Plant structural changes due to herbivory: Do changes in Aceria-infested coconut fruits allow predatory mites to move under the perianth?

Being minute in size, eriophyoid mites can reach places that are small enough to be inaccessible to their predators. The coconut mite, Aceria guerreronis, is a typical example; it finds partial refuge under the perianth of the coconut fruit. However, some predators can move under the perianth of the coconut fruits and attack the coconut mite. In Sri Lanka, the phytoseiid mite Neoseiulus baraki, is the most common predatory mite found in association with the coconut mite. The cross-diameter of this predatory mite is c. 3 times larger than that of the coconut mite. Nevertheless, taking this predator’s flat body and elongated idiosoma into account, it is—relative to many other phytoseiid mites—better able to reach the narrow space under the perianth of infested coconut fruits. On uninfested coconut fruits, however, they are hardly ever observed under the perianth. Prompted by earlier work on the accessibility of tulip bulbs to another eriophyoid mite and its predators, we hypothesized that the structure of the coconut fruit perianth is changed in response to damage by eriophyoid mites and as a result predatory mites are better able to enter under the perianth of infested coconut fruits. This was tested in an experiment where we measured the gap between the rim of the perianth and the coconut fruit surface in three cultivars (‘Sri Lanka Tall’, ‘Sri Lanka Dwarf Green’ and ‘Sri Lanka Dwarf Green × Sri Lanka Tall’ hybrid) that are cultivated extensively in Sri Lanka. It was found that the perianth-fruit gap in uninfested coconut fruits was significantly different between cultivars: the cultivar ‘Sri Lanka Dwarf Green’ with its smaller and more elongated coconut fruits had a larger perianth-fruit gap. In the uninfested coconut fruits this gap was large enough for the coconut mite to creep under the perianth, yet too small for its predator N. baraki. However, when the coconut fruits were infested by coconut mites, the perianth-rim-fruit gap was not different among cultivars and had increased to such an extent that the space under the perianth became accessible to the predatory mites

Species status of two host-associated populations of Aphytis lingnanensis (Hymenoptera: Aphelinidae) in citrus

Although Aphytis lingnanensis Compare is an important parasitoid of California red scale Aonidiella aurantii Maskell, several 'races' of A. lingnanensis exist which parasitize white louse scale Unaspis citri Comstock. The reproductive status of a white louse scale 'race' of A. lingnanensis that originated in Thailand was examined in relation to several populations (from Queensland, California and the Philippines) that parasitize California red scale. None of the wasps from red scale mated with individuals from white louse scale in small cages within 10 min, whereas control crosses all mated in that time. The two 'races' would therefore constitute independent reproductive entities (species) in sympatry in the field, although no consistent anatomical differences could be found between them, even with the aid of discriminant function analysis on the number of setae on the delta region of the forewing and the mesoscutum. Aphytis linguanensis from California red scale in Queensland mated readily with wasps derived from the same host species in California and the Philippines, and mating took place at random among individuals in mate choice tests. Although such results are equivocal, there are no reasons for suspecting that these different populations of A. lingnanensis from California red scale also comprise more than one species. The results obtained indicate that cross-mating tests designed to quantify reproductive isolation between sexual populations are inappropriate. They should rather be designed to establish whether individuals recognize one another as potential mates. The design of cross-mating tests should therefore consider the usual time to mating, of known conspecifics, under the experimental conditions to be used

Mate recognition in the South African citrus thrips Scirtothrips aurantii (Faure) and cross-mating tests with populations from Australia and South Africa

South African citrus thrips (Scirtothrips aurantii) is a pest of citrus, mango and other horticultural species in its native range, which encompasses a large part of Africa. Its adventitious establishment in Australia in 2002 was a major cause for concern. The thrips, 11 years after its incursion into Australia, has remained on plants of a single host plant genus Bryophyllum (Crassulaceae). Characterization of the Specific-Mate Recognition System of the Bryophyllum population of thrips present in Australia and behavioral bioassay experiments revealed that compounds found in the insects' body extracts play a crucial role in mate recognition of S. aurantii. Reciprocal cross-mating experiments between the Australian Bryophyllum insects and South African S. aurantii from horticultural host plants showed that mating frequencies were significantly lower in test crosses (Bryophyllum x horticultural) than in controls (Bryophyllum x Bryophyllum or horticultural x horticultural), which indicates there are at least two distinct species within S. aurantii and suggests further tests of this interpretation. The results suggest that these tiny phytophagous insects localize mates through their association with a particular host plant species (or closely-related group of species). Also, specific tests are suggested for clarifying the species status of the host-associated populations of S. aurantii in Africa