The effect of oxygen limitation on a xylophagous insect's heat tolerance is influenced by life-stage through variation in aerobic scope and respiratory anatomy

Temperature has a profound impact on insect fitness and performance via metabolic, enzymatic or chemical reaction rate effects. However, oxygen availability can interact with these thermal responses in complex and often poorly understood ways, especially in hypoxia-adapted species. Here we test the hypothesis that thermal limits are reduced under low oxygen availability - such as might happen when key life-stages reside within plants - but also extend this test to attempt to explain that the magnitude of the effect of hypoxia depends on variation in key respiration-related parameters such as aerobic scope and respiratory morphology. Using two life-stages of a xylophagous cerambycid beetle, Cacosceles (Zelogenes) newmannii we assessed oxygen-limitation effects on metabolic performance and thermal limits. We complement these physiological assessments with high-resolution 3D (micro-computed tomography scan) morphometry in both life-stages. Results showed that although larvae and adults have similar critical thermal maxima (CTmax) under normoxia, hypoxia reduces metabolic rate in adults to a greater extent than it does in larvae, thus reducing aerobic scope in the former far more markedly. In separate experiments, we also show that adults defend a tracheal oxygen (critical) setpoint more consistently than do larvae, indicated by switching between discontinuous gas exchange cycles (DGC) and continuous respiratory patterns under experimentally manipulated oxygen levels. These effects can be explained by the fact that the volume of respiratory anatomy is positively correlated with body mass in adults but is apparently size-invariant in larvae. Thus, the two life-stages of C. newmannii display key differences in respiratory structure and function that can explain the magnitude of the effect of hypoxia on upper thermal limits

A new association : Trichogramma bournieri pintureau and babault (Hymenoptera : Trichogrammatidae) and Chilo sacchariphagus Bojer (Lepidoptera : Crambidae) in sugarcane in Mozambique

Chilo sacchariphagus Bojer, a sugarcane borer indigenous to South East Asia and the Indonesian Islands, was identified from Mozambican sugarcane in 1999. Prior to a biocontrol programme being implemented against it, intensive pre-release surveys for any indigenous natural enemies of the borer were completed. Negligible parasitism of larvae and pupae was recorded. In contrast, egg batches were heavily parasitised. Parasitoid adults emerging from eggs were Trichogramma bournieri Pintureau and Babault only. The impact of T. bournieri on C. sacchariphagus eggs in Mozambique are presented, and the potential of using this parasitoid against C. sacchariphagus in an augmentation biocontrol programme is discussed. (Résumé d'auteur

Biological control of Chilo sacchariphagus (Lepidoptera: Crambidae) in Moçambique : The firsts steps

In 1999, it was confirmed that Chilo sacchariphagus Bojer was attacking sugarcane at Açucareira de Moçambique, Mafambisse, and in 2001 from Companhia de Sena, Marromeu. In 2000, Açucareira de Moçambique requested that the South African Sugar Association Experiment Station investigate a classical biological control programme against this exotic borer using Xanthopimpla stemmator Thunberg. To this end, during March and June 2001, intensive pre-release surveys for this borer and possibly already established parasitoids were completed. No pupal parasitoids were recorded, and only 1.3% parasitism of the larval population was found. However, many egg batches were parasitised by Trichogramma bournieri Pintureau and Babault. Because of the absence of pupal parasitoids in these collections, it was deemed safe to release X. stemmator, as it was likely that no native species would be displaced. Releases were planned to coincide with the C. sacchariphagus pupal peak expected during July/August 2001. One thousand mated female parasitoids were released in five selected sugarcane fields, in batches of 200 at fortnightly intervals over the two-month period. When post-release surveys were completed in October 2001, population reductions of between 31% to 90% in C. sacchariphagus larval and pupal numbers were recorded in all the release fields, when compared to control fields. In the light of these findings, it seems that a classical biocontrol programme against C. sacchariphagus using X. stemmator in Moçambiquan sugarcane is beneficial. The way forward is discussed, as well as an augmentation biocontrol programme using T. bournieri. The possibility of importing and introducing larval parasitoids of C. sacchariphagus is proposed. (Résumé d'auteur

Active defence of herbivorous hosts against parasitism: Adult parasitoid mortality risk involved in attacking a concealed stemboring host

Phytophagous insects have several defence strategies to defend themselves against attack by parasitic wasps. Larval lepidopteran hosts can defend themselves actively to prevent oviposition by the parasitoid. Among the aggressive kinds of behaviour exhibited by hosts against parasitoids are violent wriggling, biting and spitting. The behaviour of the braconid parasitoid Cotesia sesamiae attacking stemboring larvae inside their feeding tunnel in the plant stem was investigated in maize and sugarcane stem pieces and transparent artificial tunnels. Attacking a defending stemborer host inside the confined space of a tunnel was shown to be risky for the female parasitoid. A considerable proportion (25%) of female wasps were killed in their attempt to attack the spitting and biting host. No difference was found in the behaviour of C. sesamiae attacking the suitable host Sesamia calamistis or the unsuitable host Eldana saccharina. The consequences of this high mortality risk involved in each host attack is discussed in relation to the ecology of the parasitoid

Biosecurity against invasive alien Insect pests: A case study of Chilo sacchariphagus (Lepidoptera: Crambidae) in the southern African region

Conference PaperThe spotted stemborer Chilo sacchariphagus poses a major constraint to sugar production in Mozambique. Current management strategies, in combination with resistant varieties and classical and augmentative biological control tactics, have the potential to combat this serious pest. However, C. sacchariphagus poses a major biosecurity risk to surrounding sugar producing countries in southern Africa. In response to this threat, a comprehensive awareness campaign has been rolled out. It comprises dissemination of illustrative posters, convening of mini-workshops for role players to review phytosanitary measures and regulations, and provision of information on monitoring for the presence of this pest in an attempt to prevent further range expansion. Despite implementing these strategies, there has been limited success in preventing the spread of C. sacchariphagus within Mozambique. This has highlighted the importance of developing a more aggressive biosecurity strategy. In response, a comprehensive incursion plan has been developed for this pest, and the need for increased engagement of relevant policy-making bodies within this region to streamline legislation and enforcement thereof has been identified. In the longer term, the initiation of research on biosecurity and development of a research presence in Mozambique, funded by SADC countries, is necessary. This would include a plant breeding programme to develop sugarcane varieties resistant to C. sacchariphagus, and research on control tactics such as the Sterile Insect Technique (SIT) and mating disruption. Integration of these with classical and augmentative biocontrol and other more conventional control options into an area-wide integrated pest management plan is proposed. This paper documents the successes to date of the C. sacchariphagus regional biosecurity programme driven by SASRI and sets out a proposed future action plan

Detection of sugarcane African stalk borer Eldana Saccharina Walker (Lepidoptera:Pyralidae) using hyperspectral remote sensing (spectroradiometry)

The South African sugar industry is one of the world's leading sugarcane producers. The stalk borer Eldana saccharina has for many years been the most destructive pest in the South African sugar industry and is the most important factor limiting sugarcane productivity. The pest has been monitored using a traditional visual approach whereby a representative sample of stalks is taken from a field and split longitudinally to assess damage and count the number of E. saccharina. This approach is time-consuming, labour intensive and sometimes biased as, in some instances, only easily accessible areas are surveyed. To investigate a more economical but equally sensitive survey methodology, this paper aims at determining the potential use of hyperspectral remote sensing (spectroradiometry) for identifying sugarcane infested by E. saccharina. A hand-held ASD (Field Spec? 3) spectroradiometer was used to take leaf spectral measurements of sugarcane plants from a potted-plant trial taking place under shade house conditions. In this trial, nitrogen and silicon fertiliser applications as well as varieties used were known. In addition, watering regimes and artificial infestation of E. saccharina were carefully controlled. Results illustrated that severe E. saccharina infestation increased reflectance throughout the whole spectrum range (400-2500 nm). E. saccharina stalk damage was also linearly related to modified normalized difference vegetation index (mNDVI) using R2025 and R2200 (R2=0.69). It was concluded that hyperspectral data has a potential for use in monitoring E. saccharina in sugarcane rapidly and non-destructively under controlled conditions. A follow-up study is recommended in field conditions and using airborne and/or spaceborne hyperspectral sensors.