Comparative bioassays of two chloronicotinyl insecticides, acetamiprid and imidacloprid, against the whitefly Bemisia tabaci (Gennadius), using foliar and systemic applications, were conducted under laboratory conditions and in field trials. Under controlled conditions, the ovicidal activity of foliar applications of acetamiprid on cotton seedlings was much higher than that of imidacloprid. According to LC50 and LC90 values, acetamiprid was 10- and 18-fold more potent than imidacloprid. Both compounds were effective when applied to soil against whitefly adults; however, the potency of imidacloprid was somewhat higher than that of acetamiprid 2, 7 and 14 days after application; resulting (with the concentration of 25 ml a.i./l) in adult mortality of 90, 93, and 96% and 76, 84, and 76% respectively. In an experimental cotton field, the efficacy of foliar applications of 60 g a.i./ha acetamiprid and 210 g a.i./ha imidacloprid was compared. Field residual activity of acetamiprid to whitefly adults lasted for approximately ten days, compared with three days for imidacloprid.

Life-history parameters of different biotypes of the whitefly Bemisia tabaci (Gennadius) species complex were reviewed. This included the B-biotype of B. tabaci, identified as B. argentifolii (Bellows & Perring). Comparisons were made among different biotypes on cotton, among host plants for biotype B and among the whitefly species B. tabaci and Trialeurodes vaporariorum (Westwood), the greenhouse whitefly. The biotype identification of different populations of B. tabaci was summarized in a table. Biotypes discussed were A, B, Indian and biotypes of the Old World group. Temperature dependent relationships were estimated for egg development rate, development rate from egg to adult, immature mortality, adult longevity, sex-ratio, pre-oviposition period and fecundity. The fitted curves will be used as input for a simulation model of the population dynamics of B. tabaci in a greenhouse when parasitoids are released. The model makes it possible to evaluate the integrated effect of different life-history parameters and behavioural parameters of parasitoids on whitefly population levels in a greenhouse.

Host specificity of Neotropical hard ticks (Acari: Ixodidae) was analyzed by using the number of hosts species for each tick species and the index of host specificity STD*, which integrates phylogenetic and ecological information. The analyses were based on 4172 records of hard ticks collected from wild and domestic tetrapods. Most tick species included in this study were associated with three to 20 host species. No tick species has been associated either with a single species or with a single genus of host. It was found that the number of host species is sensitive to sampling effort, but not the STD*. The most frequent values of STD* were between 2.5 and 3.5, which shows that the host species more frequently used by Neotropical hard tick species belong to different families or different orders. Immature stages tend to use a broader taxonomic range of hosts than adults, and the interpretation of both measures of host specificity used in this study led to the conclusion that the impact of non-endemic hosts does not alter the patterns of host specificity in Neotropical hard ticks. The index STD* showed that a high proportion of tick species has phylogenetically unrelated species as principal hosts. The conclusion reached in this work indicates that strict host specificity is not common among Neotropical hard ticks and suggests that the influence of tick ecology and evolution of habitat specificity, tick generation time, phenology, time spent off the host and the type of life-cycle could be more important than hosts species.

Adults of Dacus spp. feed on plant surface bacteria. The responses of D. tryoni (Froggatt) and D. cacuminatus (Hering) to some components of bacterial odours and to cue-lure were tested in a field-cage olfactometer, in studies in south-eastern Queensland. One component of bacterial emission, 2-butanone, attracted D. tryoni (a species responding to cue-lure) but not D. cacuminatus (a species responding to methyl eugenol) and is suggested as the attractive portion of the cue-lure molecule. Sexually mature males and immature females of D. tryoni responded to 2-butanone, cue-lure and bacterial odours in field-cage tests. Females fed on sugar and water required protein hydrolysate to produce eggs, but males were fertile with or without protein. These different nutrient requirements, and the fact that males and females possess different crop colour and bacterial contents when feeding in the same host-plant, indicate that the sexes feed on different substrates. Consequently, the strong bacterial attractant cues in the host-tree may be a feeding attractant to females and a sex attractant to males. It is proposed that 2-butanone is an important rendezvous stimulant in nature, bringing the mature male flies into the feeding and oviposition sites (host-trees) of the developing females for mating encounters.

To study life cycle variability in Rhopalosiphum padi (Linnaeus), the responses to short days (L:D 10:14) of 70 clones were tested at two temperatures (10°C and 15°C) in the laboratory. Three clones originating from spring populations on the primary host, bird cherry (Prunus padus), were holocyclic, producing gynoparae and then males in the second generation under experimental conditions. Of the other clones, all originating from Gramineae, 78.5% were anholocyclic and 21.5% androcyclic (male-producing) at 15°C, but at 10°C only 12.7% were anholocyclic, 82.6% were androcyclic, and 4.7% showed an ‘intermediate’ response (i.e., some of the alate females produced both sexual and parthe-nogenetic offspring). There was considerable interclonal and inter-individual variation in the numbers of males produced by androcyclic clones. These results are discussed in relation to field studies on R. padi in Britanny, which indicate that 1. primary hosts are rather rare, but nevertheless commonly develop spring infestations; 2. anholocyclic genotypes are regularly decimated every few years by severe winters. It appears that the preponderance of androcyclic clones is important for the maintenance of life cycle variability.

Maize (Zea mays) is a major staple food in Africa. However, maize production is severely reduced by damage caused by feeding lepidopteran pests. In East and Southern Africa, Chilo partellus is one of the most damaging cereal stem borers mainly found in the warmer lowland areas. In this study, it was hypothesized that the future distribution and abundance of C. partellus may be affected greatly by the current global warming. The temperature-dependent population growth potential of C. partellus was studied on artificial diet under laboratory conditions at six constant temperatures (15, 18, 20, 25, 28, 30, 32 and 35 °C), relative humidity of 75±5% and a photoperiod of L12:L12 h. Several non-linear models were fitted to the data to model development time, mortality and reproduction of the insect species. Cohort updating algorithm and rate summation approach were stochastically used for simulating age and stage structure populations and generate life-table parameters. For spatial analysis of the pest risk, three generic risk indices (index of establishment, generation number and activity index) were visualized in the geographical information system component of the advanced Insect Life Cycle modeling (ILCYM) software. To predict the future distribution of C. partellus we used the climate change scenario A1B obtained from WorldClim and CCAFS databases. The maps were compared with available data on the current distribution of C. partellus in Kenya. The results show that the development times of the different stages decreased with increasing temperatures ranging from 18 to 35 °C; at the extreme temperatures, 15 and 38 °C, no egg could hatch and no larvae completed development. The study concludes that C. partellus may potentially expands its range into higher altitude areas, highland tropics and moist transitional regions, with the highest maize potential where the species has not been recorded yet. This has serious implication in terms of food security since these areas produce approximately 80% of the total maize in East Africa.

The B and Q ‘biotypes’ of Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) have been invading many parts of the world and causing severe damage to a range of crops. Recent phylogenetic analyses indicate that B and Q are cryptic species within the B. tabaci species complex. Although various attempts have been made to examine the reproductive compatibility between B and Q, few studies have tested the fertility of the F1 females and so the extent of possible gene flow remains unclear. In this study, we conducted a series of crossing experiments and behavioural observations to examine in detail the reproductive compatibility between the B and Q biotypes collected from Zhejiang, China, a region recently invaded by these whiteflies. Crossing experiments between the two biotypes using either single-pairs or small groups demonstrated that proportions of females in the F1 progeny were only 0–2% in the inter-biotype crosses compared to 58–68% in the intra-biotype treatments. Furthermore, all inter-biotype F1 females were sterile. Continuous video observations showed that B and Q adults very rarely copulated, and copulation occurred only when adults of opposite sex from different biotypes were enclosed in dense cohorts for a relatively long period of time. These data show that the B and Q biotypes examined in this study are completely isolated in reproduction. The isolation was due to mainly a copulation barrier, but post-copulation barriers were also involved.

Two of the species in Callosobruchus, C. maculatus (F.) and C. analis (F.), are compared and redescribed, together with a description of the male and female genitalia of both species. The species Bruchus vicinus Gylh., B. ornatus Boh., B. ambiguus Gylh., B. sinuatus Fhs. and B. quadrimaculatus F. are shown to be synonymous with C. maculatus (F.). Bruchus jekeli Allib. and B. glaber Allib. are almost certainly synonyms of C. analis (F.), but this could not be verified as no type specimens are available.

The genus Phlebotomus has been much studied in recent years since the transmission of various diseases by some species has been established.It has now become a matter of importance to be able to identify species accurately in connection with the study of the epidemiology of the disease they are known or thought to transmit. It has been found that those which are closely related morphologically, often show marked biological differences and vary considerably in their rôle as transmitters of certain diseases.

Discriminant function and cluster analyses were performed on 19 morphometric variables of the aculeus, wing and mesonotum to determine whether populations of Anastrepha fraterculus (Wiedemann) from different parts of Mexico could be distinguished from populations from South America., Samples were collected from seven localities across Mexico, two from Brazil, and one each from Colombia and Argentina. Results showed there were statistically significant differences between Mexican and South American populations with respect to the aculeus (tip length, length of serrated section, mean number of teeth) and wing (width of S-band and connection between S- and V-bands). The degree of morphological variation observed among Mexican populations was extremely low, and as a consequence, the Mexican populations were identified as a single morphotype by discriminant analysis. The ‘Andean morphotype’ consisting of the Colombian population, and the ‘Brazilian morphotype’ consisting of the two Brazilian populations plus the single Argentinian population were also distinguished. It was concluded that the macro-geographical morphotypes from Mexico, Colombia, and Brazil plus Argentina correspond to three distinct taxonomic entities. Comparisons of results with those obtained from behavioural, karyotypic, isozyme and DNA studies suggest that sufficient evidence now exists to name a new Mexican species from within the A. fraterculus complex. This will be done in a separate publication. A provisional key to the morphotypes of A. fraterculus studied is provided.

1. A sketch is given of the Malaria Control Organisation in Service areas in Mauritius with a summarised history of malaria work in the Island since the first epidemic in 1865.

2. Keys to Mauritian Anophelines and their larvae with notes on their field recognition characters are followed by data on the distribution of adult Anophelines in the Colony and their relation to malaria intensity in different areas. A. melas appears to be absent from coastal swamps.

3. The influence of a number of environmental factors is discussed. It is concluded that temperature is an important limiting factor generally in winter and perennially in the highlands (above 1,000 ft.), but that the flushing action of heavy rains and probably the precipitation of food supply by colloidal iron moving under high rainfall conditions (over 100 ins.) from ferrugineous lavas both play their part in the natural control of A. funestus and A. gambiae.

The behaviour of A. gambiae with respect to temperature is expressed by an area enclosed by two symmetrical catenary curves, that illustrate well the adverse influence on development of low temperatures normally occurring in winter on the coast and all the year round in the residential uplands above 1,000 ft. The thermal death point of A. gambiae larvae is about 42°C. and that of A. funestus 40°C. and the lower limit of larval activity is 16·5°C. A. gambiae develops most rapidly at an estimated temperature of about 37°C.

The effectiveness of a sex pheromone trap designed specifically to deliver conidia (infective fungal propagules) of the entomopathogenic fungus Zoophthora radicans Brefeld (Zygomycetes: Entomophthorales) to male Plutella xylostella (Linnaeus) was investigated. In field experiments in the Cameron Highlands of Malaysia, synthetic pheromone lures attracted adult males P. xylostella at all times of the day whereas lures of virgin female moths attracted males only between the hours of dusk and dawn, when females are known to produce their pheromone. Adult male moths attracted to traps baited with synthetic pheromone spent a geometric mean time of 88 seconds within the inoculation chamber, a time compatible with the period adults must spend within a shower of Z. radicans conidia produced by uniform mycelial mats in order to become infected. The field longevity of male and female P. xylostella adults was found to be similar, with individuals living for a mean time of 4.9 days. This was sufficient time for male moths to respond to the pheromone, enter the trap, become infected with Z. radicans and succumb to that infection in the field (3–3.5 days) thereby releasing infective conidia into the cabbage crop.

Although DNA barcode coverage has grown rapidly for many insect orders, there are some groups, such as scale insects, where sequence recovery has been difficult. However, using a recently developed primer set, we recovered barcode records from 373 specimens, providing coverage for 75 species from 31 genera in two families. Overall success was >90% for mealybugs and >80% for armored scale species. The G·C content was very low in most species, averaging just 16.3%. Sequence divergences (K2P) between congeneric species averaged 10.7%, while intra-specific divergences averaged 0.97%. However, the latter value was inflated by high intra-specific divergence in nine taxa, cases that may indicate species overlooked by current taxonomic treatments. Our study establishes the feasibility of developing a comprehensive barcode library for scale insects and indicates that its construction will both create an effective system for identifying scale insects and reveal taxonomic situations worthy of deeper analysis.

Deciduous oak dieback in Japan has been known since the 1930s, but in the last ten years epidemics have intensified and spread to the island’s western coastal areas. The symbiotic ambrosia fungus Raffaelea sp. is the causal agent of oak dieback, and is vectored by Platypus quercivorus (Murayama). This is the first example of an ambrosia beetle fungus that kills vigorous trees. Mortality of Quercus crispula was approximately 40% but much lower for associated species of Fagaceae, even though each species had a similar number of beetle attacks. It is likely that other oaks resistant to the fungus evolved under a stable relationship between the tree, fungus and beetle during a long evolutionary process. Quercus crispula was probably not part of this coevolution. This hypothesis was supported by the fact that P. quercivorus showed the least preference for Q. crispulayet exhibited highest reproductive success in this species. Therefore, P. quercivorus could spread more rapidly in stands with a high composition of Q. crispula. The present oak dieback epidemic in Japan probably resulted from the warmer climate that occurred from the late 1980s which made possible the fateful encounter of P. quercivorus with Q. cripsula by allowing the beetle to extend its distribution to more northerly latitudes and higher altitudes. Future global warming will possibly accelerate the overlapping of the distributions of P. quercivorus and Q. crispula with the result that oak dieback in Q. crispula will become more prevalent in Japan.

Genetic similarities between 13 samples belonging to nine reference biotypes and two field populations of Bemisia tabaci (Gennadius), one field population of B. medinae Gómez-Menor and another of B. afer Priesner &Hosny, were evaluated using amplified fragment length polymorphism (AFLP) markers. The results indicate that B. tabaci biotypes can be grouped together with a minimum similarity coefficient of 0.32 and separated from the two other species with a similarity coefficient of 0.07. Bemisia tabaci biotypes were grouped in four clusters which comprised: (i) Near East and Indian subcontinent biotypes; (ii) B and Q biotypes plus a Nigerian population from cowpea; (iii) New World A biotype; and (iv) S biotype and a Nigerian population from cassava. These results were consistent with a previous grouping of biotypes based on RAPD-PCR analysis. The AFLP assay allowed the scoring of a total of 354 polymorphic bands in two reaction events with the use of two primer combinations.

The continual recruitment of new individuals makes it difficult to study both the survival of multivoltine mosquitoes, and the size of the infectious reservoir in narural populations of malaria vectors. During long-term surveillance of a population of Anopheles gambiae Giles sensu lato in a Tanzanian village by daily light trapping, a temporary dry spell resulted in the cessation of recruitment for a period of 33 days, and a decline in numbers of A. arabiensis Patton caught from over 2000 to less than 10 in a sentinel house. Traps placed elsewhere in the village indicated similar proportionate declines although numbers caught varied according to location. A survival rate of 83% per day was estimated from the rate of population decline. Survival was unrelated to the size of the mosquitoes. The infectious reservoir (the chance of a mosquito acquiring an infection) was estimated to be 2% per feed. The exploitation of fortuitous events which temporarily eliminate a single stage in the life cycle has general applicability in the study of the bionomics of multivoltine insects.

During investigations into shoot-fly damage to guinea corn (Sorghum bicolor), millet (Pennisetum typhoides) and maize (Zea mays) in rain-grown plots at Samaru during 1966, it became obvious that attack was not attributable to a single species (Atherigona varia var. soccata Rondani (=A. indica infuscata van Emden)), as was previously believed. This species is undoubtedly the principal pest of guinea corn seedlings and young plants in northern Nigeria (Map 1), but there are also many other species involved. During the following four years field trials were undertaken to establish the relative importance of the species within the area and to learn something of their biology.

For a number of years the western grass-stem sawfly, Cephus cinctus, Norton, has been accounted one of the major insect pests of wheat in Western Canada. Originally a grass-feeder, it began to attack wheat about the beginning of the present century, at first only occasionally and at the edges of fields in Manitoba, later much more commonly and with a very wide distribution throughout the wheat-growing areas of Manitoba, Saskatchewan, and Alberta. While this sawfly was confined to native grasses it was held in check by two principal factors (Criddle, 1922) : shortage of grass stalks suitable for oviposition, and parasites. When, however, it began to attack wheat, both of these restraints were evaded. In the first place the wheat fields provided an abundance of host-plants. In the second place, the natural parasites of the sawfly did not move with it into the grain fields—whether they are unaware of the presence of their host in wheat plants or are unable to attack it in that situation is unknown.

The results of a series of catches of biting insects at human bait on platforms in the canopy of the forest at Mongiro, Bwamba, Uganda, are reported. The catches were designed to investigate differences in the numbers taken, due to platforms, season and weather, but mainly to study the short-term changes in the activity of biting insects near the time of sunset. Each catch lasted from 3 hours before to 3 hours after sunset, and was divided into 10-minute periods from 30 minutes before to 1 hour after sunset. The main analysis is of catches made on five platforms on each of 100 evenings which covered the end of the dry and beginning and end of the wet season, 1948, and the end of the dry season, 1949.

A list of the species of biting insects encountered is given. Eight species (Anopheles (M.) gambiae, Taeniorhynchus (C.) fuscopennatus, Taeniorhynchus (M.) africanus and uniformis, Aëdes (M.) nigerrimus, Aëdes (S.) apicoargenteus and africanus, and Chrysops centurionis) were found to be abundant and data relating to them has been subject to more or less detailed analysis. The remaining 27 species or groups of species are discussed shortly.

Six of the eight abundant species show statistically significant differences between the catches on the five separate platforms. Arrangement of the five platforms in order of the total numbers taken, for each of these six species, gives results which are practically identical in three species (Anopheles (M.) gambiae, T. (M.) africanus and uniformis) and in two others (Aëdes (S.) apicoargenteus and africanus) ; however, the arrangements in these two species groups differ widely from each other. The arrangement for C. centurionis differs again.

These ordinal arrangements are compared with the obvious characteristics of the platforms and no consistent relationship is found. It is pointed out that the first three species are derived, largely or even entirely, from breeding places outside the forest, in or associated with the adjacent extensive areas of open swamp, while the last three are likely to be completely confined to the forest for breeding ; both the latter two mosquito species breed in tree holes, and dense shade is characteristic of the breeding places of species of Chrysops closely allied to C. centurionis. It is considered most probable that these platform differences in the numbers yielded are due to local differences in the densities of the adult populations which in turn are related to the abundance and proximity of breeding places.

Seasonal variations in the numbers of the abundant species are also studied and are considered to be almost certainly related to the amount and distribution of rainfall affecting the profusion of breeding places at least as far as the mosquito species are concerned. The tree-hole breeding species, however, suffered a reduction in numbers before the end of the wet season, an effect also noted by Mattingly in West Africa.

The amount of the reduction of the numbers of A. (S.) africanus in the dry season is of importance in assessing the possibilities of the survival of yellow fever virus in that mosquito as a host. The estimated reduction in the dry season of 1949 was to less than one twenty-third of the population existing at the end of the previous wet season (November, 1948).

C. centurionis occurred during all the catch series but was extraordinarily abundant in late March and early April, 1948. It is considered probable that this time of increase represents a yearly period into which hatching from the pupa is compressed. This conclusion is supported by the finding that during this period the biting population was composed of two groups one of which tended to bite before, and the other after, sunset.

Evidence is produced to show that the biting activity of Anopheles (M.) gambiae was depressed by wind, that of Aëdes (S.) africanus by wind and rain but that that of C. centurionis was little affected by either of these factors.

Studies of the biting-activity changes in the nine ten-minute periods extending from 30 minutes before to one hour after, sunset are presented. Each of the species which were known to be mainly active by night and which were sufficiently abundant for study, show activity increasing about sunset, rising to a maximum shortly after, and thereafter declining again to moderate levels. This initial peak is very clearly marked in the cases of Anopheles (M.) gambiae, T. (C.) fuscopennatus, T. (M.) africanus, Aedes (S.) africanus and C. centurionis, less so, but still distinct, in T. (M.) uniformis and A. (M.) nigerrimus. Its position differs in different species being earliest in the case of C. centurionis (18.10–18.20 hours) and latest in that of T. (M.) africanus (18.40–18.50 hours). However, in any given species the peak period of biting activity was subject to only slight movement in time in relation to sunset; in analyses of the data by different platforms, by season, and by types of weather it was the exception to find the time of peak activity to be shifted more than one ten-minute period away from the position which it occupied over the whole series. Further, in studies of the curves of biting activity on individual nights, three consecutive ten-minute periods centred on the period which showed the peak over the whole series, included the peak in 21 of the 23 A. (M.) gambiae cases available, in all five of the T. (M.) africanus, in eight of the 11 A. (S.) africanus and in 15 of the 20 C. centurionis, cases. The regularity of the occurrence of the peak period of activity in any given species is considered to indicate that it is largely controlled by changes in light intensity about the time of sunset.

These findings are discussed in relation to the general problem of the mechanism controlling the rhythm of activity in insects biting by night and a hypothesis, which is based on the conception that different population groups may have different biting habits, is advanced to account for the different types of cycle commonly encountered.

Samples of larvae of Aedes aegypti (L.) were collected in three principal habitats, domestic, peridomestic and feral, in the Rabai area in eastern Kenya. The samples from the domestic habitat represent the population of the domestic form, A. a. aegypti, and the feral samples from tree holes from Bejumwa Forest represent the feral subspecies, A. a. formosus (Wlk.). The peridomestic samples from steps cut into trunks of coconut palms most probably represent hybrids between the domestic and the feral forms. These samples were brought to the laboratory where they reproduced in high numbers, and crosses were made between the three populations. Adults of the parental populations and those resulting from the crosses were marked with different colours of fluorescent pigments, released in the peridomestic habitat in the Rabai area and subsequently recaptured in biting catches on man in the domestic and peridomestic habitats. The results indicate that domesticity, particularly house-entering behaviour, in A. aegypti is genetically controlled and is a product of the action of several genes. The gene action in terms of house-entering behaviour is additive as can be clearly seen from the recapture data for the various crosses. The percentage entering houses was highest among mosquitoes of the form from inside houses (the domestic A. a. aegypti population (D)) and the percentages decreased progressively through the peridomestic (P) and hybrid forms to the feral population of A. a. formosus (F) in the following manner: D (45·)DP (15 ·5), PD (13·9), P (9·8), DF (5·7), FD (73·), PF (1·5), FP. (0·6) and F (0·6).The recaptures outdoors were in the reverse order, the highest percentage being for F (187·) and the lowest for D (8·5), DP (8·0) and PD (7·7). The data suggest that the larvae from the peridomestic habitat may represent hybrids between the domestic and feral forms

A model for the inheritance of behavioural characters in mosquitoes is presented. On the basis of isolating mechanisms and partial hybridisation, it is concluded that A. a. aegypti and A. a. formosus have developed as geographically isolated allopatric populations. This supports the existing polytypic concept of speciation in A. aegypti. Spatial distribution, non-random mating and the existing series of isolating mechanisms indicate that the domestic type form has been introduced into East Africa, most probably on ships.