The eggs of the stored grain pests, Tribolium castaneum (Herbst), T. confusum (Duval) (Coleoptera: Tenebrionidae) and Cadra cautella (Walker) (Lepidoptera; Pyralidae) belonging to three age groups, 1, 2, and 3 days-old, were exposed to ultraviolet (UV) radiation with 254nm wavelength (UV-C) for different durations to determine irradiation effects on egg-hatching and adult emergence. An increase in time of exposure to UV-rays caused a gradual decrease in the percentage of hatching of eggs in all age groups of eggs. No hatching occurred after 24 minutes of exposure in 2 and 3 day-old eggs of T. confusum. C. cautella eggs were less sensitive to UV-rays than were T. castaneum and T. confusum eggs. All the exposure periods significantly reduced the eclosion of adults in all the experimental insects. No adults emerged when 3 day-old eggs of T. castaneum were irradiated for 16 or 24 minutes, or from 2 and 3 day-old eggs T. confusum irradiated for 16 or 24 minutes.
The larvae of Tribolium castaneum (Herbst) of different ages were exposed to various concentrations viz., 0.0001, 0.001 and 0.01 ppm of triflumuron up to pupation. The adults were allowed to feed on untreated diet. The preoviposition period, fecundity, egg viability and incubation period of the eggs laid were studied. Triflumuron significantly lengthened the preoviposition and incubation periods (P < 0.001). Fecundity and egg viability were also reduced (P < 0.001) due to the treatment. Both the strains were affected by the treatment.
Eggs of the lesser mealworm, Alphitobius diaperinus (Panzer) were exposed to UV-rays of 254nm wavelength for different durations viz. 1, 2, 4 and 8 minutes. After seven days of hatching, larvae of each exposure were reared separately on triflumuron (1 x 10-3 mg/kg) treated food and observed the population of various developmental stages e.g., egg, larval, pupal and adult at storage periods of 3-, 6-and 9-months. UVrays and triflumuron treatments deleteriously reduced the populations of all the developmental stages of A. diaperinus. Egg and pupal populations of the beetle were adversely influenced by the storage periods also. Complete reduction of A. diaperinus populations was achieved from 6-9 months storage periods, when eggs were exposed to UV-rays for 8 minutes.
The efficacy of methyl iodide (MI) as a fumigant against all developmental stages of the maize weevil, Sitophilus zeamais Motsch. was investigated. Tests were conducted with concentrations of 1.5, 1.8, 2.1, 2.4, 2.7 and 3.0 mg/l, for a 6-h exposure period. Values of LC 50 , LC 95 and LC 99 of MI for immatures and adult stages were determined. The present laboratory tests showed that MI was toxic to various life stages of S. zeamais at relatively short exposure periods. At the LC 50 and LC 95 levels, the most susceptible stage was the egg stage followed by larvae, pupae and adults (1-day mortality). The egg was found to be most susceptible to MI, requiring 0.81 and 2.16 mg/l for 50 and 99% mortality, respectively, while the adult was most tolerant, requiring 2.30 and 3.02 mg/l for 50 and 99% mortality, respectively, based on 1-day mortality count. Pupae were less susceptible to MI than egg and larvae, requiring 1.47 and 3.19 mg/l for 50 and 99% mortality, respectively. Based on the present toxicity tests, MI has the potential for use as a fumigant to control all developmental stages of the maize weevil, S. zeamais.
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