The acceptance of different provenances or seed origins of lodgepole pine Pinus contorta and Scots pine P. sylvestris as suitable oviposition sites was found to vary as a function of both tree age and insect species. Experiments on seedling lodgepole pine revealed that the pine sawfly, Neodiprion sertifer Geoffroy (Hymenoptera: Diprionidae), and the larch bud moth, Zeiraphera diniana Guennée (Lepidoptera: Tortricidae), preferred more southerly provenances of lodgepole pine. The pine beauty moth, Panolis flammea Denis & Schiffermüller (Lepidoptera: Noctuidae), however, preferred more northerly provenances. On mature lodgepole pine however, P. flammea exhibited a host change, preferring the more southerly provenances. Neodiprion sertifer showed a similar preference on both seedling and mature provenances. The results of this study suggest that some provenances of lodgepole pine become more resistant to attack by P. flammea as they mature, while others become more susceptible. This may be related to the feeding, strategies of the two insects: P. flammea larvae feed on current year foliage while N. sertifer feeds only on previous year foliage. It is possible that the mechanism for chemical defence of new shoots changes as the trees mature, and to a varying degree in different provenances, while defence of the previous years foliage remains unchanged. Results also indicate that odour alone as opposed to odour plus visual stimulation may invoke different ovipositional behaviour in N. sertifer.

The role of photoperiod in controlling the termination of adult diapause in the Bombay locust, Nomadacris succincta Linnaeus (formerly Patanga succincta) was examined by exposing pairs of field-collected adults to different photoperiods at 30°C. Adults of this species appear in June and remain in diapause until March in the following spring. Female adults collected in November started laying eggs earlier at a 14 h photoperiod (L:D 14:10) than at a 12 h photoperiod (L:D 12:12), although the mean pre-ovipositional periods at the two photoperiods were not significantly different from each other. All first egg-pods produced by long-day females contained fertilized eggs while only some short-day pairs produced fertilized eggs in their first pod, indicating that mating was suppressed at a short photoperiod. In adults collected in January and exposed to a 10 h photoperiod (L:D 10:14), the mean time of first oviposition was significantly delayed compared to those exposed to a 14 h photoperiod. These results demonstrate that N. succincta uses daylength as a cue to control the time of diapause termination in the field. The time interval between the first and second egg-pod depositions was influenced not only by the physiological state of the females but also by the environmental conditions, i.e. photoperiod, and it was positively correlated with the length of pre-ovipositional period. The occurrence of a change in host preference by diapause adults and its ecological significance were also pointed out.

Primers for DNA amplification using the polymerase chain reaction (PCR) were synthesized for a microsatellite locus isolated from a partial genomic library of the aphid parasitoid Aphelinus abdominalis (Dalman). Screening for genetic polymorphism at this locus in two laboratory strains of this wasp revealed the presence of two alleles different in the number of (GT) and (GGC) repeats. The relative frequencies of the two alleles were not significantly different between the two strains or between diploid females and haploid males. Heterozygosity at this microsatellite locus was estimated to be 0.40 which is within the range in other hymenopterous species. Given that A. abdominalis is a good candidate for augmentative release programmes in greenhouses against aphids, we suggest that microsatellite markers may have application in discriminating among aphelinid sibling species and strains. The markers provide a means for studying the performance and impact of selected parasitoid lines on pest dynamics in field release experiments.

A comparative analysis was performed on 18 mitochondrial DNA sequences, or haplotypes, of Lutzomyia (Nyssomyia) whitmani (Antunes & Coutinho) isolated by PCR from 28 individual flies originating from 10 Brazilian locations 150–2500 km apart. A phylogenetic analysis using maximum parsimony indicated support for three to four major lineages (Outgroups were haplotypes of Lutzomyia (Nyssomyia) intermedia (Lutz & Neiva)). One L. whitmani lineage was found in the Atlantic Forest zone of the North East, including the species' type locality, and is distinct from a second monophyletic group of haplotypes located in the drier interior of Brazil, stretching from the Tropic of Capricorn to Teresina just outside Amazonia. This provides no support for a previous hypothesis that L. whitmani sensu stricto is a single form widely-distributed south of Amazonia, and characterized by derived anthropophilic and synanthropic behavioural traits. The ranges of both lineages include populations incriminated in the peri-domestic transmission of Leishmania braziliensis sensu stricto. A third, Amazonian, group of haplotypes was less well-defined. It appears to consist of two sub-lineages which, like the two Leishmania species associated with them, are strictly silvatic and are separated by the Amazon floodplain. The zoophily of the Amazonian populations was not shown to be an ancestral trait. The geographical distributions of the Brazilian lineages are concordant with the broad patterns of bioclimate believed to have persisted since the late Tertiary period. These findings are part of ongoing research on the behavioural genetics of L. whitmani sensu lato aimed at understanding the evolution and maintenance of peri-domestic transmission of human cutaneous leishmaniasis.

When Myzus persicae (Sulzer) feeds on healthy sugarbeet it develops a white precipitate inside its stomach which causes the stomach to enlarge. Infection of sugarbeet plants with beet yellows virus (BYV), but not beet mild yellowing virus (BMYV) results in further increases in stomach size. The influence of the white precipitate on the transmission of BYV and BMYV was investigated by rearing M. persicae on sugarbeet Beta vulgaris, Tetragonia expansa and Capsella bursa-pastoris, which are hosts for both BYV and BMYV, BYV and BMYV respectively, but the latter two hosts do not stimulate the formation of white precipitate in the aphid's stomach. Aphids reared on BYV-infected T. expansa were significantly better vectors of BYV than those reared on BYV-infected sugarbeet, but aphids reared on BMYV-infected C. bursa-pastoris did not transmit BMYV more efficiently than those reared on BMYV-infected sugarbeet. The consequences of these results for the spread of beet yellowing viruses are discussed.

Two experiments were conducted to determine Chilo partellus (Swinhoe) moth and larval response on sorghum lines differing in levels of antibiosis and antixenosis. The inbred lines were E 302, IS 2205, IS 2122 and SA 2681, all reportedly varying in levels of antibiosis and ovipositional and larval antixenosis to C. partellus. Ovipositional antixenosis was evaluated in choice tests under cage conditions and significant differences were observed in the average number of egg batches per line. E 302 received the greatest number of egg batches. Antibiosis and larval antixenosis was evaluated with artificial infestation in a greenhouse. Significant differences occurred in larval numbers and mean larval mass on different lines, with E 302 possessing the greatest level of antibiosis resistance. This study indicates that resistant genotypes such as E 302 may exhibit high levels of antibiosis or larval antixenosis, but may also be preferred for oviposition. The size of egg batches was not influenced by ovipositional antixenosis. The potential effect of ovipositional antixenosis mechanisms on pest populations under field conditions is discussed.

Studies on the lepidopterous stem borer, Busseola fusca (Fuller) and its major larval parasitoid, Dolichogenidea fuscivora Walker were carried out in the field and the laboratory in eastern Ethiopia. Larvae of B. fusca are also parasitized in the field by the braconid, Bracon sesamiae Cameron and the sarcophagid, Sarcophaga sp., but in low numbers. Parasitism of B. fusca by D. fuscivora is as high as 71% during the dry season (November-March) and approximately 18% in the wet season (June-September). Dolichogenidea fuscivora is active throughout the year. In the laboratory it requires nearly 26 days at 24 ± 1°C to complete the development of one generation (egg to egg laying). Longevity of adults is affected by the availability of food and water. Mating and oviposition reduced the life spans of males and females, respectively. Sixty five to 75 larvae emerged from eggs laid by a single female. The sex ratio ranged from 1:1 to 7:1 (female:male), the average being 5:1.

The effect of various infestation levels of Chilo partellus Swinhoe on resistant and susceptible sorghum genotypes was assessed under artificial infestation in two field trials, conducted over two seasons. In the first season, infestation levels were 0, 10, 20, 40, 60 and 80 larvae per 2 m plot row. In the second season, additional treatments of one and two larvae per plot were included. A series of all infestation levels on susceptible plants was also included with an insecticide application 5 days after inoculation. Non-linear relationships between infestation level and yield loss were observed. In susceptible plants, small increases in initial larval infestation levels resulted in sharp increases in yield loss. An opposite tendency was observed in resistant plants where a tolerant reaction at lower infestation levels was observed. Gain threshold (GT) value, indicating the yield increase necessary to compensate for control costs, economic injury level (EIL) and economic threshold level (ETL) at which control actions should be initiated were determined for each genotype. Insecticide application on susceptible plants resulted in a 10% reduction in yield loss. However, the yield was still less than that of unsprayed resistant plants. The GT values indicated that insecticide application was economically warranted at an ETL of 20% and 2% of plants with visible symptoms of whorl damage, for the resistant and susceptible genotypes respectively.

Two organophosphate (OP) resistant strains of the cattle tick Boophilus microplus (Canestrini) from Mexico and Costa Rica were used to analyse the presence of esterase activity associated with resistance. The concentrations of six major proteins in both resistant strains were increased compared to the susceptible Morelos strain, both when stained with Coomassie Brilliant Blue after SDS-PAGE, and when analysed for esterase activity by the hydrolysis of naphthyl acetate esters. Esterases were named A or B in relation to the substrate preference for alpha or beta naphthyl acetate and numbered according to their position on the SDS—PAGE. The molecular weights of these proteins were: 125, 115, 108, 77, 43 and 67 Kd for Est-Bl, Est-B2, Est-B3, Est-B4, Est-B5 and Est-A respectively. Est-B3 showed cholinesterase (ChE) activity. This study strengthens the hypothesis that the mechanism associated with OP resistance found in many other insects includes an increase of esterase activity, probably as a result of gene amplification. The genes encoding these enzymes could be potentially used as molecular markers to detect resistance in the cattle tick B. microplus using a DNA probe.

Gel electrophoresis was used to study isoenzyme variation in Panolis flammea Denis Schiffermüller from a total of eight forest sites in England and Scotland dominated by either Scots or lodgepole pine. Four polymorphic loci (esterase, malate dehydrogenase, isocitrate dehydrogenase and 6-phosphogluconate dehydrogenase) were examined in adult moths. Most of the genotype frequencies conformed to Hardy-Weinberg expectations. An estimate of standardized gene frequency variance (Fst=0.109 ±0.032) indicated that there was significant genetic differentitation between populations. There was in addition a latitudinal cline in allele frequency at the 6-phosphogluconate dehydrogenase locus. The possible role of variation between P. flammea populations in contributing to regional differences in pest status is briefly discussed.

In this paper we describe a semi-automated digital image analysis system which is capable of discriminating five closely related species of Ichneumonidae. Specimens were distinguished by differences in their wings. The system functions by (a) extracting the significant variation (principal components) among a training set of images of the same species, (b) using these principal components to efficiently represent the morphology of wings of that species, and (c) exploiting the fact that images of the same species will share characteristic principal components, while images of different species will not. Such an approach allows the construction of modular species classifiers, to which like species correlate strongly, while dissimilar species do not. A recognition accuracy of 94% was achieved when the system was tested on 175 images of wings of the five ichneumonids. The wing images were caricatured to accentuate their venation and pigmentation patterns.