Dinarmus basalis Rondani (Hymenoptera: Pteromalidae), an ectoparasitoid of bruchid pests of stored cowpeas (Vigna unguiculata), is a potential biological control agent. We investigated whether grain protectants from Hyptis spicigera and H. suaveolens (Lamiaceae) disturb parasitism and post-embryonic growth of the parasitoid. When cowpeas containing bruchid larvae were treated before being placed in the presence of D. basalis females, the rate of parasitism decreased on average up to 24% and 47% in the presence of, respectively, leaf dry powder and essential oils from both plant species. The estimated larval mortality was higher on treated (9.55 to 28.6%) than on non-treated parasitized hosts (2.8%), depending on the plant species and the plant extract tested. Additional larval mortality wa...
Ninety-five nests of Centris (Heterocentris) terminata Smith were collected in trap nests, during November/2001 and January/2003, at two fragments (PZGV e CFO-UFBA) of secondary Atlantic Forest, in Salvador, Bahia State (13 deg 01' W and 38 deg 30' S). The highest nest frequencies occurred from December to February (summer), with no nests foundations from August to October (winter - early spring). Two-hundred eight adults emerged from 347 brood cells, being 164 males and 116 females (1: 0.42). During the study period sex ratio was male biased ({chi}{sup 2} = 9.342; gl = 10; P < 0.05). C. terminata nested in holes with diameters 6, 8, 10 mm, but 84,2% were constructed in 8 and 10 mm. nests had one to seven cells arranged in a linear series with the cell's partitions built with a mixture of sand and resin or oil. Male is significantly smaller than female, which emerges from the first cells constructed. Immature mortality occurred in 14.1% of brood cells ...
In field O{sub 3}-enrichment experiments increased herbivore densities have been reported, which could be due to negatively affected host location behavior of natural enemies. We addressed the impact of doubling background O{sub 3} on the host location of the parasitoid Cotesia plutellae by conducting 24-h trials in an open-air O{sub 3}-fumigation system during two consecutive years. Two circles (radii 1.40 and 4.00 m) of Plutella xylostella-infested potted cabbage plants were placed in the O{sub 3} and ambient plots. Female wasps were released into each plot from the center, and observed 5 times over a 24-h period to assess their host location capability. Thereafter, plants were kept in laboratory conditions until larvae pupation to determine parasitism rates. No significant differences were detected between ambient and O{sub 3}-enriched environments either in the number of wasps found in the field, or in the percentages of parasitized larvae. This suggests that moderately elevated ...
During outbreaks, Microdiprion pallipes (Fall.) is the most destructive of the pine sawflies in Sweden. Its distribution includes most provinces, but damaging outbreaks have until recently occurred only in two inland areas in northern Sweden. These areas are characterised by high elevation, a harsh climate, and slow tree growth. The four recorded outbreak periods showed a 10 year periodicity. Outside these areas, a lesser outbreak occurred in 1988 to 1990, on the east coast (province of Uppland). Outbreak patterns, life history variation, and mortality factors were studied. Factors that may explain the distribution of outbreaks and the population patterns were identified.Experimental and observational evidence on the potential of various factors to influence fecundity, dispersal, and survival was evaluated. In the outbreak areas, there were few major population factors. Parasitism by Rhorus substitutor (Thunb.) was the largest cause of larval mortality and the only important ...