AN IMPROVED SUCTION TRAP FOR INSECTS

A suction trap for airborne insects, which automatically segregates the catch at pre-set intervals and standardizes the samples for volume of air, has been previously described by Johnson. Experience with this trap has shown that certain structural improvements were advisable. These have now been incorporated. Constructional details are given and the design of larger traps discussed. It is shown that aphids and lacewings taken are in good condition.     

Can acaricide‐impregnated leg bands fitted to female red grouse reduce sheep tick parasitization of chicks and increase chick survival?

In parts of northern England, North Wales and the Scottish Highlands, increasing numbers of sheep ticks Ixodes ricinus (Ixodida: Ixodidae), and the louping ill virus they can carry, are considered to be important factors that reduce red grouse Lagopus lagopus scotica productivity. The present study tested this hypothesis by fitting adult female grouse with leg bands impregnated with the acaricide cypermethrin to experimentally control ticks on their chicks on two managed grouse moors in northeast Scotland. The chicks of females fitted with acaricide leg bands showed reduced tick infestations and improved survival in one of the two study years, relative to chicks of control females. Acaricide leg bands constitute a potential management technique that may be adopted by grouse moor managers in circumstances of high tick infestations on grouse chicks.     

Use of Bullfrog Tadpoles (Rana catesbeiana) to Examine the Mechanisms of Lead Neurotoxicity

Sublethal exposure to lead elicits changes in behavior, particularlylearning. Previously, we had shown that bullfrog tadpoles exposedto 1 mg Pb/liter for 7 days exhibit learning deficits in a discriminateavoidance learning assay. The precise mechanisms involved inthese lead-induced learning deficits are not understood, butCNS monoamine neurotransmitter systems have been implicatedin the learning process. In the present study, we exposed bullfrogtadpoles to 1.7± 0.2 mg Pb/liter for 7 days and thencompared concentrations of neurotransmitters from whole brainsamples with those of controls. Serotonin or 5-hydroxytryptamine(5-HT) was significantly decreased in the lead exposed groupwhile the serotonin metabolite, 5-hydroxyindoleacetic acid,(5-HIAA) was similar to controls. No changes were observed inthe catecholamines epinephrine and norepinephijine followinglead exposure. The ratio of 5-HIAA/5-HT was significantly increasedin lead exposed animals as a result of the decrease in 5-HT,suggesting a decrease in 5-HT biosynthesis rather than an increasein 5-HT metabolism. These findings are the first to suggestthat lead exposure in bullfrog tadpoles affects the monoamineneurotransmitters that are implicated in the learning process.The results of the present study, in conjunction with previousevidence of learning deficits following lead exposure, offerthe possibility of correlating lead exposure with learning deficitsand alterations in CNS neurotransmitters in bullfrog tadpoles.The use of this tadpole model shows promise as a means to examineand understand the mechanisms involved in lead neurotoxicity.     

Landscape structure influences tree density patterns in fragmented woodlands in semi‐arid eastern Australia

Landscape and local‐scale influences are important drivers of plant community structure. However, their relative contribution and the degree to which they interact remain unclear. We quantified the extent to which landscape structure, within‐patch habitat and their confounding effects determine post‐clearing tree densities and composition in agricultural landscapes in eastern subtropical Australia. Landscape structure (incorporating habitat fragmentation and loss) and within‐patch (site) features were quantified for 60 remnant patches of Eucalyptus populnea (Myrtaceae) woodland. Tree density and species for three ecological maturity classes (regeneration, early maturity, late maturity) and local site features were assessed in one 100 × 10 m plot per patch. All but one landscape characteristic was determined within a 1.3‐km radius of plots; Euclidean nearest neighbour distance was measured inside a 5‐km radius. Variation in tree density and composition for each maturity class was partitioned into independent landscape, independent site and joint effects of landscape and site features using redundancy analysis. Independent site effects explained more variation in regeneration density and composition than pure landscape effects; significant predictors were the proportion of early and late maturity trees at a site, rainfall and the associated interaction. Conversely, landscape structure explained greater variation in early and late maturity tree density and composition than site predictors. Area of remnant native vegetation within a landscape and patch characteristics (area, shape, edge contrast) were significant predictors of early maturity tree density. However, 31% of the explained variation in early mature tree differences represented confounding influences of landscape and local variables. We suggest that within‐patch characteristics are important in influencing semi‐arid woodland tree regeneration. However, independent and confounding effects of landscape structure resulting from previous vegetation clearing may have exerted a greater historical influence on older cohorts and should be accounted for when examining woodland dynamics across a broader range of environments.     

Field resistance in cowpea, Vigna unguiculata to the cowpea moth, Cydia ptychora

Field evaluation of 26 selected cowpea cultivars showed that several of them had good levels of resistance to Cydia ptychora; TVu 946, Adzuki, ‘Vita 5’ and Igbirra were the most resistant. Percentage seed damaged by the larvae was positively correlated with days to 50% flowering (r= 0.39*), days to 50% pod ripening (r= 0.48*) and weight of 100 seeds (r= 0.56**). All four cultivars were early maturing, had semi-determinate or determinate plant types and carried their pods above the leaf canopy. No single morphological character could be related to the degree of seed damage but some association with phenological characteristics was indicated. Earliness, determinacy and uniform pod maturity were important plant characters associated with the expression of field resistance. Even if these characters are not causative, they provide a rational basis for screening of a large germplasm to identify or synthesise materials with greater resistance to this moth.     

A test of three hypotheses for ovariole number determination in the grasshopper Romalea microptera

Ovariole number in insects determines potential fecundity and can be influenced by genes, environmental conditions during development and parental effects. In the present study, three hypotheses are tested for ovariole number determination in the grasshopper Romalea microptera (Beauvois), which exhibits both intra‐ and interpopulation variation in ovariole number. In hypothesis 1, variation in ovariole number is a result of genetic variation. In hypothesis 2, ovariole number is influenced by nutrition during development. In hypothesis 3, ovariole number is influenced by maternal nutritional status. Females from four treatments are compared: low‐food, high‐food, daughters of low‐food, and daughters of high‐food. There is a relationship between parent and offspring ovariole number despite different environments, supporting hypothesis 1. Also, ovariole numbers are slightly, but significantly lower in individuals fed a low‐food diet compared with a high‐food diet, supporting hypothesis 2. Hypothesis 3 is not supported: starved and well‐fed females produce eggs of similar mass, as well as offspring with similar numbers of ovarioles, suggesting that the nutritional status of mothers does not influence offspring mass or offspring ovariole number. The results imply that genetic variation and developmental conditions determine ovariole number in this species but maternal environment does not. These results conflict with previous studies of ovariole determination in grasshoppers and locusts.