The Biology of Cephalonomia waterstoni Gahan (Hym., Bethylidae), a Parasite of Laemophloeus (Col., Cucujidae)

Abstract

The paper describes field and laboratory investigations on the bionomics of Cephalonomia waterstoni, a Bethylid parasite of Laemophloeus spp. A table is given in which are listed all the Bethylids attacking insect pests of stored products to which reference could be found in the literature.An infestation of Laemophloeus, associated with two “hot spots” in Manitoba wheat, which supported a large population of Cephalonomia is described.A simple technique for the laboratory culture of Cephalonomia is described.The life-cycle of C. waterstoni with Laemophloeus ferrugineus as host has been worked out.The lengths of egg, larval and cocoon (prepupal and pupal) stages at combinations of 25°C, 30°C. and 60 per cent., 80 per cent. R.H. are given. The egg and larval stages are short, lasting for about six days at 25°C. and four days at 30°C.Within the limits used, the relative humidity appears to have no effect on the duration of development at any stage. On the other hand, temperature exerts a considerable influence; the life-cycle at 30°C. is completed in two weeks but at 25°C. it takes three weeks.Again within the limits used, the mortality appears to increase with decrease in saturation deficit. Mortality ranged from 9 per cent, at S.D. 12·7 mm. to 36·5 per cent, at S.D. 5·0 mm.Without food or water at all combinations of 25–30°C. and 60–80 per cent. R.H. adults live for about four days, with a range of 0·5–9·5 days. There is no difference between the sexes. Unexplained contradictory results were obtained in two experiments.With normal or paralysed host larvae available at 30°C. and 80 per cent. R.H., males live no longer than when no food or water is available but females live for about five weeks at 25°C. and 80 per cent. R.H. and for about four weeks at 30°C. and 80 per cent. R.H.Males fed with sucrose solution at 30°C. and 80 per cent. R.H. live for several days longer than when starved : females live for the same length of time as when fed with host larvae.The pre-oviposition period at 25°C. and 80 per cent. R.H. is about five days; at 30°C. and 80 per cent. R.H. about one and a half days.Fecundity. At 25°C. and 80 per cent. R.H., Cephalonomia lays about 40 eggs on 30 host larvae : at 30°C. and 80 per cent. R.H., about 65 eggs on 40 larvae.Cephalonomia females readily oviposit on larvae that have been paralysed some time previously, and can be induced to oviposit on larvae already bearing eggs.Virgin females produce only male offspring (arrhenotoky).Eggs are laid in groups of one, two or three (rarely four) per larva. Single eggs produce mainly females ; pairs produce mainly one male and one female ; trios produce mainly one male and two females. At 25°C. and 80 per cent. R.H. more single eggs are laid than pairs ; at 30°C. and 80 per cent. R.H. more pairs are laid than singles. This results in the production of a higher proportion of females at 25°C. than at 30°C. The incidence of trios at both temperatures is low.C. waterstoni is equally viable on L. minutus, L. ferrugineus and L. turcicus but shows a marked preference for L. ferrugineus.