Cellular defence reactions and their depression in insects]

In insects the main cellular defence reactions are phagocytosis and encapsulation of foreign bodies. Free cells of haemolymph called haemocytes are the effectors of these reactions. They are achieved under the control of humoral factors of the plasma or of the serum. Humoral factors are able to enhance or to decrease the cellular defence reactions. As in mammals, potential parasites or pathogens need to avoid or to inhibit the defence reactions before developing inside the insect body. As an example of the depression of immunity induced by a parasite we will study the relationships between an insect and a nematobacterial complex.     

Sticky plant traps insects to enhance indirect defence

Plant‐provided foods for predatory arthropods such as extrafloral nectar and protein bodies provide indirect plant defence by attracting natural enemies of herbivores, enhancing top‐down control. Recently, ecologists have also recognised the importance of carrion as a food source for predators. Sticky plants are widespread and often entrap and kill small insects, which we hypothesised would increase predator densities and potentially affect indirect defence. We manipulated the abundance of this entrapped insect carrion on tarweed (Asteraceae: Madia elegans) plants under natural field conditions, and found that carrion augmentation increased the abundance of a suite of predators, decreased herbivory and increased plant fitness. We suggest that entrapped insect carrion may function broadly as a plant‐provided food for predators on sticky plants.     

A note on the population genetic consequences of delayed larval development in insects

Observations by Dobzhansky’s group in the 1940s suggesting that the presence of recessive genotypes could account for lower larval developmental rates in Drosophila melanogaster were not confirmed at the time and all subsequent investigations on this subject focused on the analysis of ecological models based on competition among pre-adult individuals. However, a paper published in this journal in 1991 eventually confirmed the finding made by Dobzhansky and his co-workers. In this report, we provide a theoretical analysis of the population genetic effects of a delay in the rate of larval development produced by such a genetic mechanism.     

Glutathione S-transferase in the defence against pyrethroids in insects

The correlation between the natural levels of GST and the tolerance to the insecticide decamethrin (dMT), as well as the interaction between the molecules of affinity purified enzyme and the insecticide were investigated in order to collect further information on the obscure role of the Glutathione S-transferase system (GST) as a mechanism of defence against pyrethroids. The studies were carried out, comparatively, on the larvae and pupae developmental stages of the coleopteran Tenebrio molitor, which exhibit varying natural levels of GST activity. No stage dependent susceptibility of the insect against pyrethroid insecticides was found during the first 24 h, however 48 h after treatment, the KD50 dose increased significantly due to the recovery of some individuals from the larvae stage. Simultaneous injection of decamethrin with compounds which inhibit GST activity in vitro, resulted in an increased tolerance, which was more pronounced in the pupae stage. Inhibition studies combined with competitive fluorescence spectroscopy and high pressure liquid chromatography (HPLC) showed that the insecticide binds probably to the active site of the enzyme inhibiting its activity towards CDNB in a competitive manner, but is not conjugated with GSH. According to this, GST offers a passive protection towards pyrethroid insecticides by binding to their molecule in a sequestering mechanism.     

A molecular and genomic reference system for conifer defence against insects

Insect pests are part of natural forest ecosystems contributing to forest rejuvenation but can also cause ecological disturbance and economic losses that are expected to increase with climate change. The white pine or spruce weevil (Pissodes strobi) is a pest of conifer forests in North America. Weevil–host interactions with various spruce (Picea) species have been explored as a genomic and molecular reference system for conifer defence against insects. Interactions occur in two major phases of the insect life cycle. In the exophase, adult weevils are free‐moving and display behaviour of host selection for oviposition that is affected by host traits. In the endophase, insects live within the host where mobility and development from eggs to young adults are affected by a complex system of host defences. Genetic resistance exists in several spruce species and involves synergism of constitutive and induced chemical and physical defences that comprise the conifer defence syndrome. Here, we review conifer defences that disrupt the weevil life cycle and mechanisms by which trees resist weevil attack. We highlight molecular and genomic aspects and a possible role for the weevil microbiome. Knowledge of this conifer defence system is supporting forest health strategies and tree breeding for insect resistance.     

Direct and indirect chemical defence of pine against folivorous insects

The chemical defence of pine against herbivorous insects has been intensively studied with respect to its effects on the performance and behaviour of the herbivores as well as on the natural enemies of pine herbivores. The huge variety of terpenoid pine components play a major role in mediating numerous specific food web interactions. The constitutive terpenoid pattern can be adjusted to herbivore attack by changes induced by insect feeding or oviposition activity. Recent studies on folivorous pine sawflies have highlighted the role of induced pine responses in herbivore attack and have demonstrated the importance of analysing the variability of pine defence and its finely tuned specificity with respect to the herbivore attacker in a multitrophic context.     

A note on fermentation reactions of anaerobic bacteria on a solid medium

A new technique is described for fermentation tests of anaerobes in which the fermentation reactions are carried out on cystine trypticase agar plates to which fermentable substances (Taxo discs) are added. This technique is simple, sensitive and reproducible.     

Immune reactions of insects on bacterial pathogens and mutualists

In the past few years the knowledge of insect defense mechanisms against pathogenic microorganisms and parasites has significantly increased on both the molecular and the organismic level. These investigations have led to new concepts of immune protection also relevant for mammals with the identification of the Toll receptor family as an eminent example. This review provides a brief overview of insect strategies to on the one hand defeat bacterial pathogens while on the other hand cooperating with symbiotic bacteria beneficial for the insects.     

A note on the use of dinitrosalicylic acid for determining the products of enzymatic reactions

Summary Factors contributing to non-linearity of enzyme assays incorporating detection of reaction products using dinitrosalicylic acid (DNS) are discussed. The common practice of diluting reaction products before quantification of reducing compounds is shown to be one cause of non-linearity. Insufficiency of substrate is also an important contributory factor in most modern versions of the method, although the original procedure was correctly designed to ensure a linear reaction. The inherent inaccuracy involved in expression of the results of non-linear reactions in units implying linearity (katals or International Units) is emphasized.     

A note on regression to the mean

Sex‐related Cognitive Differences: By Julia A. Sherman. Charles C Thomas, Springfield, Illinois, 1978. 262 pp. Cloth, $16.25; paper, $12.25.

Kinometrics: Determinants of So‐cioeconomic Success Within and Between Families. Edited by Paul Taubman. North‐Holland Publishing Company, Amsterdam, 1977. $28.25

Nutrition and Human Reproduction: Edited by W. Henry Mosley. Plenum Publishing Corporation, New York, 1978. 526 pp. $42.50.

Manual of the International Statistical Classification of Diseases, Injuries, and Causes of Death, Volume 1: World Health Organization, 1977. 777 pp. $12.00 (hardbound). (Also to be published in French, Spanish, and Russian.)

Women in Jamaica: Patterns of Reproduction and Family: By George W. Roberts and Sonja A. Sinclair. KTO Press, New York, 1978. $16.00.     

A defence of the calcichordates

Peterson (1994, Short Courses in Paleontology 7, Pal. Soc. & Univ. Tennessee; 1995, Lethaia 28 ) has claimed that the calcichordate theory of the origin of chordates can be dismissed on purely methodological grounds, without evaluating the anatomy of the calcichordates. He claimed this on the basis of his finding that the interrelationships for extant deuterostomes obtained by a PAUP analysis were not altered by including calcichordate fossils in the analysis, allegedly coded according to the anatomical interpretations of the calcichordate theory. This result, however, was due (1) to acceptance of dubious homologies among extant deuterostomes, (2) to reliance, when asserting that the fossils made no difference, on a majority-rule tree based on 13 equal-shortest trees; and (3) to the use of numerous multi-state characters in coding, which had the effect of denying, a priori , many of the homologies claimed by the calcichordate theory between fossil and extant forms. When these errors are corrected, a new PAUP analysis yields a tree consistent with the calcichordate theory. Peterson's claim therefore fails.