Research Paper
Biological Control of Insect Pests in Bermuda
- Fred D. Bennett, I. W. Hughes
-
- Published online by Cambridge University Press:
- 10 July 2009, pp. 423-436
-
- Article
- Export citation
-
Projects undertaken on the biological control of insect pests in Bermuda since the first introduction of Bufo marinus in 1875 and including those still in progress are discussed. Work on 15 pests or groups of pests has been undertaken involving the introduction of over one hundred species of beneficial organisms.
Icerya purchasi Mask. is considered to be under excellent control as a result of the introduction of the Coccinellid, Rodolia cardinalis (Muls.), and the fly, Cryptochetum iceryae (Will.). Pseudaulacaspis pentagona (Targ.), a serious pest of oleanders, was brought under control about 1922 by the introduction of Aphytis diaspidis (How.). However, in recent years heavy infestations have periodically developed. In addition to A. diaspidis, the Aphelinids, Aspidiotiphagus citrinus (Craw) and A. lounsburyi (Berl. & Paoli), the Coccinellids, Lindorus lophanthae (Blaisd.) and Chilocorus cacti (L.), and the Nitidulid, Cybocephalus sp., now attack it.
Comstockiella sabalis (Comst.) at one time causing severe injury to the endemic palm, Sabal bermudiana, was brought under control by the introduction of Physcus sp. Bracon gelechiae Ashm. has been established on the potato tuber moth, Gnorimoschema operculella (Zell.), but satisfactory control has not resulted.
Two cedar scales, Carulaspis minima (Targ.) and Lepidosaphes newsteadi (Sulc), have decimated the stands of Juniperus bermudiana despite an extensive programme of biological control. C. minima, which proved to be the more serious, is attacked by the Aphelinids, Prospaltella sp., Aspidiotiphagus lounsburyi, A. citrinus, probably introduced with the scale, and the Coccinellids, Lindorus lophanthae and Microweisia suturalis (Schwarz), which were liberated in large numbers. The predacious mite, Hemisarcoptes malus (Shimer), and the fungus, Myiophagus ucrainica, were established on Lepidosaphes newsteadi which for unknown causes became very scarce.
Damage by Calpodes ethlius (Cram.), a pest of ornamental cannas, is less serious since the introduction of Ooencyrtus sp. and Trichogramma sp.
Several parasites were liberated to control various species of mealybugs. Pseudococcus adonidum (L.), serious on a number of ornamentals, is under satisfactory control as the result of the establishment of the Encyrtids, Tetracnemus peregrinus Comp. and Anagyrus fusciventris (Gir.). Planococcus citri (Risso) is now attacked by the introduced Encyrtids, Leptomastidea abnormis (Gir.) and Pauridia peregrina Timb., as well as by Leptomastix dactylopii How., which was present at the start of the investigation. Acerophagus pallidus Timb. has been recovered from the mealybug, Phenacoccus gossypii Tns. & Ckll.
The Encyrtid, Microterys kotinskyi (Full.), and the Coccinellids, Azya luteipes Muls. and Cryptolaemus montrouzieri Muls., have been effectively established on the soft scale, Pulvinaria psidii Mask. Tree lizards, Anolis spp., which feed readily on Azya and Cryptolaemus, are considered undesirable and accordingly the passerine bird, Pitangus sulphuratus, has recently been liberated in an attempt to reduce their numbers.
Several species of parasites and predators were liberated against the soft scales, Saissetia oleae (Bern.), S. coffeae (Wlk.) and Coccus hesperidum L. Aphycus stanleyi (Comp.) is well established on Saissetia spp.
Although the Braconid, Opius humilis Silv., was established on the Mediterranean fruit-fly, Ceratitis capitata (Wied.), for a number of years it has now disappeared.
Parasites and predators introduced against Nipaecoccus nipae (Mask.), the onion thrips, Thrips tabaci Lind., and the red spider mite, Oligonychus ununguis (Jacobi), did not become established.
Projects at present in progress to control tree lizards, Anolis spp., and snails cannot yet be evaluated.
In the discussion a number of factors which may have contributed to the failure of establishment of some beneficial organisms are mentioned.
Observations on the Mosquito, Aëdes (Stegomyia) aegypti (L.), in East Africa. I.—The Biting Cycle in an Outdoor Population at Entebbe, Uganda
- G. A. H. McClelland
-
- Published online by Cambridge University Press:
- 10 July 2009, pp. 227-235
-
- Article
- Export citation
-
In an outdoor population of Aëdes (Stegomyia) aegypti (L.), mainly consisting of subsp. formosus (Wlk.), in Uganda, a series of ten 24-hour catches has shown a sharply-defined biting cycle which corresponds closely to an observed diurnal cycle of flight activity. A main peak of activity occurs one or two hours before sunset, and a lesser peak two or three hours after sunrise.
Comparison with recent work in Kenya suggests that, in comparing the behaviour of populations out of doors with those indoors, a distinction must be made between ssp. formosus and the other two forms of A. aegypti, in which no similar cycle has yet been demonstrated.
Ssp. formosus, which is presumed to be the wildest form of A. aegypti, is shown to have a cyclical behaviour very similar to a related forest species. A. africanus (Theo.).
Bionomics of Anopheline Mosquitos in Inland Areas of Java, with Special Reference to Anopheles aconitus Dön
- C. Y. Chow, R. Moh. Ibnoe, Soejoed Tarko Josopoero
-
- Published online by Cambridge University Press:
- 10 July 2009, pp. 647-660
-
- Article
- Export citation
-
Anopheles aconitus Dön. has long been known as an important vector of malaria in Indonesia. More recently it has been shown to be the principal, if not the only vector in the inland areas of Java. A. maculatus Theo. has been regarded as an important vector in hilly regions.
The observations recorded in the present paper were carried out in an inland area in East Java between June 1957 and May 1958, and in a hilly one in West Java between April 1956 and March 1957, and were concerned, in particular, with the resting and feeding habits of these two species in so far as they might influence methods of control.
A. aconitus is found in great numbers throughout the year with a major peak of density from March to May, about harvest time of the first and more extensive rice crop.
In the areas studied, A. aconitus is largely exophilic and, where man is concerned, exophagous, nearly three times as many examples being taken biting man outdoors as indoors, and 17 per cent. of 359 examples taken outdoors were positive for human blood as compared with 5 per cent. of 1,438 examples from all situations. Of the remainder, 93·5 per cent. were positive for ox. On the whole, therefore, this species is highly, though not exclusively, zoophilic and readily enters cattle-sheds, built of bamboo matting, to feed, and, in those sheds that have walls as well as roofs, up to 75 per cent. may remain for at least two hours after having fed, and appreciable but variable numbers of fully fed individuals may remain during day-time.
Most of the feeding on man outdoors took place before midnight, and, on cattle in sheds, between midnight and 0600 hr., with peaks between midnight and 0100 hr. and between 0400 and 0500 hr., respectively. Peak periods of entry into an animal-baited trap were during the second and fourth quarters of the night.
These results differ somewhat from those reported from certain other localities in Java by other workers. There is, therefore, a need for careful repetition, in other areas, of studies of the bionomics and for experiments on the effect on a population of A. aconitus of applications of a residual insecticide.
A. maculatus occurs in the hilly area in considerable numbers throughout the year, and there seems to be no great seasonal fluctuation. This species rests mainly on coffee and palm plants both by day and by night, but readily enters cattle-sheds at night. No blood-meals from this species were subjected to the precipitin test. It is suggested that the importance of A. maculatus in the transmission of malaria needs further investigation.
Over 1,000 examples of A. maculatus and A. aconitus, taken in the hilly area, were dissected, but no malaria infection was found.
A. vagus Dön. is present in the inland area in large numbers during the greater part of the year, with its peak from November to February, during the rainy season. It is more endophilic and endophagous than A. aconitus but is not considered important in malaria transmission.
A. annularis Wulp has its peak in March, and A. kochi Dön. in May. A. barbirostris Wulp, A. subpictus malayensis Hack, and A. tessallatus Theo. were found only in small numbers. All these species are highly zoophilic in the areas studied; they are not considered important in malaria transmission.
Lunar Rhythm of Emergence, differential Behaviour of the Sexes, and other Phenomena in the African Midge, Chironomus brevibucca (Kieff.)
- G. Fryer
-
- Published online by Cambridge University Press:
- 10 July 2009, pp. 1-8
-
- Article
- Export citation
-
Larvae of the African midge, Chironomus brevibucca (Kieff.), are abundant in the littoral zone of Lake Bangweulu, Northern Rhodesia, where, at certain times of the year, imagines emerge in vast numbers shortly after the appearance of the full moon. Attracted by light, the imagines fly to houses and alight on the protective gauze screenings, which, at peak periods of emergence, become covered with a solid mass of midges. They have not been seen at other phases of the lunar cycle, so the adult life is certainly not more than ten days and is usually much less.
Imagines, which are inactive by day, tend to settle in different situations according to their sex. On the gauze screenings there was a marked preponderance of females (4·68:1) on the day following a night's swarming but, on several adjoining whitewashed walls, males predominated (2·92:1). On grasses near the lake margin females outnumbered the males.
When, the gauze screening of a house was diffusely illuminated, imagines were attracted to it during the early hours of darkness. The first flies to arrive were almost invariably males, but females followed on rapidly and finally constituted the bulk of the population. On one evening the percentage of males fell in three hours from 95·4 at 1844 hr. to 29·5 at 2145 hr. The percentage of males reaches a minimum between 1900 and 2000 hr. and thereafter shows some rise, probably due to a secondary influx of males which are thought to have been resting during the day and not to be newly emerged.
An indication of the adult age of males seems to be given by the condition of the antennae during the early part of their adult life.
Some miscellaneous observations on the behaviour of C. brevibucca are recorded.
Some aspects of the phenomena recorded are discussed. The recent hypothesis of Korringa, which seeks to explain the periodíc swarming of certain polychaetes just after the time of full moon as being the result of an additive effect of exposure to nocturnal illumination on the maturation of organisms that are not subjected to sunlight by day, is examined and shown to be applicable to C. brevibucca.
The Biology of Nausibius clavicornis (KUG.) (Col., Cucujidae)
- M. H. Breese, Thelma E. Wise
-
- Published online by Cambridge University Press:
- 10 July 2009, pp. 237-258
-
- Article
- Export citation
-
Nausibius clavicornis (Kug.) is a cosmopolitan Cucujid that has frequently been recorded from sugar. It is commonly found in this commodity in Trinidad, where it has not been collected from any other.
The adult and other stages are described, and an account is given of the life-history on Haydak's formula at 85°F. and 75 per cent. R.H. Development has also been studied on two types of unrefined sugar.
Copulation can take place within one day of the emergence of either sex and the female may begin laying within four days of copulation. The average number of eggs laid was 275 and the overall viability was 85 per cent. The average incubation period was just under five days.
The larvae of both sexes may undergo only five moults in development, but the more usual number for females is six. When larvae are disturbed during development, both sexes tend to have six larval instars. Severe disturbance may induce a seventh moult. The mean development period from oviposition to the emergence of the adult was 30 days when there were five larval instars; when there were six, development took about two days longer. Larval mortality on Haydak's formula was low.
Ovipositing females lived for up to 163 days under controlled conditions, but males tended to outlive females by about 50 days.
On unrefined sugars (e.g., raw or yellow-crystal sugar), adults lived for almost as long (73:99) as on Haydak's formula, but oviposition was greatly reduced and the viability of the eggs was much lower. Larval mortality was high, especially in the first instar, and the total development period was greatly increased.
It is unlikely that N. clavicornis could multiply rapidly in raw or unrefined sugar, and any deterioration in stored sugar directly attributable to it would probably be small in comparison with that caused by other factors.
A Xyloryctid Moth attacking the Bark of the Rubber Tree in Malaya
- J. D. Bradley
-
- Published online by Cambridge University Press:
- 10 July 2009, pp. 9-10
-
- Article
- Export citation
Notes on Gall Midges (Cecidomyiidae) on Nigerian Crops with a Description of a New Species of Thomasiella Rübsaamen
- K. M. Harris
-
- Published online by Cambridge University Press:
- 10 July 2009, pp. 661-666
-
- Article
- Export citation
-
Investigation of the gall midges of crops in Nigeria has revealed an undescribed: species which causes sorghum stems to lodge and two species, one on rice, the other on benniseed (Sesamum orientale), which are known as pests of these crops in India.
Observations on the Association of Ants with Coccids of Tea
- G. M. Das
-
- Published online by Cambridge University Press:
- 10 July 2009, pp. 437-448
-
- Article
- Export citation
-
Certain species of COCCIDAE that excrete honeydew and are attended by ants or enclosed in their nests are quite prevalent on tea bushes and seed trees in the plains of Assam and West Bengal but those which are not attended by ants are kept under considerable check by the activities of their natural enemies. In Darjeeling, where the natural enemies are fewer, a number of species occur abundantly and are often responsible for serious damage to tea.
From the studies of the relative population of the ant, Crematogaster dohrni Mayr and the Coccid, Saissetia formicarii (Green), occurring on tea bushes it is doubtful if more than a small portion of the food requirement of the vast ant population in the nests which contain sexual forms could be met from the honeydew excreted by the small number of Coccids enclosed therein. The major part of food must, therefore, come from other sources. Insects attacking or visiting the tea bushes and tea seed trees or even those found on the ground appear to constitute the major part of the food of the ants, C. dohrni and Oecophylla smaragdina (F.).
Several factors are responsible for the decrease in the population or disappearance of the Coccids in the absence of attendant ants. In the plains, Eriochiton theae Green, Coccus hesperidum L. and S. formicarii entirely disappear in the absence of attendant ants either due to the activities of their natural enemies or by contamination with honeydew accumulation or both. Parasitism may be slightly higher in ant-free colonies, but no estimation was possible since, in the absence of ants, the Coccids are quickly destroyed by predators.
The ants do not protect the Coccids from Hymenopterous parasites; but their active movements hinder the parasites in their efforts to oviposit, and this leads to a reduction in the rate of parasitisation.
In the presence of the ants, O. smaragdina and Crematogaster dohrni, predators are rare; they are destroyed as are any other insects or any foreign bodies that happen to be near their nests, whether they constitute food or not. The larvae of predators which have a protective covering or which resemble Coccids, if they happen to have gained access to the Coccid colonies, are not attacked by the ants, because they are not recognised as different from the Coceids.
O. smaragdina does not normally transport Coccids, though young nymphs of E. theae and Coccus hesperidum may be aided in their dispersal, but Crematogaster dohrni and Crematogaster sp. are primarily responsible for the dispersal of S. formicarii and this takes place when an occasion arises to remove the Coccid to more favourable sites.
O. smaragdina does not destroy the nymphs and sedentary form of Coccus hesperidum for food, but sedentary forms which are unable to establish themselves on transfer from withered leaves to a new nest are eaten.
With the control of the attendant ants, the honeydew-producing Coccids disappear or at least they become rare. Conversely, where the Coccids are controlled, the ants automatically disappear.
An Insectary Method for Rearing Cacao Mirids, Distantiella theobroma (Dist.) and Sahlbergella singularis Hagl
- F. Raw
-
- Published online by Cambridge University Press:
- 10 July 2009, pp. 11-12
-
- Article
- Export citation
-
An insectary method for rearing the cacao Mirids, Distantiella theobroma (Dist.) and Sahlbergella singularis Hagl., is described. Adults are caged, for oviposition, on cacao seedlings grown in baskets. When the eggs hatch, the nymphs are transferred to, and reared on, unripe pods suspended in ventilated glass cages.
A Comparative Study of the Soil Conditions favoured by certain Melolonthid and Tenebrioned Pests of Tobacco in Southern Rhodesia
- G. H. Bünzli, W. W. Büttiker
-
- Published online by Cambridge University Press:
- 10 July 2009, pp. 259-263
-
- Article
- Export citation
-
An investigation was made to determine the factors governing the distribution pattern of the larvae of certain species of Melolonthids and Tenebrionids; these are known to be serious pests of tobacco plants in Southern Rhodesia.
Observations were made on mixed populations of the white grubs, larvae of Anomala exitialis Pér. and Schizonycha profuga Pér. (MELOLONTHINAE), on the one hand, and on those of the false wireworms, larvae of Psammodes similis Pér. and P. scrobicollis (Fhs.) (TENEBRIONIDAE), on the other.
It was found that the habitats favoured by white grubs had a higher clay, silt and organic matter content than those favoured by false wireworms. This was indicated by the darker brown colour of the soil; the clay ratio of the soils of the two types of habitat was as 1 to 0·725 and the nitrogen ratio as 1 to 0·524, respectively.
Heavy infestations of tobacco fields are associated with 60,000 white grubs or 1,500 false wireworms per acre. The white grubs complete their life-cycle in one year, the larvae obtaining the food requirements necessary for their develop ment in the 4 to 5 months of the wet season. The false wireworms have a two-year life-cycle, the active feeding stages of the larvae being spread over 18 to 21 months, comprising both wet and dry seasons.
The infestations by the two classes of insect do not overlap in space to any great extent but are governed by the nature of the soil, the white grubs favouring areas in which the soil has a higher nutrient value and the false wireworms areas where the soil is poorer.
Reference is made to parasitisation of white-grub larvae in two areas, where the soil had an abnormally high nitrogen content, by a species of Tiphia in the one area and by entomogenous fungi in the other.
False wireworms have not been found to be similarly attacked under field conditions.
A New Genus and two New Species of Encyrtidae (Hymenoptera, Chalcidoidea) from the Banana Scab Moth, Nacoleia octasema (Meyr.)
- R. D. Eady
-
- Published online by Cambridge University Press:
- 10 July 2009, pp. 667-670
-
- Article
- Export citation
-
The material on which this paper is based was bred from Nacoleia octasema (Meyr.) in New Guinea. The species of the new genus, herein described, was found to be an important primary parasite of the larva. The Tyndarichus species is a hyperparasite.
The new genus is close to Copidosoma and Litomastix, and very closely resembles the other genera of this group in both structure and habits. In the species described below the male is not unlike the males of some species of Copidosoma, and the female resembles Litomastix; the species appears to be polyembryonic. In the present state of the systematics of the ENcyrtidae it is deemed advisable to describe this species under a new genus.
I am grateful to Dr. J. Ghesquière, who consented to examine material of this genus and was generous in his advice and assistance.
Field Trials of the Control of Glossina palpalis (R.-D.) by Obstructive Clearing
- R. J. Kernaghan, J. B. Davies
-
- Published online by Cambridge University Press:
- 10 July 2009, pp. 449-465
-
- Article
- Export citation
-
Two field trials of obstruction (‘ obstructive clearing ’) as a means of control of Glossina palpalis (R.-D.) in locations representative of the Northern and Southern Guinea Savannah zones of Nigeria, are described.
In neither case was complete eradication achieved, pockets of G. palpalis remaining from the beginning at certain points on the main stream. Greater success was obtained in the smaller tributaries, which lent themselves more to obstruction. There was little penetration of G. palpalis for any great distance into obstructed reaches from natural ‘ reservoirs ’ left abutting on to the obstruction, but a trial of the ‘ protective ’ value of obstruction failed, owing to complete penetration in some strength of 300 yd. of obstructed stream on either side of the point to be protected. In neither case was immigration of flies from elsewhere into the trial areas an important factor. Although, at first, the surviving fly population was very localised, there were later indications that dispersal was beginning to take place.
Some accidents which may happen to obstruction are described, with their effects on its ultimate appearance. Consequent to these, a number of factors which limit the wide application of obstruction are stated. The more important of these are: the dimensions of the river-bed, which may be too large to permit of successful obstruction; the presence of wide swampy forest through which G. palpalis ranges freely; alternatively, the presence of shallow rocky stretches with low eroded banks that may be devoid of all but certain characteristic trees, where adequate obstruction is impossible; the rate of run-off of water in the catchment area, rapid run-off leading to spates which disrupt the obstruction; human interference with the obstruction in quest of firewood.
No technical difficulties were encountered in carrying out obstruction, and costs were from 40 to 50 per cent, cheaper than comparable partial clearing.
Considering the subsequent appearance of originally obstructed stream, and its frequent resemblance to partial clearing, the suggestion of ‘ destructive ’ clearing is put forward, in which the top canopy would be destroyed, but no effort made either to create obstruction or to clear away the fallen trees. Instead, reliance would be placed on the action of the various agencies encountered in these trials, which brought about the disruption of the obstruction, to produce the desired end-result.
It is concluded that successful obstruction depends too much on specialised conditions, difficult to fulfil in large-scale tsetse control schemes, and that it is unlikely to become a normal method of control of G. palpalis in the savannah zones of Nigeria.
Studies on the Chemical Control of Cacao Mirids, Distantiella theobroma (Dist.) and Sahlbergella singularis Hagl
- F. Raw
-
- Published online by Cambridge University Press:
- 10 July 2009, pp. 13-23
-
- Article
- Export citation
-
Laboratory and field tests were made to investigate the toxicity, mode of action and persistence of technical DDT and γ BHC when applied to cacao in Ghana to control the Mirids, Distantiella theobroma (Dist.) and Sahlbergella singularis Hagl. The insecticides were tested at concentrations previously used in field trials. D. theobroma, S. singularis and Tribolium castaneum (Hbst.) were used as test insects. Preliminary tests with aldrin, chlordane and dieldrin were also made.
Cacao pods were sprayed to drip point with the test insecticides and the deposit was allowed to dry. Mirid nymphs were placed on the pods and the rate of knockdown and the mortality after exposure for a test period was recorded. These tests showed that BHC had a higher toxicity and acted much more quickly than DDT. BHC greatly reduced feeding.
Fumigant action was tested by spraying cacao leaves to drip point with the test insecticides, allowing the deposit to dry, and then exposing Mirid nymphs and adults over discs cut from the leaves. BHC had a powerful but transient fumigant action; adults, fifth- and second-instar nymphs were killed after, respectively, ½, 4 and 3 hours’ exposure at 28–30°C. over leaves treated with 0·25 per cent, γ BHC. No fumigant effect was observed after prolonged exposure over leaves treated with 2·5 per cent, technical DDT.
Persistence was studied by treating cacao leaves and pods growing under natural conditions and then testing the residual deposit at intervals. Tests with T. castaneum showed that when leaves were sprayed to drip point the residual toxicity of 1·25 and 2·5 per cent, technical DDT fell steadily and was negligible after an interval of three and six weeks, respectively; that of 0·25–2 per cent, γ BHC was negligible after 2–3 days. Corresponding tests with Mirids on pods were less consistent but suggested that 2·5 per cent, technical DDT was still effective against first-instar nymphs after three weeks; 0·25 per cent, γ BHC had a residual toxic effect for at least several days and depressed feeding greatly for at least a fortnight. It is suggested that BHC may have a local systemic action which persists after the surface deposit becomes ineffective.
Of the other insecticides tested, aldrin had a high toxicity and powerful fumigant action and appeared to be the most promising alternative to BHC.
It was concluded that BHC would be more effective than DDT when treating mature cacao because, in addition to its higher toxicity and quicker action, its fumigant action would compensate for incomplete coverage by low-volume spraying.
Observations on an Abnormal Form of Callosobruchus maculatus (F.)
- G. H. Caswell
-
- Published online by Cambridge University Press:
- 10 July 2009, pp. 671-680
-
- Article
- Export citation
-
Under certain conditions, Callosobruchus maculatus (F.) produces males and females which are distinct from the normal ones. These are called here the “ active ” form, and in southern Nigeria they occur most commonly during the months March to June. The active form has a longer pre-adult stage than has the normal form and it flies readily, unlike the normal form. There is some evidence which indicates that a genetic factor is involved in the production of the active form but no clear indication as to what external factors are involved. The normal female has mature eggs in its calyces within a day of emergence, and will lay about 60 eggs. The active female was found to have immature ovaries on emergence and these did not develop to any great extent in the conditions employed. About three-quarters of the active females never produce any eggs, and the rest produce an average of seven. This difference in egg-production probably makes food reserves available which are used to prolong the life of the active female. The eggs laid by active females are rarely fertile, and when adults do emerge they are apparently normal males and females.
Bionomics of the Tea Red Spider, Oligonychus coffeae (Nietner)
- G. M. Das
-
- Published online by Cambridge University Press:
- 10 July 2009, pp. 265-274
-
- Article
- Export citation
-
The red spider, Oligonychus coffeae (Nietn.), is the most widely distributed and probably also the most serious pest of tea in north-eastern India, and also occurs on tea in other parts of India and in other countries. It attacks jute, Corchorus capsularis, in India and has been recorded on a wide variety of other plants in India and other countries.
The life-history of O. coffeae in north-eastern India is described. The duration of the life-cycle varies with the season depending on the temperature and humidity.
In May and June the life-cycle is completed in 9·4–12 days outdoors, while in the cold weather it may take as much as 28 days. The maximum length of life of a female has been found to be 29 days indoors. The males usually die within four or five days. Parthenogenetic reproduction may take place under induced conditions, the progeny being all males.
Red spider normally attacks the upper surface of the mature leaves in which the sap is not flowing freely. In a severe infestation, particularly under conditions of dry weather, the lower surface and the young leaves are almost equally attacked. The affected leaves turn brown, then bronze, and may eventually dry up and fall off.
The red spider mites live under a cover of web that they spin as a protection against inclement weather. The pest occurs in severe form from March to June but with the monsoon rains it practically disappears. A second, light, attack may, however, develop in September or October.
During the cold weather, the mites are present in very small numbers on a few old leaves of the tea bushes, and with the rise in temperature in the spring, they multiply rapidly, resulting in subsequent heavy infestations.
Various factors influence the incidence of red spider and the intensity of its attack. Pruned bushes properly cleaned out are less affected. Bushes defoliated after pruning, and medium pruned tea remain practically unaffectsd. Prolonged dry weather during the early part of the flushing season normally increases the red spider incidence. It prefers bright sun and unshaded areas are more severely attacked.
The red spider spreads from bush to bush by crawling. Dispersal is also effected by various agencies such as wind, cattle, goats and labourers.
A number of predatory insects attack eggs and other stages of the red spider, often keeping it considerably in check.
Biology and Ecology of the Garden Chafer, Phyllopertha horticola (L.). vi.—The Flight Season: Reproductive State of Females
- A. Milne
-
- Published online by Cambridge University Press:
- 10 July 2009, pp. 467-486
-
- Article
- Export citation
-
This part of the study of the garden chafer, Phyllopertha horticola (L) in the English Lake District deals with the reproductive state of the females during the flight season. Total egg-production depends entirely on stores (fat-body) accumulated in the final larval instar. On the average, the fat-body enables about 16 or 17 mature eggs to be manufactured per female, the usual range being 9–32. Rate of reproductive development is the same in the largest and smallest female adults. The outstanding mass features of the flight season are the two roughly equal and half-overlapping Phases: Phase 1, swarming over the grass sward, followed by Phase 2, swarming on the surrounding bracken, hedges and trees. Mass aspects of the female reproductive state throughout the two Phases are as follows.
At primary emergence on the grass sward, females always contain some fat-body together with some fully developed and/or immature eggs. On the average they have about one-third of their full complement of eggs matured, the range being from none (with about 50% of the original fat-body still remaining) up to four-fifths (with about 10% of the fat-body). Since primary emergences in a homogeneous population extend over about a fortnight, females taken from the grass sward throughout Phase 1 are in various reproductive states. Thus after the first few days of the Phase and until the last individual makes its primary emergence, sample females may have half their fat-body and no eggs yet fully matured or no fat-body and all their eggs actually laid, or any intergrade between these extreme states. Towards the end of Phase 1 (which finishes about a week after the last primary emergence), females have no fat-body remaining and have already laid most or all of their eggs; and a small proportion of them now has food in the gut.
In Phase 2, about 99 per cent, of females on bracken, hedges and trees contain no fat-body and therefore cannot manufacture any more eggs. On the average they have two mature or very nearly mature eggs left (range 0–26). This egg content is much the same as at death. The remaining 1 per cent, of females are aberrants with some fat-body still unconsumed. ‘ Bee-liners ’, the females which shoot out bullet-like from the bracken, hedges or trees to alight comparatively far afield, either have some fat-body remaining, or, if not, considerable numbers of eggs (mean about 9 as compared with the general mean of 2). Thus bee-liners are the phase-2 individuals with most eggs still unlaid. Obviously they are a minority.
Deductions as to individual behaviour are made from the mass aspects of the reproductive state and are to be examined in the next paper of this series.
Since females of the garden chafer have already laid all or most of their eggs before appearing on hedges and trees, gardeners will not control this pest by killing all they find on their hedges and trees.
Investigations on Heliothis armigera (HB.) in Uganda
- T. H. Coaker
-
- Published online by Cambridge University Press:
- 10 July 2009, pp. 487-506
-
- Article
- Export citation
-
A survey of the populations of eggs and larvae of Heliothis armigera (Hb.) was made on the Cotton Research Station, Namulonge, in Buganda Province, Uganda, over the four-year period, 1954–57 inclusive, on cotton, maize, groundnuts, beans and, in one year, sunflower. The populations encountered were low in comparison with some other cotton areas in Africa. The oviposition rate on each crop closely followed the flowering cycle, and there was no indication of the population from one crop influencing that on a subsequent crop, even when their flowering cycles overlapped. Under the normal crop sequence there is a sufficient gap between the attractive phases of successive crops to cause dispersal, possibly to wild host-plants, of the moths emerging from pupae bred in the preceding crop.
The variation in population from year to year on a given crop was no greater than that between different localities in any one season. Maize and sunflower did not prove successful when tested as trap crops grown adjacent to cotton.
Earias spp. and Argyroploce leucotreta Meyr. were less abundant than Heliothis and together constituted only 27 per cent, of the total population of Lepidopterous larvae on cotton.
A method is described for breeding H. armigera, in the laboratory, in which the mean duration of the various stages was: egg, 4 days; larva, 24·8 days; pupa, 22·9 days; preoviposition period, 3·1 days; and oviposition period, 10·4 days. The mean number of eggs laid per female was 751·6, of which 71·4 per cent, hatched. Larval diets consisting of differing species and parts of food-plants caused significant differences in larval and pupal periods, the former being least (21·8 days) on maize silks and greatest (33·6 days) on sunflower corolla and receptacle, and the latter least (19·7 days) after larval feeding on three-week-old maize cobs and greatest (26 days) after seven-week-old cotton bolls. Pupae developing from larvae collected from the field did not exhibit any diapause or resting stage.
Two egg parasites and 15 larval parasites (three of which were probably secondary) were bred from material of H. armigera collected in the field, but the degree of parasitism remained low throughout the year. A nuclear polyhedral virus disease of the larvae was also recorded.
It is concluded that under the climatic conditions encountered, H. armigera is active throughout the year because wild or cultivated food-plants are always available and no resting stage of the insect is induced; this continuous activity is accompanied by biologically controlling factors that maintain populations stable at a relatively low level.
The Action of the systemic Insecticide Fluoroacetamide on certain Aphids and on Pieris brassicae (L.)
- W. A. L. David, B. O. C. Gardiner
-
- Published online by Cambridge University Press:
- 10 July 2009, pp. 25-38
-
- Article
- Export citation
-
Fluoroacetamide has been tested as a systemic insecticide against Aphis fabae Scop., Brevicoryne brassicae (L.), Myzus persicae (Sulz.) and the eggs and larvae of Pieris brassicae (L.). In the majority of tests, sodium fluoroacetate and schradan have been included for comparison.
In dipping tests against A. fabae and B. brassicae, fluoroacetamide was as effective as sodium fluoroaeetate and both were much superior to schradan. Fluoroacetamide was superior to sodium fluoroacetate in preventing eggs of P. brassicae from hatching and they were about equally effective against the newly hatched larvae. Schradan was already known to have little action on the eggs or larvae. Neither of the fluorine compounds was very effective against fourth-instar larvae.
When watered on to the soil, fluoroacetamide was more readily absorbed from sand than from soil—like other systemic insecticides. Against A. fabae it was as immediately effective and persistent as sodium fluoroacetate and both were superior to schradan. To B. brassicae and M. persicae, fluoroacetamide was more toxic than sodium fluoroacetate, M. persicae being somewhat more resistant to fluoroacetamide and much more resistant to sodium fluoroacetate. Slight phyto-toxic effects were observed only at the higher dosages.
When poured on to the soil around the roots of cabbage plants, neither compound prevented eggs of P. brassicae from hatching, but the young larvae were killed when they began feeding. Applied systemically in this way, fluoroacetamide was more toxic than sodium fluoroacetate to these young larvae and to fourth-instar larvae.
When John Innes potting compost was treated with solutions of the fluorine compounds and stored in the greenhouse it was found that both compounds were quickly decomposed at the dosages necessary for systemic action against aphids, but higher dosages were much more persistent.
In solution, given systemically via the roots to broad beans, fluoroacetamide and sodium fluoroacetate were about equally effective and both were more toxic than schradan to A. fabae. Fluoroacetamide was the more toxic of the fluorine compounds.
The technique of the cut tap-root showed that the approximate LD 100 for A. fabae on broad beans was: fluoroacetamide between 0·09 and 0·9 mg./kg.; sodium fluoroacetate 0·7 mg./kg.; schradan 50 mg./kg. When taken up by cabbage leaves through the cut petioles, 5 mg. of the fluorine compounds or 50 mg. of schradan per kg. of fresh plant tissue killed all B. brassicae in 2–3 days.
Leaves of cabbage treated in the same way with fluoroacetamide were fed to larvae of P. brassicae. It was found that the growth of the larvae feeding on the leaves was not prevented until a dose of about 20 mg./kg. was reached. The same value was found for sodium fluoroacetate. For schradan, more than 2,900 mg./kg. were required.
Finally, with applications made to the older leaves against all these species of aphids feeding on the younger leaves of their host-plants, fluoroacetamide was equally effective or slightly superior to sodium fluoroacetate as a systemic insecticide. Schradan was nearly as effective against B. brassicae but much less effective against the other two aphids.
Even after repeated applications none of the compounds acting systemically prevented eggs of P. brassicae from hatching or had a detectable toxic action on fourth-instar larvae.
The Breeding Behaviour of the Type Form of Aëdes (Stegomyia) aegypti (L.) in south-western Nigeria in Relation to Insecticidal Control
- Gordon Surtees
-
- Published online by Cambridge University Press:
- 10 July 2009, pp. 681-686
-
- Article
- Export citation
-
The type form of Aëdes (Stegomyia) aegypti (L.) is widespread in southwestern Nigeria, breeding in the basins of rotting tree stumps in the coastal mangrove swamp, in holes in living trees in the freshwater swamp zone and near Lagos and in domestic containers restricted to village clearings in the inland forest zone. Pot surveys were carried out in a rain forest village 50 miles north-west of Lagos and in the capital itself. Baked clay pots holding half a gallon of water were used in each case and were placed in three situations, inside houses, outside but in otherwise sheltered positions, and in fully exposed positions. The degree of larval infestation in both cases was greatest inside houses, but the behaviour pattern was less domestic in Lagos. Larvae were found in pots contaminated with decaying vegetable matter in Lagos but not in the village. Spraying tests indicated that houses and foliage afforded varying degrees of protection to the immature stages of the mosquito. Control of this species is made difficult by the localisation of the immature stages in relatively inaccessible sites and it is suggested that individual treatment of larval habitats by insecticidal pellets before the commencement of the rainy season would ensure a high mortality of first-generation larvae. The toxicity hazard to man is not considered to be great. The development of resistant and wild populations is discussed.
Transect Fly-rounds in Field Studies of Glossina
- J. Ford, J. P. Glasgow, D. L. Johns, J. R. Welch
-
- Published online by Cambridge University Press:
- 10 July 2009, pp. 275-285
-
- Article
- Export citation
-
The fly-round has for long been regarded as the most satisfactory way of following fluctuations in populations of tsetse flies (Glossina) and locating areas of concentration. It consists of a path cut through bush so as to traverse the principal vegetation communities and is divided into sections, corresponding to the latter, on each of which the flies are caught. A modification now widely used but not previously described in detail is termed a line transect or transect fly-round; this follows an arbitrary course along straight lines that may be orientated with regard to the topography and is divided into numerous short sections of equal length terminating at posts at which flies are caught. In its simplest form it follows a straight course, but various patterns are used including an angular spiral. It facilitates the collection of quantitative data on tsetse density and the factors (such as vegetation) that affect it, and their analysis is possible in more detail than was the case when the fly-round was laid out according to a pre conceived notion of vegetational relationships. This is illustrated by data from a fly-round at Shinyanga, Tanganyika, consisting of six sides, each of 2,000 yd., of two diagonally adjoining squares, that was divided originally into nine sections of varying lengths representing the floristic communities traversed, and subse quently into 120 sections each 200 yd. long. Comparison of the catches of non-teneral males of G. swynnertoni Aust. grouped according to the two methods emphasises the much greater detail provided by the second of them. The transect fly-round is easy to lay out and operate and is thought likely to be particularly useful in connection with reclamation work.
The effect of varying the section length was investigated for G. swynnertoni at Shinyanga, G. pallidipes Aust. in Nyanza Province, Kenya, and G. austeni Newst. in Zanzibar. With the first, progressively fewer flies of all categories except teneral males were caught as the section length was increased progressively from 50 to 200 yd.; with the other species a similar tendency was apparent, but not significant. The results emphasise a point long recognised but often neglected, that data from fly-rounds reflect, in part, the reaction of tsetse populations to the behaviour of the catching party. That this reaction, termed the availability, is itself inconstant is shown by catches of G. pallidipes on a fly-round done daily for a month, in which differences between catches on consecutive days, sometimes exceeding 3:1, must represent changes in availability, not in absolute population.
Data from the transect fly-round can be analysed so as to indicate sections where the catches deviate significantly from those expected on the assumption that they are distributed according to a Poisson series, and where there may thus be presumed to be areas of concentration of the population, or the reverse. A Table is provided to facilitate such analysis.