Argentine stem weevil (Listronotus bonariensis) (Kuschel) is a pasture pest of Lolium spp. in New Zealand and is the target of a classical biological control programme using the parasitoid Microctonus hyperodae Loan. However, laboratory experiments have indicated a strong density-dependent egg laying response which may have important implications for the biological control effort. Two field experiments were conducted using a manipulated range of weevil densities within 2.0–2.4 m–2 field enclosures and oviposition activity measured by weekly sampling of grass tillers within the enclosures. In both experiments, density had no effect on general oviposition behaviour although the percentage of tillers found to be infested with eggs increased significantly at higher densities. In experiment 1, L. bonariensis exhibited strong density-dependent oviposition with a significant decline in eggs/tiller/female with increasing adult density. An initial population of five L. bonariensis m−2 oviposited 32 times more eggs/tiller/female than 200 L. bonariensis m−2. By comparison, density-dependent oviposition was absent in experiment 2 with eggs/tiller/female comparable for all densities. The dramatic difference between the two experiments in the expression of density-dependent oviposition was attributed to prevailing spring temperatures during the sampling interval, which in the second experiment were much cooler and delayed the onset of egg laying. It is probable that in experiment 2, oviposition was not regulated by density-dependent cues but limited by temperature and age related mortality in the adult population. The mechanism for density-dependent oviposition, its occurrence in the field and impact on the effectiveness of the parasitoid M. hyperodae are discussed.

A central paradigm of life-history theory is the existence of resource mediated trade-offs among different traits that contribute to fitness, yet observations inconsistent with this tenet are not uncommon. We previously found a clonal population of the aphid Myzus persicae to exhibit positive genetic correlations among major components of fitness, resulting in strong heritable fitness differences on a common host. This raises the question of how this genetic variation is maintained. One hypothesis states that variation for resource acquisition on different hosts may override variation for allocation, predicting strong fitness differences within hosts as a rule, but changes in fitness hierarchies across hosts due to trade-offs. Therefore, we carried out a life-table experiment with 17 clones of M. persicae, reared on three unrelated host plants: radish, common lambsquarters and black nightshade. We estimated the broad-sense heritabilities of six life-history traits on each host, the genetic correlations among traits within hosts, and the genetic correlations among traits on different hosts (cross-environment genetic correlations). The three plants represented radically different environments with strong effects on performance of M. persicae, yet we detected little evidence for trade-offs. Fitness components were positively correlated within hosts but also between the two more benign hosts (radish and lambsquarters), as well as between those and another host tested earlier. The comparison with the most stressful host, nightshade, was hampered by low survival. Survival on nightshade also exhibited genetic variation but was unrelated to fitness on other hosts. Acknowledging that the number of environments was necessarily limited in a quantitative genetic experiment, we suggest that the rather consistent fitness hierarchies across very different plants provided little evidence to support the idea that the clonal variation for life-history traits and their covariance structure are maintained by strong genotype×environment interactions with respect to hosts. Alternative explanations are discussed.

The following paper deals with insect pests of various minor crops and fruit trees in the Colony of Mauritius. The damage caused by most of the pests dealt with is often not very apparent, as many of these crops are not grown extensively, and have not been the object of any special investigation up to the present. If extensive cultivation of any of these should be undertaken, it is clear that there might be created a new environment favourable to increase of the insects, and that the pest problem would then have to be dealt with seriously. Our knowledge of these pests is very deficient, as their life-history and habits have never been studied in detail locally. It is also quite probable that extended cultivation may bring to light many potential pests which at present escape our attention.

A description is given of an artificial stream for studying pupation times and pupal periods of Simulium spp., of emergence traps for studying emergence times in rivers, and of a convenient arrangement for rearing batches of pupae in the laboratory.

S. damnosum Theo., S. kenyae De Meillon and S. unicornutum Pomeroy pupate mainly by day, each species having a characteristic period of peak pupation.

In S. damnosum and S. kenyae the time of pupation influences the pupal period, and for these and other species the pupal period is prolonged by lower temperatures. The pupal period is partly independent of these influences in so far as emergence by night is normally avoided.

The timing of adult eclosion is influenced by the temperature on the day of eclosion. On warm days (midday temperature of the river 24·1–28°C) S. damnosum and other forest zone species show a peak of emergence between 06.00 and 09.00 h, while on cool days (midday temperature of the river 20·1–24°C) the peak is delayed until 09.00 to 12.00 h. On artificially cold days (refrigerator temperature 16–20°C), the peak is shifted to the late afternoon.

The study of the timing of adult eclosion from pupae brought into the laboratory is complicated by the fact that the normal pattern of emergence is liable to disturbance.

In the laboratory a seasonal fluctuation in the sex ratio of emerging flies occurred in S. damnosum.

Trichogramma zahiri Polaszek sp. n. is described from Bangladesh. It has been collected at several localities from the major pest of rice Dicladispa armigera (Olivier) on which it has an important controlling impact. Trichogramma zahiri is compared with known Trichogramma species from the region, and diagnostic differences are presented. Data on developmental period, adult longevity, egg-laying frequency, host egg age preference and seasonal parasitism rate are presented and discussed. Other records of parasitoids of D. armigera are briefly reviewed and discussed.

A generalist predator's ability to contribute to biological control is influenced by the decisions it makes during foraging. Predators often use flexible foraging tactics, which allows them to pursue specific types of prey at the cost of reducing the likelihood of capturing other types of prey. When a pest insect has low nutritional quality or palatability for a predator, the predator is likely to reject that prey in favour of pursuing alternative, non-pest prey. This is often thought to limit the effectiveness of generalist predators in consuming aphids, which are of low nutritional quality for many generalist predators. Here, we report behavioural assays that test the hypothesis that the generalist predator, Grammonota inornata (Araneae: Linyphiidae), preferentially forages for a non-pest prey with high nutritional quality (springtails), and rejects a pest prey with low nutritional quality (aphids). In no-choice assays, molecular gut-content analysis revealed that spiders continued to feed on the low-quality aphids at high rates, even when high-quality springtails were readily available. When provided a choice between aphids and springtails in two-way choice tests, spiders did not show the expected preference for springtails. Decision-making by spiders during foraging therefore appears to be sub-optimal, possibly because of attraction to the less frequently encountered of two preys as part of a dietary diversification strategy. These results indicate that behavioural preferences alone do not necessarily compromise the pest-suppression capacity of natural enemies: even nutritionally sub-optimal pest prey can potentially be subject to predation and suppression by natural enemies.

In a highly interesting article in a previous number of this journal (vol. iii, p. 343) J. Dewitz discussed “The bearing of physiology on economic entomology,” and gave in this connection, amongst other things, an account of the various kinds of tropisms and their use, besides which he also pointed out the necessity for studying these for the purpose of discovering weapons for fighting noxious insects. It strikes me, however, as if the importance of chemotropism had not been emphasised in this survey as in my opinion it ought to have been, and the purpose of these modest lines is partly to draw attention to two important researches in this branch of science, recently carried out independently of each other, partly to point out that with the aid of chemotropism we shall in all probability be able to discover new weapons for the fight against noxious insects.

A laboratory colony of Glossina morsitans submorsitans Newst. originating from Nigeria exhibits an excess of females over males. The sex ratio distortion of more than two females to one male was studied by the maintenance of individual flies. Five males sired more than ten daughters without producing any sons when mated to several females, whilst other males fathered approximately equal numbers of male and female offspring; there was no evidence for selective abortion of male embryos. The presence of these ‘distorter’ males, which produce only female offspring, was found to cause the sex ratio distortion. The results are discussed with reference to data from the field which indicate that this genetic aberration is not confined to the laboratory; possible implications for chemical control programmes are assessed.

Discrimination of conspecific and heterospecific signals is a key element in the evolution of specific mate recognition systems. Lepidopteran pheromone signals are typically composed of several compounds that synergize attraction of conspecific and inhibit attraction of heterospecific males. Blends convey specificity, but not their single components, that are typically shared by several species. Many sex pheromones are blends of geometric or positional isomers of straight-chain acetates, while species-specific blends of analogous alcohols have not been described. We have, therefore, studied the attraction of tortricid moths to the geometric isomers (E,E)-, (E,Z)-, (Z,E)- and (Z,Z)-8,10-dodecadien-1-ol. Only one species responding to these alcohols seemed to be attracted to a blend of two isomers, while most species are attracted to only one alcohol isomer. Lack of a pronounced synergist or antagonist effect of the other geometric isomers explains the lack of specific attraction to isomer blends and reduces accordingly the number of specific communication signals composed of these alcohols. In comparison, many more species respond to the analogous (E,E)-, (E,Z)-, (Z,E)- and (Z,Z)-8,10-dodecadienyl acetates and their binary blends. The acetate isomers all play a behavioural role, either as attractants, attraction synergists or antagonists, and thus promote specific communication with acetate blends. Male moths seem to discriminate the acetate isomers with greater precision than the analogous alcohols. It is proposed that discrimination is facilitated by steric differences between the four acetate isomers, as compared to the more uniform steric properties of the alcohols.

The life-cycle and immature stages of the Eulophid, Syntomosphyrum albiclavus Kerrich, a pupal parasite of tsetse flies (Glossina), are described. Measurements of the widths of the cephalic skeletons of larvae of all ages fell into four well separated groups, and confirmation that these represented the existence of four larval instars was given by Dyar's law, the application of which in this instance is not invalidated by the disproportionate length of the fourth instar or the effects of overcrowding, which do not become apparent before that stage.

A key for the identification of males of all Afrotropical species of the subgenus Atherigona of Atherigona described to date is presented. Four new species, A. alaotrana sp. n. from Madagascar, A. bowdeni sp. n. from Uganda, A. dentifolia sp. n. from Kenya and A. palpalis sp. n. from Nigeria, are described.

The yellow tea-mite should in future be known as Hemitarsonemus latus (Banks) Ewing.

The males have a curious habit of carrying female pupae to younger leaves. The pupa is held above the male's body by means of a sucker-like organ near the tip of his tail-like, posterior terminus. Thus the male plays an active part in distributing the pest.

Mating has not been observed, but normally it occurs as soon as the female becomes adult. It may also occur later in her life.

Unfertilised females give rise to male offspring only, but mated females have mixed families.

Rhynchophorus ferrugineus, known as the Red Palm Weevil (RPW), is reported as a pest of up to 40 palm species. However, the susceptibility degree and the defense mechanisms of these species against this weevil are still poorly known. In Europe, the RPW is a major pest of Phoenix canariensis while other palm species, including the congeneric Phoenix dactylifera, seem to be less suitable hosts for this insect. The aim of our study was to compare the defensive response of P. dactylifera, Chamaerops humilis and Washingtonia filifera against R. ferrugineus and try to define the mechanisms of resistance that characterize these species. Bioassays were carried out to evaluate the mortality induced on RPW larvae by extracts from the leaf rachis of the studied palm species. Tests at semi-field scale were also conducted, based either on forced palm infestation, with larvae of RPW, or on natural infestation, with adult females. Rachis extracts from C. humilis and W. filifera caused 100% larval mortality after 2 days of exposure, while extracts of P. dactylifera did not impair larval survival. Independently of the effect of the leaf extracts, the weevils were unable to naturally infest the three palm species, although larval survival was high after forced infestation of the plants. We concluded that the observed lack of infestation of P. dactylifera by RPW is due to factors other than antibiosis. In W. filifera and C. humilis, although the presence of antixenosis mechanisms cannot be excluded, resistance to R. ferrugineus seems to rely on the presence of antibiosis compounds.

Fruit flies (Diptera: Tephritidae) are major pests worldwide. The sterile insect technique, where millions of flies are reared, sterilized by irradiation and then released, is one of the most successful and ecologically friendly methods of controlling populations of these pests. The mating behaviour of irradiated and non-irradiated flies has been compared in earlier studies, but there has been little attention paid to the anti-predator behaviour of mass-reared flies, especially with respect to wild flies. Tephritid flies perform a supination display to their jumping spider predators in order to deter attacks. In this study, we evaluated the possibility of using this display to determine the anti-predator capabilities of mass-reared irradiated, non-irradiated flies, and wild flies. We used an arena setup and observed bouts between jumping spiders (Phidippus audax Hentz) and male Mexican fruit flies (Anastrepha ludens Loew). We show that although all flies performed a supination display to their predator, wild flies were more likely to perform a display and were significantly more successful in avoiding attack than mass-reared flies. We suggest that this interaction can be used to develop a rapid realistic method of quality control in evaluating anti-predator abilities of mass-reared fruit flies.

Descriptions are given of two new species of pentatomid bug, one known to transmit the disease ‘marchitez’ (caused by Phytomonas staheli) of oil palm in Ecuador and the other associated with hartrot (caused by the same flagellate) in coconut palm in French Guiana. Notes are included on a third species also associated with hartrot in French Guiana. The species are Lincus lethifer sp.n., L. apollo sp.n. and L. croupius Rolston.

The leaf-cutting ant Atta sexdens Forel (Hymenoptera: Formicidae) is one of the most damaging agricultural pests in the Neotropics. Management strategies predominantly rely on the use of general insecticides. What is needed are more species-specific and environmentally friendly options. Parasitioids such as phorid flies (Diptera: Phoridae) may be one such option, but a greater understanding of the ecology of the flies and their ant hosts is essential to devise biological control strategies. Here we report parasitism rates, ant host size, parasitoid abundance per host and resultant sex ratios of two phorid species Apocephalus attophilus Borgmeier and Eibesfeldtphora tonhascai Brown parasitizing A.sexdens. The two species achieved parasitism rates of 1.48 and 1.46%, respectively and the pupal period was 14.7 ± 1.1 days and 22.1 ± 2.8 days, respectively. There was no significant difference between the head capsule width of ants parasitized by either A. attophilus or E. tonhascai. Likewise, there was no significant effect between the head capsule width of parasitized and unparasitized ants for both species. A significant positive correlation was found between the head capsule width of the parasitized ants and the number of adult parasitoids A. attophilus emerged. Ants parasitized by E. tonhascai survived significantly longer than those parasitized by A. attophilus. There was no significant effect of ant head width on the sex ratio of the offspring of either parasitoid species and no significant difference in the sex ratio (male: female) of their offspring. In summary, these data addressed here are important steps when considering natural enemies for biological control. Studying survival of the parasitized ants, parasitoid offspring sex ratio and host size preference allows for a better understanding of ant natural biological control in the field and can help in rearing of A. attophilus and E. tonhascai in laboratory.

Many insects show a greater attraction to multimodal cues, e.g. odour and colour combined, than to either cue alone. Despite the potential to apply the knowledge to improve control strategies, studies of multiple stimuli have not been undertaken for stored product pest insects. We tested orientation towards a food odour (crushed white maize) in combination with a colour cue (coloured paper with different surface spectral reflectance properties) in three storage pest beetle species, using motion tracking to monitor their behaviour. While the maize weevil, Sitophilus zeamais (Motsch.), showed attraction to both odour and colour stimuli, particularly to both cues in combination, this was not observed in the bostrichid pests Rhyzopertha dominica (F.) (lesser grain borer) or Prostephanus truncatus (Horn) (larger grain borer). The yellow stimulus was particularly attractive to S. zeamais, and control experiments showed that this was neither a result of the insects moving towards darker-coloured areas of the arena, nor their being repelled by optical brighteners in white paper. Visual stimuli may play a role in location of host material by S. zeamais, and can be used to inform trap design for the control or monitoring of maize weevils. The lack of visual responses by the two grain borers is likely to relate to their different host-seeking behaviours and ecological background, which should be taken into account when devising control methods.

Our knowledge of the Aphididae of Africa is as yet very limited, this important group of insects having been but little studied, except in Europe and North America. At present only thirty-five species are recorded for the whole African continent, about the number one can collect in a single afternoon in one's own garden in England. It will be noticed that several common European species are recorded, and that they are as destructive in Africa as in Europe, such as the Common Cabbage Aphis (A. brassicae) and the Ribes and Lettuce Aphis (Rhopalosiphum lactucae). Several others occur which have a world-wide distribution, such as the Black Peach Aphis (Aphis persicae), and the Woolly Aphis (Eriosoma lanigerum), doubtless having been distributed on nursery stock, the former as ova and the latter as adults. Fuller has reported destroying and fumigating strawberry plants attacked by Aphis sent from Europe, and Lounsbury records the presence of Apple Aphis eggs on imported stock. Undoubtedly these insects are constantly being distributed from country to country with imported plants, trees and shrubs.

The flight activity of Hydrotaea irritans (Fall.) was investigated in western Scotland using an unbaited suction trap, a carbon-dioxide-baited suction trap and a Manitoba trap. Consistently more female flies were caught than males. Trapping experiments showed that carbon dioxide and visual or thermal stimuli influence long-range attraction and short-range orientation in host-seeking flies. The seasonal activity of adults was determined from the geometric means of catches from a suction trap baited with carbon dioxide and a Manitoba trap. H. irritans was shown to be univoltine. The activity of females was greatest in the middle of July and declined sharply in the first week of August. Male activity reached a peak at the same time as that of the females, then declined until no males were caught after mid-August. Females were most active between 10.00 and 18.00 h B.S.T., with a peak about 13.00 h. There was no variation in sex ratio during the day. Multiple regression equations of climatic and seasonal factors with log catches of flies were very similar for the two types of trap. Radiant temperature, illumination, wind speed and date were shown to influence activity of females and, with the exception of illumination, male activity also. Seasonal activity curves calculated from the regression equations were plotted for both sexes in the two traps.

In the “Bulletin of Entomological Research” for December 1920 Dr. J. M. Dalziel deals in a most interesting and instructive way with the various, and sometimes curious breeding-places of mosquitos in Lagos. He mentions the occurrence of mosquito larvae in saline waters, and in a foot-note refers to a number of salt-water species.