The use of biogeographical techniques for monitoring, mapping and predicting seasonal changes in the distribution of migrant noctuid moths in a country or region, can lead to timely and effective control of infestations of the larvae of international pest species like the African armyworm, Spodoptera exempta (Wlk.); the American bollworm, Heliothis armigera (Hub.); the Black cutworm, Agrotis ipsilon (Hufn); the cotton leafworm, Spodoptera littoralis (Boisd.) etc., and hence to the protection of crops and pasturelands. Methods of data collection include the establishment of national and regional networks of monitoring devices such as light and pheromone traps, and the introduction of regular or periodic standard procedures for recording, reporting and assessing infestations of larvae. Techniques for collecting and analysing the data include the use of: (a) dots, circles or similar marks on topographic or weather maps to plot the occurrence of moths and/or larvae at the latitudes and longitudes of outbreak sites, followed by the dates when infestations were confirmed; (b) numerical symbols (e.g. 1–12 for January to December) on the above maps in order to summarize periodic (e.g. monthly) shifts in the distribution of populations within or across neighbouring countries; (c) colour codes or other graphic symbols to plot maps of pest distribution and migration over the required time-scale, followed by the study of appropriate synoptic weather charts, particularly streamline wind charts showing surface and low-level wind convergence zones over the distribution areas. Successful application of these techniques have included studies of changes in the distribution and migration of: (a) A. ipsilon worldwide; (b) Desert locust in Africa and Asia; (c) S. exempta in Africa and S.W. Arabia etc. In the 1981/82 outbreak season, for example, dots (•) were used to map out and date south-to-north displacement of populations of S. exempta across eastern Africa from Tanzania to Ethiopia between November 1981 and June 1982; while in 1980/81, numbers (1–12 for January-December) were plotted to summarize outbreaks developing between Ethiopia and Tanzania. Successful monitoring and assessment of mass movement of moths between Tanzania, Kenya and Uganda early in the 1981/82 season, for example, enabled the Armyworm Forecast Service to issue accurate forecasts for the first cross-border migrations of moths between the three countries from the second week of February 1982, leading to effective control of larvae to save cereal crops, sugar-cane and pasture grasses in East Africa.

The seasonal distribution and abundance of adult Temnoschoita quadrimaculata Gly., a pest of oil palm in Ghana was studied. The weevil occurred throughout the year with a peak of abundance from March to June. It preferred breeding in cut fronds which result from harvesting or pruning and was more abundant in 3–6 days old cut fronds.

Adult weevils preferred the upper third portion in comparison to the lower and middle third portion of the palm tree. Their incidence and abundance in pruned plantations was statistically greater (P < 0.05) than in unpruned plantations. Older palm trees were relatively more susceptible to attack than younger ones. Adult weevils preferred feeding on the fresh frond tissues than on leaflets.

The queen's fresh weight can be deduced from her external dimensions, or less accurately from the size of the royal cell in the case of single queens. Cell shapes and methods of enlarging the cell are described.

The African armyworm is a migrant moth which, in its larval form, can cause severe plagues which destroy cereal crops, sugarcane and pastures in many parts of Africa. This paper reviews the relevant aspects of a multidisciplinary study into the dispersal behaviour and re-concentration of moths, migratory flight, source areas, population upsurges and the seasonal movement of moths. It introduces the new concepts of primary and critical outbreaks.

Mythimna separata, the oriental armyworm, is a major agricultural pest of China. Five breeding regions are colonized successively by each generation of moths during the course of the year as a result of long-range migration. Three regions are colonized from south to north of China during the first half of the year and two in the second half of the year, possibly from north to south. The regularity of the seasonal displacements of the armyworm populations are an important basis for forecast and control. This paper presents a summary of research on migration of the oriental armyworm in China and discusses management strategies for this pest.

Field and laboratory evidence now suggests that the African armyworm, Spodoptera exempta, is specifically adapted for survival at low population densities, providing a new basis for understanding the significance of its phase polyphenism and migratory strategy. This conclusion allows deductions to be made as to the expected extent of displacement of flying moths from low and, when they occur as a result of impeded or inadequate dispersal of parent moths, high density populations. The proposed migratory strategy which depends on the genetic determination of flight potential also provides a framework for interpreting observed patterns of armyworm outbreaks through the season and in relation to rainfall. Traits associated with a low-density, “armyworm” strategy are shared by other Noctuids which may have similar life histories.

The effects of larval population density and food quality on the velvetbean caterpillar, Anticarsia gemmatalis Hübner, were compared with investigations of other migratory noctuids. Crowded larvae of the velvetbean caterpillar responded with: (1) an increase in the degree of dark pigmentation; (2) a decrease in larval, pupal and adult size; (3) a prolongation of the larval stage and a decrease in weight gain in the ultimate stadium; and (4) low juvenile hormone and juvenile hormone esterase haemolymph titres.

The effects of flight, throughout a 4 hr flight period, on the haemolymph titres and whole body contents of carbohydrate and lipid are presented for the velvetbean caterpillar and discussed relative to other noctuid moths. Total carbohydrate concentration decreased during the first 30–45 min of flight, and total fatty acid concentration increased during the first 30–60 min of flight, after which it declined and stabilized at preflight levels. Lipid reserves and the small amount of lipid depletion after long periods of flight indicated that velvetbean caterpillar adults are capable of making long distance movements in which lipid is the principal flight fuel.

Juvenile hormone regulated the effect of density on larval colour, size and growth rate. Applications of juvenile hormone to crowded larvae increased the proportion of the lighter (green), larger and faster developing phase. This hormone action suggests that the juvenile hormone titre of crowded larvae is lower than that of uncrowded larvae.

Genetic differentiation among populations of velvetbean caterpillars suggests that south-central United States populations originate from overwintering populations in Mexico or south Texas. A system has been developed, using pheromone-baited bucket-type traps, to investigate the population dynamics and migration of the velvetbean caterpillar in Louisiana and Texas.

Each summer the true armyworm, Pseudaletia unipuncta (Haw.), like many other noctuid species, establishes temporary populations in habitats considerably north of areas where permanent populations persist. Data are presented in support of the hypothesis that P. unipuncta is a seasonal migrant and not a victim of an agricultural “Pied Piper” phenomenon. It is proposed that the spring northward migration occurs to avoid the deleterious effects of summer temperatures and the southward fall one to escape severe winter conditions. It is also argued that both spring and fall migrations are initiated by similar short-day, low temperature conditions, which serve as predictable environmental cues for an impending habitat deterioration.

Comparisons of numbers of Heliothis armigera moths, caught in a light trap at ICRISAT Center (17°N 78°E), with wind direction has provided circumstantial evidence for windborne migration in India. The evidence is less convincing than that from northern Europe, possibly because flying populations are present around the trap throughout the year, although varying greatly in numbers between seasons. Comparisons were made for occasions when trap catch rose or fell over four successive nights with a correlation coefficient ≥0.9 and rate of catch change > 1 moth/night. Catch rises were used from only those parts of the lunar cycle when falls would be expected, and catch falls from those parts when rises would be expected. During the period May 1977 to December 1983 there were 23 rises and 16 falls. Rises occurred mostly during the seasons of maximum catch. All seven rises in February–April occurred with southeasterly winds, even though such winds blow on average only half the time in those months. These rises sometimes coincided with onset of southeasterlies; at other times there was a lag, consistent with flight from distant sources. Similar migrations seem possible in October–December, sometimes in the presence of cyclones over the Arabian Sea. The evidence for migration in August at ICRISAT, and in all seasons at ICRISAT Sub-Center, Hisar (29°N 76°E), is inconclusive.

This symposium has been one of the most stimulating and enjoyable I have attended, both for the content of the invited papers which have been of a high standard and which have complemented each other so well and for the informal talk and discussions they have generated. The task of summing up has, therefore, been easy on the one hand in that there is no shortage of themes and points to develop but difficult in that there are far too many to do justice to in the time available.

For convenience, I shall consider the points I want to raise under three main headings.

In the first section of this review, the stimuli involved in orienting biting flies to their hosts from a distance are discussed under the following headings: (1) Appetitive search—driven by endogenous rhythms and hunger. (2) Activation—the switchover from search behaviour to active host-location brought about in the insect by host-originating stimuli including, depending on species, carbon dioxide, visual contact, and specific host odours. (3) Attraction—the process of active host-location through which the insect comes into the immediate vicinity of the host. This relies on host-originating stimuli including visual contact and olfactory stimuli such as carbon dioxide, volatiles such as acetone, and specific, usually very potent host-related odours.

The second part of this review discusses the properties of the odour plumes biting flies rely on to locate the host. Possible methods of host-location using air-borne odour plumes are presented and the “positive anemotaxis” model based on moth pheromone work is stressed.

Defensive behaviour is one of the principal ways vertebrate hosts regulate the blood-feeding success of vector insects. Intrinsic variation in the intensity and efficiency of this biting avoidance behaviour depends on host: (1) species, (2) size, (3) age, (4) health and (5) individuality. In this paper we summarize data on the relative importance of each of these host-associated factors in regulating mosquito feeding and transmission of mosquito-borne diseases.

Gorging is stimulated in some insects by plasma components alone. In other insects engorgement is maximal only when blood cell components are present in addition to the plasma. Plasma components recognized by insects are NaCl, NaHCO3 (some anopheline mosquitoes) and albumin (Anopheles dirus and Pediculus humanus). Those requiring blood cells recognize this fraction by its adenine nucleotides which, for optimal engorgement, have to be offered in the presence of isotonic NaCl solution buffered by NaHCO3 (i.e. Rhodnius, culicine mosquitoes, Simulium, tsetse and Tabanus). The presence of albumin in the feeding medium may lower the level of nucleotides required to induce gorging (i.e. Aedes).

For most haematophagous insects requiring the cellular fraction, ATP is the most effective phagostimulant. It may however be replaced quite effectively by non-hydrolyzable analogues, indicating that ATP is not essential as a source of energy for the gustatory receptors involved in blood meal recognition.

The morphology of the sensilla sensitive to vertebrate host-associated stimuli is diverse reflecting the numerous independent origins of haematophagy within the insects. Using electron microscopic techniques, the sensilla of mosquitoes and blackflies have been the most thoroughly studied, although numerous works have been conducted on other blood-feeders. Notably lacking are fine structure studies on blood-feeding maggots and ectoparasitic, adult Muscomorpha.

In comparing blood-feeders with other insects it becomes apparent that: (1) carbon dioxide plays a significantly greater role in location of food by haematophagous insects than by phytophagous and saprophagous species; (2) only in blood-feeders do the adenosine phosphate nucleotides, a single group of compounds, appear to be the phagostimulants for almost all species; and (3) feeding deterrents are unknown in haematophagous insects.

When the sensory complements of the various groups of blood-feeders are compared, three points emerge. First, reduction in numbers of olfactory chemosensilla that mediate odour cues used in long-distance, host-orientation occurs in male nematocerans and in females of completely autogenous species of mosquitoes and black flies. Second, there is a striking correlation between the number of labial chemo- and mechanosensilla and the feeding behaviour of the insect. Third, there is a possible positive correlation between the number of chemosensitive antennal neurones and the distance travelled by the insect to the host.

The behavioural process by which a mosquito finds a potential host organism is mediated by olfactory receptors on the insect's antennae. Lactic acid (LA) is a host-related odour common to all potential hosts. On the antennae of the female are two LA-sensitive neurons; one of these is excited by LA but the other is inhibited by LA. Furthermore, the sensitivity of the LA-excited neuron is correlated 1:1 with the presence of host-seeking behaviour such that when host-seeking behaviour is inhibited following a blood meal, the sensitivity of the LA-excited neuron is markedly decreased. The inhibition of host-seeking behaviour and the decrease in LA-sensitivity are induced by a hemolymph-borne factor released during oocyte maturation. The source of this factor is the fat body of blood-fed females, which requires a vitellogenic ovary for its production and/or release. The combined activity of the two types of LA-sensitive neurons together with the shift in sensitivity of the LA-excited neuron from a range where host levels of LA are present to a range exceeding LA levels expected from a host are sufficient to account for the inhibition of host-seeking behaviour following a blood meal.

Host location and feeding among ticks involves positioning for host findings, probing, attachment, imbibing blood and thereafter detachment. Different species of ticks fulfil this sequence of events in different ways. Behavioural differences are mainly due to sensory inputs obtained by a tick and the processing of that input by the central nervous system. Tick receptors responsible for perceiving stimuli originating in the general environment and the host in particular are located on the tarsi and mouthparts. This review gives a brief account of current knowledge on sensory receptors involved in the above behavioural patterns.

Economics can make an important contribution to the evaluation of pest management projects. It provides a conceptual basis and tools for assessing the economic losses caused by pests and, therefore, the potential benefits of control. Economics is also concerned with the degree of adoption and the extent to which the potential benefits of a project are likely to be realized in practice. Since agricultural pest problems and control options are continuously changing, with changes in cropping practices, policies and economics, and technological developments, research evaluation must also take these aspects into account. Examples concerning rice pest control in Malaysia and cattle pest management in Brazil are used to illustrate these points.