Elimination ofSitotroga cerealella (Olivier) bySitophilus zeamais Motschulsky from mixed laboratory cultures on maize

This paper describes a series of experiments conducted to determine why Sitophilus zeamaisMots . and Sitotroga cerealella (Oliv. ) could not survive together in maize cultures in the laboratory. The effect of S. zeamais on different developmental stages of S. cerealella was investigated. The presence of adult S. zeamais slightly affected moth copulation, egg laying and moth eggs in a mixed culture, but large numbers of developing moths inside maize grains were killed by the adult weevil through feeding on the grains. The major cause of elimination of S. cerealella by S. zeamais from mixed cultures was therefore found to be damage to the immature moths in grain and such moth mortality increased as the developing moths became bigger in the grains. A weevil: grain ratio of approximately 1.4∶1 was found to be the critical weevil density at which the moth disappeared from the mixed cultures.     

Dynamics ofSitotroga cerealella (olivier) (lepidoptera: gelechiidae) andSitophilus zeamais motschulsky (Coleoptera: Curculionidae) populations in a small bulk of stored corn

The dynamics of Angoumois grain moth, Sitotroga cerealella (Olivier ), and maize weevil, Sitophilus zeamaisMotschulsky , populations breeding in a small bulk (initially 5.36 t) of shelled corn were studied over an 8-year period by monthly sampling. The weevil population showed wide fluctuations in density superimposed on a general decline with time. The moth population showed no upward or downward trend for the first 60 months, although it fluctuated widely. Following a decline that occurred between 56 and 60 months, the moth population fluctuated within a much narrower range, and there was a general decrease in density with time. The decline of the weevil population paralleled deterioration of the corn as did that of the moth population after ca 60 months, and the decline of both species probably resulted from increasing scarcity of suitable breeding sites. Both populations exhibited seasonal variation in density with minima in late summer and early fall, following periods of adversely high temperatures in the storage shed. The populations increased during the fall, leveled off or declined slightly during the winter months, and then increased to maximum levels in late spring or early summer. It thus appears that high temperatures had a greater adverse effect on the populations than low temperatures. The grain moth and the maize weevil both tended to be randomly dispersed at low population levels and moderately aggregated at intermediate and high levels, although the degree of aggregation was not correlated with population density when low population levels were considered separately, and the maize weevil showed a greater tendency for aggregation than did the grain moth. Analysis of individual samples at fixed points in time showed a conspicuous bias for negative correlation between numbers of the two species within sampling quadrats, suggesting a tendency for the two species to segregate within the grain mass. This process could have resulted from behavioral differences or from the destruction of one species by the other. Competitive displacement of the grain moth by the maize weevil has been demonstrated in laboratory experiments but has rarely been observed under natural conditions, and in our study the two species coexisted for 8 years in a relatively small grain bulk.     

Insecticidal activities of some medicinal plants against Sitophilus zeamais (Motschulsky) (Coleoptera: Curculionidae) on stored maize

A study was carried out to evaluate the insecticidal activity of Zanthoxylum zanthoxyloides, Aristolochia ringens, Garcinia kola, Morinda lucida, Euphorbia hirta, Croton zambesicus, Colocasia esculenta, Ficus exasperata and Tetrapleura tetraptera on Sitophilus zeamais at ambient temperature of 28?±?2?°C and 70?±?5% relative humidity. The plants powder was applied at 5, 10 and 20% (wt/wt) of maize grain. Weevil mortality, adult emergence, percentage damage, percentage reduction and weevil perforation index were observed. The result obtained showed that only the powder of Z. zanthoxyloides and A. ringens effect mortality on the weevil as they both achieved more than 50% weevil mortality within 96?h of application. However, powder of Z. zanthoxyloides had the highest mortality effect on the weevil as it achieved 100% within 72?h at 5%(wt/wt) and its effect was significantly (p?<?0.05) different from other powders. Also, powder of Z. zanthoxyloides, A. ringens and M. lucida showed a reduction capacity on the emergence of the adult weevil at 20%(wt/wt). Moreover, Z. zanthoxyloides prevented the emergence of the adult weevil even at 5%(wt/wt) but effect was not significantly different from A. ringens and M. lucida at 20%(wt/wt) as they both achieved 0% and 0.67% adult emergence. The powders also reduced the damage of the treated seeds. Z. zanthoxyloides prevented the damage of the seeds at 5, 10 and 20%(wt/wt) while A. ringens prevented the seed damage at 20%(wt/wt). However, effect of all the powders increased with increase in the powder concentration.     

Interspecific competition among larvae ofHemipyrellia ligurriens (Calliphoridae) andBoettcherisca formosensis (Sarcophagidae) (Diptera)

1. The effects of larval rearing density and species relative proportions on life-history parameters of two necrophagous Diptera, Hemipyrellia ligurriens (Wiedemann) (Calliphoridae) and Boettcherisca formosensis Kirner and Lopes (Sarcophagidae), were investigated in mixed cultures. Larval rearing density had a significant effect on larval to adult survivorship, duration of immature development, adult size and relative performance (measured by the composite index of performance, r′) of both species. However, species relative proportions affected adult size of both flies and the duration of immature development of B. formosensis only.
2. B. formosensis had a higher survivorship than H. ligurriens in all mixed cultures and showed a similar survivorship pattern to that in pure cultures. By contrast, survivorship of H. ligurriens was lower in mixed than in pure cultures.
3. H. ligurriens adults reared from mixed cultures were smaller than those from pure cultures of comparable density, but B. formosensis adults from pure and mixed cultures were of similar size.
4. The results suggest that competition between B. formosensis and H. ligurriens larvae was asymmetric and the former was the superior competior.
5. At low larval densities in mixed cultures, the presence of H. ligurriens enhanced the performance (as measured by r′) of B. formosensis, a consequence of suspected interspecific facilitation of larval growth.

     

Dynamics of infestation and losses of stored maize due to the larger grain borer (Prostephanus truncatus Horn) and maize weevils (Sitophilus zeamais Motschulsky)

The dynamics of infestation and losses of stored maize due to the larger grain borer (Prostephanus truncatus Horn) and maize weevils (Sitophilus zeamais Motschulsky) were investigated in Tanzania. In single species populations, significantly higher maize damage (P ≤ 0.05) was caused by P. truncatus (23.3%) compared to S. zeamais (6.4%). Weight losses caused by P. truncatus were higher (12.7%) than for S. zeamais (6.7%) under similar conditions. A higher proportion of P. truncatus in the initial infestation population led to significantly higher (≤0.05) maize damage compared to equal or higher proportions of S. zeamais. Irrespective of the initial number of S. zeamais, population size increased to levels higher than for P. truncatus. Maize losses in unimproved storage structures were >80% compared to <2.5% in improved structures under natural infestation. Inter-specific competition appeared to influence the dynamics of infestation, damage levels and weight losses. The first two months of storage were critical for damaging insect populations to build up.     

The effect of crowding on adult populations ofDelia (=Hylemya) antiqua (Meigen)

Using 5 density levels, the effect of increasing density was studied on several population statistics of adult Delia (=Hylemya) antiqua. Amongst the statistics studied were adult lifespan; female mating frequency, fecundity and egg hatchability. It was shown that females lived significantly longer than males and that increasing density significantly reduced lifespan. Density had no effect on mating frequency. Total fecundity/female was significantly reduced with increasing density but oviposition rate was density independent. Using these statistics, mean generation time T, net reproduction rate R₀ and capacity for increase r_c were calculated at the different density levels. Values of R₀ showed a one-tailed response but there was no clear effect of density on r_c. Multiple comparisons between variables revealed several important relationships.

1. Adult lifespan was the most important factor affecting egg production.
2. Number of mated females was more important in affecting total fecundity/cage than adult density.

It could also be calculated that to produce the effect of one single mated female on total fecundity/cage the overall density would have to be reduced by 0.0023 individuals/cm³. These results are discussed in the context of efficient laboratory rearing of the onion fly.     

The dynamics of laboratory populations ofCallosobruchus chinensis andC. Maculatus (Coleoptera: Bruchidae) in patchy environments

Experiments are described showing the long-term dynamics of two species of bruchid beetles (Callosobruchus chinensis and C. maculatus) in arenas in which the resource of 50 black-eyed beans is divided between 5, 10 or 50 ‘patches’. Both species of adult beetles exhibit clumped distributions between patches. Within a patch there is a tendency for a density dependent reduction in (1) eggs laid per female, (2) the proportion of eggs hatching per bean (C. chinensis only) and (3) larval survival which is strongly overcompensating (particularly in C. maculatus). A discrete generation model is used as a framework to draw these results together and show how the different factors affecting natality and mortality can influence the population dynamics. Finally, the importance of the resource renewal interval in influencing the period of the population cycles is discussed.     

Regulatory processes and population cyclicity in laboratory populations ofAnagasta Kühniella (Zeller) (Lepidoptera: Phycitidae) II. Parasitism,predation, competition and protective cover

The population dynamics of Anagasta kühniella has been studied in standardized conditions in replicated ecosystems in which the variables have been increased one at a time. Additional to the variables reported earlier (WHITE and HUFFAKER, 1969), the present ecosystems included larval and pupal parasitism by Venturia canescens, both in the presence and absence of the egg-predator Blattisocius tarsalis, and also in the presence and absence of two levels of protective cover for the host. In the presence of V. canescens, parasitism was generally of major importance as a regulating instrument in determining host population densities and it characteristically produced cycling and discrete host generations that arose from a parasite-induced discontinuity in the age-structure of the host populations. When the predatory mite and/or protective cover was also present, modifying interactions arose but these were not sufficient to dispel completely the discontinuous age-structure and the cycling induced by the parasite. The actual degree of protective cover was particularly important insofar as it modified the levels and patterns of parasitism and permitted competition for food among host larvae to assume greater importance in the collective regulating process. Three forms of population cyclicity are described and discussed: a four-generation cyclicity which was the basic pattern of cycling and occurred both in the presence and absence of protective cover; an eight-generation cyclicity that arose from disturbed four-generation cycling in the presence of a minimal level of host protection; and a nine-generation cyclicity in which extensive protection compounded the collective nature of density-dependent regulation.     

Efficacy of intercropping and harvest time modification for reducing field infestation of maize by Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae)

Most management practices of Sitophilus zeamais Motschulsky, a field-to-post-harvest insect pest of cereals, have focused on post harvest control methods. This experiment was designed to investigate the potential of cropping system and modification of time of harvest to control S. zeamais. Intercropping and harvest time modification had significant (P < 0.05) effect on the number of S. zeamais emerging 42 days post-harvest. For the early harvest (15 weeks after planting (WAP)), the mean number of S. zeamais recorded from a maize monoculture (7.39) was significantly (P < 0.05) higher than the mean numbers of weevils emerging from a maize–soybean intercrop (2.31), but not significantly higher than the number recorded in maize–groundnut (3.87) intercrop. For the late harvest (18 WAP), the mean number of emerged adult observed in the maize–soybean intercrop (6.13) was significantly lower than the mean number of adult emerging from the monocrop maize (13.24). Maize–groundnut intercrop did not significantly reduce field infestation of S. zeamais compared with monocrop maize. Percentage weight loss observed in early harvested maize was significantly (P < 0.0001) lower than what was observed in late-harvested maize. Percentage weight loss was highest in stored maize harvested from monocrop maize plots for the early harvest, whereas intercropping maize with soybean reduced percentage weight loss when harvest was delayed.     

Impact of developmental variance on behavior of models for insect populations I. Models for populations with unrestricted growth

The concept of developmental variance is discussed with reference to its use in models for insect populations. When included in a model, developmental variance is typically used to describe the variation of developmental periods among individuals. However, its presence in a model can also have indirect impact on survival and fertility schedules. This impact can lead to significant changes in population growth rates and generation times. These relationships between developmental variance and population growth in models are quantified and discussed.     

Efficacy of some plants powder and extract in the management of Angoumois grain moth,Sitotroga cerealella (Olivier) [Lepidoptera: Gelechiidae] infesting stored wheat grains

Powders and extracts prepared from part and products of four plants species indigenous to Nigeria were tested under laboratory condition at 28?±?2?°C and 75?±?5% relative humidity for their insecticidal potential against Angoumois grain moth, Sitotroga cerealella. Adult S. cerealella were exposed to three concentrations at rate 0.5, 1 and 2?g of Capsicum frutescens, Cymbopogon citratus, Moringa oleifera and Anacardium occidentale powders and extracts at the rate of 1, 2 and 3%/20?g of wheat grains. Parameters evaluated were adult moth mortality, adult emergence and % hatchability in treated wheat grains after infestation. Results show that significant differences (p?<?0.05) existed among the powders and the concentrations. The powder of C. frutescens had the highest mortality rate of 100% after two?days of application at all tested concentrations. There were no adult emergence of moth in samples treated with C. frutescens and A. occidentale powders. The extracts completely killed all the adult moths introduced at all tested concentrations. The survival of the moth from egg to adult when treated with the plant powders showed that there was significantly (p?<?0.05) more adult in the control (71.3) compared to others. Extracts of all the tested plants were toxic to adult moth and also prevent hatching of the eggs of S. cerealella.     

Detection of single and mixed covert baculovirus infections in eastern spruce budworm, Choristoneura fumiferana populations

We surveyed for covert baculovirus infections in the eastern spruce budworm, Choristoneura fumiferana (Clemens) and compared the prevalence of virus detected in a laboratory and a field population. DNA was extracted from budworm adults and then PCR with degenerate primers was used to identify individuals carrying baculovirus DNA. Multiplex PCR was then applied to the positive samples to distinguish between the multiple baculovirus types that could potentially be found in C. fumiferana populations. Covert infections were found in both the laboratory and the field population of C. fumiferana, although the frequency of infection and the composition of viruses found were very different. Overall 28% of insects from the laboratory population were positive for baculovirus DNA. Individual adults supported both single and mixed covert infections with CfMNPV plus CfDEFNPV, CfDEFNPV plus a GV and mixtures of all three viruses together. However, the majority of insects supported single virus infections, and surprisingly this virus was CfDEFNPV, a virus that is reported not to have per os activity in C. fumiferana larvae. Insects from field populations showed a very different pattern; 70.5% of individuals were baculovirus positive and all of these were positive for CfDEFNPV only.     

Studies on the interspecies competition between the azuki bean weevil,Callosobruchus chinensis,and the southern cowpea weevil,C. maculatus V. The role of adult behavior in competition

Summary One strain (iC) ofC. chinensis and two strains (aQ and tQ) ofC. maculatus were used to study the temporal pattern in adult distribution in oviposition site. The density of iC in the oviposition site decreased faster than the density in the population cage, but the pattern was not affected by the presence of the other species. The density in ovipositon site of aQ and tQ controls was far lower than that of iC. The density changes in the controls of both strains were rather parallel to the pattern in the population cage. The density of aQ and tQ in the oviposition site in mixed cultures was affected by the presence of the other species. The density of aQ was less than half that in the controls. The pattern of density change was almost the same as in the controls. The density of tQ in the mixed cultures, although lowered initially by the presence of iC, increased after the density of iC decreased. Coupled with its longer female longevity, this characteristic of tQ behavior at the oviposition site apparently contributed to its winning the competition with iC. The adult distribution pattern observed in the present experiments provides an explanation for the peculiar two-fold increase in mean individual weight ofC. chinensis in mixed cultures compared with controls, whileC. maculatus adults were a little lighter in mixed cultures than the controls. Contribution from the Entomological Laboratory, Kyoto University, No. 432.     

The influence of population density on fission and growth of Holothuria atra in natural mesocosms

Investigation of the population dynamics, asexual reproduction (fission) and growth of holothuroids has been impeded by the difficulty of tagging individuals. We conducted the first tests on the interactions between population density, fission and growth of holothuroids in experimental populations placed in natural mesocosms (microatolls) at One Tree Reef (OTR), Great Barrier Reef. Similarly sized Holothuria atra were translocated to the microatolls in low (LDT) and high (HDT) density treatments. We hypothesised that holothuroids in lower density treatments would have more resources per individual and that this would promote higher frequencies of asexual reproduction and smaller individuals. The seasonal pattern of fission was similar in natural (unmanipulated) and experimental populations, with the maximum number of fission products occurring in winter and spring. The overall density of the LDT (0.19 ind. m^- 2) and HDT (0.59 ind. m^- 2) did not vary over time. This ‘steady state’ suggested that some fission products died and that asexual reproduction compensated for overall mortality and emigration. There was no difference in sediment chlorophyll pigments between treatments indicating that the different densities of H. atra did not affect benthic microalgal biomass. The percentage of fission products was greater in the LDT than the HDT but this difference was not statistically significant, providing some support for the hypothesis that H. atra in the LDT exhibit a higher fission rates. At the end of the experiment H. atra in LDT were significantly longer and heavier than in HDT. H. atra surpassed their initial deployment weight and length after 13 months in the LDT by 115.2% and 45.2% respectively and in the HDT 86.9% and 24.6% respectively, changing from the small to the large phenotype known for this species. This differential growth may be linked to habitat stability and high benthic productivity and demonstrates the phenotypic plasticity of holothuroids and potential to achieve ‘Optimum Individual Size’ with respect to environmental conditions. Our results will assist in finetuning conceptual models on asexual reproduction and future experimental studies on the phenomena of fission and plastic growth in holothuroids.     

Estimation of the attraction range of a human bait forAedes albopictus (Diptera,culicidae) adults and its absolute density by a new removal method applicable to populations with immigrants

The attraction range of a human bait for Aedes albopictus (Diptera, Culicidae) adults and its absolute density in the range were estimated by a new removal method which is applicable to populations with immigrants. In this model, the number of mosquitoes removed during the kth collection unit y_k, is expressed as where x₀ is the initial number of mosquitoes in the attraction range, a is an index directly proportional to collection efficiency, b is the number of immgirants per collection unit and s(=e^−a) is the survival rate of mosquitoes in the attraction range per collection unit. From the result of successive two collections with various interval distances, it was considered that Aedes albopictus adults are attracted to a human bait from the distance of 4–5 m in the bamboo forest on the calm day. The applicability of this method for the population census of forest mosquitoes was discussed.     

The effect of population density on the reproduction ofTrichogramma japonicum Ashmead (Hymenoptera: Trichogrammatidae)

When a fixed number of the hosts, the eggs of the almond moth were exposed experimentally to various numbers of the parasites, Trichogramma japonicum, the following changes were observed with increasing parasite density:

1. The percentage of parasitism rises and approaches to 100 with gradually diminishing rate.
2. The number of parasite progeny increases and reaches a maximum, then decreases gradually.
3. The number of eggs laid per parasite female decreases gradually.
4. The proportion of hyperparasitized hosts progressively rises. The frequency distribution of parasite eggs in a host is of an intermediate type between random and uniform.
5. The competition among parasite larvae becomes severe. The progressive rise in mortality, the declining percentage of females in progeny and the emergence of stunted adults at the higher densities are observed.

In connection with both the nature of the parasitizing behaviour of adult and that of the competition among larvae, the nature of the density effect on the parasite population was discussed.