Search

Resistance involving penetrability of cotyledons of subterranean clover Trifolium subterraneum (Leguminosae) by the redlegged earth mite, Halotydeus destructor Tucker, was examined in this study using several approaches. Values of penetrability, presented as mechanical strength measured with a penetrometer with a tubulated probe, of cotyledons tested 11–13 days after seeding, from nine varieties of two subspecies of subterranean clover (T. subterraneum subsp. yanninicum and subsp. brachycalicinum) were negatively correlated with feeding damage caused by H. destructor in both 3 h pairwise choice tests in a Petri dish with detached cotyledons, and in 2 week multiple choice tests in containers with seedlings. Simulation tests with different artificial membranes (Parafilm and Gladwrap) making up sachets, containing 5% glucose as a feeding stimulant, indicated that within 3 h H. destructor preferred membranes with lower strength. Field-collected young adults had significantly higher physical fitness to feed and/or gather on the artificial membrane sachet containing 5% glucose, than those from the laboratory culture, when the sachet was compared with cotyledons of either resistant (DGI007) or susceptible (Dalkeith) varieties in the choice tests. Electron microscopic observations of mite infested cotyledons of the resistant variety (DGI007) reveal that upper epidermal cell walls around penetration holes are bent inwards. Anticlinal cell walls of palisade cells appear buckled following attack by H. destructor. The results from these studies were taken as further evidence for the involvement of mechanical factors in antixenotic resistance of subterranean clover cotyledons to H. destructor.

Rhodnius prolixus Stȧl was successfully reared for three generations on a diet of defibrinated pig blood fed through Parafilm or silicone-rubber membranes. Reproduction in terms of the number and sizes of eggs produced was superior to, while survival from egg to adult was equal to that reported for, insects fed on live hosts. The technique appears equally applicable to the rearing of Panstrongylus megistus (Burm.), Triatoma infestans (Klug) and T. brasiliensis Neiva. The inadequacy of cow blood as a diet for R. prolixus was manifested in a decrease in adult size after two generations and in a reduction of egg weight from 30 to around 16 mg per female per week. This was accompanied by a corresponding reduction in egg hatch from 90 to about 50%.

A successful technique for feeding colonies of Glossina morsitans morsitans Westw. and G. austeni Newst. in the absence of living hosts is described. Insects are fed through membranes made of silicone rubber or of agar and Parafilm, overlying blood pools poured onto grooved glass plates. The diet employed is fresh pig blood, collected at slaughter, and aseptic procedures are adopted at every stage of diet preparation and presentation. The reproductive performance of these in vitro-fed colonies in terms of adult survival, fecundity, and offspring size, is the same as that of colonies fed on living hosts, when compared over a long period of time. The fact that the technique is successful when used with a diet of pig blood, but is not successful when used with cow blood prepared in the same way, suggests that the technique per se is adequate to elicit a normal feeding response from these tsetse species. The nature of the nutritional superiority of pig blood is not understood.

In laboratory experiments at Langford, Bristol, agar membranes were superior to Parafilm membranes for thein vitrofeeding ofGlossina morsitansWestw. andG.austeniNewst. Temperature appears to be the primary stimulus for probing but agar membranes stimulate some probing, probably because of the humidity gradient above the membrane. Agar membranes also stimulate gorging, and enhance the effect of the phagostimulant adenosine 5' triphosphate (ATP). Agar membranes may simulate conditions on and in the skin of a living host by stimulating tactile and/or hygroreceptors in the mouthparts of the probing fly.G. morsitansfemales fed on blood containing ATP concentrations up to 5 × 10−3M gave a higher reproductive rate and higher pupal weights. The rate of breakdown of ATP in bovine blood during one hour at 37°C indicated the amounts that need to be added to maintain optimal concentrations during feeding. There was positive correlation between pupal weight and reproductive rate ofG. morsitanswith the membrane-feeding system, but a maximum of only 80% of the optimal rate of reproduction and 80% of the optimal pupal weight was achieved. On living hosts this correlation did not hold, the pupal weights being higher, suggesting that the membrane-feeding system constitutes a stress factor. The stress ofin vitrofeeding does not apparently involve probing or gorging stimuli but its symptoms are those of nutritional deficiency. It is concluded that post mortem changes in vertebrate blood may affect quantitative aspects of feeding, or they may affect either the nutritional content of the blood or the ability of the insects to metabolise it correctly.

The preparation and use of a simple, durable silicone membrane for feeding females of Glossina morsitans Westw. are described. Mean fecundity and mean pupal weight were nearly as good on the silicone membrane as on agar/Parafilm or rabbit ears, and survival of females after 108 days was 46·7%, as against 4·4% and 24·7%, respectively.