Predation and parasitism of cotton leafworm eggs,Alabama argillacea [Lep.: Noctuidae]

The identification and efficiency of arthropod predator and parasites related to natural control of cotton leafworm eggs,Alabama argillacea (Huebner), were studied in a cotton field, Jaboticabal, SP, Brazil. Plants were marked randomly and the eggs found on them were indicated by arrow tapes for predation and parasitism observations. To evaluate and identify the arthropod fauna in the row-meter containing the marked plant, visual countings and collections using D-Vac ® and “beat sheet” were used. The average predation rate during the season, in the presence of 23.0 predators per row-meter, was 50.6% and the parasitism byTrichogrammatoidea annulata was 44.9% totaling 95.5% of egg reduction. In decreasing order of abundance, the arthropod predators found were the antPheidole sp., the spiderChrysso clementinae Petrunkevitch, the hemipteraOrius insidiosus Say andCeratocapsus mariliensis Carvalho & Fontes, and the coccinellidHyperaspis festiva (Mulsant).     

Multiline varieties and disease control

Summary Existing theoretical models have led to conflicting predictions concerning the likely effect of the widespread use of dirty crop multilines on the evolution of virulence in pathogen populations. Here we attempt to clarify these problems by extending existing models to include selection against unnecessary genes for virulence at two different stages in the life cycle of the pathogen. The results of these studies indicate that the stage of the life cycle at which selection occurs can significantly influence the evolution of virulence in pathogen populations growing on multiline varieties.     

Effect of oxygen limitation on the formation of the electron transport system of the phytopathogenic fluorescent bacteriumPseudomonas cichorii

The composition of the membrane-bound electron transport system of the phytopathogenic bacteriumPseudomonas cichorii underwent modification in response to oxygen supply. Growth adaptation to low oxygen concentrations was characterized by repression of cytochromes involved in ubiquinol-cyt.c oxidoreductase and cyt.c oxidase activities. By contrast, cyto.o, i.e., the alternative cyanide-insensitive oxidase ofP. cichorii, was unaffected by low oxygen tension. Noa-type cytochromes could be detected at any stage of growth.     

A reinvestigation of the Gn-RH (gonadotrophin-releasing hormone) systems in the goldfish brain using antibodies to salmon Gn-RH

Summary The organization of Gn-RH systems in the brain of teleosts has been investigated previously by immunohistochemistry using antibodies against the mammalian decapeptide which differs from the teleostean factor. Here, we report the distribution of immunoreactive Gn-RH in the brain of goldfish using antibodies against synthetic teleost peptide.Immunoreactive structures are found along a column extending from the rostral olfactory bulbs to the pituitary stalk. Cell bodies are observed within the olfactory nerves and bulbs, along the ventromedial telencephalon, the ventrolateral preoptic area and the latero-basal hypothalamus. Large perikarya are detected in the dorsal midbrain tegmentum, immediately caudal to the posterior commissure. A prominent pathway was traced from the cells located in the olfactory nerves through the medial olfactory tract and along all the perikarya described above to the pituitary stalk. In the pituitary, projections are restricted to the proximal pars distalis. A second immunoreactive pathway ascends more dorsally in the telencephalon and arches to the periventricular regions of the diencephalon. Part of this pathway forms a periventricular network in the dorsal and posterior hypothalamus, whereas other projections continue caudally to the medulla oblongata and the spinal cord. Lesions of the ventral preoptic area demonstrate that most of the fibers detected in the pituitary originate from the preoptic region.     

In vitro production of zoospores by the mosquito pathogen Lagenidium giganteum (Oomycetes: Lagenidiales) on solid media

Reliable, large-scale production of Lagenidium giganteum zoospores was obtained on solid media. The fungus was grown for 7 days in a liquid medium of wheat germ, hemp seed, yeast extract, and glucose, then placed onto hemp-seed agar. Zoosporogenesis was induced on agar by immersing the fungal cultures into water. Zoospore production began 10 hr postimmersion, peaked at 18 hr, and ceased by 36 hr. A single, 10-cm Petri dish of fungus on hemp-seed agar produced 1.7?3.8 × 10⁷ zoospores during the 26 hr of zoosporogenesis. Optimal zoospore production occurred with 4- to 7-day-old cultures; cultures older than 10 days produced few zoospores. The temperature range for zoosporogenesis was 15–35°C. The extent of zoosporogenesis was directly related to the volume of water used to induce zoospore formation and inversely proportional to agar thickness. Bioassay of zoospores against second instar Culex quinquefasciatus larvae yielded an LD₅₀ of 400 zoospores/ml.     

Effect of Aedes aegypti (Diptera:Culicidae) Age on Sex Ratios in Romanomermis culicivorax (Nematoda:Mermithidae)

First, second, third, early and late fourth-instar larvae, and pupae of Aedes aegypti were infected with Romanomerrais culicivorax and reared at 20, 25, and 30 C. An increase in the ratio of male to female nematodes was observed with increase in host age at the time of infection at each temperature. The number of pupal and late fourth-instar infections was low, but R. culicivorax continued to develop in adult A. aegypti. Since male nematodes were recovered from both male and female hosts infected as late fourth instars or pupae, the sex of the host did not influence the sex of the nematode.     

Biological studies including population growth parameters of the predatory miteAmblyseius barkeri [Acarina.: Phytoseiidae] at 25°C in the laboratory

Amblyseius barkeri (Hughes) fed onThrips tabaci (Lind.) at 25°C showed an average duration of 2.2, 0.8 and 3.2 days for the egg, larval and nymphal stages, with mortalities at 1.0, 1.0 and 3.1%, respectively. Females represented 63% of the population and required multiple matings for optimal fertility. The oviposition period was 20.3 days and the average oviposition rate 2.3 eggs per day. The intrinsic rate of increase was 0.22 per day. The expected life span was 29.6 days for ♀♀ and 27.4 days for ♂♂.A. barkeri ♂♂ and ♀♀ both consumed 3.3 nymphs of thrips per day (mean value for the feeding stages). The larva does not take up food. In the absence of thripsA. barkeri was able to consume two-spotted spider mites,Tetranychus urticae (Koch), and their eggs, adult broad mites,Polyphagotarsonemus latus (Banks), and pollen of various plants. Cannibalism was observed when food was lacking. Certain morphological features, egglaying, mating and predatory behaviour are described.      

Bionomics ofTrioxys indicus [Hym.: Aphidiidae], a parasitoid ofAphis craccivora [Hem.: Aphididae]: 31. Effect of host haemolymph on the numerical response of the parasitoid

The influence of kairomones on the numerical response of the parasitoidTrioxys indicus against its hostAphis craccivora at its varying density was studied. The kairomones (applied as aqueous extract of the host) significantly enhanced the rate of parasitisation and multiplication and the area of discovery of the parasitoid and also the K-values of mortality of the host at all parasitoid densities introduced (1, 2, 4, 8, 12 and 16 parasitoids) into troughs having about 200 hosts. The sex-ratio of F₁ offspring decreased at lower parasitoid densities and remained more or less unchanged at higher parasitoid densities after the application of kairomones. The present findings indicate that if kairomones are applied properly, the number of hosts destroyed by a stimulated parasitoid will be about 200, twice the number reported earlier, thus fewer parasitoids will be needed to regulate an estimated population of the hosts.      

Intracellular recordings from nonspiking interneurons in a semiintact,tethered walking insect

Nonspiking interneurons were investigated in a tethered, walking insect, Carausius morosus, that was able to freely perform walking movements. Experiments were carried out with animals walking on a lightweight, double-wheel treadmill. Although the animal was opened dorsally, the walking system was left intact. Intracellular recordings were obtained from the dorsal posterior neuropil of the mesothoracic ganglion. Nonspiking inter-neurons, in which modulations of the membrane potential were correlated with the walking rhythm, were described physiologically and stained with Lucifer Yellow. Interneurons are demonstrated in which membrane potential oscillations mirror the leg position or show correlation with the motoneuronal activity of the protractor and retractor coxae muscles during walking. Other interneurons showed distinct hyperpolarizations at certain important trigger points in the step cycle, for example, at the extreme posterior position. Through electrical stimulation of single, nonspiking interneurons during walking, the motoneuronal activity in two antagonistic muscles—protractor and retractor coxae—could be reversed and even the movement of the ipsilateral leg could be influenced. The nonspiking interneurons described appear to be important premotor elements involved in walking. They receive, integrate, and process information from different leg proprioceptors and drive groups of leg motoneurons during walking.