Mosquitoes transmit a variety of diseases to humans. Their abundance and distribution are related to the characteristics of larval habitats. Mosquito larvae were collected from 120 natural and artificial habitats in 30 villages of 16 counties using standard 350 ml dippers and pipette, on a monthly basis from May–December 2014 in Mazandaran Province, northern Iran. Larval habitat characteristics were recorded separately, based on the conditions of the habitats (permanent or temporary, stagnant or running), type of habitats (natural or artificial), vegetation, exposure to sun, type of bed, water condition (clear or turbid), expanse (m), depth (cm, m) and temperature (°C) of habitats. The relationship between larval density and environmental variables was assessed by Chi-square tests. Totally, 19,840 larvae from three genera and 16 species were collected and identified. Anopheles maculipennis s.l. and Culex pipiens were the dominant species and collected with the highest density in plain areas. The highest number of larvae were collected from natural habitats (60.34%), including; river edge, marsh, pit and wetlands; with temporary and stagnant water, expanse of 0–5 m, depth of 1–25 cm, without plant, shadow-sun, muddy floor, turbid water, temperature 20–25°C and in sunny conditions. River edge and rice fields for An. maculipennis s.l and, wetlands and discarded tires for Cx. pipiens were the main larval habitats in the province. Statistical analysis revealed significant relation between occurrence of An. maculipennis s.l., Cx. pipiens, Culex torrentium, Culex mimeticus and Cs. annulata with each of the environmental variables (P < 0.001). These findings are essential in expanding our knowledge of the vectors ecology specially the type of habitat preference and will be beneficial in larval control programs.

Two strains of a virus disease, “A” and “B,” which possibly may be two distinct viruses, occur on cacao in Trinidad. These are compared with the more virulent “swollen-shoot” and related viruses that are widespread in West Africa.

The most important resemblance between the Trinidad and the West African viruses is that both are carried exclusively by mealybugs of the family Pseudococcidae. There are also points of similarity in the symptoms, which in the Trinidad virus consist mainly of a transient red vein-banding, with or without a more or less discontinuous yellow vein-flecking (which does not disappear when the leaf matures) and, on certain varieties of cacao, red-mottle on the pods. Swellings on the shoots, a conspicuous symptom of most of the strains of the West African viruses, have not been observed in Trinidad.

Four species of mealybugs are definitely known to be vectors: Pseudococcus citri, which is the commonest and undoubtedly responsible for most of the natural spread of the disease; P. brevipes; a species near P. brevipes but almost certainly distinct; and Ferrisia virgata. Certain other mealybugs have been found on cacao in Trinidad but the virus has not yet been transmitted by them.

Most transmission experiments have been made with mealybugs bred up on potato tubers and with Posnette's technique of feeding potential vectors, after infection-feeding, on cacao beans from which one of the cotyledons has been removed, so that the insects can feed on the convoluted surface of the remaining cotyledon or on the radicle. Notwithstanding some drawbacks to this method it has many advantages over using young growing plants as tests.

The “latent period” of the virus in the test plants grown from dissected beans has varied between 20 and 123 days, though the symptoms most commonly appear from 30 to 50 days after infection of the bean. The symptom of red vein-banding has appeared much more often than that of yellow vein-flecking, irrespective of the symptoms on the virus source plant. When both symptoms appear the red veinbanding almost always shows up first.

All three immature instars, and young adults, of all four vector species are probably almost equally efficient as vectors, except that there is some indication that P. brevipes may be slightly more efficient than the other three species.

Starvation of the mealybugs before infection-feeding does not increase their capacity to transmit, though it usually helps to make them settle and feed more readily on the source plant.

The time for which the mealybugs feed on the virus source plant has little if any effect on their capacity to transmit the virus. Mealybugs have become infective in just over one half-hour infection-feeding, though the proportion of transmissions obtained when the infection-feeding time has been between one-half and two hours is rather less than that for over two hours, probably because in the former tests some of the insects had not actually fed.

The duration of feeding on the test bean is probably also immaterial, provided of course that the mealybugs do actually feed. The shortest test-feeding time that has resulted in transmission is 90 minutes, but this included a considerable “settling” time.

Transmission may be effected whether a mealybug feeds on the cotyledon or the radicle of a test bean.

Mealybugs can still transmit the virus if they are starved after infection-feeding for a period up to 22½ hours, but no transmission has yet been obtained when the post-infection starvation has been over 23 hours. It is not yet known whether a short period of feeding after infection-feeding renders the mealybugs incapable of transmitting, but post-infection feeding for 66 hours does so.

A transmission rate of just under 14 per cent, has been obtained with single mealybugs to each test bean but with larger numbers the rate has not risen in accordance with the mathematical expectation. A possible explanation for this might be that there are “active” and “inactive” races of P. citri, but so far practically no evidence for this has been obtained.

Mealybugs can become infective by feeding on the symptom-free parts of flush leaves showing symptoms in other parts, on entirely symptom-free flush leaves from infected trees, on the stem of a young infected plant, and on the leaves of a young infected plant after the disappearance of the transient symptoms of red vein-banding. It appears, however, that they pick up the virus more readily from flush leaves actually showing symptoms, and these have been used as the source of the virus in most of the experiments.

Few experiments have yet been made with strain “B” of the virus, but this strain has been transmitted with P. citri and P. brevipes.

All stages of P. citri, but especially young adults, often wander about of their own accord and are thus capable of spreading the virus, particularly to trees actually in contact with an already infected tree. The transport within a plantation of cacao pods during harvesting is thought to be a likely cause of isolated new infections.

Holocyclic populations of aphids of the Chaetosiphon (Pentatrichopus) fragaefolii (Cockerell) group from Fragaria in British Columbia were found to have a homozygous 2n = 12 female karyotype, whereas samples from predominantly anholocyclic populations in Oregon, California, England and New Zealand have 13, 14, 15 or 17 chromosomes showing various degrees of structural heterozygosity. The 17-chromosome form is a morphologically recognizable taxon, C. jacobi Hille Ris Lambers. The other karyotypes apparently represent a series of parthenogenetic lineages derived from the 2n = 12 holocyclic form and carrying one, two or three autosome dissociations. The North American populations showed no correlation between karyotype and the number of submarginal setae, a character previously used in attempts to differentiate taxa within this species complex in western North America. Submarginal setal number varied greatly within and between clones and tended to increase in successive generations from the fundatrix, confirming that this character varies both genetically and seasonally and has little taxonomic value. Populations of the fragaefolii group from Rosa spp. in North America have a shorter rostrum than those from Fragaria. The name C. thomasi Hille Ris Lambers is assigned to this rose-feeding species, which is holocyclic on R. rugosa in British Columbia and colonizes Potentilla spp. (but apparently not P. anserina) as alternative hosts. Old World populations on Fragaria, presumably originating from North America, have longer siphunculi than North American populations of fragaefolii and few or no submarginal setae; these differences are probably due to founder effects. Both Old and New World populations of fragaefolii use P. anserina as an alternative host-plant.

The Asian chestnut gall wasp, Dryocosmus kuriphilus, is an invasive pest causing significant damage to chestnut trees (Castanea spp., Fagaceae). Originating from China, it has recently invaded a wide range of regions in Europe and North America. Understanding the population genetic structure of important invasive pests is very useful for improving the knowledge concerning routes of expansion and colonizing capacity. Despite its economic importance, limited attention has been given to D. kuriphilus origin and spread, or to its genetic structure. In this study, D. kuriphilus populations sampled in eight European countries were screened using both mitochondrial (cytochrome c oxidase subunit 1; COI) and nuclear (internal transcribed spacer 2; ITS2) sequences, and Amplified Fragment Length Polymorphism (AFLP) markers. The molecular markers COI and ITS2 highlighted the presence of a single haplotype in all the studied populations. The recorded mitochondrial haplotype was identical to one of the most widespread haplotypes occurring in the native area (China). AFLP results indicated that D. kuriphilus individuals belong to two genetically distinct clusters without any further geographic clustering. These results suggest that D. kuriphilus populations in Europe could be the result of a single introduction of a Chinese founder population characterized by two genetically distinct lineages that subsequently spread rapidly across Europe. However, the possibility that populations originated from multiple introductions of the same Chinese mitochondrial haplotype cannot be excluded. The reported results provide useful information concerning this invasive species, potentially facilitating integrated pest management.

The Palaearctic pine aphids, Eulachnus agilis (Kaltenbach) and Eulachnus rileyi (Williams) have both been introduced into other continents where they have been reported causing damage to economically important pines. In Euorpe, they are attacked by the specialist parasitoid Diaeretus leucopterus (Haliday) which has been suggested as a possible biological control agent. Here we report on several aspects of the ecology of the parasitoid, conducted on E. agilis in Germany in 1993–94, to provide a more scientific basis for judging its potential for use in biological control. Parasitism of all instars in the field rarely exceeded 10% and was independent of host density. A high percentage of parasitized aphids were hyperparasitized. Measurements of the impact over 16 weeks in a greenhouse-release experiment showed that parasitism rates increased from 2 to 19% but were insufficient to suppress the aphid population below a damaging level. There was evidence of a density-dependent response. Studies on foraging behaviour showed that female parasitoids searched pines by quite extensive walks. There was no relationship between the number of aphids per tree and number of ovipositions, and the mean number of ovipositions per female per tree was 2.5 ± 0.4 eggs. The majority (55.1%) of encountered aphids did not respond to the parasitoids. However, female parasitoids attacked a much higher proportion of aphids that did respond but oviposition success on this group was poor. The number of aphid-infested needles on seedlings increased significantly owing to the parasitoid's foraging activity. On the basis of these results, it is suggested that D. leucopterus is only likely to be of benefit in biological control if used in conjunction with other complementary natural enemies.

The present paper revises the Australian and South African species of Halotydeus Berlese. The redlegged earth mite H. destructor(Tucker) is redescribed, and four new species are described (H. anthropus, H. bakerae, H. castellusand H. spectatus). A key to species is provided. Halotydeus destructor is an important pest of leguminous pasture and other crop plants, but the three Australian species (H. bakerae, H. castellus and H. spectatus)occur in native vegetation and are not believed to be of any economic significance. The pest status of the South African species H. anthropus has not yet been determined.

Previous reports and field observations at Ibadan and in northern Nigeria have established the occurrence of a dry-season form and a wet-season form of Zonocerus variegatus (L.). The wet-season form in the savanna areas of northern Nigeria is shown to be virtually identical with that from southern Nigeria on the basis of breeding seasons, habitat and morphometrics. Morphometrics show the wet- and dry-season forms to be distinct. It is suggested that the dry-season form in the wet rain forest zone spread into the dry savanna areas giving rise to a wet-season form adapted to the different climatic conditions. The increasing occurrence of the wetseason form in the south probably represents a re-invasion by the northern wetseason form.

Macdunnoughia crassisigna Warren (Lepidoptera: Noctuidae) is a highly destructive herbivore that poses a serious risk to cotton, maize, soybean, and cruciferous vegetables in East Asia. Examining the effects of various biotic and abiotic factors on the flight performance of M. crassisigna is crucial for a better understanding of its trans-regional migration. In this study, the flight activity of M. crassisignai moths of different ages, under different temperatures and relative humidity (RH) levels, was evaluated by tethering individuals to computerized flight mills for a 24-h trial period. The results showed that M. crassisignai had the capacity for sustained flight and the flight ability was strongest in 3-day-old individuals, and then their flight performance decreased significantly in older moths. For both sexes, temperature had a significant effect on their flight performance, and the flight activity was relatively higher at 24–28°C than other temperatures. There was a significant effect of RH on all flight parameters of the tested moths, and the flight activity was relatively higher at RH of 60–75% than other RH levels. For 3-day-old moths under the optimum conditions (24°C and 75% RH) throughout the 24 h scotophase, their mean flight distance reached 66 km, and the mean flight duration reached 13.5 h, suggesting M. crassisigna possess strong potential to undertake long-distance migration. These findings will be helpful for developing sound forecasting systems of this pest species.

Choice between prey species by Chilocorus nigritus (Fabricius) and C. bipustulatus (Linnaeus) adults and larvae was determined. Strong preferences were absent and differences in the predators' feeding histories, were not reflected in their choices. The deleterious effects of a prey substitution, during larval development and adult maintenance, were investigated using C. nigritus with supplementary work on C. bipustulatus. These diet changes significantly retarded larval development rate, and subsequent adults were smaller than control individuals. Prey substitutions in the adult diet, suppressed oviposition for several days and feeding rate was reduced at one day after substitution. Larvae were more sensitive than adults to such diet changes. This was not a case of classical unsuitability of the new prey, as the fecundity and feeding rate returned to the same levels as before the substitution after a few days of exposure to the new prey. Furthermore, both prey types were suitable for larval development of C. nigritus when they fed on one exclusively, but unsuitable when substitutions were made. The effects of prey substitutions may possibly be attributed to the presence, in the new prey, of plant toxins, which the predators are initially not physiologically capable of dealing with in large quantities. These results present difficulties for the concepts of monophagy and polyphagy, being less well defined than normally thought. In view of coc-cinellid foraging behaviour and larval habitat selection by adults, the temporary reduction in fitness following a diet change is considered to be adaptive.

Adults of Cnaphalocrocis medinalis (Gn.), a widely distributed pest of rice, were found to require an exogenous source of sugar, life-span and fecundity being greatly increased in the laboratory when sugar was available. Their sources of sugar in the field are not known, but evidence is presented which shows that in the laboratory they can utilise the honeydew produced by Nilaparvata lugens (Stål), a common pest of rice.

Dentichasmias busseolae Heinr., an important pupal parasite of Pyralid graminaceous stem-borers in East Africa, is widely distributed in the Ethiopian Region but is more abundant in areas with an equatorial humid climate. In the laboratory adults mated immediately after emergence and started oviposition the same day. The female oviposits only in a borer pupa without a cocoon in a stem, and oviposition is stimulated by the presence of the frass of Chilo partellus (Swinh.) larvae. D. busseolae does not attack Busseola fusca (Fuller), Sesamia calamistis Hmps. or Eldana saccharina Wlk. in the field but these were accepted for oviposition when exposed in C. partellus pupation tunnels or with frass of C. partellus larvae, and were suitable for development. D. busseolae could complete its development in one- to eight-day-old C. partellus pupae when the pupal period of C. partellus was 10·5 days. The life-cycle was completed in 15–19 days at a mean temperature of 25°C, but could not be completed at a constant temperature of 30°C; temperatures fluctuating between 22°C and 30°C were not detrimental. At Namulonge (Uganda) percentage parasitism showed a positive correlation with rainfall, with a lag of about a month.

Bathycoelia thalassina (H.-S.), of which the developmental stages and life history are described, is responsible for premature ripening of cocoa pods in Ghana. Experiments conducted at Tafo to determine the nature of the damage to pods showed that the insect feeds directly on the beans, and that beans so attacked turn brown and subsequently die: only the empty shell of the bean remains.

The saliva of the insect kills any tissue of the pod that it penetrates and within four days the injured areas cease to grow and become yellow, then brown, and finally black.

The symptom most characteristic of damage is the change in colour. The pod may become completely yellow, or yellow in the basal or distal half only (usually the latter) or yellow in spots, depending on the size of the pod, the site of attack, and the duration of feeding at each site.

The insect usually attacks pods of the Amazon varieties, 10–17 cm. long. The incision made by the stylets is microscopic, and is covered by a jelly-like substance, and no evident lesions develop on the surface as in damage caused by cocoa mirids or coreids.

Damage caused by B. thalassina on young pods resembles cherelle wilt of physiological origin, and the two can be distinguished only by slicing the pods, whereupon the former can be recognised by the presence of injured beans.

According to the survey of damage caused by B. thalassina in Ghana, this species seems to be an economic pest on some Amazon and hybrid types of cocoa, whereas Amelonado cocoa usually suffers little.

In Zimbabwe, catches of Glossina morsitans morsitans Westwood and G.pallidipes Austen at odour baited traps were increased in the presence of residues of a solution of the skin secretions of oxen (hereafter sebum) by 80% and 29% respectively, and catches at F3 traps were significantly increased when sebum was presented on adjacent screens. Testing of fractions of sebum revealed active components(s) in the phenolic and non-acidic fractions but not in the acidic fraction. Furthermore, the activity of the phenolic fraction could not be explained by the presence of the known phenolic tsetse attractants. The effect of sebum was to attract more flies to the target rather than to induce a landing response in a higher proportion of attracted flies. Whether or not tarsal contact responses are involved remains conjectural. However, targets that were electrified over only one quarter of the surface caught more than one quarter the catch of targets electrified over all the surface both with and without sebum, indicating that many tsetse habitually alight more than once on baited targets. Data on the catches of other Diptera are also presented

Since December, 1942, a supply of adult house-flies, averaging approximately 2,500 a day, has been required in this Laboratory for experimental work on fly sprays. The production in quantity of insects suitable for such use is by no means a straightforward matter and a considerable amount of work was undertaken before a satisfactory technique was established.

Laboratory investigations with the mosquito AËdes aegypti (L.) have shown that air pressure has the following effects on flight activity:

The effects of pressure changes are consistently large enough to constitute an important factor in determining activity provided the mosquitos are acclimatised first to a particular pressure level.

The period of constant conditions necessary for complete acclimatisation was between three and six hours for all pressure conditions investigated.

When the period of acclimatisation had been fulfilled, the flight activity was approximately the same at all levels of static pressure investigated between 550 mm. and 800 mm. Hg.

After complete acclimatisation the activity following a moderate decrease in pressure was 1·5 to 2·4 times that following a similar increase in pressure when the general pressure level exceeded 735 mm. Hg.

When the general pressure level was less than 735 mm. Hg., the activity following a decrease in pressure was less than that following an increase; it would appear that 735 mm. is a critical pressure level for the stock of A. aegypti employed.

The activity during a uniform rise in pressure from 530 mm. to 730 mm. at 7·7 mm. /min. was at least 10 times that during a reverse fall in pressure fall in pressure at the same uniform rate.

Provided the rate of change was not greater than 1 mm./sec., the maximum flight activity for falling pressures was observed at 780 mm. while the maximumfor rising pressures was observed at 735 mm.

The study of crop loss following insect attack on cotton in Uganda, described in Part I of this work, was continued for two further seasons (1954–56), using the same experimental procedure, except that half the DDT in the spray formulation was replaced by toxaphene, only three periods of protective treatment were used for each date of sowing, and the late-season ones were continued until boll-opening was complete, so as to give maximum control of boll worm.

Methods are described of estimating an index of leaf damage caused by Lygus spp., based on comparisons with standard grades. At Serere (Eastern Province), the index of leaf damage was closely related to Lygus populations in the crop, and at Namulonge (Buganda) it was markedly reduced on plots protected from Lygus attack, but in the 1954–56 experiments no relationship could be found between the mean seasonal index and the loss of fruiting bodies attributable to Lygus attack, or the final yield.

Analysis of the cause and incidence of shedding of developing fruit bodies (flower buds or young bolls, the latter predominating among those recovered) showed that the total amount of shedding was roughly the same whatever the treatment, that due to insect damage tending to be balanced by that due to other causes, which were probably physiological in nature. There was thus some over-riding factor, other than pest attack, that governed the crop finally held by the plant.

Damage caused by insects to older bolls, which do not shed, constitutes a real loss that is reflected in the final harvest. The proportion of clean seed cotton was higher in the treated plots, particularly in the early-sown cotton, in which analysis of the harvested locules showed that the damage was predominantly due to bollworm, but there were no significant differences in yield between the various treatments in either date of sowing or in either season.

It is concluded that under such conditions as those experienced at the Research Station in the three seasons of the experiments, insect damage to cotton is small in relation to other environmental factors governing crop production.

The sexual performance of Anastrepha ludens males of the Tapachula-7 genetic sexing strain, produced via selection based on mating success, was compared with that of males produced without selection in competition with wild males. Mating competition, development time, survival, mass-rearing quality parameters and pheromone production were compared. The results showed that selection based on mating competitiveness significantly improved the sexual performance of offspring. Development time, survival of larvae, pupae and adults, and weights of larvae and pupae increased with each selection cycle. Differences in the relative quantity of the pheromone compounds (Z)-3-nonenol and anastrephin were observed when comparing the parental males with the F4 and wild males. The implications of this colony management method on the sterile insect technique are discussed.

This study was carried out to establish the extent to which an invasive stored products pest, Prostephanus truncatus Horn exploits wood as a feeding and breeding resource in Kenya. Twenty seven out of 84 native and agroforestry trees and shrubs supported the breeding of P. truncatus under laboratory conditions. Adult survival (<1% to 18%) for 8 weeks was recorded on 51 tree species that did not support breeding. The breeding success of this beetle varied widely between host tree species and showed no obvious trends based on tree systematics or wood hardness. Studies of P. truncatus survival on two host tree species found that the greatest increase in the P. truncatus population occurred on stem sapwood, whilst the smallest population increase was on twigs. Breeding also varied greatly from season to season; studies on ten selected host species showed that reproduction was often greatest in wood samples collected and tested during the dry season in September. The implications of these findings for the management of P. truncatus infestations in farm stored maize are discussed.

A field study was undertaken in Uganda using highland cooking banana (cv. Atwalira) to test the hypothesis that bananas grown under stressed conditions are more susceptible to attack by Cosmopolites sordidus (Germar). Four banana treatments were employed to create different levels of host-plant vitality: (1) high stress: intercrop with finger millet; (2) moderate stress: monoculture without soil amendments; (3) low stress: monoculture with manure; (4) high vigour: monoculture with continuous mulch and manure. Adult C. sordidus were released at the base of banana mats 11 months after planting and populations were monitored for three years using mark and recapture methods. Cosmopolites sordidus density was greatest in the mulched plots which may have reflected increased longevity and/or longer tenure time in moist soils. Lowest C. sordidus numbers were found in intercropped banana. Damage, estimated as percentage corm tissue consumed by larvae, was similar among treatments. However, the total amount of tissue consumed was greater in mulched banana than in other systems. Plants supporting the heaviest levels of C. sordidus damage displayed bunch size reductions of 40–55%. Banana yield losses ranged from 14–20% per plot with similar levels in the intercropped and mulched systems. Yield reductions, reported as t ha-1, were twice as high in the mulched system as in the intercrop. The results from this study indicate that C. sordidus problems are not confined to stressed banana systems or those with low levels of management, but that the weevil can also attain pest status in well-managed and productive banana stands.

In an attempt at some assessment of the errors to which fly-round data obtained for the study of populations of Glossina are subject, three fly-rounds at Shinyanga, Tanganyika, were worked every weekday for four weeks. The species studied was G. swynnertoni Aust. One of the rounds was a ‘transect fly-round ’, the others, the older type, divided into a few long sections according to the vegetation. The catches showed no obvious trend during the experiment, suggesting that the true population had not altered in the period, but in all three rounds there were considerable day-to-day variations in catch and, in this respect, the transect fly-round did not differ from the older method. An analysis of variance of the transect fly-round data showed that the variance between days was greater than could be accounted for by random errors

By considering separately the data collected on certain days of the week, it is concluded that a 7,500-yd. fly-round done once a week could not detect less than a five-fold change in the mean catch. To detect a two-fold change, a 15,000-yd. fly-round done twice a week would be necessary.

The relation between fly-round catch and true density is discussed. This relation is usually termed ‘ availability ’. Earlier workers have shown that its mean value, over periods of about one month, is not necessarily constant; the present work shows that it varies in one place from day to day.