Chemical inhibition of feeding has been studied in detail for only a few insect species, but inhibitory chemicals play a considerable part in host-plant selection by a wide range of phytophagous insects from several orders. Many different chemicals are involved, some of them amongst the normal constituents of plants. A few have a general effect, preventing feeding by all the insects which have so far been tested, but the majority are effective only against some species.

Inhibition may function by blocking the input from receptors normally responding to phagostimulants or by stimulating specific ‘deterrent’ cells. The former may have a general effect on all insects, but chemicals in the latter category will only be effective if the insect has neurones capable of responding to them. Hence these will have more specific effects.

Inhibitory chemicals may be applied to plants in the same way as insecticides, their advantage being that the parasite/predator complex of species not feeding directly on the plant will be unharmed. An alternative approach is to breed resistant varieties of plants by selecting for inhibitory attributes. Although many varieties of crops are known which are insect-resistant, the basis of the resistance is generally unknown. A more thorough understanding of the mechanisms involved in inhibition of feeding by chemicals would enable a more logical approach to be made to the development of resistant plants.

The stage of egg formation and density of follicular relics enable Lucilia cuprina (Wied.) females to be sorted into 16 ovarian stages, covering the period from emergence to the beginning of the fourth ovarian cycle. The correspondence between the actual age of a fly and its stage of ovarian development was determined at constant temperatures. Where developmental delays were absent, “reproductive age” gave reliable estimates of actual age under both constant and fluctuating temperature regimes. In the field protein shortages and lack of oviposition sites may prolong the time required to complete each ovarian cycle, and flies will be older than their ovaries would indicate. In practice the ovarian stages described provide estimates of minimum age for L. cuprina females.

A method is described by which Culicoides variipennis (Coq.), C. riethi Kieff. and C. nubeculosus (Mg.) have been maintained as laboratory colonies for over five years. Techniques are given for the maintenance of adults, larvae and pupae; with some modifications these could probably be applied to a range of other species. Adult midges were held in waxed card pill boxes, and provided with sugar solution. Anaesthetised mice provided a blood-meal source. Larvae were reared in pans on a substrate of glass fibre in a medium which contained nutrient broth, grass meal and Bemax. The life-cycle of these species occupies 10–21 days at 23–25°C.

A pheromone trap is described which records the exact time individual male moths enter a trap. This apparatus was operated for approximately three months at two sites in Cyprus. Continuous recordings were made of wind speed, wind direction, temperature and relative humidity near the trap site. Males of Spodoptera littoralis (Boisd.) were generally attracted to a trap baited with S. littoralis virgin females for the first two to three hours after dark. Males of S. exigua (Hb.) arrived most frequently at a trap baited with S. exigua females between 03.00 and 04.00 h. A relationship between wind speed and numbers of males of S. littoralis recorded was found at one site; for winds at a height of 1–37 m varying between 0·8 and 5·2 m s-1, increased wind speed resulted in an increase in the numbers of males recorded. Increase in relative humidity at one site was associated with a decrease in the number of males recorded. No apparent relationship was established between temperature and the number of males recorded, other than the fact that below 13°C many fewer males arrived at the trap. The implications of these findings in relation to movement of adult male S. littoralis are discussed.

A study was made between 1967 and 1971 at Edinburgh University and at EAVRO, Muguga, of the variability in feeding performance of all three instars of Rhipicephalus appendiculatus Neum., with a view to better prediction of transmissions of Theileria parva. Variability could be definitely ascribed to factors within the ticks only when vigour was reduced after prolonged storage and when mating opportunity was withheld from attached females. Lower environmental temperatures prolonged engorgement, but it was arguable whether this effect was produced through the tick or through the host. All other sources of variability arose from influences within the host. The most significant of these were recognised in responses by rabbits in which resistance had been induced by successive infestations. Resistance was manifested by prolonged engorgement, by a reduction in numbers engorged and in degree of repletion, and by an increasing severity in host reaction. Three resistance mechanisms were suggested by host reactions—one appearing at the earliest stages of attachment, a second with the deposition of cement, and a third at the start of salivation. Each varied in efficacy, and each was capable of arresting an infestation. Cumulative and synergistic responses were ascribed to interactions between these mechanisms. Storage periods, sizes of infestations and sex ratios of R. appendiculatus were standardised within routine procedures, and abundant records of previous and subsequent performances on rabbits and cattle are presented for comparison and reference. Comparison of feeding performances on different animals suggests that cattle, buffalo, eland, waterbuck and oryx are as satisfactory as hosts as the rabbit, whereas Thomson's gazelle, wildebeest, sheep and goat are less so. Immature instars successfully completed engorgement on mongoose, cane rat, genet, domestic fowl and spur-fowl.

The occurrence and causes of plagues of tropical Locusta spp. are compared for the three major outbreak areas, Middle Niger of Mali (L. migratoria migratorioides (R. & F.)), south-west Madagascar (L. m. capito (Sauss.)), and Mindanao (Philippines) (L. m. manilensis (Meyen)). Multiplication and concentration are the two most important processes involved and may occur concurrently or sequentially depending on the outbreak area. In the Middle Niger and Madagascar heavy rainfall, through its effect of increasing multiplication, is the key density-disturbing factor, whereas on Mindanao the factor is drought leading to concentration of locusts. Variations in multiplication rates are determined by the response of eggs and hoppers to desiccation and by the density-dependent effects of fecundity and natural enemies. Concentration is caused by the restriction of favourable breeding habitats in relation to the seasonal population displacements and, because it occurs at different seasons in the three outbreak areas owing to their differing climates and geographies, profoundly modifies the timing of outbreaks. Man's modification of the environment, particularly in relation to the dry season survival of Locusta, has caused outbreaks to occur in new areas. Long-term solutions to the problem of controlling such outbreaks lie in the field of management rather than in the continued use of insecticides because of the continued reinfestation from surrounding populations. The use of natural enemies does not as yet show any promise as a means of controlling outbreaks of tropical Locusta.

The amounts eaten by Locusta migratoria migratorioides (R. & F.) on seedling grasses was less than on mature grasses in four other Acridids, Nomadacris septemfasciata (Serv.), Chortoicetes terminifera (Wlk.), Melanoplus sanguinipes (F.) and Schistocerca gregaria (Forsk.). Palatability of the young grasses increases with age, becoming maximal 6–10 weeks from the time of germination. Similar preferences were shown by other Acridids. Time-lapse film studies on Locusta showed that not only is less time spent feeding on seedling grasses, but that locomotor activity levels are considerably higher. Survival studies on the same species showed higher mortality on the seedlings as compared with the mature leaves at all stages of nymphal development, while on seedlings no individuals survived to the adult stage. Lipid-soluble materials were removed from seedling leaves with chloroform or acetone and this rendered them more acceptable, while the extract applied to mature leaves resulted in reduced palatability.

The embryonic development of Dysdercus fasciatus Sign. is described in terms of 15 arbitrary stages based on external morphological characters. The effects of treating eggs early in development with juvenile hormone and a mimic (JH) are then described in terms of the stages at which embryonic development is arrested and the resulting morphological aberrations are summarised. The effects of the treatment of two strains of D. fasciatus with two JH (Law's mimic and Ayerst synthetic juvenile hormone) are described and compared in terms of both the hatchability of the eggs and the stage distributions of the arrested embryos. Law's mimic was more effective than Ayerst SJH in preventing egg hatch, and the Malawi strain was less susceptible than the Reading strain. Embryonic development was never arrested earlier than the commencement of blastokinesis (Stage VIII). After treatment with Ayerst SJH most embryos of both strains were arrested during dorsal closure (Stages XI-XII) or at the time of eclosion (Stages XHI-XIV). Treatment of the Reading strain with Law's mimic resulted in the majority of embryos being arrested during blastokinesis (Stages VIII-X) at all doses. Examination of the timetable of development in both control and treated eggs reveals a dramatic reduction in developmental rate in treated eggs at the commencement of blastokinesis. It is suggested that JH may act on eggs of D. fasciatus in three ways: interference with eclosion, differentiation and the embryonic movements during blastokinesis.

The subgenus Larroussius of Phlebotomus includes several vectors of visceral leishmaniasis. A key is given for the tropical African species, three of which are described for the first time. Notes on the species include a discussion of the status of P. langeroni orientalis Parrot, one of the three species from the Ethiopian Region known to transmit leishmaniasis.

This paper describes the method used to produce maps of the incubation and hopper development periods of the desert locust Schistocerca gregaria (Forsk.). From these maps it is possible to calculate the likely development periods of eggs and hoppers for, respectively, laying and hatching on any date and at any place within the invasion area of the species. Maps could not be based on actual observations of development periods because such observations are few in number, irregular in distribution and are not for standard dates. Instead, expected mean development periods for laying and hatching on the first of each month were calculated for a large number of meteorological stations for which long-term mean temperatures were available, using relationships between the rates of development and mean daily screen temperatures. These relationships were, in the main, derived from earlier work by one of the authors (K.G.W.) and his associates. Some assessment has been made of the accuracy of development periods derived from the maps.

The north-western European species of the glomeratus-group of Apanteles are revised. Sixty-four species are dealt with, of which twentythree are described as new. Two species, A. pieridis (Bouché) and A. pilicornis Thomson, are lifted from synonymy. Host records are based mainly on reared specimens examined by the author.