Host plant phenology (as influenced by seasonality) and light-mediated changes in the phenotypic and phytochemical properties of leaves have been hypothesised to equivocally influence insect herbivore performance. Here, we examined the effects of seasonality, through host plant phenology (late growth-season = autumn vs flowering-season = winter) and light environment (shade vs full-sun habitat) on the leaf characteristics of the invasive alien plant, Chromolaena odorata. In addition, the performance of a specialist folivore, Pareuchaetes insulata, feeding on leaves obtained from both shaded and full-sun habitats during autumn and winter, was evaluated over two generations. Foliar nitrogen and magnesium contents were generally higher in shaded plants with much higher levels during winter. Leaf water content was higher in shaded and in autumn plants. Total non-structural carbohydrate (TNC) and phosphorus contents did not differ as a function of season, but were higher in shaded foliage compared to full-sun leaves. Leaf toughness was noticeably higher on plants growing in full-sun during winter. With the exception of shaded leaves in autumn that supported the best performance [fastest development, heaviest pupal mass, and highest growth rate and Host Suitability Index (HSI) score], full-sun foliage in autumn surprisingly also supported an improved performance of the moth compared to shaded or full-sun leaves in winter. Our findings suggest that shaded and autumn foliage are nutritionally more suitable for the growth and reproduction of P. insulata. However, the heavier pupal mass, increased number of eggs and higher HSI score in individuals that fed on full-sun foliage in autumn compared to their counterparts that fed on shaded or full-sun foliage in winter suggest that full-sun foliage during autumn is also a suitable food source for larvae of the moth. In sum, our study demonstrates that seasonal and light-modulated changes in leaf characteristics can affect insect folivore performance in ways that are not linear.
In the family Miridae (Hemiptera), females and males attract each other by means of sex pheromones. Among insects, these pheromones are characterized by a variety of chemical structures, including saturated and unsaturated, long- and short-chain esters, as well as unsaturated ketoaldehydes. The aim of this study was to assess the chemical emissions in Eccritotarsus catarinensis (Carvalho) and Eccritotarsus eichhorniae Henry to determine their similarity and their possible role in reproductive isolation mechanisms that led to speciation. Chemicals emitted by adults inserted in air-entrainment chambers were collected in absorbent tubes and were analyzed using gas chromatography–mass spectrometry (GC-MS). Results from the GC-MS library indicate that E. catarinensis females and E. eichhorniae males have chemical emissions that their conspecific and the same sex of the other species lack. Also, E. catarinensis males lack benzenebutanoic that the other sexes have, while E. eichhorniae males have 1,2,3,4-tetrahydro-6-(phenyl methyl) that other sexes lack. Further analysis using statistical approaches (e.g., cluster analysis, multidimensional scaling plot, and principal component ordination) indicated that cross-breeding pairs have similar chemical emissions in that E. eichhorniae females had similar chemical emissions to those of E. catarinensis males, while E. catarinensis females had similar chemical emissions to those of E. eichhorniae males. These unique differences in chemical emissions could be caused by the recently identified differences in the metathoracic scent glands and the antennae of the two Eccritotarsus species, and they may serve as a basis in explaining the interbreeding and mating incompatibilities reported in these two Eccritotarsus species.
The sap-sucking mirid, Falconia intermedia (Distant) (Hemiptera: Miridae), released as a biological control agent of Lantana camara L. (Verbenaceae) in South Africa in 1999, has established at only one site. We investigated the role of induced plant defences as a possible explanation for this lack of establishment. F. intermedia inoculated plants from the five test varieties significantly increased the toughness of their new leaves compared to control plants. Additionally, plants from three L. camara varieties significantly increased leaf trichome density on new leaves after prolonged feeding by F. intermedia, significantly reducing F. intermedia oviposition, survival and feeding damage. The defensive responses were systemic and rapidly induced about eight weeks after insect feeding. We suggest that these leaf quality responses played a role in the non-establishment of F. intermedia in South Africa.
In South Africa, Thaumatotibia leucotreta is a key pest of citrus impacting its production and trade. Detection of newly infested fruit by visual inspection is challenging and poses a risk of packing infested with healthy fruit for export. Agathis bishopi is a larval endoparasitoid of T. leucotreta, attacking early larval instars. Understanding how A. bishopi parasitoids locate fruit infested with their host is of interest for developing an efficient detector for T. leucotreta infested fruit. The response of female adult A. bishopi parasitoids to olfactory and visual cues associated with T. leucotreta infested fruit were evaluated using a Y-tube olfactometer and flight tunnel. Agathis bishopi parasitoids were strongly attracted to infested fruit over healthy fruit, either when only olfactory or combinations of visual and olfactory cues were offered. Among the four synthetic compounds tested, D-limonene and ocimene elicited a strong attraction to parasitoids with response rates of 92 % and 72 % respectively. A blend of four synthetic compounds simulating T. leucotreta infested fruit odour equally elicited strong attraction to parasitoids (84 % response rate). Attraction of parasitoids to infested fruit cues was heightened by prior experience, suggesting the occurrence of associative learning. Results from this study indicate that A. bishopi parasitoids mainly rely on olfactory cues in host habitat location and that D-limonene and ocimene are the major attractants in infested fruit volatiles. These findings and the potential for manipulating A. bishopi for detection of infested fruit in the packhouse are discussed.
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