Best Timing to Determine Field Parasitism by Released Diachasmimorpha longicaudata (Hymenoptera: Braconidae) Against Anastrepha (Diptera: Tephritidae) Pest Populations.

Our objective was to determine the timing of the highest parasitic activity by released Diachasmimorpha longicaudata (Ashmead) (Hymenoptera: Braconidae) in areas with fruits of sour orange and hog plums infested by Anastrepha ludens (Loew) and Anastrepha obliqua (McQuart) (Diptera: Tephritidae), under shaded and sunny conditions. Percent parasitism along fruit sampling period was related to host availability, which was influenced by the fruit size rather than environmental conditions. The highest parasitism in sour orange was obtained just the first day after release, but in hog plums this was observed during the first 3 days without significant differences between them. The levels of fruit infestation and parasitism were higher in shaded trees in sour orange as in hog plums. The high availability of larvae and the small size of hog plums were decisive for obtaining high levels of parasitism and keeping parasitoids near the release points. By contrast, the size and thick rind of sour orange provided to the larvae a physical refuge that was associated with lower parasitism, causing that parasitoids spread out in search of hosts more accessible. In sour orange, parasitism was exclusively by D. longicaudata, while in hog plums, we additionally found the coexistence of four native parasitoid species. This information suggests that in sour orange, the sampling should be performed 1 day after release, while in hog plums, the samplings can be extended to within the first 3 days. Such sampling can serve to better estimate the effect of D. longicaudata releases against Anastrepha pest populations in different fruit types.

Susceptibility of Nezara viridula (L.) (Hemiptera: Pentatomidae) Egg Masses of Different Sizes to Parasitism by Trissolcus basalis (Woll.) (Hymenoptera: Platygastridae) in the Field.

Egg masses of Nezara viridula (L.) are commonly parasitized by Trissolcus basalis (Woll.), and we investigated the role of size of egg masses on parasitization by T. basalis. Sentinel egg masses were exposed to parasitism in the field for 6-7 days, when they were collected for evaluation of parasitoid emergence. We recorded the number of eggs per egg mass, the number of emerged hosts, and the number of empty and parasitized eggs. We calculated the proportion of attacked host egg masses (DE), the proportion of parasitized eggs per attacked egg mass (PE), and total parasitism (PI). The total number of egg masses exposed to parasitism was 330. The minimum, mean, and maximum egg mass sizes were 25, 75.2, and 111, respectively. DE and PE varied widely between different fields, and they were independent of egg mass size. In 14.2% of all parasitized egg masses, we found simultaneous emergence of T. basalis and N. viridula independently of host egg mass size. PE exhibited low variability compared with PI and DE, which were linearly related. PI and DE values from other field studies are consistent with the linear relationship, suggesting that PI is mostly related to the proportion of the DE. This also suggests that total parasitism is independent of egg mass size, of possible differences in plant species, and T. basalis density and strains.

Distribuição de ovos de Plutella xylostella (L. ) (Lepidoptera: Plutellidae) e o parasitismo por Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae) / Egg distribution of Plutella xylostella (L. ) (Lepidoptera: Plutellidae) and the parasitism by Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae)

Oviposition site preference of Plutella xylostella (L.) and the parasitism by Trichogramma pretiosum Riley on cabbage plants at pre- and post-head formation were investigated in commercial cabbage field. Groups of six plants were randomly caged. In each cage three pairs of 24h-old P. xylostella moths were released, followed by 1,200 T. pretiosum females released 12h later. After 48h from parasitoid release, plants were harvested and fully inspected with the oviposition mapped according to the leaf position and their parts (basal, median and border) and upper and bellow leaf surfaces. Moth oviposition and egg parasitism were equally distributed across the plant leaves at the pre-head formation stage. At this stage, the basal part and the upper leaf surface were the preferred places for oviposition and egg parasitism, respectively. Cabbage plants at the post-head formation stage exhibited greater oviposition and egg parasitism in the inner leaf attached to the head. At this stage, the leaf border and the upper leaf surface were the preferred places for oviposition and egg parasitism, respectively. The infestation of P. xylostella on cabbage can be determined by egg counting at the pre- and post-head formation stages at the basal part of the leaves or at the border of the leaf attached to the head, respectively. And, in both plant stages parasitized eggs by T. pretiosum are more likely to be found at the upper leaf surface.