Effects of temperature and humidity on development and oviposition of Sitotroga cerealella (Lepidoptera: Gelechiidae).

The fecundity of Sitotroga cerealella (Olivier) in wheat was greatest at 25 to 30?C. Development of pupae was shortest at 30-32?C, and differences due to rela tive humidity were not significant. Optimum conditions for development, attain ment of adult weight, and percentage emergence were 30-32?C and 65-80% RH. Considerable interest has been expressed in the potential of Tricho gramma spp. as a biological control agent (Knipling and McGuire 1967). One of the factors limiting production of the wasp is incomplete knowledge of the optimum rearing conditions of its host, the Angoumois grain moth, Sitotroga cerealella (Olivier), which spends the entire larval-pupal period within kernels of grain. Spencer et al. (1965) and Grewal and Atwal (1969) reported the optimum temperature of the macroenvironment for development of all stages to be 30?C; the opti mum for oviposition was shown to be 15-32?C, 70-75% RH (Schiefen decker 1968). However, Grewal and Atwal (1969) reported 80% as the optimum humidity for development of all stages and for adult oviposi tion. Also, Warren (1956) reported that females reared from corn with 17% moisture were heavier than those reared from corn with 15% mois ture but the differences in fecundity were not significant. Tests were therefore made at the Biological Control of Insects Re search Laboratory to determine the optimum microenvironmental tem perature and humidity for producing adult and eggs of Sitotroga. 1 Received for publication May 20, 1973. 2 Mention of a proprietary product in this paper does not constitute an endorse ment of this product by the USDA. This content downloaded from 157.55.39.138 on Mon, 27 Jun 2016 06:58:57 UTC All use subject to http://about.jstor.org/terms Vol. 47, No. 1, January, 1974 31 Table 1. Longevity and fecundity of female Sitotroga cerealella held at various temperatures. Temperature Longevity1'2 Fecundity (?C) (days) (% egg wt/body wt) 20 14.6 ? 2.2a 31.6 ? 7.1a 25 10.8 ? 1.5ab 39.2 ? 7.7a 30 9.7 ? 1.2bc 38.1 ? 8.5a 35 8.3 ? 1.7bc 30.9 ? 8.4a 40 6.1 ? 1.2c 8.4 ? 4.9b 1 Mean and 95% confidence interval. 2 Means in same column followed by same letter are not significantly different (Pr^O.05) (Duncan's new multiple range test). Experimental Procedures and Results A colony of Sitotroga was maintained in the laboratory by using methods of R. K. Morrison (unpublished) of the USDA, ARS Cotton Insects Laboratory, College Station, Texas. Rearing cribs containing 9.1 kg of recleaned locally-grown wheat were infested with 1-day-old eggs at a rate of 2 eggs/wheat grain. Subsequently, samples of the infested wheat were removed and placed in a single layer in 30-cm3 plastic cups prepared by replacing the bottom of each cup and a hole (2 cm in diam) in the cardboard lid with 6 strand/cm mesh Saran? screen. The cups were placed on their sides on wire racks in humidity chambers made of 1.1-liter polystyrene containers covered with a plastic lid. A 8-cm-diam area of the lid was replaced with polyethylene. The chambers were then placed in dark incubators at desired constant temperatures. The test RH, produced by combining glycerin and distilled water, was tested weekly with a Honeywell W611A Portable RH Indicator,? and was adjusted when necessary. Specific gravity was determined with precision hydrometers (Grover and Nicol 1940; Braun and Braun 1958). Moisture content of the grain was measured with a Steinlite? moisture tester. Moths were collected and sexed daily until all were emerged. Moth and egg weights were measured to the nearest 0.01 mg. The number of emerged adults/100 wheat grains was used to determine percentage wheat kernels yielding moths. Temperature and humidity experiments on oviposition and for larval-adult and pupal adult development were arranged in randomized complete block designs. Significance of differences were tested by analysis of variance (P ^ 0.05). Tests of Oviposition Virgin females (reared at 30 ? 0.5?C and 80 ? 10% RH) were anesthetized with C02, weighed, and placed individually with a male in 3 Identification by Dorothy Fennel, USDA ARS Northern Utilization Research Laboratory, Peoria, IL. This content downloaded from 157.55.39.138 on Mon, 27 Jun 2016 06:58:57 UTC All use subject to http://about.jstor.org/terms 32 Journal of the Kansas Entomological Society Table 2. Developmental time in days from pupation to adult of Sitotroga cerealella at 4 temperatures and relative humidities. RH Developmental time (%)_(days) 24?C 50 11.6 ? 1.8a 70 9.7 ? 1.4 80 10.7 ? 1.1 90 10.8 ? 1.4 27?C 50 11.6 ? 1.8 70 14.9 ? 2.1 80 11.0 ?1.9 90 10.0 ? 1.4 30?C 50 8.1 ? 1.4 70 8.5 ? 1.2 80 9.3 ? 1.4 90 7.6 ? 0.9 32?C 50 8.3 ? 1.3 70 7.9 ? 1.8 80 5.9 ? 0.9 90 8.4 ? 1.7 a Mean and 95% confidence interval from 6 replications. a 50-dr oppositional chamber similar to the unit described by Mills (1965). Eggs were oviposited in the crack between 2 pieces of construc tion paper. Moths had access to water from saturated cotton wicking. In the 1st of 2 experiments, the chambers were held in constant light at 30 ? 0.5?C and 80 ? 10% RH. Eggs produced were counted daily. Mean weight of the 79 females was 6.03 mg (range 2.87-8.69); the average was 150.83 eggs (range 28-237). Fecundity increased sig nificantly with body weight: y = 29.45X -26.85. Of the total sums of squares, 59.2% was accounted for by the regression. Moths laid 84.0 ? 2.50% (mean+ 95% confidence interval) of their eggs in 4 days. In a rearing program, cost of eggs from moths held beyond this point would increase rapidly because of reduced oviposition. Fecundity was not significantly related to length of the female's development. In the 2nd experiment, females were held at 20, 25, 30, 35, and 40 ? 1?C and 80 ? 10% RH, and the proportion of body weight laid in eggs was analyzed rather than the actual weight of the eggs (fecundity = % egg weight/body weight) to remove the variation due to female body weight. Differences in fecundity were nonsignificant at temperatures of 20 This content downloaded from 157.55.39.138 on Mon, 27 Jun 2016 06:58:57 UTC All use subject to http://about.jstor.org/terms Vol. 47, No. 1, January, 1974 33 Table 3. Percentage kernels yielding moths, weight, and developmental time of Sitotroga cerealella when held from larva to adult at 3 temperatures and relative humidities. Percentage kernels yielding moths Female Female RH weight development (%)_$ + 9_g only_(mg)_ (day) 25?C 50 34.0?11.3a 21.0 ?12.3 5.1 ? 0.4 34.1 ? 1.3 65 42.5 ?10.5 23.0 ?12.2 6.0 ? 0.4 34.8 ? 1.8 80 47.5 ? 10.0 24.0 ? 12.1 5.7 ? 0.4 31.5 ? 1.2