Performance of Two Fruit Fly (Diptera: Tephritidae) Pupal Parasitoids (Coptera haywardi [Hymenoptera: Diapriidae] and Pachycrepoideus vindemiae [Hymenoptera: Pteromalidae]) under Different Environmental Soil Conditions

We evaluated the performance of Coptera haywardi (Ogloblin) (Diapriidae) and Pachycrepoideus vindemiae (Rondani) (Pteromalidae), both hymenopteran pupal parasitoids of Anastrepha spp. (Diptera: Tephritidae). Performance was studied by manipulating the following environmental conditions in the laboratory: (1) soil type, (2) soil moisture content, (3) soil compaction, and (4) depth at which pupae were buried in the soil. There were two experiments: in the first, exposure time of pupae was held constant and in the second, it varied. In the first experiment, C. haywardi was significantly more effective than P. vindemiae in parasitizing fly pupae. With exposure time held constant (36 h), only soil type and pupal burial depth were significantly related to parasitism rates. While P. vindemiae only parasitized pupae located on the soil surface, C. haywardi attacked pupae that were buried up to 5 cm deep, performing better in clayey than in loamy soil. In the second experiment, exposure time (24, 36, 48, and 72 h) had no significant effect on parasitism rates, but soil type did. P. vindemiae again only attacked pupae on the soil surface while C. haywardi was also able to parasitize pupae that were buried up to 5 cm deep. We conclude that C. haywardi represents a viable candidate to replace the environmentally unfriendly P. vindemiae in augmentative biological control programs against fruit flies.     

Suppression of the rotifer Polyarthra remata by the omnivorous copepod Tropocyclops extensus: predation or competition

Indirect evidence from observations in the field suggested thata common and often abundant cyclopoid copepod, Tropocyclopsextensus, despite its small size (0.5 mm) and largely algaldiet, is an important predator of the rotifer Polyarthra remata.Laboratory experiments showed that copepodids and adults, butnot nauplii, markedly suppressed the population growth of thisrotifer. The suppression could be attributed entirely to predation,rather than to exploitative competition for shared food resourcesor to interference. Mortality rates predicted from a separatefeeding-rate experiment weresufficient to account for the declinein population size observed in the Tropocyclops treatment ofculture experiments. Also, monitoring the availability of cryptomonadfood in treatments with and without Tropocyclops throughoutthese experiments showed that cryptomonad densities always remainedhigh and were just as high or significantly higher in the copepodtreatments. Furthermore, direct videographic observations ofP. remata from cultures with and without Tropocyclops demonstratedno significant differences in swimming velocity, tendency todeviate from a straight-line path, or frequency and length ofspontaneous escape responses. Per capita ingestion rates ofT. extensus on P. remata varied from 2 to 8 day^-1, were significantlyhigher for adult females than adult males or copepodids V, andincreased significantly with rotifer density. A tendency ofcopepods to have higher ingestion rates on young than adultrotifers was not significant. Copepods cultured since birthwith cryptomonads and P. remata ate significantly fewer rotifersthan those cultured only with cryptomonads; this may be explainedby a more sated condition of the former and provided no evidencefor the idea that previous experience with this rotifer mightincrease predation efficiency. The results show that T. extensusin natural communities has the potential to deplete naturalpopulations of susceptible rotifer prey. Accordingly, it mayshift the species structure of rotifer assemblages in favourof resistant species, and provide selection pressure for avoidanceresponses.     

Evaluating Hypotheses on the Evolution of Helping Behaviour in the Bell Miner (Manorina melanophrys)

In an analysis of the pattern of helping at the nest in bell miners (Manorina melanophrys), Clarke (1989) examined five hypotheses that could explain the evolution of helping behaviour in this species. We applaud the attempt by Clarke to consider many different hypotheses, but believe that more careful formulation of the hypotheses, more appropriate statistical analyses, and eventual experimental testing are required before his conclusions can be accepted.     

Absorption of x-radiation by single crystals of proteins containing labile metal components: the determination of the number of iron atoms within the central core of ferritin

The number of metal atoms contained within a displaceable inorganic component of a metalloprotein was determined by considering X-ray absorption by single crystal samples of holo- and apo-proteins. Since this method is non-destructive, it can be used to determine the number of metal atoms associated with the molecules forming the crystal actually used for X-ray diffraction data collection and subsequent structure solution. The method has been applied to the iron storage protein ferritin, isolated from horse spleen, to give a reliable estimate of the average iron content of the ferritin molecules within the crystal. This value, of around 2000 iron atoms per molecule is consistent with that found for a typical ferritin preparation in solution and suggests non-selectivity of the crystallisation process for ferritin in terms of molecular iron content.     

Membrane-trafficking RabA4c involved in the effect of glycine betaine on recovery from chilling stress in Arabidopsis

Glycine betaine (GB) can confer tolerance to several types of stress at low concentrations, either after application to plants or in transgenics engineered to overproduce GB. Based on earlier studies on levels of GB in plants and evidence for effects on gene expression, we hypothesized that at least part of this effect could be ascribed to the activation of the expression of stress tolerance genes. Using a strategy based on high-throughput gene expression analysis with microarrays followed by confirmation with northern blots, we identified Arabidopsis genes upregulated in roots that reinforce intracellular processes protecting cells from oxidative damage and others that appear to be involved in reinforcing a scavenging system for reactive oxygen species (ROS) in cell walls. Upregulated genes in roots include those for the membrane-trafficking RabA4c, the root-specific NADPH-dependent ferric reductase (FRO2) localized to the plasma membrane, mitochondrial catalase 2 and the cell wall peroxidase ATP3a. Comparative studies with wild-type Arabidopsis and knockout mutants for the membrane-trafficking RabA4c gene demonstrated that the mutants respond only slightly to GB, if at all, compared with wild-type in relation to root growth recovery after chilling stress, demonstrating the role of RabA4c in relation to the GB effect. The results point toward links between oxidative stress, gene expression, membrane trafficking and scavenging of ROS such as superoxide and hydrogen peroxide in relation to GB effects on chilling tolerance in plants.     

LEAF CAVITY SIZE DIFFERENTIATION AND WATER RELATIONS IN CAREX ELEOCHARIS

Carex eleocharis leaves contain large intercellular cavities that traverse the length of the leaf above rows of stomata and are roughly constant in size throughout a leaf. Semithin sections (1–2 μm) demonstrate that the substomatal chambers are directly continuous with the intercellular cavities. Leaves of plants inhabiting moist swale regions of the shortgrass steppe, in northeastern Colorado, were found to have larger cavities as compared to leaves of plants inhabiting dry hilltops. Plants collected from a common hilltop site were grown in a controlled environment chamber, and, by manipulating the watering schedule, we obtained water potentials similar to those in the field. Leaves of “well-watered” plants were found to have larger intercellular cavities as compared to “water-stressed” plants. Leaf mesophyll cell sizes did not differ significantly between “well-watered” and “water-stressed” plants, suggesting that cavity size differences are not the result of developmental differences. Leaf cavities were shown to contain gases and to occur along the leaf length above rows of stomata. Additionally, the cavities in unstressed plants were continuous with substomal chambers. It is proposed that the reduction of cavity size is a mechanism to reduce water loss from the leaves during periods of plant water stress.     

Trypsin and α-amylase inhibitors are differentially induced in leaves of amaranth (Amaranthus hypochondriacus) in response to biotic and abiotic stress

Seeds of Amaranthus hypochondriacus L. are known to accumulate a trypsin-inhibitor (ATI) member of the potato-I inhibitor family and an α -amylase inhibitor (AAI), possessing a knottin-like fold. They are believed to have a defensive role due to their inhibition of trypsin-like enzymes and α -amylases of insect pests. In this work, both inhibitory activities were found in leaves of young A. hypochondriacus plants. High constitutive levels of foliar inhibitory activity against bovine trypsin and insect α -amylases were detected in in vitro assays. Trypsin inhibitory activity was further increased by exposure to diverse treatments, particularly water stress. Salt stress, insect herbivory and treatment with exogenous methyl jasmonate (MeJA) or abscisic acid (ABA) also induced trypsin inhibitor activity accumulation, although to a lesser degree. In gel and immunoblot analyses showed that foliar trypsin inhibitor activity was constituted by at least three different inhibitors of approximately 29, 8 (including ATI) and 3 kDa, respectively. These inhibitors showed differing patterns of accumulation in response to diverse treatments. On the other hand, significant increases in α -amylase inhibitor activity and AAI levels were detected in leaves of insect-damaged, MeJA- and ABA-treated A. hypochodriacus plantlets, but not in those subjected to water- or salt-stress. A differential induction of trypsin inhibitor activity and α -amylase inhibitor accumulation in response to insect herbivory by two related species of lepidopterous larvae was observed, whereas mechanical wounding failed to induce either inhibitor. The overall results suggest that trypsin and α -amylase inhibitors could protect A. hypochondriacus against multiple types of stress.