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Effects of Ultraviolet (254nm) Irradiation on Egg Hatching and Adult Emergence of the Flour Beetles, Tribolium Castaneum, T. Confusum and the Almond Moth, Cadra Cautella

S. I. Faruki*
Department of Zoology, Rajshahi University Rajshahi, 6205, Bangladesh

D. R. Das
Department of Zoology, Rajshahi University Rajshahi, 6205, Bangladesh

A. R. Khan
Department of Zoology, Rajshahi University Rajshahi, 6205, Bangladesh

M. Khatun
Department of Zoology, Rajshahi University Rajshahi, 6205, Bangladesh

Abstract/ Executive Summary:

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.

Keywords: Physical control, Red flour beetle, Confused flour beetle, Almond moth, Tropical warehouse moth

Location: Department of Zoology, University of Rajshahi

Start Date:

End Date:

Program Area: Pest Management

Commodity: Beetle

Objectives:

The present investigation was, therefore, aimed at determining the effects of UV-rays (UV-C) on hatching and adult emergence in T. castaneum, T. confusum and C. cautella eggs of various ages.

Methodology:

Sources and rearing of test insects T. castaneum was originally received from the Pest Infestation Control Laboratory, Slough, England, and T. confusum was obtained from the Food Entomology Laboratory, National Food Research Institute, Tsukuba, Japan. They were cultured for a few years in the Insect Research Laboratory, Department of Zoology, University of Rajshahi, on a rearing medium containing whole-wheat flour and Brewer’s yeast (19:1). C. cautella was collected from a Government Warehouse at Rajshahi as larvae and reared on groundnut kernels (Arachis hypogaea L.). Egg production, collection and sorting of eggs The eggs of Tribolium spp. were collected by placing large numbers of beetles on the rearing medium. On the following day the culture medium was sieved to separate the adults and eggs that were 1 day-old. The eggs were kept in Petri dishes to obtain the eggs of 2 and 3 day-old eggs. For collecting the eggs of C. cautella, a number of healthy pupae were sexed and kept in beakers until adult eclosion. Freshly emerged moths were allowed to mate and placed in beakers for oviposition. A piece of hard white paper was inserted inside the beaker for resting of the adults and the top of the beaker was covered with a netted cloth. The beakers with moths were inverted over Petri dishes for an easy collection of the eggs. On the following day 1 day-old eggs were collected. Some of these eggs were kept in Petri dishes to obtain 2 and 3 day-old eggs. The incubation period of the eggs of T. castaneum and T. confusum varies from 6–7 days and of C. cautella from 5–6 days at 30° C. UV-irradiation technique of eggs The aim of these experiments was to determine age-specific resistance of the developing eggs to UV-irradiation. The experiments were conducted at a mean room temperature of 30 ± 2° C under an illumination of two 40W fluorescent bulbs with a photoperiod of 10:14 L:D without any humidity control. A 15W UV germicidal lamp (GE15T8)(F.G. Bode & Co. Gmbh, www.optiker-bode.de) measuring 20 cm x 4 cm, emitting at a wavelength of 254nm (UV-C) was only the source of irradiation. During irradiation the room was illuminated with two 40W fluorescent bulbs. For irradiation of T. castaneum and T. confusum, eggs in a Petri dish (9cm) were placed on a surface (20.5 cm² ) 12 cm from the lamp. Eggs were irradiated for 2, 4, 8, 16 or 24 minutes. Exposure period was determined using a stopwatch. At the end of the exposure period the UV-lamp was turned off and the Petri dishes were removed immediately. After exposure, the irradiated and non-irradiated control eggs of different age groups were kept separately at 30 ± 2° C until hatching. Neonate larvae from both irradiated and non-irradiated eggs were transferred to plastic containers with rearing medium to observe adult eclosion. The experiment was replicated 3 times with 50 eggs for each exposure period and an equal number of non-irradiated eggs were raised as controls for each age group. C. cautella eggs of desired ages were irradiated similar to the procedure of Tribolium eggs. Eggs of different ages and exposure periods, either irradiated and/or non-irradiated, were kept in separate pieces of black adhesive tape to observe hatching. The black tape was used to prevent the hatched larvae from crawling away. To observe the emergence of adults, eggs were kept in separate Petri dishes with groundnut kernels until adult eclosion. All the experiments including controls for each age group were replicated 3 times with 100 eggs each. Data and statistical analyses Data were analyzed by Factorial analysis of variance (ANOVA) using Minitab Inc. and a comparison test was done between means of control and exposure periods by Tukey’s test of multiple comparisons (1953). The percent reduction in hatching of eggs in comparison to control was calculated using the formula: Percent reduction = (X1 − –X2 − )/X1 − x 100, where, X1 − = mean hatching of control eggs and X2 − = mean hatching of irradiated eggs. The adult recovery (%) was also analyzed by computing standardized normal deviate values (d, the difference between the mean and the value of interest divided by the standard deviation) for determining the differences in parameters having binomial distribution.

Source of Information: Journal of Insect Science: Vol. 7, Article 36, ISSN: 1536-2442

Article Link (Online Journal): www.insectscience.org

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

The significantly reduced hatching and adult emergence caused by UV-irradiation in the experimental pests is promising from pest management point of view. It may be concluded that irradiation is a very safe and clean method for food preservation and pest control. However, much more comprehensive research is needed.

Knowledge Management: Journal