Field Observations on the Cacao Mirids <i>Sahlbergella singularis</i> Hagl. and <i>Distantiella theobroma</i> (Dist.), in the Gold Coast. PART II. Geographical and Habitat Distribution

Williams, G.

doi:10.1017/s0007485300025542

Cited by 10 publications

(5 citation statements)

References 4 publications

(9 reference statements)

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“…This is explicable by a change in supervision at this time for. as described previously (Williams, 19536), it had become clear, from the distribution of S. singularis and D. theobroma as determined by the Collections, that collections were not being made at random. Consequently, supervision was increased to ensure that strict randomisation was achieved and this change of technique was sufficient to lower the number of Mirids found.…”

Section: Maximum Population Levelsmentioning

confidence: 84%

“…The endogenous adults, therefore, do not stay long in the plot and a comparable amount of random tree to tree movement was observed for unmarked adults. Furthermore, Williams (19536) has shown that there is no difference between the time spent on a tree by an adult which had developed there and an adult which had arrived there by migration. It may be concluded that the difference between the number of adult/days spent by marked individuals and by unmarked individuals, during the second marking period, is not a result of a difference of behaviour between endogenous and exogenous adults, but is due to a difference in numbers of adults.…”

Section: S Singularismentioning

confidence: 99%

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Field Observations on the Cacao Mirids,Sahlbergella singularisHagl. andDistantiella theobroma(Dist.), in the Gold Coast. Part III. Population Fluctuations

Williams

1954

Bull. Entomol. Res.

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For both of the important cacao Mirids, Sahlbergella singularis Hagl. and Distantiella theobroma (Dist.), there is a well-marked annual population cycle. Numbers are at their lowest in March and, although showing fluctuations from month to month, remain low until July. After this period, there is an increase in numbers to a peak level which may be bimodal, an earlier peak corresponding with the maximum numbers on pods and a later peak on stems alone in January or February. This is followed by an abrupt drop in the dry season to the minimum values of March.The period of increasing numbers is, at first, associated with the presence of more cacao pods but evidence is given to prove that Mirid increase is nor determined by pod increase but that both reflect the action of some common cause. The final peak population is associated with the symptoms of seasonal blast, but although Mirid numbers beneath the canopy are at their maximum at this time, there is no corresponding increase in the resident canopy population, the blast symptoms being produced by a transient population of adults from the sub-canopy levels.Even at their highest the numbers of Mirids are small compared with most crop pests, the normal maximum being of the order of 1,000 per acre in mature stands of cacao.Such aspects of mortality as could be studied from field observations are described. There is a steady loss during nymphal life, more dying during the later stages because these last longer. Parasitism, food supply and predation appear to be the main controlling factors, but, of these, only predation is examined quantitatively. Mantids, ants and Reduviids kill between 16 per cent. and 21 per cent. of the nymphs with which they are associated and the proportion of Mirids killed by such predators increases as the number of Mirids increases. Predation plays an important part in the natural controla of Mirid populations but, although optimum conditions for predation exist in Mirid pockets, economic control is not effected.The use of ants as a Mirid control measure is examined and rejected. Infestation of healthy trees by ants does not protect nearby attacked trees and the association between ants and healthy trees is due to the colonisation of such trees as the only ones suitable in an area subject to Mirid damage. A single instance is quoted where Oecophylla longinoda (Latr.) appeared to exert a control but only at a level where the ants were so numerous as to constitute a hazard to humans in the plot.A final discussion of the three papers of the series is included to focus attention upon those aspects of Mirid biology which need immediate investigation. These include an evaluation of the loss caused by Mirids and the need for experimental work to determine the effect of physical factors on Mirids. Suggestions are made for sampling which could be employed in any future field observations.

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Section: Maximum Population Levelsmentioning

confidence: 84%

Section: S Singularismentioning

confidence: 99%

Field Observations on the Cacao Mirids,Sahlbergella singularisHagl. andDistantiella theobroma(Dist.), in the Gold Coast. Part III. Population Fluctuations

Williams

1954

Bull. Entomol. Res.

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“…Our results showed that S. singularis female longevity can exceed 60 days and fecundity can reach 236 nymphs per female. To the best of our knowledge, maximum adult longevity has previously been assessed at 30 days and fecundity at 30-60 eggs per female, with a maximum value of 179 (Williams, 1953b;Entwistle, 1972;Youdeowei, 1973;Kumar & Ansari, 1974). Consequently, our results suggest that S. singularis reproductive ability has been underestimated in the past, possibly because of inappropriate rearing techniques (Youdeowei, 1973).…”

Section: Discussionmentioning

confidence: 57%

“…To the best of our knowledge, maximum adult longevity has previously been assessed at 30 days and fecundity at 30-60 eggs per female, with a maximum value of 179 (Williams, 1953b;Entwistle, 1972;Youdeowei, 1973;Kumar & Ansari, 1974). To the best of our knowledge, maximum adult longevity has previously been assessed at 30 days and fecundity at 30-60 eggs per female, with a maximum value of 179 (Williams, 1953b;Entwistle, 1972;Youdeowei, 1973;Kumar & Ansari, 1974).…”

Section: Discussionmentioning

confidence: 99%

Effects of cocoa tree phenology and canopy microclimate on the performance of the mirid bug Sahlbergella singularis

Babin¹,

Anikwe²,

Dibog³

et al. 2011

Entomologia Experimentalis Et Applicata

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Populations of the cocoa mirid, Sahlbergella singularis Haglund (Hemiptera: Miridae), on cocoa, Theobroma cacao L. (Malvaceae), display sharp seasonal fluctuations in population size. To better understand factors and mechanisms involved in seasonal variation, we studied the life history traits of 10 successive generations of a caged population under field conditions. Nymphal survival and development were assessed on pods stored under cocoa canopy, whereas female survival and fecundity were evaluated on sleeved pods in cocoa trees. At the same time, cocoa phenology and cocoa canopy microclimate were characterized. A life table analysis was conducted with survival and fecundity temporal data. Reproductive parameters showed far more variation than nymphal development parameters, both within and among generations. We obtained low intrinsic rates of natural increase (about 0.04), the variation of which was mainly linked to the decrease in fecundity. Fecundity as well as life table parameters varied in accordance with natural population fluctuations, suggesting that S. singularis seasonal variation might be mainly linked to variation in female fecundity. A multiple regression analysis showed that variation in female fecundity was first correlated with the presence of young fruits on cocoa trees. Fecundity was also weakly affected by daily minimum r.h. and daily mean temperature. The usefulness of our results for modeling of S. singularis population dynamics and for the improvement of IPM strategies is discussed.

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“…The development of novel-integrated pest management strategies implies intensive laboratory experimentation, which requires a large number of insects. However, low densities and seasonal fluctuations of on-farm mirid populations make field collections unpractical (Williams 1953b;Lotodé 1969;Youdeowei 1971;Nwana and Youdeowei 1978). In the past, many rearing attempts were not successful (Raw 1959;Prins 1964;Lavabre 1969;Piart 1970;Cross and King 1971;Kumar and Ansari 1974).…”

Section: Introductionmentioning

confidence: 99%

Rearing method and life‐table data for the cocoa mirid bug Sahlbergella singularis Haglund (Hemiptera: Miridae)

Babin

Bisseleua

Dibog

et al. 2008

J Applied Entomology

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The mirid bug Sahlbergella singularis feeds on cocoa pods and shoots, causing considerable crop losses. As laboratory experimentation requires numerous insects, this study aimed at improving available rearing method of S. singularis for Cameroon. Fifty second to fifth nymphal stages were collected at a cocoa farm and reared to the adult stage on cocoa pods in an insectary (T = 24.7 AE 0.9°C, RH = 84.5 AE 6.8%, photoperiod: 12 : 12 L : D). Newly emerged females were confined for 5-6 days on cocoa twigs for sexual maturation and each female paired with a male for 24 h. The pairs were returned to the field and enclosed in mousseline sleeves on attached cocoa pods, for egg laying. After 16 days (expected egg lifetime), the sleeve cages were checked daily to detect newly hatched nymphs. Then, the pods were collected and brought to the insectary, where nymphs continued to emerge and develop into adults. Our method allowed the production of 14.6 AE 6.7 nymphs per female per generation, for 15 consecutive generations. Nymphal survival was calculated to be 68.2% and the mean duration of the nymphal development was measured at 22.7 AE 3.1 days. The rearing performance was evaluated using life-table calculations. The net reproductive rate (R 0 ) was 6.59; the intrinsic rate of increase (r) was 0.037 per female per day with a population doubling time (T d ) of 18.9 days. On average each female contributed 9.70 individuals to the population given a mean generation time (T c ) of 52.1 days. The percentage of reproductive females and the mean number of nymphs per female were significantly different between generations, with 86.8% and 18.1% in generation G7 as compared to 45.8% and 8.4% for generation G5, respectively. As rainfall showed concordant variations during the period of investigation, we discuss the impact of this factor on mirid fecundity.

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Field Observations on the Cacao Mirids Sahlbergella singularis Hagl. and Distantiella theobroma (Dist.), in the Gold Coast. PART II. Geographical and Habitat Distribution

Cited by 10 publications

References 4 publications

Field Observations on the Cacao Mirids,Sahlbergella singularisHagl. andDistantiella theobroma(Dist.), in the Gold Coast. Part III. Population Fluctuations

Field Observations on the Cacao Mirids,Sahlbergella singularisHagl. andDistantiella theobroma(Dist.), in the Gold Coast. Part III. Population Fluctuations

Effects of cocoa tree phenology and canopy microclimate on the performance of the mirid bug Sahlbergella singularis

Rearing method and life‐table data for the cocoa mirid bug Sahlbergella singularis Haglund (Hemiptera: Miridae)

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