1_Maternal and grand-maternal photoperiodic responses of Trichogramma buesi, T. embryophagum, T. evanescens, T. piceum, T. principium, and T. telengai were investigated in laboratory conditions. During the experiment, grand-maternal and maternal generations developed at 20°C and one of the 4 photoperiodic regimes: L : D = 12 : 12, 14 : 10, 16 : 8, and 18 : 6 (in total, 16 combinations) while the progeny developed at L : D = 12 : 12 and one of the 3 thermal regimes: 13, 14, and 15°C. The proportion of diapausing individuals in the progeny of all the studied species was significantly dependent on the direct influence of temperature and on the maternal photoperiodic response. The influence of the photoperiodic conditions during development of the grand-maternal generation was statistically significant in 5 of the 6 studied species, being relatively weak in T. embryophagum and T. telengai, whose geographical ranges extend up to north-western regions of Europe (possibly, these wasps enter diapause so early that the grand-mothers of the diapausing generation develop under long day conditions). Comparative analysis showed that the thresholds of the maternal and grand-maternal photoperiodic responses coincided or almost coincided. The grand-maternal effect was stronger in the progeny of maternal females which developed under short day conditions than in those that developed under long day conditions. This pattern of interaction probably synchronizes the life cycle with seasonal changes because diapause is induced under decreasing day length and thus mothers of diapausing individuals develop at shorter daylength than do grand-mothers., 2_We conclude that the grand-maternal and the maternal effects on Trichogramma progeny diapause are based on one and the same photoperiodic response. In nature, the grand-maternal effect increases the proportion of diapausing individuals in the progeny of females which have developed under short day conditions during two generations, thus achieving a "cumulative" photoperiodic effect., Natalia D. Voinovich, Nina P. Vaghina, Sergey Ya. Reznik., and Obsahuje seznam literatury
The influence of host intrapatch spatial distribution on parasitoid host acceptance behavior was investigated with Trichogramma principium parasitizing eggs of grain moth, Sitotroga cerealella. Single females were placed in Petri dishes, each containing 60 host eggs arranged either as a compact patch or partitioned into 60 or 12 clusters each consisting of 1 or 5 eggs, respectively. Partitioned patches provoked parasitization more often than compact patches. The percentage of ovipositing females (i.e., females parasitizing at least one of 60 host eggs) increased with the number of clusters, while it was independent of the intercluster distance over intervals of 2.5-15 mm. The mean number of eggs parasitized by ovipositing females during 48 h was almost independent of the host egg spatial pattern. As a result, the rate of parasitization was higher when the hosts were sparsely distributed within a patch than when they were aggregated., Nataliya D. Voinovich, Taisiya Ya. Umarova, Sergey Ya. Reznik, and Lit
Intraguild predation of a generalist predator, Orius niger Wolff (Hemiptera: Anthocoridae) on Trichogramma evanescens Westwood (Hymenoptera: Trichogrammatidae), was determined in choice and no-choice experiments using a factitious host, Ephestia kuehniella Zeller (Lepidoptera: Pyralidae), under laboratory conditions. Choice and no-choice experiments were conducted in order to assess the level of intraguild predation of O. niger on E. kuehniella eggs parasitized by T. evanescens. In no-choice experiments, approximately 50 sterile (1) non-parasitized, (2) 3-day-old parasitized, or (3) 6-day-old parasitized E. kuehniella eggs were offered to 24-h-old females of O. niger in glass tubes. In choice experiments approximately 25 eggs of two of the three groups mentioned above were offered to 24-h-old O. niger females. In both choice and no-choice experiments, O. niger consumed more non-parasitized eggs of E. kuehniella. However, intraguild predation occurred, especially of 3-day-old parasitoids, but very few 6-day-old parasitized eggs were consumed. The preference index was nearly 1 indicating O. niger preferred mainly non-parasitized E. kuehniella eggs. A lower level of intraguild predation is expected under field conditions but needs to be investigated using further experiments.
Trichogramma dendrolimi, T. ostriniae, T. confusum and T. evanescens are the four most commonly occurring Trichogramma species with overlapping distribution in China. They are the most frequently used egg parasitoids for biological control of lepidopterous crop pests in China. It is difficult to differentiate Trichogramma species because of their small size and lack of differences in morphological characters. Different molecular markers were employed to molecularly characterize and differentiate these species, including direct amplification of the internally transcribed spacer 2 (ITS2) of ribosomal DNA by polymerase chain reaction (PCR), restriction fragment length polymorphism (RFLP), random amplified polymorphic DNA (RAPD) and species-specific primers. The results showed that direct amplification of ITS2 could not clearly discriminate these species, but they could be differentiated using RFLP pattern obtained with endonucleases EcoRI and HindIII. The banding pattern produced by RAPD is irreproducible so it is not a suitable way to identify Trichogramma species. Finally, the species-specific primers designed based on ITS2 sequences could unequivocally distinguish the four species. The species-specific primer-based protocol proved to be the most convenient and time saving method for the identification of Trichogramma species by creating a unique PCR product, which can be used in surveying natural populations of Trichogramma species. This is the first report of the prompt identification of the four most commonly occurring Trichogramma species in China.