Bionomics and behavior of the bethylid parasitoid, Goniozus triangulifer Kieffer, were studied in the laboratory with leaffolders, Cnaphalocrocis medinalis (Guenee) and Marasmia patnalis (Bradley), as hosts. Female parasitoids lived twice as long as males (22 and 11 d, respectively) and laid about 80 eggs during their lifetime. Single male broods occurred in 64% of the samples and were significantly more frequent than expected from the binomial distribution only when the brood size was six. Females exhibited complex behavior upon encountering a host. Malaxation occurred before the female parasitoid paralyzed the host. Parasitoids laid an average of 4.5 eggs on unparasitized hosts and 2.4 eggs on previously parasitized ones, but commonly did not lay at all on these. Total handling time for experienced parasitoids on parasitized hosts was significantly shorter than that for unparasitized hosts. G. triangulifer displays the ability to discriminate between unparasitized hosts and those parasitized by conspecific females.
Host discrimination was investigated in two related species of ichneumonid wasps: Diadegma eucerophaga Horst. and D. fenestralis (Holmgr.) attacking a common host, the diamond-back moth Plutella xylostella (L.). In the laboratory, I studied: (1) the relative amounts of time spent between patches containing unparasitized or parasitized hosts, (2) the results of parasitoid encounters with parasitized and unparasitized hosts,(3) dissections to reveal whether or not the wasps preferred to oviposit in unparasitized hosts. D. eucerophaga showed discrimination by (1) avoiding patches containing parasitized hosts and by (2) preference to oviposit in unparasitized larvae. No discrimination was detected for D. fenestralis at any of the three levels.In the field, a population consisting primarily of D. eucerophaga was presented to plants containing either unparasitized or previously-parasitized larvae. Although superparasitism occurred, the wasps preferred to oviposit in the unparasitized larvae.
A field experiment was performed to determine the effects of different times and frequencies of handweeding on grain yields in upland rice. Five weeding treatments were done. These treatments consisted of single weedings at 20 and 35 days after emergence (d.a.e.) and double weedings at 10 and 15 d.a.e., 20 and 35 d.a.e. and 30 and 45 d.a.e. Two controls were made: a weed-free control where weeds were continuously removed and a weedy control where no handweeding was done. Aboveground destructive harvests on the controls were used to determine dry matter partitioning. These were performed at 10, 30, 50, 70 and 90 d.a.e. and at harvest. Rice and weed heights were measured for the controls and all treatments. Grain yields were compared and analyzed statistically. Absence of weed control produced only 50 kg/ha of grain. Single weeding increased yield to about 2000 kg/ ha and double weeding to about 2500 kg/ha. However, no significant differences were found between treatments of the same weeding frequency. Complete weed control produced 3000 kg/ha of grain. During grain formation, stem weight of weed-free rice declined by 24% as compared to 74% in weedy rice.
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