Robert B. Mills

Radiographic Studies of Sitophilus zeamais Mots. in Wheat Kernels

Abstract Ninety-nine wheat kernels infested by Sitophilus zeamais Mots., were radiographed daily, to study development from egg to adult and behavior of the insects within the kernels. Enlarged photographic prints were prepared from these radiographs to facilitate interpretation. Instars were identified by examining prints and by measuring the widths of tunnels on radiographs and also by measuring the widths of the head capsules of the larvae dissected from kernels. On hatching, each larva was observed to increase the width of the tunnel for a few days, then for 1–3 days the width of the tunnel remained static after which it was again widened. There were four periods of tunnel widening. Since there were four corresponding distinct sizes of head capsules for larvae dissected from kernels, we conclude that the four periods of tunnel widening represent the periods of larval growth and that the periods of static tunnel width define the time of moulting. The average widths of tunnels were successively 0·33, 0·55, 0·90 and 1·49 mm. The mean developmental periods for stadia 1–4 at 27°C and 69 ± 3% r.h. were 3·6, 4·7, 4·8 and 5 days, respectively. Average developmental periods for prepupa, pupa and pre-emerged adult stages were 1, 5·3 and 5·3 days. The average length of the developmental cycle from the start of a 3-day oviposition period to emergence of the adult was 36·3 days. Of the eggs in dissected kernels, 42, 37 and 21 per cent were deposited in endosperm, germ perimeter, and germ center of the kernels, respectively. Of 26 emerged adults, 6 prepared the pupal chamber in one side of the kernel; 8 diagonally across the crease; and 12 parallel to the crease but occupying portions of both kernel halves. Data obtained from these studies are compared with data from previous radiographic studies of Sitophilus oryzae (L.) and S. granarius (L.).

Influence of medium and physical disturbances during rearing on development and numbers of Sitophilus progeny

Abstract Four Sitophilus populations ( Sitophilus zeamais Motschulsky from Mexico, S. zeamais from Arkansas, U.S.A., Sitophilus oryzae L., and Sitophilus granarius L.) were studied. Hard red winter wheat, sorghum, and maize were used to determine effects of rearing media on progeny production of insects from the four populations. Mechanically disturbing infested samples to remove newly-emerged adult weevils every 48 hr reduced numbers of progeny surviving to the adult stage, especially for Arkansas S. zeamais and S. granarius reared in any of the three grains. With one exception, reproduction for all populations in all three grains was highest when parents were reared in wheat; other differences are discussed. Also, progeny developmental periods for all four populations were shortest when parents were reared in wheat. Progeny of all four populations had the longest developmental periods when reared in maize regardless of the medium in which their parents were reared. In 250 g samples of wheat, and 125 g samples of sorghum, 50 parent S. oryzae produced statistically as many progeny as in 500 g and 625 g samples of wheat and 250, 500, and 625 g samples of sorghum, respectively. In maize, 625 g samples produced significantly more progeny than 500 g samples. Sex ratios of progeny from each grain were 1:1, except that females of S. oryzae reared in maize outnumbered males.

Development and oviposition of Ahasverus advena (Waltl) (coleoptera, silvanidae) on seven species of fungi

Abstract Development and oviposition of the foreign grain beetle, Ahasverus advena (Waltl), were studied on pure cultures of seven species of fungi. The insects developed on Aspergillus amstelodami (Mangin) Thom and Church, Penicillium citrinum Thom, and a Cladosporium sp. but not on A flavus Link, A. niger Van Tiegham, or A. ochraceus Wilhelm; a few larvae reached the adult stage on A. candidus Link. Females preferred to oviposit in the fungi where larval development was successful, in both no-choice and 3-choice tests.

Influence of rearing medium on size and weight of adults of four Sitophilus populations and on weight loss of host kernels (Coleoptera: Curculionidae)

Abstract Four populations of Sitophilus (S. zeamais Motsch. from Mexico, S. zeamais from Arkansas, U.S.A., S. oryzae (L.) and S. granarius (L.) were studied. Hard red winter wheat (“Cloud” variety), brown commercial sorghum, and yellow and white “dent” maize (mixed varieties) were used to determine the effect of parent-and progeny-rearing media on the adult elytron length in each population. Kernel weight loss caused by individuals of each population and weevil weights were determined. Elytron lengths of S. oryzae progeny were significantly ( P S. granarius progeny from wheat were significantly larger than those from maize or sorghum; progeny from all other populations were significantly larger from maize than from wheat or sorghum. S. oryzae caused less weight loss in kernels of wheat and sorghum, and were significantly lighter ( P S. zeamais was significantly heavier than Mexican S. zeamais in wheat, otherwise their weights were similar. Weight losses (actual and percentages) of kernels of all grains were similar for Arkansas S. zeamais and Mexican S. zeamais. S. granarius were heavier and produced greater weight loss in wheat kernels than other populations did.

Olfactory responses of adultTribolium castaneum (Herbst), to volatiles of wheat and millet kernels, milled fractions, and extracts

Olfactory responses of 72- to 96-hr-old, 24-hr starved adult male, female, or mixed-sex groups of the red flour beetle,Tribolium castaneum (Herbst), to volatiles from wheat and millet kernels, certain milled fractions, and solvent extracts were recorded by using a lightsensitive apparatus. Wheat-germ volatiles from intact germ or solvent extracts were generally more attractive than volatiles of wheat endosperm or wheat bran. Volatiles of whole wheat kernels were the least attractive among test materials of wheat origin, whereas there were no significant differences among whole wheat flour, germ, and endosperm. Wheat-germ extracts, however, were more attractive than were extracts of the other fractions. Whole millet flour or fermented millet flour volatiles were more attractive than those from whole millet kernels or millet starch. Beetles reached maximum responsiveness to grain volatiles by 72–96 hr after adult ecdysis. Groups of virgin female beetles generally were more responsive than male or mixed-sex groups to volatiles of substances tested.

Gamma radiation effects on mating frequency and delayed mating of male Cadra cautella (Walker) (Lepidoptera: Pyralidae)

Gamma radiation doses of 0, 10, or 20 krad to 8-day-old pupae of Cadra cautella (Walker) did not significantly affect (P<0.05) the mating frequency of male moths kept constantly with female moths (1♂:5♀ per vial) for 72 hr but there were fewer matings by males exposed to 30 krad. When the opportunity of mating was restricted to 24 hr and delayed for 1–7 days, the mating frequency, and the numbers and fertility of eggs laid by young females all progressively declined with age. Increasing the radiation dose accentuated the reduction in male reproductive potential. Range of male longevity was not so critical as the period of significant male mating activity. Males in constant association with excess females had significantly lower (P < 0.01) mean longevity (4.25 ± 1.11 days) than did unmated and mated males (7.75 ± 1.99 days) in the delayed-mating studies; that was related to the increased mating frequency (maximum 8 ×) in the free-choice situation.

Development of Sitophilus zeamais Motschulsky, in maize kernels and pellets made from maize kernel fractions

Abstract As a means of studying certain aspects of resistance of maize varieties to Sitophilus zeamais , various types of pellets were prepared using ground maize and compared with whole, pericarpless, and germless kernels. Numbers of weevil progeny (from six females and three males, and usually a 7-day oviposition period) were greatest in pellets made of flour moistened with water containing agar. More progeny was produced in pellets than in whole kernels. Damaged kernels (hot-water treated, pericarpless, germless) were more susceptible than undamaged kernels and fewer weevil progeny were produced in pellets made of germless kernels than from pellets of whole kernels. Additions of small amounts of extra germ tissue to whole maize flour enhanced the susceptibility of pellets to the weevil, but adding larger amounts of germ of pericarp reduced progeny number, weight and developmental speed.

Influence of mechanical damage and repeated infestation of sorghum on its resistance to Sitophilus oryzae (L.) (Coleoptera: Curculionidae).

Abstract Abrading the pericarp rendered resistant sorghum cultivars as susceptible as abraded susceptible cultivars to attack by Sitophilus oryzae (L.). A previous exposure of selected sorghum cultivars to S. oryzae broke down pericarp resistance factor(s). Damage to sorghum kernels during harvesting and handling could therefore destroy resistance to rice weevil attack.

Radiation-induced sterility in Ephestia cautella (Walker) (Lepidoptera: Pyralidae): Recovery of fertility during five generations after gamma irradiation☆

Abstract Male Ephestia cautella were exposed to 0, 10, 20 or 30 krad of gamma irradiation and mated with untreated females. There were no offspring from males treated at 30 krad. Some of the offspring from the other three treatments were paired and the remainder paired with untreated adults of the opposite sex. This procedure was repeated for a further five generations for all the lines that yielded offspring, no further individuals being irradiated. Data on the reproductive behaviour of control males and their progeny through five generations were statistically homogeneous between generations. The offspring of the irradiated males were predominantly male, but this became less marked in the succeeding generations from those irradiated at 10 krad, and more or less disappeared by the fourth. Sex ratio distortion appeared to be correlated with reduced reproductive rate. A partially sterilizing dosage of 20 krad given to the male E. cautella parents induced complete sterility in their first progeny. The practical significance of radiation-induced inherited sterility to control or suppress the moth is further discussed.

Intraspecific Kernel-Entry Behavior and Competition among Larvae of the Angoumois Grain Moth

The internecine activities of internal-feeding Angoumois grain moth larvae, Sitotroga cerealella (Oliv.), were studied by placing newly-hatched larvae with kernels (with or without pre-drilled holes) already infested, by placing 1, 2, or 4 larvae with each kernel (with or without holes), and by introducing 2 larvae/kernel in holes pre-drilled at different locations on the kernel. A larva placed with an infested kernel usually entered by the hole previously used. The second larva was usually killed or driven from the kernel by its original inhabitant. Two larvae introduced into predrilled holes in a wheat kernel intercepted each other faster when the holes were on opposite sides of the germ than when one hole was in the germ and one in the mid-kernel, and still slower when one hole was in mid-kernel and the other at the brush end. Two larvae could develop to maturity concurrently in one kernel with an aluminum foil barrier cemented between its halves. The Angoumois grain moth (Sitotroga cerealella (Oliv.), Family Gelechiidae) is a buff moth 13 mm long that usually oviposits among grain kernels. The eggs hatch in a few days and the newly-hatched larvae bore into kernels, or enter through cracks, and develop to adults inside the kernels. Duhamel and Tillet (1762) noted internecine activities among newly-hatched Angoumois grain moth larvae. They reported that M. de Reamur also had observed that phenomenon at least 20 years earlier. Others, including Crombie (1944 and 1946), reported competition of larvae for kernel-entry sites and also defensive behavior shown by established larvae as their tunnels were opened during dissections of infested kernels. This study obtained further details of intraspecific competition. Transactions of the Kansas Academy of Science, Vol. 72, No. 2, 1969. Published September 17, 1969. 1 Contribution No. 973, Department of Entomology, Kansas Agricultural Experiment Station, Kansas State University, Manhattan, Kansas, U.S.A. Supported in part by PHS Grant EF-114 and UI 095; Cooperative Agreement 12-14-100-8404(51) United States Department of Agriculture, Agricultural Research Service, Market Quality Research Division, Stored Product Insects Research Branch; and NSF Undergraduate Research Participation Grant GY-45. 2 Formerly NSF Undergraduate Research Participant (now with U.S. Naval Disease Vector Control Center, Alameda, Calif.); and Assistant Professor of Entomology, respectively.