Trichograrnma australicum were reared on eggs of Helicoverpa arrnigera. Immature T. australicurn were studied with a confocal laser scanning microscope and a light microscope. Development of egg, larva, prepupa and pupa required about 24-26, 24-26, 42-47 and 84-92 h, respectively, at 2 8 T , 45% RH and 12L:12D photoperiod. The eggs of T. australicurn increased significantly in size during incubation. The larval mandibles were gradually revealed as the larva increased in size. Exuviae were not found during the larval stage, and we conclude that T. australicurn has one larval instar. Staining larvae and pre-pupae with 1 % aniline blue dissolved in Neisenheimer's solution induced fluorescence. Stained larvae and pre-pupae gave a clear image of anatomy when observed with a confocal laser scanning microscope. Urate bodies appeared at the onset of the prepupal stage. The vitelline membrane of host egg gradually blackened. Legs, wings, antennae, body segmentation, genitalia, colour of compound eyes and ocelli became distinct during the prepupal stage. Larval integument and mandibles were shed at the onset of pupation. The adult wasps emerged 182.40 + 0.40 h (n = 10) after oviposition, 2.80 + 0.25 (n = 10) wasps emerged from a host egg, and the sex ratio was 16 :3 Eo.

We studied ovipositional synergists and artificial diets for rearing Trichogramma australicurn. Artificial "diet A" included 40% haemolymph of Helicoverpa armigera (Hiibner) final instar larvae, 30% of a 10% malt solution in deionised water, 20% chicken egg yolk and 10% Neisenheimer's salt solution with 76 units Penicillin and 76 units Streptomycin/ml diet. Artificial "diet B" was identical except Grace's insect medium@ replaced Neisenheimer's salt solution. The number of T. australicum larvae in artificial eggs filled with diet A and diet B was not significantly different (P > 0.05). Significantly fewer (P < 0.05) larvae developed to pupae and adults in artificial eggs filled with diet A. Quantity and quality of artificial diet affected the mortality of T. australicum larvae reared in vitro. Ovipositional synergists included 10% gelatine solution, 10% polyvinyl alcohol solution or 1 Vo agar solution in deionised water. Synergist test-solutions were individually smeared on the external surface of artificial eggs (hemispherical depressions in plastic membrane). Eggs laid and number of T. australicum larvae produced were significantly higher in artificial eggs smeared with gelatine than artificial eggs smeared with polyvinyl alcohol, agar or non-smeared (control) eggs.

Key wordsDevelopment of Trichogramma uustrulitum in eggs of Helicovcr/w urtnigera and in artificial diet was compared. Females required significantly more time to insert their ovipositors into artificial eggs than into host eggs. The number of eggs deposited by a female wasp in artificial diet was significantly higher than in H . urniiger'a eggs. Duration of egg, larval and prepupal stages was longer in artificial diet than in host eggs, but the pupal stage was shorter in artificial diet. lnimatures and adults of T. crustralicum reared in artificial diet were significantly larger than those reared in host eggr. Compared with controls, mortality of immature T. uustralicum was not significantly different in host eggs. but was significantly different in artificial diet. A higher number of abnormal wasps emerged from artificial diet, whereas no abnormal wasps emerged from host eggs. Differences in the amount of dict or ooplasm consumption, varying chemical constituents and physical properties of artificial diet and host eggs may have contributed to the observed differences in development of T. uustralic~uni. artificial diet, development, Helicoverpa armigera, host eggs, Trichogranimu.

No abstract

Trichogramma australicum wasps were reared in fertile and infertile Helicoverpa armigera eggs. In one experiment, all parasitised and unparasitised infertile moth eggs collapsed 48±60 h after they were laid and no wasps emerged. In a second experiment, 20% of parasitised infertile eggs (<12 h old) produced adult wasps but their number was signi®cantly lower (P < 0.05) than those from fertile eggs. Conversely, almost all parasitised fertile eggs produced T. australicum adults and all unparasitised fertile eggs produced H. armigera larvae. The number of wasps emerging per egg from fertile and infertile host eggs was not signi®cantly dierent (P > 0.05). No signi®cant dierences (P > 0.05) were noted in the number of progeny produced by female wasps reared in fertile or infertile eggs. It is recommended that only fertile H. armigera eggs be used to mass rear T. australicum.