Effects of intercropping on maize stemborers and their natural enemies

1996 ◽  
Vol 86 (5) ◽  
pp. 599-607 ◽  
Author(s):  
Henrik Skovgård ◽  
Peeter Päts
Keyword(s):  
Chilo Partellus ◽  
Natural Enemies ◽  
Inverse Relationship ◽  
Host Density ◽  
Sesamia Calamistis ◽  
Density Dependent ◽  
Pupal Parasitism ◽  
Egg Parasitism

AbstractThe effects of maize–cowpea intercropping on three lepidopteran stemborers (Chilo partellus (Swinhoe) C. orichalcociliellus (Strand) and Sesamia calamistis Hampson) and their natural enemies were studied in Kenya. Oviposition was not affected by intercropping, but significantly fewer larvae and pupae were found in the intercrop. Egg parasitism was significantly higher in the intercrop reaching as high as 80% and was positively density dependent. Larval and pupal parasitism remained between 3 and 20%, but neither of these were affected by intercropping or host density. The main predators, ants and wandering spiders, were not augmented by intercropping, but an inverse relationship in abundance was found between these two predator groups. It is concluded that maize intercropped with cowpea has only limited potential as a method of controlling the key pests in maize.

3.5 SUPPRESSION OF SPRUCE BUDWORM POPULATIONS BY TRICHOGRAMMA MINUTUM RILEY, 1982–1986

1990 ◽  
Vol 122 (S153) ◽  
pp. 56-81 ◽  
Author(s):  
S.M. Smith ◽  
D.R. Wallace ◽  
G. Howse ◽  
J. Meating
Keyword(s):  
Choristoneura Fumiferana ◽  
Host Density ◽  
Spruce Budworm ◽  
Mass Rearing ◽  
Egg Parasitoid ◽  
Curvilinear Relationship ◽  
Egg Masses ◽  
Trichogramma Minutum ◽  
Egg Parasitism ◽  
Release Timing

AbstractThe ability of the egg parasitoid, Trichogramma minutum Riley, to suppress outbreak populations of the spruce budworm, Choristoneura fumiferana (Clemens), was studied annually near Hearst, Ont., from 1982 through 1986. Timing of broadcast parasitoid-releases was linked to spruce budworm moth emergence and oviposition. These phenological relationships were predicted from a regression based on larval development at least 2 weeks before expected emergence; this allowed sufficient time to regulate (program) parasitoid emergence during mass-rearing. Emergence of caged spruce budworm adults was used to monitor moth eclosion in the field. Pheromone traps provided daily information on the activity of male moths and helped to synchronize the parasitoid releases with spruce budworm oviposition. Information on parasitoid activity was obtained from sentinel (laboratory-reared) and naturally occurring spruce budworm egg masses. A curvilinear relationship between the rate of parasitoid release and parasitism of sentinel egg masses was developed. Two parasitoid releases, 1 week apart, early in the oviposition period of spruce budworm, significantly increased parasitism of host eggs by 14–83% and reduced larval populations correspondingly from 42 to 82%. Single releases were less effective and increased parasitism by 0.3–52% (single ground release, 1986). Two parasitoid releases, combined with a spring application of Bacillus thuringiensis Berliner to larval populations, was the most effective strategy and resulted in 83% egg parasitism and 93% larval reduction. Release rates greater than 12–16 × 106 ♀ ♀ T. minutum per hectare were not warranted based on impact and costs. The effects of release timing, weather, host density, and parasitoid quality on the future successful use of T. minutum are discussed.

scholarly journals Comparative evaluation of Cotesia flavipes and C. sesamiae (Hymenoptera: Braconidae) for the management of Chilo partellus (Lepidoptera: Pyralidae) in Kenya

1999 ◽  
Vol 89 (2) ◽  
pp. 185-191 ◽  
Author(s):  
M.N. Sallam ◽  
W.A. Overholt ◽  
E. Kairu
Keyword(s):  
Chilo Partellus ◽  
Sesamia Calamistis ◽  
Cotesia Flavipes ◽  
Cotesia Sesamiae ◽  
Female Progeny ◽  
Northern Tanzania ◽  
Significant Difference ◽  
Total Progeny ◽  
Lepidoptera Pyralidae ◽  
Searching Ability

AbstractCotesia flavipes Cameron, a gregarious larval endoparasitoid native to the Indo-Australian region, was imported from Pakistan and released in Kenya in 1993 for management of the exotic stemborer, Chilo partellus (Swinhoe). Recent reports confirmed the successful establishment of the parasitoid in three locations in Kenya and in northern Tanzania. Functional response studies on this parasitoid and an indigenous congener, Cotesia sesamiae (Cameron), indicated that C. flavipes had a higher searching ability and attacked more larvae when Chilo partellus was the host. When a native stemborer, Sesamia calamistis Hampson, was the host, there was no significant difference between numbers attacked by both parasitoids. Numerical response studies showed that Cotesia flavipes produced more total progeny and female progeny per female parasitoid on Chilo partellus than did Cotesia sesamiae. No significant difference in progeny production was detected between the two parasitoids on S. calamistis. Functional and numerical responses tested in the laboratory gave the same ranking of the two parasitoids on the two hosts as in the field. This study suggests that Cotesia flavipes is a more efficient parasitoid and it is anticipated that it will contribute to the control of both exotic and native stemborers in Kenya.

Influence of intercropping on the abundance, distribution and parasitism of Chilo spp. (Lepidoptera: Pyralidae) eggs

1997 ◽  
Vol 87 (5) ◽  
pp. 507-513 ◽  
Author(s):  
P. Päts ◽  
B. Ekbom ◽  
H. Skovgård
Keyword(s):  
East Africa ◽  
Chilo Partellus ◽  
Field Experiments ◽  
Plant Density ◽  
Coastal Areas ◽  
Positive Density ◽  
Abundance Distribution ◽  
Significant Difference ◽  
Egg Parasitism ◽  
Lepidoptera Pyralidae

AbstractTwo of the most common and serious pests of maize and sorghum in the coastal areas of East Africa are the pyralid species, Chilo partellus (Swinhoe) and C. orichalcociliellus (Strand). Maize monocrop (with high and low plant density) and maize/cowpea mixed intercrop field experiments were conducted in Kenya to test if intercropping decreased the number of egg batches laid, altered the distribution of the egg batches and influenced egg parasitism. There was no significant difference in the number of egg batches per plant between treatments and the egg batches were randomly distributed on and among plants in most of the plots for all three treatments. There was a tendency for higher egg parasitism in the intercrop. The proportion of eggs parasitized was significantly correlated with total number of eggs per plot suggesting a positive density dependent response. It is concluded that intercropping does not affect C. partellus nor C. orichalcociliellus oviposition behaviour but egg parasitism is likely to be augmented.

Heterogeneity and the dynamics of host—parasitoid interactions

1990 ◽  
Vol 330 (1257) ◽  
pp. 203-220 ◽  
Keyword(s):  
Population Dynamics ◽  
Continuous Time ◽  
Population Regulation ◽  
Host Density ◽  
General Rule ◽  
Field Studies ◽  
Simple Description ◽  
Density Dependent ◽  
Total Heterogeneity ◽  
Local Host

This paper is concerned with the dynamical effects of spatial heterogeneity in host-parasitoid interactions with discrete generations. We show that the dynamical effects of any pattern of distribution of searching parasitoids in such systems can be assessed within a common, simple framework. In particular, we describe an approximate general rule that the populations of hosts and parasitoids will be regulated if the coefficient of variation squared (CV 2 ) of the distribution of searching parasitoids is greater than one. This criterion is shown to apply both generally and in several specific cases. We further show that CV 2 may be partitioned into a density-dependent component (direct or inverse) caused by the response of parasitoids to host density per patch, and a density independent component. Population regulation can be enhanced as much by density independent as by density-dependent heterogeneity. Thus the dynamical effects of any pattern of distribution of searching parasitoids can be assessed within the same common framework. The paradoxical impact of density-independent heterogeneity on dynamics is especially interesting: the greater the density independence, and thus the more scattered the data of percent parasitism against local host density, the more stable the populations are likely to be. Although a detailed analysis of host-parasitoid interactions in continuous time has yet to be done, evidence does not support the suggestion of Murdoch & Oaten (1989) that non-random parasitism may have quite different effects on the dynamics of continuous-time interactions. There appears to be no fundamental difference in the role of heterogeneity in comparable discrete- or continuous-time interactions. A total of 65 data sets from field studies have been analysed, in which percentage parasitism in relation to local host density have been recorded. In each case, estimated values of have been obtained by using a maximum likelihood procedure. The method also allows us to partition the CV 2 into the density dependent and density-independent components mentioned above. In 18 out of the 65 cases, total heterogeneity was at levels sufficient (if typical of the interactions) to stabilize the interacting populations (i.e. CV 2 > 1). Interestingly, in 14 of these it is the host-density-independent heterogeneity that contributes most to the total heterogeneity. Although heterogeneity has often been regarded as a complicating factor in population dynamics that rapidly leads to analytical intractability, this clearly need not necessarily be so. The CV 2 > 1 rule explains the consequences of heterogeneity for population dynamics in terms of a simple description of the heterogeneity itself, and provides a rough rule for predicting the effects of different kinds of heterogeneity on population regulation.

Sign in / Sign up

Export Citation Format

Share Document