Vines avoid coiling around neighbouring plants infested by polyphagous mites.

Vines that coil around plants heavily infested with ambulate polyphagous mites can be heavily damaged by the mites. To explore whether vines avoid mite-infested plants, we observed the coiling responses of morning glory (Ipomoea nil var. Heavenly Blue) vines and bush killer (Cayratia japonica (Thunb) Gagnep) tendrils around nearby kidney bean (Phaseolus vulgaris L.) plants that were either uninfested or heavily infested with the two-spotted spider mite (Tetranychus urticae Koch). The proportions of I. nil vines that coiled around spider mite-infested and uninfested bean plants did not differ significantly; however, no C. japonica tendril coiled around spider mite-infested plants. The proportion of such tendrils was thus significantly lower than that around uninfested plants. The ability of C. japonica tendrils to avoid spider mite-infested plants would prevent serious "contact infections" by mites. We further found that tendril avoidance seemed to be attributable to the mite webs that covered infested plants; neither spider mite-induced bean volatiles nor spider mite intrusion onto tendrils seemed to explain the avoidance.

Wolbachia both aids and hampers the performance of spider mites on different host plants.

In the last few decades, many studies have revealed the potential role of arthropod bacterial endosymbionts in shaping the host range of generalist herbivores and their performance on different host plants, which, in turn, might affect endosymbiont distribution in herbivore populations. We tested this by measuring the prevalence of endosymbionts in natural populations of the generalist spider mite Tetranychus urticae on different host plants. Focusing on Wolbachia, we then analysed how symbionts affected mite life-history traits on the same host plants in the laboratory. Overall, the prevalences of Cardinium and Rickettsia were low, whereas that of Wolbachia was high, with the highest values on bean and eggplant and the lowest on morning glory, tomato and zuchini. Although most mite life-history traits were affected by the plant species only, Wolbachia infection was detrimental for the egg-hatching rate on morning glory and zucchini, and led to a more female-biased sex ratio on morning glory and eggplant. These results suggest that endosymbionts may affect the host range of polyphagous herbivores, both by aiding and hampering their performance, depending on the host plant and on the life-history trait that affects performance the most. Conversely, endosymbiont spread may be facilitated or hindered by the plants on which infected herbivores occur.

Developmental and reproductive response of Brachmia macroscopa (Lepidoptera: Gelechiidae) to three host plants.

The sweet potato leaf folder, Brachmia macroscopa Meyrick (Lepidoptera: Gelechiidae), which is a significant pest of plants in the family Convolvulaceae, is rapidly expanding its range in South China and other subtropical regions. Studies were designed to examine the effects of three different host plants (sweet potato, Ipomoea batatas (L.) Lam.; water spinach, I. aquatica Forsskål; and morning glory, Pharbitis purpurea (L.)) on the development and life table parameters of B. macroscopa under laboratory conditions. We found that the intrinsic rates of increase of B. macroscopa were 0.17 ± 0.004, 0.21 ± 0.005 and 0.16 ± 0.004 on I. batatas, I. aquatica and P. purpurea, respectively. The highest net reproduction rate was 158.06 ± 18.22 per female reared on I. aquatica. The larvae had five instars when reared on I. batatas and I. aquatica, but required six instars on P. purpurea. The mean generation lengths of B. macroscopa ranged from 24.32 ± 0.18 days when reared on I. aquatica to 29.40 ± 0.24 days on P. purpurea. The survival of all stage and fecundity curves was intuitively manipulated using the age-stage-structured and two-sex population life table method, to enable comprehensive descriptions of the stage and population trends of B. macroscopa on the three Convolvulaceae plants. Our results indicated that I. batatas and I. aquatica were more suitable host plants than P. purpurea.