Growth patterns of the ladybird (Harmonia axyridis Pallas) relative to variations in population genetics

Differences in population growth among four variation types of the ladybird beetle, Harmonia axyridis Pallas, namely succinea, conspicua, spectabilis and aulica, were investigated using various growth parameters. The variation types showed three growth patterns from the intrinsic growth rates (rm), with rates of 0.093–0.099 (for conspicua and aulica), 0.073 (for succinea) and 0.040 (for spectabilis). The growth rates of these patterns were realised in different ways. Spectabilis differed from the other three types in the age and per cent distribution of the specific period to the rm values.

Resistance of different host plants and cultivars of cassava to the mealybug Phenacoccus manihoti: Effect of infestation on leaf extract composition

The effect of a 2-month infestation by the cassava mealybug (Phenacoccus manihoti Mat. Ferr.) on the metabolism of nitrogen (amino acids) and carbon (carbohydrates), leaf area and total dry weight of five cassava varieties (Manihot esculenta Crantz), faux-caoutchouc (a hybrid of M. esculenta and M. glaziovii Muell, Arg.), poinsettia (Euphorbia pulcherrima Wild) and talinum (Talinum triangulare Jack) was studied. Free amino acid and free sugar contents as well as relative free amino acid composition in the leaf extracts, although found to be very different from one plant to another, were not significantly modified by P. manihoti infestation, except for the total amino acid contents of the cassava variety 30M7. Variations in one particular amino acid induced by mealybug infestation were not linked to the antibiotic resistance of these plants. Infestation by the cassava mealybug did not modify the total dry weight but reduced the total leaf area although this reduction was only significant in cassava varieties 59M2, 30M7 and M'pembe, and in faux-caoutchouc. Within the genus Manihot, the reduction in leaf area was strongly correlated (r= -0.878, P≤0.05) to the degree of antibiotic resistance and was coupled to an increase in the ratio of sugars to amino acids, suggesting a similarity between the effects of water stress and those of mealybug infestation.

Evaluating an insect pest management system in an irrigated rice environment

The efficiency and profitability of an integrated pest management system consisting of a phytosanitary survey and threshold interventions (based on levels of insect damage) was tested at the Vallée du Kou irrigated rice scheme in Burkina Faso, for two consecutive crop seasons in 1987. There was a considerable advantage in cost, number of insecticidal applications and yield of a threshold intervention-based system over arbitrary or routine insecticidal application methods. The proposed method is considered to be environmentally friendly.

Survival and development of Chilo partellus (Swinhoe) on sorghum cultivars

Survival and development of Chilo partellus were studied on five sorghum cultivars (IS-18363, IS-18520, ICS-1, ICS-2 and IS-4660) in the laboratory at Mbita Point Field Station, Kenya, at 26 ± 2°C and 65 ± 5% RH. Larval developmental period differed significantly on different cultivars. Number of instars was numerically greater for the females than for the males on all cultivars. Average pupal weight varied with sex; females were twice as heavy as males. The pupal period was longer for males than for females on all cultivars, with the exception of ICS-1, where the pupal period of males was equal to that of females. Ovipositional period was significantly longer on IS-18520 (5.18 ± 0.30 days) than on other cultivars. The shortest ovipositional period (3.70 ± 0.27 days) was recorded on IS-4660. There were no statistically significant differences in adult longevity. Sex ratio of the moths also did not affect the adult longevity of C. partellus reared on the five sorghum cultivars. The variations found in the development of C. partellus on different cultivars were attributed to the nutritional value of the food source.

Screening of Florida mango fruits from germplasm for resistance to immature stages of Caribbean fruit fly

Mature fruits from 21 mango, Mangifera indica L., cultivare grown in the Miami National Clonal Germplasm Repository were examined for resistance under laboratory conditions to identify those resistant (antibiotic or antixenotic) to the eggs and larvae of the Caribbean fruit fly, Anastrepha suspensa (Leow). The bioassay consisted of artificially infesting a slice of fruit with eggs obtained from a laboratory colony and counting the adults that emerged. Emergence ranged from 26.6% (on Tobago Small Red) to 119.0% (on Sabre) of controls (on artifical diet). Tobago Small Red, Becky, Saigon Seedling, Zilate, Sandersha, 13–1, Keitt, Turpentine, Rumani, Tommy Atkins, Irwin and Peach had the highest level of resistance observed with less than 80% emergence. The most resistant cultivars are promoted to breeders and growers for production in areas under quarantine for Caribbean fruit fly.

Movement of Cicadulina storeyi (Homoptera: Cicadellidae) in maize fields and its behaviour in relation to maize growth stage

The movement of Cicadulina storeyi China (Homoptera: Cicadellidae), vector of maize streak geminivirus, within maize (Zea mays L.) fields was studied using mark, release and recapture experiments. Cicadulina storeyi, marked with fluorescent dye, were released at dusk and monitored for 14 days using yellow sticky traps placed at different distances (5–160 m) and directions from the release point. The suitability of maize growth stage for settling by C. storeyi was also investigated. Catches decreased steadily with distance from the release point and exponentially with time following the release. The mean leafhopper dispersal rate varied between 2.6 and 2.8 m/day for dry season and rainy season tests, respectively. The dispersal rate increased with distance from 1.4 m/day at 5 m to 13.6 m/day at 160 m. Wind was a major factor affecting direction of leafhopper movement with the largest proportion of C. storeyi collected downwind. Investigations on the suitability of maize growth stage for settling by C. storeyi revealed that the leafhopper preferred young plants (2–6 weeks after planting) to old ones.

Inheritance of resistance in grain sorghum to Chilo partellus (Swinhoe)

The inheritance of resistance in grain sorghum to the spotted stemborer, Chilo partellus (Swinhoe) (Lepidoptera: Pyralidae) was studied in F3 plants derived from crosses between nine locally adapted inbred lines and two sources of resistance. Antibiosis resistance was measured as the relative growth rate of larvae in the whorls of 6-week-old plants. Most F3 plants were either as resistant as, or more resistant than, the resistant parent. This indicated dominance of resistance over susceptibility and the occurrence of transgressive segregation. The segregation pattern in the F3 generation suggested the presence of at least four dominant genes. Two families homozygous for these genes were identified.