An investigation of the breeding habits of the yellow fever mosquito, Aëdes aegypti, Linn., in West Africa was begun in December 1925. This was undertaken for the purpose of ascertaining if the selection of breeding-places of this mosquito in Africa differs from that in the Western Hemisphere, and, if so, to learn if this difference is sufficient to be of material importance in yellow fever control work.

Since it was believed that breeding in tree-holes constituted a problem worthy of investigation, it was decided to make a survey of the rot-holes and fork-hollows in trees in the vicinity of Lagos, in the Southern Province of Nigeria. This survey was begun on 8th December 1925, shortly after the rainy season had passed and the dry season had set in. However, after inspecting a number of trees, the fact became evident that this was not a propitious time of the year for finding larvae in such places, since practically all of the holes were without water, and their contents, consisting of leaves and débris, were dry.

This early drying of the material in the holes drew my attention to the probability of mosquito eggs remaining in the holes, surviving the drought of the dry season and producing larvae with the beginning of the rains. In furtherance of this question, an examination of the dry holes was then began, and material collected from all those that were suitable. The term “ suitable ” in this sense signifies that the hole was in a living tree—of a formation to contain water, for a short time at least—that the aperture was of sufficient size to allow the débris to be removed and the inside of the hole scraped, and that the contents were dry. The distance of the trees from habitations, their location in open areas or thick bush, the height of the holes from the ground, the exposure of the holes to the sun, or the amount of débris contained caused no discrimination to be made.

Multiple mating was investigated in two tephritid species when females were under minimal male pressure because they were each confined with a single male in cages 20×20×20 cm and observed daily until they died. Laboratory-reared females of Bactrocera cucumis (French) lived up to 274 days and refractory periods averaged 59–63 days. However, the distribution of matings among B. cucumis females was not significantly different to that expected by chance. Wild females of Bactrocera cacuminata (Hering) reared from field-collected fruits of Solanum mauritianum Scopoli lived for up to 134 days and mated up to three times with refractory periods between matings averaging 27–39 days. The distribution of the number of matings among females of B. cacuminata was non-random because of the high proportion of non-maters (50%); but, when only females mating more than once were considered, there was no significant departure from random expectation.

Communication between adult male and female Spodoptera littoralis (Boisd.) was disrupted by spraying microencapsulated formulations of pheromone inhibitor (IIA) (Z)-9-tetradecen-1-yl-acetate on lucerne plots in north-west Crete. Polyurea-based microcapsules applied at the rate of 100 g/ha active ingredient caused a 97% disruption for a period of seven days, as measured by the reduction of catches in the treated area in traps baited with the pheromone attractant (III) (Z)-9, (E)-11-tetradecadien-1-yl acetate, compared with catches in control areas. At lower rates of application both the level of disruption after seven days and the subsequent persistence of the effect were reduced. When applied at a rate of 100 g/ha active ingredient, disruption of 80% and above was achieved for a period of three weeks. Slower release microcapsules containing IIA based on polyurea/polyamide appeared more effective in that a level of disruption was achieved at one-tenth the amount of active ingredient required for the polyurea-based formulations.

III dispensed in polythene vials caused 97% disruption when distributed at the rate of one vial per 9 m2, with lower levels of disruption at distributions of one vial per 25 m2 or 50 m2. IIA was much less effective in causing communication disruption at the same rates of distribution and no clear dose/response relationship was established.

Inside enclosures of 10 100 and 1 000 m2 fenced by single-strand polythene impregnated with IIA at the rate of 1 mg/5 cm and maintained at a height of 0·5 m, a high level of disruption in excess of 93% was achieved for the first five days. The effect persisted in the smaller enclosures in that disruption in excess of 80% was maintained for a period of 40 days. In the 1 000 m2 enclosure the effect declined much more quickly.

When IIA and III were dispensed together in WT traps the inhibitory effect persisted for at least 60 days. Similarly the polyurea-based microcapsules containing IIA together with III in WT traps maintained an inhibitory action for periods of 30–40 days. Polyurea/polyamide formulations of IIA were generally less effective, probably because loss from these slow releasing formulations became too low. Small numbers of mostly unmated female moths were attracted to the traps when IIA was exposed together with III, either when dispensed in the polythene vials or in microencapsulated formulations.

Analysis of catches of Chrysoperla carnea (Steph.) in a light-trap and a suction trap at Rothamsted, southern England, showed that the light-trap catch varied as predicted from a model proposed to describe the functioning of a light-trap: catch = constant × , where W = trap illumination and I = background illumination. After adjustment to allow for changes in illumination during the flight period of C. carnea, the light-trap catch was very similar to the suction-trap catch. For C. carnea, a light-trap provides as unbiased a sample as a suction trap, but because of variation in trap effectiveness with variation in illumination, light-trap catches obscure changes in activity and abundance. Although similar studies are desirable to confirm this for other species, it is suggested that in light-trap studies catches should be adjusted to allow for changes in illumination during flight or trapping periods.

Because the lettuce root aphid, Pemphigus bursarius (L.), is gall-inhabiting on poplar in spring and lives underground on lettuce during summer, its naturalenemy complex differs from that associated with foliage-feeding aphids. It suffers little from parasites and only fundatrices have been found attacked. The only species reared from parasitised individuals was the Pteromalid, Pachyneuron sp., which is assumed to be hyperparasitic. When the galls open at migration time, Syrphid larvae and Anthocorids can enter and attack the contents. Anthocoris nemorum (L.) and A. nemoralis (F.) are the main predators at this stage. Before they begin feeding, they kill all the aphids within a gall extremely quickly and efficiently. It is suggested that the aphids may be killed by a secretion from the stink glands of the Anthocorids working as a fumigant within the confines of the gall. Several Staphylinids and Carabids are frequently associated with subterranean colonies of P. bursarius and are almost certainly predators. The larvae of the Chloropids, Thaumatomyia glabra (Mg.) and T. notata (Mg.), are common predators of P. bursarius in the soil. The sexuparae, both before they leave the lettuce plants and on their arrival on poplar, are attacked by three species of Coccinellid.

Acetone at a dose of 1 μl was one of the least toxic of 11 solvents applied topically to fifth-instar nymphs of Dysdercus fasciatus Sign., while ctronellal, n-dodecane and n-tridecane at a dose of 0.5 μl were the most toxic. Acetone applied at 0.3 μl to third- and fourth-instar numphs caused negligible mortalities but about 60% of the treated nymphs gave rise to abnormal adults which, although capable of mating, laid eggs which were significantly less fertile than those from treated individuals which emerged as normal adults. These abnormalities could be attributed to a hormonal imbalance. Apparently normal adults arising from nymphs treated at the third instar with 0.6 μl acetone had 35% fertile matings (controls 70%) due to interference in the production and transference of motile sperm. The effects of acetone as a solvent in laboratory experiments could therefore be confounded with those attributed to juvenile hormones.

Twenty one species of ticks belonging to five genera of the family Ixodidae (Order Acari, sub-order Ixodida) – Amblyomma, Haemaphysalis, Hyalomma, Ixodes and Rhipicephalus (including the sub-genus Rhipicephalus (Boophilus)) – were collected from 1260 mammals, representing 29 species, 14 families and 6 orders, in four vegetation zones in Ghana during the period 1971–1978. Four other species were collected from humans in 1977. In all, eight species appeared to be new records for Ghana: Amblyomma tholloni Neumann; Dermacentor circumguttatus Neumann; Haemaphysalis houyi Nuttall & Warburton; Ixodes loveridgei Arthur; Ixodes oldi Nuttall; Ixodes vanidicus Schultze; Rhipicephalus complanatus Neumann; Rhipicephalus cuspidatus Neumann. The updated list of tick species in Ghana given here includes 41 species of ixodid ticks and four species of argasid ticks. Most species have been found in neighbouring regions of West Africa but 56 of the 121 different combinations of ixodid tick species and host species found in the collection described here have not apparently been reported before. The new combinations recorded here bring the total number of different combinations of ixodid tick species and mammalian host species now reported in Ghana to 151. The tick species found on wild mammals in Ghana mostly differed from those reported from domestic stock by other authors. The data showed that different tick species occurred in different vegetation zones and that most species displayed a pronounced preference for certain groups of related host species. Some tick species were found in the savanna feeding mainly on large bovids and/or suids; others were found in forests feeding mainly on small bovids, large rodents or small carnivores.

The rate of oocyte development in Spodoptera exempta (Walker) was investigated in the laboratory and in the field in Kenya. Stages and rates of development were examined in relation to moth size and timing of mating and oviposition. The stage of oocyte development was established by measuring the widths of the second or third oocyte at the distal end of one ovariole. Data from moths of known age showed that oocytes were partially developed at eclosion and that a linear progression in development occurred up to 30 h after emergence, by which time the oocytes had reached approximately half their mature size. Oocyte development continued unbroken in some moths up to the time of oviposition on the second night after emergence, whilst the remainder arrested oocyte development for a varying number of days. Mating occurred after midnight, but only once the oocytes had reached a certain size, irrespective of whether development was continuous or arrested. In the latter case, this stage was reached immediately after development resumed. Oviposition usually occurred the night after mating, mainly around midnight and with a second peak towards dawn. The dawn peak derived from mature moths which mated and oviposited on the same night. It is suggested that moths arrest oocyte development to minimize wing loading during migration and that, since moths stay in arrested development for varying lengths of time (thought to be genetically regulated), dispersal is greatly enhanced.

Females of both A. gambiae and A. funestus were found to enter buildings throughout the night, but more A. gambiae entered between 1 and 4 a.m. and more A. funestus just before dawn. Males of both species entered only just before dawn.

The rate of development of the ovaries was studied in individual mosquitos isolated in cages in the laboratory. The mean period between egg layings at a mean temperature of 25·5°C. was about 4¾ days in both species.

It was found that females of A. gambiae and A. funestus did not normally spend more than 24 hours in any one hut; but that they rested outside buildings during the day time only when newly emerged and just before and just after egg-laying.

Observations were made on the feeding and oviposition habits. It was found that females of both species would sometimes feed daily, whereas digestion of a full blood-meal occupied 24–72 hours in A. gambiae and 24–96 hours in A. funestus. The average dry season clutch of A. gambiae was 175 eggs and of A. funestus 123; wet season clutches appeared to be smaller.

The citrus pest Scirtothrips aurantii Faure shows a positive phototactic response to yellow surfaces, particularly fluorescent yellow with peak reflectance at about 525 nm. A fluorescent yellow sticky trap was devised. Impact of individuals on the trap surface was principally random. Taylor's power law gave a generalized value of 1·42 for slope of b. Widespread geographical locations gave similar values for biologically significant values of b. Habitat differences within one geographical area influenced b, which was highest in natural vegetation and lowest in certain citrus monocultures. Three traps per orchard (>5000 trees) were practicable, and produced statistically realistic results. The period during which S. aurantii can damage fruit was divided into a longer risk period and a shorter, central critical period. Where S. aurantii was present on the traps at less than nine individuals per set of three traps throughout the central critical period and 20 during the late risk period, the percentage of fruit so damaged as not to be of export grade was less than 1·0. This method of monitoring was sufficiently robust to allow for some human error in reading the traps under commercial conditions, and to permit variability in placement of the traps in the orchard.

In the province of Hälsingland in central Sweden, mosquitoes were sampled in 1983 with rabbit-, guineapig-, hen- and dove-baited and unbaited suction traps and similarly baited net traps. Blood-meals were identified by the precipitin test. Aedes cantans (Meigen), Ae. cinereus Meigen, Ae. communis (De Geer), Ae. diantaeus Howard, Dyar & Knab, Ae. excrucians (Walker) s.l. and Ae. intrudens Dyar were mainly attracted to the mammals, and Culex pipiens pipiens L., Culiseta morsitans (Theobald) and Cs. ochroptera (Peus) mainly to the birds. Significantly larger numbers of Cx. p. pipiens and Cs. morsitans were caught in dove- than in hen-baited traps. Of all identified feeds of engorged Aedes females, 95% were from mammals and 5% from birds. Only feeds from birds were found in engorged Cs. morsitans females. Movement of engorged females between the traps was demonstrated. Some Aedes females entered baited traps shortly after having fed on cervids and/or cattle. In the study area, suspected vectors between birds of Sindbis virus, the causative agent of Ockelbo disease, are Cx. p. pipiens, Cx. torrentium Martini and Cs. ochroptera in late spring and summer and Cs. morsitans in late summer. The isolation of this virus from Cx. p. pipiens and Cs. morsitans females captured in this area supports their role as suspected primary vectors. Ae. communis and other abundant Aedes species are suspected vectors of this virus from birds to man. Ae. cinereus may be a vector of tularaemia (caused by Francisella tularensis) in this area.

Dispersion behaviour in adults of the saw-toothed grain beetle, Oryzaephilus surinamensis (L.), was studied under controlled laboratory conditions. The effect of density, temperature and moisture content on surface dispersion was studied using groups of insects in jars of 500 g. grain and vertical dispersion by using groups of insects in thin vertical plates of wheat held between two sheets of glass. The ethological basis of group behaviour was investigated by using isolated individuals.

Over the range of conditions used, 1–10 per cent, of the individuals comprising the groups studied appeared on the surface of the grain. In grain at 14 per cent, moisture content, at 25°C., 3·4 per cent, of the group appeared on the surface. A greater proportion was found on the surface of grain at 9 per cent, moisture content than at higher moisture contents at all temperatures tested (15–35°C.). At all moisture contents, surface numbers were relatively high at 15°C.

In grain at 14 per cent, moisture content and 25°C., individuals moved vertically and laterally at random but were more active in the evening than in the morning. In grain at 9 per cent, moisture, there was marked irritability, and at 15°C. and 14 per cent, moisture, there was continual but slow movement without any detectable diurnal pattern of activity. Activity was reduced at 30°C., and at 25°C. it was reduced in grain of 17 per cent, moisture content.

The significance of these results is discussed in relation to the detection of populations, group formation and the initiation of foci of heating in patches of damp grain.

A time series analysis of noctuid and sphingid moths caught at light traps in East Africa revealed the existence of sources of periodic variation in catch with three different wavelengths: lunar, annual and four-year. A comparison of catches of Spodoptera exempta (Walker) at different sites showed that site characteristics influence a light trap’s catch and confirmed the northward advance in flight period with season in the early part of the year. This species apparently goes through periods of increased abundance every four years. Of eight other species examined, all but one showed signs of a four-year cycle in abundance, although the peaks occurred in different years. Catches of all nine species were reduced by moonlight, but not equally. The size of the insect influenced its susceptibility to interference by moonlight. This was apparently mediated by the height of flight. High and low flying moths were more strongly influenced by moonlight than those at intermediate heights.

The randomly amplified polymorphic DNA technique was used to trace the geographic origin of Liposcelis bostrychophila Badonnel populations in Australia from unknown geographic sources internationally. Haplotype (or clonal) diversity was high, with 474 unique haplotypes found from 616 individuals genotyped. Gene diversity estimates (0.10–0.28) and percent polymorphic loci (38.1–88.1%) were moderate to high for most populations. This resulted in genetic distance estimates that ranged from 0.04 to 0.26 and were significantly different for most pairwise population combinations. GST values for all populations were also moderate (0.04–0.54) and again were significantly different for most pairwise population comparisons. Analysis of molecular variance revealed that the majority of variation was apportioned among individuals within populations regardless of the level at which they were grouped. Gene flow (Nm) was mostly low for all pairwise populations comparisons with an average Nm = 1.8. A non-significant negative correlation between genetic distance and geographic distance was found for worldwide populations. In contrast, within Australian populations a significant positive correlation between genetic distance and geographic distance was detected. Genetic relationships explored using unweighted pair group method analysis and non-metric multidimensional scaling indicated a mixed pattern of genetic similarities among all populations. Multiple introductions, from a wide range of international source populations, have obscured the ability to accurately determine the geographic origin of L. bostrychophila in Australia.

Three traditional tribes of Fordini, Pemphigini and Eriosomatini comprise Pemphiginae, and there are two subtribes in Fordini and Pemphigini, respectively. Most of the species in this subfamily live heteroecious holocyclic lives with distinct primary host specificity. The three tribes of Pemphigini (except Prociphilina), Eriosomatini and Fordini use three families of plants, Salicaceae (Populus), Ulmaceae (Ulums) and Anacardiaceae (Pistacia and Rhus), as primary hosts, respectively, and form galls on them. Therefore, the Pemphigids are well known as gall makers, and their galls can be divided into true galls and pseudo-galls in type. We performed the first molecular phylogenetic study of Pemphiginae based on molecular data (EF-1α sequences). Results show that Pemphiginae is probably not a monophylum, but the monophyly of Fordini is supported robustly. The monophyly of Pemphigini is not supported, and two subtribes in it, Pemphigina and Prociphilina, are suggested to be raised to tribal level, equal with Fordini and Eriosomatini. The molecular phylogenetic analysis does not show definite relationships among the four tribes of Pemphiginae, as in the previous phylogenetic study based on morphology. It seems that the four tribes radiated at nearly the same time and then evolved independently. Based on this, we can speculate that galls originated independently four times in the four tribes, and there is no evidence to support that true galls are preceded by pseudo-galls, as in the case of thrips and willow sawflies.

Hormesis induced by insecticides at the dosage lower than what ostensibly directly causes death on insects was studied. This paper reports the effects of the in vivo application of varied concentrations of chlorpyrifos (CPF) on Plutella xylostella (DBM). The insecticide concentrations applied included 0.000025–2.5 mg l−1, which are far lower than LC1 (7.2 mg l−1), for the CPF-susceptable (Si) DBM, and 250 mg l−1 which is far below LC1 (1286 mg l−1), for the CPF-resistant (Rc) DBM, as well as LC10- and LC50-doses for both strains. Significant hormesis was found with the ‘hermetic-CPFs’, i.e., 0.0025 mg l−1 for Si DBM and 2.5 mg l−1 for Rc DBM, at the normal or high temperature either in a 24 h or under a long-term treatment. These doses of CPF significantly stimulated the development and increased the fecundity of Si and Rc DBM at 25°C with approximately 23.5–29.8% activity increase on acetylcholinesterase (AChE) and 30.5–91.3% increase on glutathione S-transferases (GSTs) at 25 or 38°C in 4–24 h. The enzymatic activities were significantly reduced by LC50-CPF at 25°C in vivo, but the inhibition was relieved significantly, if the insects were first subjected to a hormetic-CPF pretreatment. It was remarkable that the average rates of enzymatic activity increase were 67.5–76.6% for AChE and 366–546% for GSTs. Consequently, it was concluded that the hormesis on Si and Rc DBM could be induced by CPF doses far below LC1 at normal or high temperature in short- or long-term treatment. These findings might help to improve the current insect control practices in the field.

It is likely that under some conditions apterous aphids are significantly involved in the spread of plant viruses, most importantly by walking across soil from plant to plant. Various factors which affect their importance are considered in the paper.

Figures are given for the frequency of movement of apterae of Myzus persicae (Sulz.) under settled conditions; this was found to vary with the species of host-plant that the aphid was on.

Eourth-instar and adult apterae can walk proficiently on soil. The effect of soil condition on this is described. The walking speed of adult apterae on soil is 5.2 cm./min. at 18°C, and 1.2 cm./min. at 8.5°C. The walking speed of fourth-instar aphids on soil is 3.2 cm./min. at 18°C.

Experiments showed that walking aphids are well able to locate a new host-plant, and that the attraction is visual.

The significance of these observations is discussed, and it is concluded that apterae have a greater potential as virus vectors than has been generally realised.

In the present work, we carried out a comparative molecular study of Stenoponia tripectinata tripectinata isolated from Mus musculus from the Canary Islands, Spain. The Internal Transcribed Spacers 1 and 2 (ITS1, ITS2) and 18S ribosomal RNA partial gene and cytochrome c-oxidase 1 (cox1) mitochondrial DNA partial gene sequences of this subspecies were determined to clarify the taxonomic status of this subspecies and to assess inter-population variation and inter-specific sequence differences. In addition, we have carried out a comparative phylogenetic study with other species of fleas using Bayesian, Maximum Parsimony, Maximum Likelihood and Neighbor-Joining analysis. A geographical signal was detected between the cox1 partial gene sequences of S. t. tripectinata isolated from M. musculus from different islands and those isolated from Apodemus sylvaticus from the Iberian Peninsula. Our results assess the monophyletic origin of Stenoponiinae and a different genetic lineage from Ctenophthalmidae. Thus, the elevation of subfamily Stenoponiinae to family level (Stenoponiidae) is suggested.

The efficacy of two entomopathogenic biocontrol agents, Steinernema feltiae (Filipjev) and Verticillium lecanii (Zimmerman) Viégas (reclassified now as Lecanicillium muscarium (Petch) Zare & Gams), against Thrips palmi Karny was investigated. Assessments of the effect of temperature on the efficacy of S. feltiae indicated that higher mortality of T. palmi was recorded at 20°C compared to either 15 or 25°C, whereas significantly higher T. palmi mortality followed application of L. muscarium at 25°C. Testing the control agents efficacy on three host plants; chrysanthemum, sweet pepper and cucumber, under constant temperature and high humidity conditions produced no significant difference in the level of T. palmi larval mortality on each host plant. Incorporating the chemical insecticide imidacloprid with both biological agents in a combined control strategy increased T. palmi juvenile mortality. The potential role of S. feltiae and L. muscarium within integrated pest management programmes for the control of T. palmi is discussed.

Aircraft were used to apply a bait containing aldrin, soyabean oil and citrus meal against leaf-cutting ants (Acromyrmex octospinosus (Reich) and Atta cephalotes (L.)) in Trinidad. The distribution patterns of bait applied by different aircraft were measured. Plain bait applied at 2.2 kg/ha to an uncultivated island in the dry season destroyed 91% of nests of Acromyrmex, and waterproofed bait applied in the wet season to cultivated land on the mainland destroyed 85%. Small nests of Atta were also destroyed by this treatment but large nests in forest required much heavier dosages applied to the nest itself. Lizards and crabs living in the baited areas were contaminated with aldrin but there was no evidence to show that they were harmed.