Simulation studies on the effects of solar heat on egg-laying, development and survival of Callosobruchus maculatus (F.) and Callosobruchus subinnotatus (Pic) in stored bambara groundnut Vigna subterranea (L.) Verdcourt

The effects of simulated solar heat on oviposition, development and survival of Callosobruchus maculatus (F.) and Callosobruchus subinnotatus (Pic) in stored bambara groundnut, Vigna subterranea (L.) Verdcourt, were evaluated at three high temperatures (40°C, 45°C and 50°C) at a constant, low humidity (30% relative humidity). Exposure to these temperatures for 6 h significantly reduced oviposition in C. maculatus and C. subinnotatus females. Females of both species that were exposed to 50°C laid significantly fewer eggs than those exposed to 40°C; and in the case of C. maculatus, females exposed to 45°C also laid significantly fewer eggs than those exposed to 40°C. The percentage of eggs laid by females of both species that reached adulthood after exposure to 50°C for 2–6 h was significantly lower than the percentage that developed from eggs laid by females that were exposed to 40°C. No adult developed from eggs of C. maculatus exposed for 6 h at 50°C or from eggs of C. subinnotatus exposed for 2 h at this temperature. For both species, no adult progeny subsequently emerged from seeds harbouring first instar larvae when exposed at 50°C for 2, 4 or 6 h. Older larvae of C. maculatus were more tolerant of exposure at 50°C: 26.8, 10.2 and 0.9% of late instar larvae exposed for 2, 4 and 6 h, respectively, developed to the adult stage. In contrast, no adults of C. subinnotatus emerged from seeds harbouring late instar larvae when exposed at 45°C for 6 h nor in seeds exposed to the temperature of 50°C for 4 or 6 h. On average, immature stages of C. subinnotatus were more susceptible to heat treatment than those of C. maculatus.     

Collective oviposition and larval aggregation in Zabrotes subfasciatus (Boh.) (Coleoptera, Bruchidae)

In populations of Zabrotes subfasciatus (Boh.) attacking stored azuki beans, about 30–40 per cent of the total number of eggs were deposited in clumps of 2 or more eggs. The differences between the larvae hatching from the eggs deposited singly and those from the eggs deposited in a clump were examined. There was hardly any significant difference between them in the duration of larval and pupal stages, but the mortality was lower in larvae hatched from the eggs in clumps than in larvae living singly. Even where the same number of eggs was deposited on a bean, larval mortality was different according to whether the eggs had been deposited in a scattered way or in a clump. This aggregation effect was seen especially when the observations were made on relatively dry beans. It can be assumed, therefore, that the water produced by aggregated larvae is absorbed and softens the bean, and thereupon the mortality is lower. Collective oviposition seems to be an adaptation to life in stored beans.     

Evaluations of the new deltamethrin-treated all-in-one hermetic bag for the control of the Khapra beetle,Trogoderma granarium (Everts)

The khapra beetle, Trogoderma granarium (Everts), is a highly destructive stored product insect that presents a significant threat to stored bagged grain. Hermetic packaging is designed to maintain the quality and safety of stored grain, while continually protecting the grain from insect infestations during storage. The objective of this research was to evaluate a prototype deltamethrin, all-in-one treated hermetic bag on contact efficacy, larval mobility, and the control of T. granarium in artificially infested wheat. The insecticidal activity of the deltamethrin-treated packaging was tested against larvae and adults of T. granarium through contact bioassays. There was a significant reduction in responsive adults after 5 day and >86% of larvae were unresponsive after 9 d of exposure on the treated bag. Trogoderma granarium movement toward a food bait was <10% after a 24 h exposure on the treated bag compared to ~45% of larvae on untreated bag. Lots of 15 kg of wheat were artificially infested with 100 T. granarium larvae and placed inside treated and untreated storage bags, sealed, and stored in a semi-field warehouse, and observed after 2, 6, and 8-weeks for T. granarium survival and grain quality attributes. The weight and number of insect damaged kernels was lower across all storage intervals for grain held in the treated bags, as compared with control bags. Live adult T. granarium were observed at 2-weeks in treated and untreated bags, but there were no live adults observed after 8-weeks of storage in both bags. The new prototype hermetic bags maintained positive grain qualities, however more information on the hermetic parameters are needed to understand how some individuals survived.     

Susceptibility of the gelatinized wheat product bulgur to Sitophilus zeamais Motsch. and Rhyzopertha dominica (F.)

The development of Sitophilus zeamais and Rhyzopertha dominica was studied at relative humidities of 71, 58 and 43% in bulgur and wheat. Male and female adult weevils, introduced into 6 bulgur and 6 wheat media of different particle sizes, were allowed to oviposit for 7 days. Thirty R. dominica eggs were placed in each replicate of a similar set of bulgur and wheat media.

S. zeamais produced more adult progeny in whole kernels of bulgur and of wheat and in the larger-sized particles, and a high percentage of R. dominica larvae developed into adults in these media. S. zeamais progeny produced and R. dominica larvae surviving were fewer, and developmental periods for both species longer, the smaller the particles and the lower the relative humidity. Males and females collected from bulgur and wheat media of the same particle size tended to weigh the same; but the smaller the particle size, the less the weights.     

Susceptibility of Sitotroga cerealella (Oliv.) (Lepidoptera: Gelechiidae) to two insect juvenile hormone analogues

The effect of topical application of the insect juvenile hormone analogues methoprene (isopropyl-11-methoxy-3,7-11-trimethyl dodeca-2,4-dienoate) and hydroprene (ethyl-3,7,11-trimethyl dodeca-2,4-dienoate) on last instar larvae and newly-formed pupae of Sitotroga cerealella was examined. Topical application of methoprene at 10 μg/pupa to maize grains containing pupae resulted in 94% adult emergence whereas the same treatment applied to pupae removed from the grains reduced adult emergence to 45%. At 100 μg methoprene/pupa, adult emergence was 91% when grains containing pupae were treated and 32% when pupae were treated after removal from grains. Hydroprene (10 μg/pupa) was more effective than methoprene against insects both inside grains and after removal from grains, giving adult emergence of 48% and 8% respectively. At 100 μg/pupa, hydroprene completely prevented adult emergence when applied to insects removed from the grain. After treatment of the pupal stage with 10 or 100 μg methoprene per insect, adult males produced the same numbers of spermatophores as untreated males and the treatment did not affect either the number or fertility of eggs deposited by adult females.     

Toxic and antifeedant action of nutmeg oil against Tribolium castaneum (Herbst) and Sitophilus zeamais Motsch

The essential oil extracted from nutmeg seeds using steam distillation was tested against the stored product insect pests, Tribolium castaneum (Herbst) and Sitophilus zeamais Motsch., for contact toxicity, fumigant toxicity and antifeedant activity. Filter paper impregnation was employed for contact and fumigant toxicity studies, whereas a flour disc bioassay was used to investigate antifeedant effects. Adults of S. zeamais were about ten times more susceptible than T. castaneum adults to contact action (LC₅₀ values of 1.7 mg/cm² and 18 mg/cm² respectively). However, S. zeamais adults were only 1.7 times more susceptible than T. castaneum adults to fumigant action (LC₅₀ values of 4.5 mg/cm² and 7.7 mg/cm² respectively). Furthermore, the larvae (10–16 days old) of T. castaneum were more susceptible than the adults, but the susceptibility of the larvae decreased with age. Nutmeg oil also significantly (P < 0.05) affected the hatching of T. castaneum eggs and the subsequent survival of the larvae in the concentration range 1.4–3.2 mg/cm². The production of F1 progeny of both T. castaneum and S. zeamais exposed to media treated with nutmeg oil was significantly (P < 0.05) reduced at all concentrations tested. F1 progeny production was totally suppressed at nutmeg oil concentrations of 1.05 g/100 g rice for T. castaneum and 0.35 g/100 g wheat for S. zeamais. Nutritional studies showed that nutmeg oil significantly (P < 0.05) affected the growth rate and food consumption of both insect species, depending on the concentrations used, but the antifeedant activity was more pronounced against S. zeamaisthan against T. castaneum. At 20 g nutmeg oil/100 ml, the feeding deterrence index of T. castaneum was only about 7%, whereas that of S. zeamaiswas 33%. These results suggest that nutmeg oil may be useful as a grain protectant with contact, fumigant and antifeedant activities against these insects.     

气体分析法监测粮食储藏安全性的研究与应用进展

粮食在储藏过程中易受到虫害和霉菌的侵染,造成粮食的损耗。凭借灵敏的储粮监测技术,可以早期发现虫霉的发生,确保粮食储藏的安全性。在不断研发的储粮安全监测技术中,利用虫霉活动可以产生特征物质改变粮食可挥发气体组分,或使粮堆中某种气体成分含量发生变化的特点,通过测定相关气体的含量可了解储粮的状态。大量的研究表明,储粮的气体分析监测技术具有快速、灵敏度高、结果准确等优点。本研究主要介绍气体分析技术在监测粮食品质变化,储粮霉菌和昆虫的危害判断、预测等方面的研究和应用进展,并对方法的特性、作用以及可能的发展方向进行评价。     

Intraspecific and interspecific competition in Callosobruchus maculatus (F.) and Callosobruchus subinnotatus (Pic) on stored bambara groundnut, Vigna subterranea (L.) Verdcourt

Intraspecific competition was studied in Callosobruchus maculatus and Callosobruchus subinnotatus. Interspecific competition between the two bruchids was also studied to determine which of these species is likely to cause more damage to stored bambara groundnuts, Vigna subterranea in cases of joint infestation. Results showed that increasing the adult density up to 8 females per 10 g of bambara groundnut seeds did not significantly reduce the mean number of eggs laid per female, the number of eggs developing to the adult stage, or the weight of emerged adults of either species. The developmental period of the two species was also not significantly affected. The adult emergence curve of C. maculatus was similar to that of C. subinnotatus and was of the scramble type. C. maculatus performed better than C. subinnotatus in interspecific competition and it achieved this through a higher egg-laying ability and a higher rate of progeny production coupled with a shorter life-cycle. The implications of these findings with respect to damage and possible loss of stored bambara groundnut are discussed.     

Predicting insect density from probe trap catch in farm-stored wheat

Insect populations infesting wheat stored in four bins on two Kansas farms were monitored from early July 1996 through to the middle of January 1997. Estimates of adult insect density based upon the numbers of adult insects caught using probe traps differed from those based upon the number of insects found in grain samples. These differences were a result of differences in numbers of insects found and percentages of traps or grain samples with insects. Traps detected insects 15 to 37 d earlier than grain samples. The depth of traps below the grain surface tended to influence both the total number and species composition of the insects that were caught. Traps inserted with the top just below the grain surface collected an average of 1.9 times more Cryptolestes ferrugineus (Stephens), 1.2 times more Rhyzopertha dominica (F.), 4.1 times more Ahasverus advena (Waltl) and 77.4 times more Typhaea stercorea (L.) than traps inserted with the top 7.6 cm below the grain surface. However, trap depth did not have a significant effect on the number of R. dominica caught and on only 12 to 21% of sampling dates did trap depth have a significant effect on the number of insects of other species that were caught. Grain temperatures in three of the bins averaged 30°C during the first 70 d of storage and then decreased by 0.2°C/d. Grain in the other bin was initially more than 10°C warmer and grain temperature decreased by 0.2°C/d over the full storage period. The numbers of insects captured in traps decreased as grain temperature decreased even though grain samples indicated that insect populations were still growing. Thus, trap catches did not estimate insect population density consistently throughout the storage period. A method was developed in the current paper to adjust for the effect of seasonal changes in temperature on trap catch.     

马六甲肉食螨防控储粮害虫研究进展

储粮害虫绿色生态防控是我国粮食绿色仓储提升行动的重要任务之一,捕食螨防治储粮害虫是一种利用生态因子抑制储粮害虫的生物防治技术。马六甲肉食螨通过取食害虫和害螨的卵及低龄幼虫达到控制有害生物种群的目的。具有分布广、数量多、捕食虫谱广和捕食量大等优点,是我国粮库中的优势捕食螨。本文简述了储粮害虫捕食螨的防控技术,并结合团队近几年的研究,分析了马六甲肉食螨防控储粮害虫优势与进展,以及马六甲肉食螨人工扩繁技术和粮库防控释放技术,实仓应用情况。该技术成本低廉、操作便捷,而且无污染、无抗性,为绿色、生态、安全的储粮害虫综合防控和化学药剂减量提供参考。     

Technique to isolate Callosobruchus chinensis (L.) (Coleoptera: Bruchidae) eggs

A simple technique to isolate the eggs of Callosobruchus chinensis from the surface on which they are laid is described. An aqueous extract of their natural food, green gram, Vigna radiata, is used to coat glass beads that attract adult females for oviposition. The thin layer of extract on the glass beads allows separation of the eggs from the bead surface after a 15–20 s immersion in water. When transplanted onto fresh grain treated with glue, the separated eggs exhibit normal development and up to 97% hatching.     

History of an insect infestation in durum wheat during transport and storage in an inland terminal elevator in Canada

A bulk of 242 tonnes of infested durum wheat from a primary elevator was sampled when it was loaded into four boxcars in August 1974, when it was unloaded at the inland terminal elevator and when it was turned in the terminal elevator. During a storage period of 1 year, the wheat was cleaned once and turned 4 times. Grain temperature was recorded each time samples were taken. Three methods of collecting 1-kg samples were used; dip sampling during transfer of the grain at both elevators, vacuum probe sampling in the terminal elevator bin and drop sampling from the bottom of the terminal elevator bin. Samples were placed in Berlese-Tullgren funnels for 6 hr to remove insects. Adults and larvae of Cryptolestes ferrugineus (Stephens) and of Tribolium castaneum (Herbst) were found, with larvae of the former species being most prevalent. In insect traps placed in the loaded boxcars, an adult C. ferrugineus was caught in one, T. castaneum adults in three, and adult Lathridius minutus (L.) in all of the boxcars; no insects were found in traps placed in the grain in the terminal elevator bin in September and October. Cleaning the grain during storage was ineffective as a means of disinfestation. The number of insects in the samples decreased as the duration of storage increased and as grain temperature decreased. Only four insects were found after November, three of which were C. ferrugineus larvae (one third and two fourth instar) and one was a Trogoderma larva. The last insect found was a fourth instar larva of C. ferrugineus in February 1975. It had a starved desiccated appearance. Even after 1 year of storage, grain temperature did not exceed the 19°C recorded at the time the grain was placed in the elevator.     

Development and evaluation of sequential sampling plans for Cryptolestes ferrugineus (Stephens) (Coleoptera: Cucujidae) infesting farm-stored wheat

The development and evaluation of appropriate sampling plans are needed for cost-effective management of stored-product insects. Sequential sampling plans, which are based on a variable sample size, are generally more cost effective than plans based on a fixed sample size. For adults of the rusty grain beetle, Cryptolestes ferrugineus (Stephens), we developed sequential sampling plans based on complete counts and the presence/absence of insects in 0.5 kg grain samples removed with a trier from the top 1 m of wheat stored in farm bins. Insect count data were used to develop a sampling plan for estimating the density of C. ferrugineus with a fixed level of precision. The presence/absence data were used to develop a sampling plan for classifying the C. ferrugineus infestation level relative to an action threshold. The performance of these sampling plans was evaluated (validated) using independent data sets and an IBM-PC software program specifically designed to test the plans. This is the first paper illustrating the development and evaluation of sequential sampling plans for a stored-product insect.     

Electronic and manual monitoring of Cryptolestes ferrugineus (Coleoptera: Laemophloeidae) in stored wheat

Trapping studies were conducted with field populations of Cryptolestes ferrugineus in small steel bins filled with stored wheat. Traps tested in a comparison experiment included two types of commercially available probe-pitfall trap and the trapping body of the electronic grain probe insect counter (EGPIC) system. Quantities of insects captured were compared among the three traps. Insect captures in PC pitfall traps, whether at the grain surface or 17 cm below the surface, exceeded those found in WB II probe and EGPIC probe bodies. The number of adult C. ferrugineus captured was similar between the EGPIC probe bodies and WB II probe traps. With probes positioned near the grain surface, insect counts generated by the EGPIC system were analyzed for changes in rate of capture after inserting the probe, changes within a single 24-h period, and variation with temperature. EGPIC counts varied from 0.5 counts per hour to 5.9 counts per hour throughout the study. Cryptolestes ferrugineus counts increased with increasing daily mean air temperature and decreased when air temperature decreased. There was a consistent increase in the rate of counts during the early evening hours. Increased activity of C. ferrugineus in the early evening hours may have been due to insect response to higher air temperatures near the grain surface late in the day, although grain temperature near the trap varied little throughout the day. Alternatively, diel periodicity in C. ferrugineus may be due to an independent circadian rhythm as evidenced in other grain insects. Variation in counts among days after the probe was inserted was not consistent.     

Comparative performance of Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) across populations,resource types and structural forms of those resources

The significance of Tribolium castaneum (Herbst) as a pest of stored grains will likely be influenced by the relative availability of different resources regionally and the beetles’ ability to utilize each of them. Therefore the performance across the life cycle of laboratory and field populations of T. castaneum on commonly available structural forms of wheat and sorghum, as conventional resources, was quantified and compared to that on cotton seed. The latter is not usually associated with T. castaneum, but large beetle infestations have been recorded commonly in cotton gins in Australia. The highest number of individuals of each stage (from a given number of eggs) developed on wheat and sorghum flour and kibbled seeds. Cotton seed did not support the development of laboratory population beetles and all neonate larvae died before pupation. In contrast, some of the field population larvae did develop on cotton flour, but their number was significantly lower in comparison to development on wheat and sorghum. Field population beetles produced significantly more eggs than did laboratory population beetles, on both the whole seed and flour. Field population females had a consistently higher fecundity (～78% more eggs) than the laboratory population females, at least over the first three weeks of adult life. These results suggest that field populations of T. castaneum should be used in experiments if we are to develop a more realistic understanding of the field ecology of this species. The relative rate at which these insects infest available resources in the field also warrants further investigation.     

Methods for collecting eggs and monitoring egg-hatch and immature development of Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae)

Methods are described for collecting large numbers of R. dominica eggs, assessing the proportion which hatch and rearing first instar larvae to adults. The proportion of eggs which hatched and duration of immature development were estimated at 26 and 30°C, 56% r.h. Mature adults in healthy cultures laid rafts of eggs in between layers of filter papers. The proportion of eggs that hatched was assessed after incubation. The first instar larvae which hatched out of the eggs were reared to adults in individual wells of 96-well polystyrene ELISA plates. They were fed with kibbled wheat while their survival and rate of development was monitored. About half the eggs which were collected shrivelled up without developing. Over 80% of the remaining eggs hatched normally at both temperatures. The mean duration of development from egg to adult through four larval instars was 44 d at 26°C and 34d at 30°C on kibbled wheat. These development times are similar to those on whole wheat reported by other researchers. The methods are much less disruptive or destructive than other methods of monitoring development on flour or whole wheat. Potential applications for these techniques are discussed.     

The ability of powders and slurries from ten plant species to protect stored grain from attack by Prostephanus truncatus horn (Coleoptera: Bostrichidae) and Sitophilus oryzae L. (Coleoptera: Curculionidae)

Powders and slurries prepared from parts of 10 different plant species indigenous to Ghana were tested under laboratory conditions for their ability to protect stored grain from damage by Sitophilus oryzae L. and Prostephanus truncatus Horn on wheat and maize, respectively. Two concentration levels 10% and 1% (wt/wt) were used. Powders and slurries of all plant species of 10% (wt/wt) significantly (P < 0.001) reduced insect damage by the grains and caused mortality of both insect species. Powders of four species; Cissampelos owariensis, Azadirachta indica, Ricinus communis and Solanum nigrum, gave a significant (P < 0.001) reduction in grain damage by the insect species as well as high mortality, even at the lower concentration level of 1% (wt/wt). The slurry preparations were generally better protectants than the powders especially against S. oryzae where complete control was achieved except with Chromolaena odorata and Sida acuta, which permitted some survival. The pattern of action of the slurries against P. truncatus was similar to that of S. oryzae, except that P. truncatus was relatively more tolerant.     

米扁虫对玉米中黄曲霉毒素B1含量影响的研究

了解在非霉变和不产毒的储存条件下,原粮中昆虫对真菌毒素含量的影响具有重要生态学意义。测定了含黄曲霉毒素B1(AFB1)的玉米分别接入15、45和135头/kg米扁虫幼虫和成虫后不同存放时间AFB1含量。结果表明,米扁虫幼虫和成虫接入一定时间后均可导致玉米中AFB1含量和霉菌总数显著降低,米扁虫成虫对AFB1含量降低的作用大于幼虫,玉米破碎粒率越低时AFB1含量降低越显著,虫口密度越大、接入时间越长,AFB1含量降低越显著。     

Cooking oils and “Triplex” in the control of Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae) in farm-stored maize

The uses of some cooking oils viz., noug oil, soybean oil, sunflower oil, corn oil and olive oil, and the reputedly non-toxic botanical “Triplex”, were evaluated against maize weevil, Sitophilus zeamais, in stored maize grain under local Ethiopian storage conditions in 2003. For comparison, an untreated sample and the synthetic insecticides, malathion 5% dust and Actellic 2% dust, at the recommended rates of 0.05% (w/w) were included. All the cooking oils tested had a significant toxic effect on the weevils in stored grains. The oil treatments showed significantly higher mortality of adult weevils at each sampling period compared with the untreated grains. The cooking oil treatments also significantly reduced weight loss and grain damage as compared with the untreated control. The Triplex treatment was of comparable effectiveness to the synthetic insecticides, causing high mortality of adult weevils, low-percentage grain damage and low-percentage weight losses. These promising oils and Triplex could be recommended for use as part of an integrated pest management program in stored maize, particularly at low levels of pest infestation and, in the case of cooking oils, for grain intended for home consumption.     

利用监测CO_2方法预警储藏玉米中黄曲霉菌产毒

本文研究了玉米储藏期间真菌产生二氧化碳(CO2)气体的特点,试验结果表明,当灰绿曲霉等干生性真菌生长时,储藏容器中CO2浓度恒速升高;具有快速生长或产毒特点的真菌生长时则出现CO2产气率加速的过程,如玉米中以黄曲霉菌为优势菌时,储藏10 d后产生CO2气体的速率提高4.6倍。进一步研究玉米储藏期间不同原始优势菌、不同真菌生长速率及温度对产生CO2的影响,结果表明,在不同原始优势菌的玉米中均可出现黄曲霉菌的生长和产毒,黄曲霉菌为原始优势菌的AFB1产生量比其他试验组高3~7倍,它们均表现产气速率加速的特征;真菌生长速率及温度可影响储藏玉米中CO2和AFB1的产生量,但在产生AFB1的玉米中,均有CO2产气速率加速的现象。将储藏玉米中CO2产气速率变化与检出AFB1的时间相比,发现前者可提前7 d以上。因此,利用玉米储藏中真菌产生CO2的特征可预警黄曲霉毒素的污染。