In 1988/89 the nature and degree of hyperparasitism in two newly introduced parasitoids of exotic mealybug plant pests were examined in Togo. Associated with Phenacoccus manihoti Matile-Ferrero (Hemiptera: Pseudococcidae) (cassava mealybug) five indigenous hymenopterous hyperparasitoids were found adapted to the primary parasitoid Epidinocarsis lopezi (De Santis): Chartocerus sp. A (Signiphoridae), Prochiloneurus insolitus (Alam), P. aegyptiacus (Mercet) (Encyrtidae), Tetrastichus sp. (Eulophidae), and Marietta leopardina Motschulsky (Aphelinidae). The rate of hyperparasitism varied considerably (20–90%). At one sampling site Chartocerus sp. A was most frequent (52%), at the other site P. insolitus was found to dominate (55%). The same hyperparasitoids were associated with Rastrococcus invadens Williams (Hemiptera: Pseudococcidae), but with an additional Chartocerus (sp. B). Hyperparasitism ranged from 56 to 86%, with Chartocerus sp. A being the most important species. Multiple parasitism was observed on several occasions. In spite of generally high hyperparasitism, no detrimental effect on the control efficiency of either primary parasitoid was noticed.

Schembria eldana, a new species of goniine Tachinidae, is described (both sexes) from north-eastern Natal, South Africa, where it is parasitic on larvae of the sugarcane borer, Eldana saccharina Walker, in Cyperus papyrus umbels. The genus Schembria Rondani was previously known only from two females of S. meridionalis Rondani from Malta and Israel.

The comparative influence of Busseola fusca (Fuller) and Chilo partellus (Swinhoe), both as separate and mixed populations, on growth and yield of grain sorghum was investigated in a field experiment, using an artificial infestation in cages. C. partellus was more injurious than B. fusca as indicated by whorl damage, stalk injury and yield loss. In the case of mixed populations, dispersion of larvae and damage were independent of B. fusca numbers. A regression equation, Logit Y = 0.24 + 2.06 logit x, relating visible plant damage to yield loss was determined. Control strategies in the case of mixed stem borer populations should be directed against C. partellus.

During initial screening of the synthetic pyrethroid lamdacyhalothrin (PP 321) at a concentration of 44 and 22 mg/l and applied as a 30 ml drench over each plant against third to fourth instar cutworms, Agrotis segetum (Denis & Schiffermüller) in microplots, few died but they did not damage the plants. Reducing the concentrations to 11 and 5.5 mg/l increased mortality and plant damage. When A. segetum were confined on soil treated with the insecticide at concentrations of 22, 11 and 5.5 mg/l and sprayed at an equivalent rate of 500 l/ha, they all died within one day. The higher concentrations appeared to have a repellent and/or antifeedant effect, and it has been possible to reduce the concentration of lamdacyhalothrin to 12.5 mg/l (≡5.6g a.i./ha) for the drench treatment without risking economic plant damage. For insecticides that have repellent and/or antifeedant properties, it should be possible to balance lower concentrations with adequate protection of plants from pest damage.

Aponephus lentiformis, a new genus and species of Coccinellidae, is described from southern India and placed in the tribe Scymnini. It was found during searches for natural enemies of Rastrococcus spp.

Lactic acid, carbon dioxide and human sweat stimuli were presented singly and in combination to female Aedes aegypti (Linnaeus) within a wind-tunnel system. The take-off, flight, landing and probing responses of the mosquitoes were recorded using direct observation and video techniques. The analyses determined the nature of the response to different stimuli and the concentration ranges within which specific behaviours occurred. A threshold carbon dioxide concentration for taking-off of approximately 0.03% above ambient was detected. Lactic acid and human sweat samples did not elicit take-off when presented alone, however, when they were combined with elevated carbon dioxide, take-off rate was enhanced in most of the combinations tested. Flight activity was positively correlated with carbon dioxide level and some evidence for synergism with lactic acid was found within a narrow window of blend concentrations. The factors eliciting landing were more subtle. There was a positive correlation between landing rate and carbon dioxide concentration. At the lowest carbon dioxide concentration tested, landing occurred only in the presence of lactic acid. Within a window of low to intermediate concentrations, landing rate was enhanced by this combination. At the highest carbon dioxide concentration, landing was however inhibited by the presence of lactic acid. The sweat extract elicited landings in the absence of elevated carbon dioxide. This indicated the presence of chemical stimuli, other than lactic acid, active in the short range. Probing occurred only at low carbon dioxide concentrations and there was no probing when lactic acid alone was tested. There was however probing in the presence of combined stimuli, the level of response seemed to be positively correlated with the ratio of carbon dioxide and lactic acid concentrations.

Rice plants, infested with eggs of Nilaparvata lugens (Stål) or Nephotettix spp. in laboratory cultures, were used to trap egg parasitoids in rice fields at two sites over a period of four days in Sri Lanka. Levels of egg parasitism per plant varied from 0 to 54% in N. lugens and 45 to 100% in Nephotettix spp. Egg predation was a minor cause of mortality, but attack by a species of Panstenon (Hymenoptera: Pteromalidae) killed up to 18% Nilaparvata lugens eggs. N. lugens eggs were parasitized by Anagrus sp. nr flaveolus Waterhouse, A. optabilis (Perkins) (Hymenoptera: Mymaridae) and Oligosita sp. (Hymenoptera: Trichogrammatidae). Nephotettix spp. eggs were parasitized by two species of Gonatocerus (Hymenoptera: Mymaridae) and one of Paracentrobia (Hymenoptera: Trichogrammatidae). There was no overlap in field host range between the two parasitoid assemblages. Gonatocerus spp. and Paracentrobia spp. seldom attacked the same Nephotettix sp. egg batch, suggesting the possibility that these species compete in the field. Overall egg parasitism of Nilaparvata lugens was positively related to host egg density at the spatial scale of the rice plant, but unrelated at the tiller or batch scale. Nephotettix spp. egg parasitism showed a negative density dependent relationship at the spatial scales of the tiller and plant and no relationship at the batch level. The potential role of these egg parasitoids in preventing outbreaks of hopper pests in Sri Lanka is discussed.

The coccinellid biocontrol agent Chilocorus nigritus (Fabricius) can be established on the non-target scale Asterolecanium sp. (Hemiptera: Asterolecaniidae) on giant bamboo Dendrocalamus giganteus. When these sites are adjacent to citrus orchards, the coccinellid readily moves across to reduce population levels of the target prey, red scale Aonidiella aurantii (Maskell) (Hemiptera: Diaspididae). C. bipustulatus (Linnaeus) and C. infernalis Mulsant are potential new biocontrol agents against A. aurantii in South Africa. Each life stage of C. nigritus, C. bipustulatus and C. infernalis has advantages and disadvantages for field introductions. This paper investigates different methods of introduction of the different life stages for field establishment. A number of synthetic materials were tested as egg pads for C. infernalis without success. Introduction of eggs adhering to stiff paper cards was unsuccessful and impractical for all species. Eggs, young larvae (first and second instars), older larvae (third and fourth instars) and adult C. nigritus were introduced into stands of bamboo. The adult was the most suitable life stage for establishment followed by older larvae, then younger larvae, with the least suitable being the egg stage. Adults of the three species were released on to scale-infested bamboo at two sites to evaluate the viability of such introductions and to compare their persistence at these sites. C. nigritus and C. infernalis persisted at one release site through the winter and the hottest period of the summer.

The effects of crowding and photoperiod during rearing of Mythimna convecta (Walker) on oocyte development in adult females were measured in the laboratory and field. Most larvae reared under isolated conditions in a Light 12 h: Dark 12 h photoperiod had mature oocytes within 72–84 h of eclosion. Females were slower to mature when reared under longer daylengths. The mean oocyte width in 3–10 days old females was significantly lower for moths reared under long (Light 16 h: Dark 8 h) than equal (Light 12 h: Dark 12 h) daylengths. Crowding of larvae also prolonged the pre-reproductive period. In the laboratory, 47% of females had arrested oocyte development of 3–6 days after eclosion and, in the field during late winter/spring, 48% of females required 3–9 days to mature. Larvae were collected from late spring/summer populations and caged under high and low density conditions. All females emerging from both treatments had arrested oocyte development of at least seven days. In catches from baited moth traps run over the same period, the proportion of immature female M. convecta was lower during spring (18–30%), than in summer (60%) and, in both seasons, mating commenced before oocytes had matured, but after oocyte arrest. Long daylength appears to be only one of several contributing factors causing delays in ovarian development during summer. Delays in achieving reproductive maturity, induced by either crowding or summer conditions, may assist M. convecta to emigrate from unfavourable habitats. This is particularly relevant in the winter rainfall areas of south-eastern Australia where most food plants senesce in summer and suitable habitats are usually confined to the coast.

The new age determination technique for tsetse flies based on the accumulation of fluorescent pigments in the head capsule has the minor problem that it is not possible to accurately identify very young flies. In this paper we describe a technique for the identification of very young Glossina morsitans morsitans Westwood based on their high levels of abdominal fluorescence. Under our holding conditions these fall back in a linear fashion to a minimum at five days post-emergence. The variability in the levels of head fluorescence at eclosion is mainly influenced by the size of the emerging fly, with the number of blood meals taken by the female parent, and intra-uterine larval and puparial periods of the emerging flies also playing a part.

Cypermethrin, profenofos, and a mixture of these insecticides were evaluated against resistant and susceptible whitefly, Bemisa tabaci Gennadius, from Sudan using (a) laboratory technology which simulates the aerial spraying of whitefly infestations on cotton crops, and (b) standard residue-bioassays. Simulator tests in which adult cohorts were given a single insecticide treatment produced results that were unexpected on the basis of standard bioassay data. Resistance to cypermethrin, for example, was expressed in the bioassays but not in the simulator, resistance to profenofos was expressed both in bioassays and in the simulator, resistance to the mixture was expressed in the simulator but in the bioassay the chemicals acted synergistically and there was no resistance. Repeated treatment of resistant populations, comprised of all life stages, over three generations gave further unpredicted results: cypermethrin failed to contact larvae on the under surfaces of leaves and hence did not prevent population growth; profenofos sprayed at field rates controlled all life-stages (despite the expression of resistance) provided the insecticide vapour was not dissipated. An alternation of cypermethrin and profenofos – cypermethrin timed against maximum adult emergence and profenofos timed to coincide with high larval densities – gave the best control. The disparities between the simulator experiments and standard bioassays suggest that techniques simulating the field treatment of all life-stages are better suited for evaluating the practical significance of resistance and potential curative strategies.

Density-specific sampling plans were developed under African conditions for the exotic spider mite, Mononychellus tanajoa (Bondar), a serious pest of cassava, Manihot esculenta. The within-plant distribution of Mononychellus tanajoa was found to favour new foliage, regardless of time of planting or plant age. Consequently, the first developed leaf near the top of the foliage was selected as the sampling unit and related to whole plant populations of M. tanajoa. The relationship between the mite population's variance and mean as measured by Taylor's Power Law proved to be stable over a range of planting dates, seasons and locations. Two binomial sampling plans, one based on Taylor's dispersion parameters and another based on direct field observations, were developed and compared. Binomial sampling, appropriate only for densities below 30 mites per leaf, was replaced by an enumerative procedure based on a ‘quick count’ protocol at higher mite densities.

Species of the chalcidoid genus Eurytoma associated with stone fruits are studied for the Palaearctic region. The eight species known to have such an association are: E. amygdali Enderlein, E. maslovskii Nikol'skaya, E. padi Veresh-chagin, E. samsonowi Vasiljev, E. schreineri Schreiner, E. turkestanica sp. n., E. paramygdali sp. n. and E. armenica sp. n. The first six species are phytophagous, developing in the stones, and the last two are entomophytophages, starting their development as parasitoids of a phytophagous species and completing development feeding on plant tissue. Four species, E. amygdali, E. schreineri, E. samsonowi, and E. maslovskii are of economic importance. Information is given on the economic importance, biology, distribution and taxonomy of these species, and includes several new records for hosts and distribution. A key is given to distinguish the species.