Morphological Changes in the Midgut of Aedes aegypti L. (Diptera: Culicidae) Larvae Following Exposure to an Annona coriacea (Magnoliales: Annonaceae) Extract

Bioinsecticides are important in the control of disease vectors, but data regarding their physiological effects on target insects are incomplete. This study describes morphological changes that occur in the midgut of third instar Aedes aegypti L. (Diptera: Culicidae) following treatment with a methanolic extract of Annona coriacea (Magnoliales: Annonaceae). Dissected midguts were subdivided into anterior and posterior regions and analyzed by light and scanning electron microscopy. Insects exposed to the extract displayed intense, destructive cytoplasmic vacuolization in columnar and regenerative midgut cells. The apical surfaces of columnar cells exhibited cytoplasmic protrusions oriented toward the lumen, suggesting that these cells could be involved in apocrine secretory processes and/or apoptosis. We report that A. coriacea extracts induced morphological alterations in the midgut of A. aegypti midgut larvae, supporting the use of plant extracts for control of the dengue vector.     

Circadian locomotor rhythms in individual honeybees

ABSTRACT. The circadian locomotor (walking) rhythms of individual forager honeybees ( Apis mellifera ligustica L.) were measured under a variety of conditions. In constant dark the rhythms exhibited endogenous periodicities that were less than 24 h, whereas under constant light the periods tended to be greater than 24 h. Individual honeybees readily entrained to photoperiods, displaying a diurnal pattern of entrainment with most of the activity occurring in late photophase. Evidence is presented which suggests that foraging behaviour and general locomotor behaviour may be governed by two different circadian clock systems.     

Effect of previous crops on the incidence of eyespot on winter wheat

Surveys of winter wheat from 1939 to 1946 show that eyespot (Cercosporella herpotrichoides Fron.) occurs throughout Britain and that its incidence depends largely on previous cropping and on weather. Examination of 551 crops on land whose cropping for the previous 4 years was known showed that the incidence rose steadily with increasing numbers of preceding wheat and barley crops: where neither crop had been taken for 4 years the proportion of crops with more than 70% infected straws was 2%, rising to 45% where three or four such crops had been taken and the average straws infected rose from 6 to 55%.
The percentage infection to be expected in various groups of crops was calculated from previous cropping; it was compared with the actual infection and so used to assess the importance of other factors in determining the incidence of eyespot. High spring rainfall, early sowing and a dense plant increased incidence and low spring rainfall, late sowing and a thin plant reduced it.
Eyespot was not usually severe on newly ploughed grassland until the third or fourth crop of wheat, but under very wet conditions it was sometimes severe in the second crop.
Oats is much less susceptible than wheat or barley, but some crops were found with a third of their straws infected.
A brief survey of winter wheat in Holland suggested possible causes for the rise and fall of eyespot in recent years and for its present lower incidence there as compared with East Anglia.