Life History of Immature Maize Weevils (Coleoptera: Curculionidae) on Corn Stored at Constant Temperatures and Relative Humidities in the Laboratorv

Life history of immature maize weevils, Sitophilus zeamais Motschulsky, was studied at 10-40°C and 43-76% RH. The optimal quantity of corn for minimizing density effects and the optimal observation frequency for minimizing disturbance effects were determined at 30°C and 75% RH. The quantity of corn (32-256 g) provided to five females ovipositing for 24 h did not affect duration of development, but the number of progeny produced increased asymptotically as the quantity of corn provided increased. Frequency of observation (from 1- to 14-d intervals) did not affect duration of development or number of progeny produced. Using moisture contents measured in the life history study, an equation was developed for predicting equilibrium moisture content of corn from temperature and relative humidity. Duration of immature development did not vary with sex, but did vary with test. This suggests that insect strain or chemical composition of the corn must be included as factors in a model predicting effects of environment on duration of immature development. Survival from egg to adult emergence was greatest at 25°C. Sex ratio of emerging adults did not differ from 1:1. The number of multiply-infested kernels was low at all environmental conditions, and survival from egg to adult emergence in these kernels averaged 18%. Maximum daily rate of fecundity, duration of development, and number of progeny produced were optimal at 30°C and 75% RH. An index of environmental suitability indicated that 30°C and 75% RH was the optimal environment for growth of maize weevil populations on corn. Implications of the results for managing maize weevil populations are discussed

Development Rates for the Seed Maggots Delia platura and D. florilega (Diptera: Anthomyiidae)

Duration of immature stages of seedcorn maggots (SCM), Delia platura (Meigen), and bean seed maggots (BSM), D. florilega(Zetterstedt), was determined at eight constant temperatures from 5 to 40°C. No SCM or BSM survived to second instar at either 5 or 40°C. No BSM survived to the adult stage at 35°C. Duration of immature stages varied from 240 days at 10°C to 17 days at 35°C. A computer model developed using the SCM development rate data closely simulated SCM development in the field during the growing seaso

SEASONAL FLIGHT ACTIVITY OF THE MAIZE WEEVIL, \u3ci\u3eSITOPHlLUS ZEAMAIS\u3c/i\u3e MOTSCHULSKY (COLEOPTERA: CURCULIONIDAE), AND THE RICE WEEVIL, \u3ci\u3eS. ORYZAE\u3c/i\u3e (L.), IN SOUTH CAROLINA

Flight activity of Sitophilus zeamais Motschulsky (Coleoptera: Curculionidne) and S. oryzae (L.) was monitored during 1987-88 with sticky traps at three sites in South Carolina. Weevils were caught from late March to early November. The results indicate that temperature is the major factor determining seasonal flight activity of these weevils. More S. zeamais than S. oryzae were trapped at all sites. Sitophilus oryzae were abundant only at the site at which wheat was stored. There was no apparent pattern to flight activity within a storage site. The results indicate that there is little night activity around bins in which recommended pest control practices are followed

Development Rates for the Seed Maggots \u3ci\u3eDelia platura\u3c/i\u3e and \u3ci\u3eD. jlorilega\u3c/i\u3e (Diptera: Anthomyiidae)

Duration of immature stages of seedcorn maggots (SCM), Delia platura (Meigen), and bean seed maggots (BSM), D. florilega (Zetterstedt), was determined at eight constant temperatures from 5 to 40°C. No SCM or BSM survived to second instar at either 5 or 40°C. No BSM survived to the adult stage at 35°C. Duration of immature stages varied from 240 days at 10°C to 17 days at 35°C. A computer model developed using the SCM development rate data closely simulated SCM development in the field during the growing season

Effects of Diet on Population Growth of Psocids \u3ci\u3eLepinotus reticulatus\u3c/i\u3e and \u3ci\u3eLiposcelis entomophila\u3c/i\u3e

We investigated the suitability of 11 diets as culture media for the psocids Lepinotus reticulatus Enderlein (Psocoptera: Trogiidae) and Liposcelis entomophila (Enderlein) (Psocoptera: Liposcelididae). The culture media comprised six diets made of plain cereals, namely, wheat (Triticum aestivum L.), corn (Zea mays L.), milo Sorghum bicolor (L.), barley (Hordeum vulgare L.), oats (Avena sativa L.), and rice (Oryza sativa L.), and five artificial diets. We found that, with the exception of corn, L. reticulatus population increase was greater on plain cereal diets than on artificial diets, and the greatest population growth was on oats. There was an inverse relationship between L. reticulatus population growth and diet compactness. L. entomophila populations grew fastest on wheat, barley, and a mixture of cracked wheat, rice krispies, and brewer\u27s yeast (97:2:1, wt:wt). The proportion of females was greater in diets that were less suitable for L. entomophila population growth compared with that in the more suitable diets. Diet compactness had a weak effect on L. entomophila population growth. This study also has established the relative level of suitability of damaged wheat, corn, milo, barley, oats, and rice to L. reticulatus and L. entomophila

Insect Infestation of Farm-Stored Maize in South Carolina: Towards Characterization of a Habitat

Protecting stored grain from insect damage, with minimum pesticide risk, will require pest management based on comprehensive understanding of storage environments and their interactions with pest populations. Computer modeling offers the means to this understanding. To obtain data sets for modeling selected pests of stored maize, we studied maize storages on six farms in a four-county area of southwestern South Carolina. Grain moisture content was measured monthly, and grain temperatures were recorded hourly for one storage season. Insect populations were monitored by taking grain and pitfall trap samples at weekly or monthly intervals. Hourly mean grain temperatures remained below optimal levels for growth and development of insects during most of the storage period. Grain moisture content varied from 11.2 to 16.4%. Forty three species of insects and one species complex, representing 26 families in four orders, were detected. The estimated importance of each species in the farm storage habitat, as measured by relative abundance and frequency of occurrence, depended on whether grain sampling or trapping was used. With trapping, Cryptolestes species (mostly C. pusillus (Schonherr)), the Carpophilus dimidiatus complex (C. dimidiatus (F.), C.freemani Dobson and C. mutilatus Erichson), Sitophilus species (mostly S. zeamais Motschulsky), Xylocoris flavipes (Reuter) and Oryzaephilus surinamensis (L.) appeared most important. With grain sampling, S. zeamais, Sitotroga cerealella (Olivier) and C. pusillus appeared most important. Insects were most abundant (or active) in the fall and again in the spring, if storage extended that long. Grain samples indicated more insects near the grain surface, but traps sometimes detected more near the bottom of the bulk

Control of Sawtoothed Grain Beetles (Coleoptera: Silvanidae) in Stored Oats by Using an Entomopathogenic Fungus in Conjunction with Seed Resistance

We tested the hypothesis that the entomopathogenic fungus Beauveria bassiana would be more efficacious on oat cultivars that prolonged the immature developmental period of sawtoothed grain beetle, Oryzaephilus surinamensis (L.), a storage pest. However, percentage of reduction in progeny production was similar on whole \u27Don\u27 and \u27Paul\u27 oats treated with fungus, even though immature developmental time was longer on whole \u27Don\u27 than on \u27Paul\u27 oats. In our initial test at 10 mg of conidia per kilogram of oats, the number of beetle progeny produced was reduced by 38-67% in whole oats, and there was no effect of the fungus on insects developing on cracked oats. Therefore, we conducted two dose-response studies that showed that adding 150 mg of conidia per kilogram to cracked or whole \u27Paul\u27 oats resulted in a 70 and 98% reduction, respectively, in number of progeny produced. No further reduction was obtained by adding 200 mg of conidia per kilogram of cracked or whole \u27Paul\u27 oats. Presence of the fungus did not affect developmental time in any of our tests. A previous study showed that cleaned oats should limit insect population growth to allow long-term storage of oats without insect damage. However, the current study shows that if the oats are not cleaned, and not cleaning oats is the normal storage practice, then B. bassiana could be used to help control sawtoothed grain beetles

Distribution of psocids (Psocoptera) in temperature gradients in stored wheat

Psocids have become important pests of stored products during the last two decades, but little is known about their behavior or ecology. We examined distribution of Liposcelis bostrychophila Badonnel (Psocoptera: Liposcelididae), Liposcelis entomophila (Enderlein), and Liposcelis paeta (Pearman), three of the main psocid pests of stored grain throughout the grain growing regions of the world, in temperature gradients of 20°-24°C, 20°-30°C, and 20°-42°C in small bulks of wheat to determine their ecological preferences. Psocids consistently preferred the warmest regions of the gradients, except in the 20-42°C gradients. Over 80 and 78% of psocids moved to the warmest region of the grain in the 20°-24° and 20°-30° gradients, respectively. Liposcelis bostrychophila females and both sexes of L. paeta preferred the warmer region of the grain in the 20°-42° gradient, while densities of L. entomophila males were higher in more moderate temperature regions of the grain and densities of L. entomophila females were evenly split between the warm and hot regions of the grain. Temperatures can be below 20°C during much of the storage season for grains, so the current results help to explain why psocids move to warmer regions of the grain which occur toward the center of the grain mass as grain temperatures cool in the fall. This may allow psocid populations to continue to grow during the colder months

Population Growth and Development of Psocid \u3ci\u3eLepinotus reticulatus\u3c/i\u3e at Constant Temperatures and Relative Humidities

We investigated the effects of temperature and relative humidity on population growth and development of the psocid Lepinotus reticulatus Enderlein. Part of this study assessed the effects of marking psocids by using methylene blue, chalk powder, and fluorescent powder to differentiate nymphal stages during development. We found that marking psocids by using methylene blue increased mortality and took twice as long to accomplish compared with marking by using fluorescent powder. Using chalk powder shortened the duration of third and fourth nymphal instars. Marking psocids by using fluorescent powder had no effect on mortality or duration of nymphal instars. Therefore, we recommend using fluorescent powder for marking psocids. L. reticulatus did not survive at 32, 43, and 55% RH, whereas populations increased from 22.5 to 32.5°C at 75% RH. The largest population growth was recorded at 30 and 32.5°C, whereas only 9% of nymphs developed to adults and populations declined at 35°C. We developed temperature-dependent developmental equations for eggs, individual nymphal, combined nymphal, and combined immature stages. These equations showed predicted optimal temperatures for the development of eggs, combined nymphal, and combined immature stages to be 32.3, 34.5, and 34.4°C, respectively; development at these temperatures was completed in 6.3, 16.7, and 23.3 d, respectively. Our study shows that psocids that consume their exuviae develop faster than those that do not, and this effect is more pronounced at lower temperatures. These data give us better understanding of L. reticulatus population dynamics, and they can be used to develop effective management strategies for this psocid