Insect Science and its Application.

Progress in Protozoology. Proceedings of the VIIth International Congress of Protozoology. Volume 7 Number 3.

Due to an oversight the Editor regrets that the title of the Special Issue, Volume 7 Number 3, should have read; “Progress in Protozoology” not “Progress in Entomology.”

The pearl millet, Pennisetum americanum L., a major food crop in the Sahel, is regularly attacked by a complex of spike worms, of which Raghuva albipunctella De Joannis (Noctuidae: Lepidoptera) is the most common and abundant species. The research on taxonomy, economic importance, biology and ecology of spike worm and control measures used to suppress its populations is reviewed from 1972 (period of its first outbreak) to 1984. Further studies are proposed to develop a viable pest management strategy which would be effective, practical, economical and easily adopted by the farmers. The present paper also discusses the difficulties and possibilities of such approach in relation to subsistence farming systems.

Injection of antiserum prepared against accessory reproductive gland (ARG) secretions of the male desert locust, Schistocerca gregaria, disrupted the normal growth and function of the ARG complex in sexually maturing adults. Male locusts were injected with either antiserum or normal guinea-pig serum on days 3, 7 and 10 after adult ecdysis. When the injection of ARG antiserum began as early as day 3 of adult development a marked inhibition of ARG growth was accompanied by the suppression of other characteristics of sexual maturation (yellow body coloration and mating behaviour). Inhibition of ARG growth, while significant, was less pronounced when antiserum injections began on day 7 of adult development, and the injected males did not exhibit normal mating behaviour when placed with virgin females. When single antiserum injections were administered on day 10 of adult development, the males still attained their yellow body coloration by day 19 and copulated normally with virgin females, although their ARGs were only equivalent in size to those 13-day-old males.

Adult ticks of Rhipicephalus appendiculatus were fed on rabbits immunized with antigen–antibody complexes derived from the immunodiffusion reaction in agarose of tick extracts with antisera from rabbits immunized previously with tick extracts. Ticks feeding on the precipitin complex immunized rabbits displayed delayed attachment, prolonged engorgement and extended periods to drop off the host. While final engorgement weight was not affected, the immunization was observed to produce an adverse effect on egg hatchability. Fewer than 10% eggs from ticks fed on immunized animals hatched live larvae compared to greater than 90% live hatchings from ticks fed on controls. The tick antigens responded to by the immunized rabbits were characterized by crossed immunoelectrophoresis. Antisera from precipitin complex immunized animals precipitated four to five separate antigens from immunizing extracts. One (or more) of these antigens may be the target for the observed deleterious effect on tick reproduction.

Immune resistance to infestation by an ixodid tick, Rhipicephalus appendiculatus, the vector of the African cattle disease, East Coast Fever, was induced in rabbits by either repeated tick feeding or immunization with tick extracts. In addition to resistance to tick infestation, tick extract immunization led to a reduction in the viability of eggs laid by ticks feeding on the immunized host. Resistance to infestation by ixodid ticks has previously been reported by others to have a humoral immune component. Therefore, antibodies from resistant host animals were used to detect the tick antigens they recognized as an approach to identification of the target antigen(s) for the observed immune responses on feeding ticks. In crossed immune electrophoresis two antigens were detected using sera from animals made resistant by multiple tick infestations. Sera from extract immunized animals detected these antigens and nine others. The tick antigens detected by both sets of sera in crossed immune electrophoresis were radiolabelled with [35S]amino acids. No labelled antigens were detected by Staphylococcus aureus mediated immune precipitation with sera from hosts made resistant by multiple infestations. Antibodies from extract-immunized animals identified nine protein antigens by S. aureus immunoprecipitation. The molecular weights of these antigens as assessed by sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis were 180,000; 140,000; 130,000; 98,000; 92,000; 88,000; 85,000 and 82,000. The rate of synthesis of these antigens appeared to vary in relation to the tick feeding cycle.

Various alkaloids from Adhatoda vasica (Acanthaceae) were found to be responsible for the antifertility and antifeedant activity of the extracts of the plant against insects. Among the major alkaloids vasicine, vasicinol and vasicinone severe antifertility effects were exhibited by vasicinol against Dysdercus skoenigii and Tribolium castaneum due to blocking of oocytes in the oviduct. Feeding deterrence was observed against Aulacophora foveicollis and Epilachna vijintioctopunctata at 0.05 and 0.1% levels of these compounds. These allelochemics appear to show a dual activity vis-à-vis a species specificity.

Limonin, deoxylimonin, citrolin, obacunone, harrisonin and acetoxyharrisonin were assayed as potential antifeedanfe against the African crop pests, Spodoptera exempta, Eldana saccharina and Manica testulalis. Even at the highest applied concentration, limonin, deoxylimonin, citrolin and acetoxyharrison were not active against S. exempta. At high concentrations, obacunone and harrisonin were mildly active in S. exempta assays. Harrisonin and obacunone displayed potent activity against E. saccharina and M. testulalis.

The structure of hildecarpin, an insect antifeedant 6a-hydroxypterocarpan isolated from the roots of Tephrosia hildebrandtii has been confirmed by a combination of degradation reactions, NMR and mass spectra. Hildecarpin has been dehydrated to the corresponding pterocarpene 3-hydroxy-2-methoxy-8,9-methylenedioxypterocarpene. Hydrogenation and hydrogenolysis of the pterocarpene has afforded the isoflavan 2′, 7-dihydroxy-6-methoxy-4′,5′-methylenedioxyisoflavan, acetylation of which has led to 2′, 7-diacet6xy-6-methoxy-4′,5′-methylenedioxyisoflavan. The NMR and mass spectra of the degradation products confirm the structure previously assigned to hildecarpin.

Between 1979 and 1982, H. hampei spread itself from a small area in the lowlands of central Jamaica, to the entire coffee growing region (alt. 15–1603 m) of the island. The levels of infestations in the 390 farms surveyed ranged from less than 5–100%; in plains it was about 45% but only about 3.4% at altitudes of over 1000 m. On a parish basis the infestation ranged from 2.8 to 19.17% (mean 9.45%) in June 1982, before the spraying with thiodan EC35 began.

In November 1982, 8 weeks after the last spray of the three-spray cycle, the infestation levels ranged between 1 and 20.21% (mean 9.56%). In fact, it had increased from about 6.7% in 1979 to 9.56% in 1982, despite the multi-million dollar spraying programme over 4 years. The shortcomings of the chemical control strategy are discussed and an integrated approach involving chemical and cultural practices is advocated.

No insect parasite or predator of H. hampei were found in Jamaica; the fungus Beauvaria bassiana was however, found to have inflicted 6–40% mortality in the adult borer.

Arthropods feeding on horses in the stables situated in three towns in south-western Nigeria were investigated. Flies were caught on horses with trap-net while ticks and lice were picked from them with forceps. Stomoxys, Tabanus, Glossina and Hippobosca species were the main blood-sucking flies caught, while myiasis flies and Musca species were also found. Furthermore, three genera of ticks, Boophilus, Hyalomma and Rhipicephalus and two species of lice, Haematopinus equi and Damalina equi, were recorded. The veterinary importance of the association of these arthropods with horses is discussed.

A Glossina community inhabiting a peridomestic agroecosystem encircling Orie-Orba in the Nsukka area was investigated with unbaited biconical traps for species composition, population characteristics and trypanosome infections. Only Glossina tachinoides Westwood and G. palpalis (Robineau–Desvoidy) were encountered, the former comprising over 99% of all 2877 tsetse caught. G. tachinoldes occurred at a weekly mean apparent density of 8.41 ± 0.98/trap which fluctuated in a manner characterized by decrease in the wet season and increase in the dry season. Traps caught males and females in equal proportions during the wet season but during the dry season males outnumbered females in the monthly trap catches. During either season, the female samples comprised mostly old flies. Pregnancy rate was high during both seasons and abortion was the only reproductive abnormality manifested. The size of mature eggs in utero varied in a manner suggesting the occurrence of nutritional stress during both seasons. Approximately 5% of 347 G. tachuinoides examined for trypanosomes were infected with procyclic trypanosomes only.

These observations, which have formed the basis of further investigations now in progress, are discussed in the light of earlier studies at this location and elsewhere, and in the context of certain peculiarities of intensively cropped agroecosystems.

Piper guineense Schum and Thonn, mixed with cowpea seeds, Vigna unguiculata (L.) Walp, was significantly superior (P < 0.05) to the large, red and mild Capsicum annum var connoides (Miller) and the small, red and pungent Capsicum frutescens L. in causing up to 96% mortality to adults of Callosobruchus maculatus F. within 48 hr. When applied as ground pepper, P. guineense was more active insecticidally than when applied as whole fruits.

Adult bruchids in contact with P. guineense showed significant reduction (P < 0.05) in the numbers of eggs laid, and in the numbers of F1, offspring that emerged compared with adult bruchids exposed to the same doses of C. annum or C. frutescens respectively.

Neither of the peppers reduced the viability of the cowpea seeds or the absorption of water needed to soften the seed testa for decortication before cooking or processing.

At a cost price of U.S.A. $0.003 per 1 g of black pepper, and an effective application rate of 1 g black pepper to 20 g cowpea, there is a saving of over $750 by disinfesting a ton of cowpea with black pepper for a storage period of 2–3 months in a metallic drum which costs less than $50.00

Laboratory-reared Xenopsylla brasiliensis and X. cheopis obtained from several parts of Tanzania were tested with 0.5% malathion, using the standard WHO test kit.

Two strains of Xenopsylla brasiliensis (Mbulu and Amani) were more susceptible as 100% mortality was obtained after 12 hr exposure. With the remaining populations, 100% mortality was obtained after 24 hr exposure. LT50 of X. brasiliensis were 3.1, 3.3 and 4.5 hr for Mbulu, Tawalani and Amani strains respectively. Similarly, LT50 of X. cheopis were 8.1, 7 and 5.4 hr for Chunya, Amani and Tawalani strains respectively.

It was generally concluded that malathion was a suitable insecticide for use in flea and consequently plague control in Tanzania as X. brasiliensis and X. cheopis are the commonest flea vectors of the disease in the country. Moreover, the insecticide is locally available and it has limited toxicity on non-target organisms and little persistence in the environment.

Prococenes I or II (20–100 μg/insect) were topically applied to third instar nymphs of the grasshepper, Heteracris littoralis. Both compounds led to different degrees of precocious metamorphosis, irreversible with time, at the subsequent moults. Precocene-treated third instar nymphs gave rise to precocious adults at the following moult, though some of the nymphs responded and metamorphosed precociously in the fifth instar. Ovarian development was inhibited by precocene II. Meanwhile, juvenile hormone (20/μg/insect) restored normal ovarian development to some extent.

Tanzanian strains of Tribolium castaneum (Herbst), Gnatocerus maxillosus (F.), Sitophilus oryzae (L.) and Sitophilus zeamais Motschulsky were confined to maize grain treated with a dilute dust of permethrin at the rates of 1.5, 3.0 and 6.0 ppm active ingredient. The adult mortality and resulting F1 generation were recorded. G. maxillosus was very susceptible to the insecticide and even the lowest dose brought complete control. T. castaneum adults survived all treatments but few F1 were produced. Adult survival of s. oryzae and S. zeamais was progressively reduced by increasing dosage, although S. zeamais was much less susceptible to the treatment than S. oryzae.

The repellency of grain, treated with 3.0 ppm permethrin, to S. oryzae, S. zeamais and T. castaneum was tested in a simple choice chamber. Neither male nor female T. castaneum were repelled but significantly fewer eggs were laid on treated grain. For both Sitophilus spp there was no significant difference between the numbers of females or eggs observed on treated or untreated grain, but males were repelled from permethrin.

The importance of these results is discussed in relation to a recent recommendation that the treatment of shelled grain with 3.0 ppm permethrin should be adopted in Tanzania in order to control Prostephanus truncatus (Horn), a new and serious storage pest.

Zea mays L. and Rottboellia exaltata L. were the main graminaceous plant species infested by Eldana saccharina Walker, the major pest of sugar-cane in southern Ghana. Other stem-borers of sugar-cane, Sesamia botanephaga Tams and Bowden, Sesamia penniseti Tams and Bowden, Sesamia calamistis Hampson and Chilo zacconius Bleszynski, were recorded on Zea mays, Echinocloa pyramidalis (Lamk.) et Chase, Rottboellia exaltata, Panicum maximum Jacquin and Oryza sativa L.

All the stem-borer populations except E. saccharina on Rottboellia exaltata increased on their host plants. Sesamia and Chilo species were present from January to December on Echinocloa pyramidalis. It is concluded that these alternative host plants provide a potential source of stem-borer infestation on sugar-cane at Asutsuare in southern Ghana.

Observation on natural enemies of the stem-borer complex on sugar-cane in southern Ghana indicated that Descampsina sesamiae Mensil (Diptera:Tachinidae) is the most important larval parasite of Sesamia species. The relative abundance of this tachinid parasite appeared to vary with the rainfall pattern throughout the year and with the phenology of the sugar-cane plant. The rate of parasitism was found to be higher in the outgrowers fields than in the sugar estate's fields. Differences in cultural practices used as well as the type of vegetation bordering the sugar-cane fields, were believed to be responsible for the difference in the rate of parasitism of D. sesamiae on Sesamia species.

An economic threshold on fresh cabbage affected by Plutella xylostella (L.) and Crocidolomia binotalis Z., based on visual estimates of defoliation and a determination of this damage on the marketable yield was developed. An initial survey of unprotected cabbage field for determination of general levels of number of holes caused by feeding of both the lepidopterous pests formed a prerequisite for conducting visual damage threshold experiments. Maintaining a low visual damage threshold of up to 1.0 mean hole (mean of two leaves) on the wrapper leaves, after initial protection of primordia, was found to be an effective alternative in reducing present reliance on weekly or fortnightly sprays for the control of both the pests on cabbage. The possibility of eliminating precupping sprays is supported by the study since the larval populations causing damage to either outer leaves or leaves about to cover the head did not reduce the yield to a significant extent. The use of thresholds based on larval counts of either P. xylostella or C. binotalis failed to give enough lead time during scouting and resulted in loss of marketability.

Various planting patterns of cabbage and tomato were investigated to assess whether such a cultural practice could fcring about reduction in the incidence of Plutella xylostella (L.) and Crocidolomia binotalis Z. on cabbage. No reduction in the larval incidence of both the pests was observed when different combinations of cabbage and tomato were planted at the same time. A slight reduction in the incidence of both the lepidopterans had ensued in all the planting patterns, when cabbage was planted 15 days later than tomato. Maximum reduction, however, was observed following planting pattern of one row cabbage and one row tomato (cabbage planted 30 days later than tomato). It is further opined that this type of cultural practice cannot be used as a sole control measure for both the pests, since the marketable yield of cabbage recorded in the promising intercrop combination was well below the attainable yield that could be expected when insecticide sprays are undertaken on pure cabbage. Significant reduction in net return was also obtained following this cultural practice as compared to cabbage receiving insecticidal sprays based on different management programmes.

Assessment of the damage potential of Cydia ptychora (Meyrick) was carried out in Ife Brown cowpea at different levels of larval infestation and different pod growth phases. The results showed that C. ptychora caused significant shrivelling in pods of Ife Brown cowpea when infested with either one, two or three first-instar larvae per pod at either the young or mid-fill growth phases, relative to the corresponding controls. A significant reduction in seed yield was also recorded in plants subjected to an infestation level of either one, two or three first-instar larvae per pod at both mid-fill and mature pod growth phases. Thus, an infestation level of one first-instar larva per pod at either the mid-fill or mature pod growth phases would be adequate for intensive screening of cowpea varieties for resistance to C. ptychora, using Ife Brown as a standard for comparison.