Sitophilus Zeamais Motsch Research Articles

The laboratory assessment of the inherent susceptibility of maize varieties to post-harvest infestation by Sitophilus zeamais Motsch. (Coleoptera, Curculionidae)

A biological technique for assessing the susceptibilities of varieties of maize to post-harvest infestation by Sitophilus zeamais Motsch. has been developed. The effects of the age and population density of the parent insects upon the results obtained were investigated, and the possible effects of insect selection due to breeding upon particular maize varieties were looked at. Twenty-five Malawi, two Colombian and three Indonesian maize varieties were tested for susceptibility, and the results obtained were summarized using an ‘Index of Susceptibility’ which took into account both the F 1 progeny developing during the tests and a measure of the average development period of these progeny. The effects of the proportion of floury endosperm in the maize kernels, the mean kernel weight, the 70% r.h. equilibrium moisture contents of the varieties, and the amylose contents of the varieties upon susceptibility were investigated using regression techniques. It was concluded that the hardness of the kernels, as estimated by the proportion of floury endosperm was related to susceptibility, and that the hardness was closely correlated with amylose content. However amylose may have a small effect upon susceptibility in addition to that associated with hardness. Egg plugs placed in the kernels of different varieties during standard susceptibility tests were counted, and no evidence was found that there was any relationship between the numbers of eggs laid and susceptibility. Therefore it was concluded that susceptibility was determined in these varieties by factors operating after oviposition.

Contribution to the morphology and ecology of Sitophilus zeamais Motsch. in Yugoslavia

After we established the existence of Sitophilus zeamais in Yugoslavia in 1968, we examined the various morphological characters given in the literature in which this species differs from S. oryzae. In an experiment S. zeamais has infested maize in the field, but was unable to survive the winter in the field in Zagreb in any stage of development. It is quite possible that some might survive some winters in the warmer southern parts of the country. When each species was placed separately on samples of wheat, more progeny were obtained from S. zeamais than from S. oryzae. Sitophilus zeamais is more resistant to starvation than S. oryzae. Differences in the suitability of individual maize hybrids for the development of S. zeamais were found. Differences in preference for individual maize hybrids and wheat for oviposition have been determined.

Development of Sitophilus zeamais Motsch. in WURLD wheat

WURLD wheat, a parboiled, lye-peeled product, was tested, along with untreated white wheat and pearled white wheat, and a hard red winter wheat bulgur, for susceptibility to the maize weevil, Sitophilus zeamais Motsch. The order of suitability of the wheats for multiplication of the weevils was pearled, untreated, bulgur and WURLD.

The control of insects in exported Zambian groundnuts using phosphine and polyethylene lined sacks

When a 0·6 g aluminium phosphide pellet was applied to groundnuts in a jute or woven polypropylene sack, of 32–82 kg capacity and lined with polyethylene 63·5–127·5μ thick, the C × T product for phosphine exceeded 50 mg hr/1, and 100 per cent mortality of all stages of Tribolium castaneum (Herbst), Oryzaephilus surinamensis (L) and Sitophilus zeamais Motsch. was recorded. Twelve weeks after treatment groundnuts contained 0·4 ppm phosphine, but no residue was found when pellets were enclosed in paper envelopes. Many liners in sacks of groundnuts transported from Zambia to Britain split, but this did not affect the efficiency of the phosphine fumigation or permit reinfestation. When lined sacks containing groundnuts were pierced with a sampling probe 72 hr after treatment, the efficiency of the phosphine fumigation was not affected, and the sacks were not penetrated by insects even after 70 days in a heavily infested store. The fumigation with phosphine, storage, and transportation in polyethylene-lined sacks did not affect the flavour, moisture content, aflatoxin content, or physical condition of groundnuts. All experimental consignments were commercially acceptable for confectionery purposes in Britain.

A study of pre-harvest infestation of maize by Sitophilus zeamais Motsch. (Coleoptera, Curculionidae) in the Kenya highlands

The incidence of attack by Sitophilus zeamais Motsch in maize ears in the growing crop and in cribs during storage has been studied in the Kitale district of Kenya. There was no evidence that wild plants or cultivated wheat varieties supported high populations of this insect, the principal source of field infestation being stocks of stored maize. Ears from the previous crop ploughed in at time of cultivation and sowing rarely support S. zeamais long enough to allow cross-infestation of susceptible new crop ears. In a growing crop of the variety ‘Kitale synthetic’, 50–60 per cent of the ears were tightly enclosed by the sheath. The remainder had loose or open sheaths. In the same crop the numbers of infested grains and infested ears present immediately before harvest were estimated by placing ears in separate polythene bags just after harvest and recording daily the emergence of adults over a 5 week period. As a result it was estimated that 42 per cent of the tightly sheathed ears were infested, compared with 51 and 84 per cent respectively in the loosely and open sheathed ears. Assuming one insect per infested grain the number of infested grains for infested ears from all three categories combined was 10 per cent. The overall level for infested grains in all ears from the crop as a whole was 6 per cent. These data compare well with a field experiment in which two different pre-harvest infestation levels were measured, e.g. where the kernel damage shortly after harvest was less than 1 per cent it took 16 weeks to reach a level of 7 per cent, compared with an initial level of 3 per cent which reached 16 per cent after only 8 weeks. In a comparison of the susceptibility of six white dent maize varieties to pre-harvest infestation, Hybrid 622 proved far superior to the others in three important aspects. It had a low incidence of ears with open tips (27·5 per cent), a lower level of insect attack even when compared to another variety with a similar level of open tipped ears and a much lower moisture content at harvest. Field experiments indicated that S. zeamais would not develop in the kernel before harvest until the moisture content fell to below 60 per cent, which in Kitale district would be mid-September i.e. 3 months before harvest. As was appreciated many years ago, the most practical method of reducing pre-harvest attack is by preventing insect development in harvested grain. Lindane admixed with harvested ears from which the sheaths had been removed, killed emerging adults and achieved this. Unfortunately there are signs of resistance developing to this insecticide and alternative treatments are required. The admixture of an effective contact insecticide to prevent breeding after harvest, combined with careful cleaning and spraying of empty stores not later than pollination of the next field crop, and selection of maize varieties resistant to attack before and after harvest, appear to be the most effective way of reducing pre-harvest infestation.

On the flight activity of Sitophilus zeamais Motsch. (Coleoptera, Curculionidae) and some other grain-infesting beetles in the field and a store

The diurnal periodicity in the flight activity of Sitophilus zeamais and other grain-infesting beetles was studied in the field and a store using a 12-in. Johnson-Taylor suction trap. The aerial density of S. zeamais in the field when the crop of maize was due for harvesting was generally low but increased substantially within 3 days of the opening of the sheath at the tips. Field and store trapping data for Sitophilus zeamais were subjected to analysis on arithmetic probability paper and used in the description of the flight periodicity curves. The fitted probability distributions showed that there was a marked difference in the flight activity of field and store populations of S. zeamais. In the field the flight periodicity curve was normal and unimodal and very little flight occurred during the night, whereas in store the flight periodicity curve was flat-topped and flight activity was prolonged far into the night. Light intensity does not appear to have a limiting action on flight activity but temperature appears to be the most important factor. A temperature threshold of 20–21°C for flight was established from field studies and the marked difference in the flight activity in the store was accounted for by the incidence of higher temperatures longer into night. The flight periodicity curves for Carpophilus dimidiatus in the field and Tribolium castaneum in the store are described. Both species exhibited wide single distribution flight curves and the ability to fly intermittently throughout the 24 hr-day cycle.

Observations in Kenya on the flight activity of stored products insects, particularly Sitophilus zeamais Motsch

The periodicity and intensity of the flights of stored products insects at various sites out of doors on farms in the West Kenya Highlands was assessed using a suction trap. The following insects were caught: Cadra cautella, Sitotroga cerealella, Carpophilus dimidiatus, C. fumatus, C. obsoletus, Cryptolestes ferrugineus, C. pusillus, C. ugandae and other Laemophloeinae, Oryzaephilus surinamensis, Sitophilus zeamais, Tribolium castaneum and Typhaea stercorea. In S. zeamais, which was the most common, the flight periodicity curve had a peak at between 15.00 and 17.00 hours. The intensity depended upon the numbers present and climatic factors, particularly the temperature at 15.00 hours and the amount of sunshine between 13.00 and 18.00 hours, although other related climatic factors should not be overlooked. The practical significance of these findings is discussed. Periodicity in four other species, Cadra cautella, Sitotroga cerealella, Tribolium castaneum and Typhaea stercorea is also described. Attempts to determine the flight range of Sitophilus zeamais were disappointing but it was shown that the distance can be at least a quarter of a mile. The practice of growing seed maize at least half a mile from any store appears to have resulted in a significant decrease in the rate of field infestation.

Laboratory evaluation of some additional organophosphorus insecticides against stored-product beetles

Abstract The relative susceptibilities of Tribolium confusum Duv. and T. castaneum (Hbst) to seven new organophosphorus insecticides were determined by applying the compounds topically at four dosage rates. SD 8447 (0,0-dimethyl 2-chloro-1-(2,4,5-trichlorophenyl, vinyl phosphate) was more effective than malathion against both species and was evaluated against eight more species of stored-product beetles. It was more toxic than malathion to Rhyzopertha dominica (F.), Lasioderma serricorne (F.), Stegobium paniceum (L.) and Sitophilus zeamais Motsch. but less so against Oryzaephilus surinamensis (L.), O. mercator (Fauv.), Ptinus tectus Boield and Sitophilus granarius (L.). S. zeamais was about eleven times more susceptible to this compound than S. granarius .

Lindane resistance in Sitophilus oryzae (L.) and Sitophilus zeamais Motsch. (Coleoptera, Curculionidae) in Queensland

The responses of two field strains of Sitophilus oryzae (L.) and a field strain of Sitophilus zeamais Motsch. to lindane, malathion, ronnel and diazinon have been compared. Each strain was characterized by its response on exposure to insecticide-impregnated filter paper; lindane median lethal concentrations at 24 hr for S. oryzae were 0·0057 per cent for a strain substantially susceptible to lindane and 0·44 per cent for a strain substantially resistant. No resistance to malathion and diazinon was recorded for this species, but a small increase in tolerance to ronnel was detected. No resistance was recorded from S. zeamais. These results were confirmed by assays using insecticide-treated grain and both immature and adult stages. Minimum concentrations of insecticide in treated wheat for efficacious control were for lindane susceptible S. oryzae, lindane <0·8 ppm, malathion 2 ppm, ronnel <20 ppm, diazinon 5 ppm; for lindane resistant S. oryzae, lindane 39 ppm, malathion 2 ppm, ronnel 50 ppm, diazinon 5 ppm; and for S. zeamais, lindane <0·8 ppm, malathion 2 ppm, ronnel 50 ppm, and diazinon 10 ppm. For reference, laboratory-selected lindane-susceptible and resistant strains of S. oryzae have been included in assays. Some aspects of lindane resistance in Queensland are discussed.

The insect infestation of sorghum stored in granaries in Northern Nigeria

The majority of sorghum in Northern Nigeria is stored unthreshed in farmers' granaries made of dried mud or plant materials such as grass matting and cereal stems. During the course of survey work and insecticide trials in 1959–61 it was possible to examine many samples of unthreshed sorghum from granaries throughout Northern Nigeria. It was found that the distribution of insect species within the Region is not uniform. Sitophilus oryzae (L.) and Sitotroga cerealella (Ol.) are the major pests. Sitophilus zeamais Motsch. was found only in the southernmost area. Heavy infestations of Rhyzopertha dominica (F.), Lasioderma serricorne (F.), Cryptolestes ugandae Steel &amp; Howe, Oryzaephilus mercator (Fauv.), Tribolium castaneum (Hbst.) and T. confusum Duv. usually occur. Attagenus gloriosae (F.), Ahasverus advena (Waltl), Palorus ficicola (Woll.), P. ratzeburgi (Wissm.) and P. subdcpressus (Woll.) are occasionally important.R. dominica, Bruchidius sp., G. ugandae, Planolestes cornutus (Grouv.), S. oryzae, Brachypeplus sp., T. castaneum, Sitotroga cerealella (all of which occurred on the standing crop), L. serricorne, Typhaea stercorea (L.), O. mercator, Palorus spp. and Tribolium confusum were found in sorghum sampled before storage. Insects from infested stores were found to infest sorghum growing nearby. Prestorage infestation alone can result in subsequent heavy populations of insects in the store. Cross-infestation between granaries almost certainly occurs.Under Samaru conditions, where sorghum is harvested in November–December, insect populations remain at a low level in granary-stored unthreshed sorghum until after June, when the moisture content rises in the rainy season. In sorghum stored for nine months in provincial trials, more damage occurred during the last three months than during the previous six months of storage.Sorghum heads stored in granaries made of plant materials such as grass matting and cereal stems are more severely damaged by insects than those stored in dried-mud granaries. This is probably due to a higher rate of immigration in the former.In threshed grain stored in a mud granary, moisture content and damage by the most abundant insect, Sitophilus oryzae, decreased with depth. The insect population rose to a peak in November, two months after the maximum moisture content. The numbers fell rapidly during the following dry season. The annual cycle of insect damage was also assessed by taking fortnightly samples of threshed grain from a local market. S. oryzae was the most numerous insect, but even this species was uncommon from December to May, during the dry season.