The nature, number, structure and behaviour of chromosomes during the meiotic and mitotic sequences in the armoured ground cricket, Acanthoplus speiseri Brancsik, were investigated from testicular and ovariole material. The karyotype of A. speiseri is 2n ♂=25 (24 autosomes + XO) and 2n ♀=26 (24 autosomes + XX). The species exhibits the primitive XO ♂ /XX ♀ type of sex determination mechanism. All chromosomes in the cell complement (including the X sex chromosome), in both sexes, are acrocentric in shape. The X sex chromosome is the largest element in the karyotype while the autosomes comprise three large, four medium and five small pairs. The behaviour of the chromosomes during the meiotic and mitotic processes is normal and typically orthopteran. The study discusses the important role that karyology and cytogenetics can play for species diagnostics in the subfamily Hetrodinae.

The development of a single cohort of the armoured ground cricket, Acanthoplus speiseri Brancsik was followed in the environs of the University of Zambia campus, Lusaka and a preliminary life table of the grain pest constructed. The pest's total generation mortality was influenced by: failed egg eclosion, failed ecdysis, cannibalism/predation and parasitism. The egg stage had the highest percent real mortality (98.57%) and sub-mortality k-value, indicating that this was the main contributor to the total generation mortality. The rest of the developmental stages suffered lower mortalities, although that of the 6th instar was comparatively higher. A mermithid nematode, Mermis sp., and another unidentified nematode species caused 2.61% sub-mortality in the 6th nymphal instar. The constructed preliminary life table of A. speiseri is analysed and the possible causes of the observed high mortalities in the egg and 6th instar stages are discussed.

The dispersal characteristics of a population of 124 marked adult individuals (62 males and 62 females) of the armoured ground cricket (AGC), Acantliophis speiseri Brancsik (Orthoptera: Tettigoniidae, Hetrodinae), released at the centre of a circular study site, were investigated using the capture-mark-release-recapture method for five successive days. The 110 m-diameter study site comprised five grass-trap annuii (each 1 m wide) spaced at 10-m intervals from the centre.

The frequency curve of numbers derived from recapture data for day 1 departed from normal (Kurtosis = 2.7), indicating that the released AGC population was heterogeneous in its dispersing behaviour. A comparison of mean numbers of recaptures from grass-traps per quarter portion of the study site revealed no drift in the dispersal of the population (P > 0.05), though differences in the variances of the recapture frequencies indicated a tendency towards non-random movement in the AGC population.

The population covered a mean distance of 24.47 m in the first 24 h following release and the rate of dispersal changed daily in the five-day study. The implications of the dispersal characteristics observed in this study to future design of control strategies for the pest in Zambia are discussed.

Acanthoplus speiseri Brancsik, a pest of grain crops in Zambia, was reared in the laboratory at different temperatures. Mean development times of the eggs, nymphs and adults were determined at the different temperatures and used to develop a thermal unit model for use by farmers to predict the appearance dates of the different nymphal instars and the adults in the field in a given season. The predictions generated by the developed model for the 1990/1991 season, were compared to the actual dates on which the first specimen of each developmental stage was collected in the field during the season. The predicted dates of appearance all fell within 1 week of the observed dates of collection. Reasons for the slight deviations between the predicted and observed dates and the significance of the developed thermal unit model to the future control of A. speiseri in Zambia, are discussed.

Observations on the reproductive behaviour of the armoured ground cricket, Acanthoplus speiseri Brancsik were made in the laboratory and field. In the field a male ready to mate attracted both receptive females and mature “silent males” by stridulating. A receptive female moved to the stridulating male and upon reaching it courtship begun. Silent males also moved towards the stridulating male, but stopped at a mean distance of 1.07 ± 0.14 m from him and either seduced females that passed their way to the stridulating male, to copulate with them, or joined the stridulating male singing. Chorusing of the calling song involving more than two males was not uncommon in both the field and laboratory.

Due to stiff competition for mates in the environmental chamber in the laboratory male A. speiseri combined acoustic and substrate signals to attract receptive females. The male ground crickets vibrated their appendages, while they stridulated. Substrate signalling through body/appendage vibration or tremulation is here being reported for the first time in the tettigoniid subfamily Hetrodinae, to which A. speiseri belongs. The courtship behaviour, orientations of members of a copulating pair relative to each other, copulation, spermatophore transfer from the male to the female during copulation and oviposition and postoviposition behaviours of the species are described. Finally, the differences in the reproductive behaviour of A. speiseri in the field and laboratory are discussed.

Food plant preferences and spatial dispersion patterns of the armoured ground cricket, A canthoplus speiseri Brancsik were investigated. The average numbers of the ground cricket found feeding on each food plant per transect in each of the three study areas were tested for differences at the 0.05 level of probability by Duncan's multiple range test. The variance/mean ratio was used to analyse spatial dispersion patterns. A. speiseri fed on 12 plant species from the Compositeae, Gramineae and Solanaceae families. Hyparrhenia nyassae (Rendle) Stapf., (Gramineae) and Rottboelia exaltata Linn, f., (Gramineae), were the most preferred food plants. The armoured ground cricket densities on the two food plants were insignificantly different from each other. The cultivated plants, Zea mays L., and Sorghum vulgare Pers., were fed upon opportunistically by the ground crickets. The variance/mean ratio identified aggregation in the armoured ground cricket populations in all three study areas . The significance of the findings on food plant preferences and dispersion patterns are discussed in relation to future sampling and control of A. speiseri.

Plant associations and rates of population interchange between two food plant areas for the armoured ground cricket, Acanthoplus speiseri Brancsik were investigated. A. speiseri was associated with 40 species of plants spread over 11 families. The ground cricket had a significantly high frequency of association at P = 0.05 with Rottboelia exaltata Linn. F. and Hyparrhenia nyassae (Rendle) Stapf. The ground cricket preferred members of the Gramineae to those of other families, 69% of the total number of ground crickets collected from the plants in this study were from grasses and among these Zea mays L. and Sorghum vulgare Pers. were opportunistic associations.

The rates of population interchange between two areas dominated, respectively, by Nicandra physaloides (L.) Gaertn. and R. exaltata with several species of Hyparrhenia were unequal. There was net emigration of 76.69 ground crickets to the N. physaloides area in 10 days.

The significance of the findings on plant associations and rates of population interchange between food plant areas of A. speiseri to future sampling and control of the ground cricket is discussed.

Spatial dispersion patterns of Acanthoplus speiseri were inestigated. Four indices of dispersion derived from either Iwao's measure or Taylor's Power Law were used to study spatial dispersion patterns. All indices were in agreement in identifying aggregated dispersion patterns in the cricket populations sampled. Iwao's index of basic contagion revealed that individual crickets formed the basic components in the aggregated dispersion of the populations.