in 1983 and 1984. Density‐dependent mortality among first‐instar larvae indicated that a lack of available root nodules, the primary resource for first instars, contributed to the 66.2±5.2% and 80.7±4.1% mortalities of first‐instar larvae in 1983 and 1984, respectively. Initial densities of larvae entering the soil were 31.7±2.4 and 15.6±1.3 per soil sample (10.5 cm diam. ×15 cm deep) in 1983 and 1984, respectively (±SEM). Survivorship and number of first‐instar larvae per soil core sample were significantly related to number and biomass of nodules per soil sample. Percentage soil moisture was not consistently correlated with survivorship and number of larvae per soil sample. Numbers of second‐ and third‐instar larvae were not consistently correlated with either nodule or taproot biomass. Numbers of fourth‐instar larvae were associated with taproot biomass, suggesting that taproot surface area may also limit population levels of S.hispidulus. No correlations were found between taproot and nodule biomass on any sampling date indicating that high numbers of fourth‐instar larvae associated with larger taproots were not merely due to a greater survival of first instars associated with larger taproots. The study suggests that population levels of nodule‐herbivores are controlled by the availability of root nodules. A sparse distribution of nodules results in high levels of mortality among nodule‐herbivores of Medicago sativa.

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