Influence of Olfaction in Host-Selection Behavior of the Cassava Whitefly Bemisia tabaci

Cassava is a vital food-security crop in Sub-Saharan Africa. Cassava crops are, however, severely affected by viral diseases transmitted by members of the whitefly species complex Bemisia tabaci. We have here investigated the role of olfaction in host selection behavior of the cassava whitefly B. tabaci SSA-ESA biotype. Surprisingly, we find that the whiteflies appear to make little use of olfaction to find their favored host. The cassava whitely shows a highly reduced olfactory system, both at the morphological and molecular level. Whitefly antennae possess only 15 sensilla with possible olfactory function, and from the genome we identified just a handful of candidate chemoreceptors, including nine tuning odorant receptors, which would afford the whitefly with one of the smallest olfactomes identified from any insect to date. Behavioral experiments with host and non-host plants, as well as with identified specific volatiles from these sources, suggest that the few input channels present are primarily tuned toward the identification of unwanted features, rather than favored ones, a strategy quite unlike most other insects. The demonstrated repellence effect of specific volatile chemicals produced by certain plants unflavored by whiteflies suggests that intercropping with these plants could be a viable strategy to reduce whitefly infestations in cassava fields.

Plant Volatiles and Oviposition Behavior in the Selection of Barley Cultivars by Wheat Stem Sawfly (Hymenoptera: Cephidae)

Wheat stem sawfly, [Cephus cinctus (Hymenoptera: Cephidae)], females display complex behaviors for host selection and oviposition. Susceptible hollow stem wheat (Triticum aestivum L.) cultivars release a greater amount of attractive compound, (Z)-3-hexenyl acetate and receive a greater number of eggs compared to resistant solid stem wheat cultivars. However, barley (Hordeum vulgare L.) is becoming a more common host for C. cinctus in Montana. Therefore, how do host selection and oviposition behaviors on barley cultivars compare to what happens when encountering wheat cultivars? To answer this question, we carried out greenhouse experiments using two barley cultivars: ‘Hockett’ and ‘Craft’. Between these cultivars at Zadoks stages 34 and 49, we compared host selection decisions using a Y-tube olfactometer, compared oviposition behaviors on stems, and counted the number of eggs inside individual stems. In Y-tube bioassays, we found a greater number of C. cinctus females were attracted to the airstream passing over ‘Hockett’ than ‘Craft’ barley cultivars. Although the frequencies of oviposition behaviors were similar between these cultivars, the number of eggs was greater in ‘Hockett’. Volatile profiles indicated that the amount of linalool was greater in the airstream from ‘Craft’ than in ‘Hockett’ at Zadoks 34 while the amount of (Z)-3-hexenyl acetate was greater in airstream from ‘Hockett’ at both Zadoks 34 and 49. These results suggest that volatiles of barley plants influenced host selection behavior of ovipositing C. cinctus females, while other discriminating behaviors do not differ between cultivars.

Maize Bushy Stunt Phytoplasma Favors Its Spread by Changing Host Preference of the Insect Vector

Plant pathogenic bacteria may influence vector behavior by inducing physiological changes in host plants, with implications for their spread. Here, we studied the effects of maize bushy stunt phytoplasma (MBSP) on the host selection behavior of the leafhopper vector, Dalbulus maidis (DeLong and Wolcott). Choice assays contrasting leaves of healthy (mock-inoculated) vs. infected maize (Zea mays L.) were conducted during the asymptomatic and symptomatic phases of plant infection, with leafhopper males or females previously exposed to infected plants (bacteriliferous insects) or not. In each assay, 40 adults were released in choice arenas where only the leaves of two plants from each treatment were offered and visible, and the insects landed on the leaves were counted 1, 2, 3, 5, 7, 9, 11 and 23 h after release. During the asymptomatic phase of plant infection, an effect was observed only on bacteriliferous females, who preferred leaves of healthy plants 5 h after release or later. The symptomatic phase triggered a pull–push effect on non-bacteriliferous females, who were first attracted to symptomatic leaves but hours later moved to healthy leaves. Non-bacteriliferous males initially preferred symptomatic leaves (up to 5 h after release) and later became equally distributed between treatments. Bacteriliferous males and females initially did not discriminate between healthy and symptomatic leaves, but only the females tended to move to healthy leaves 9 h after release. Oviposition was drastically reduced on symptomatic leaves. The changes in vector behavior induced by MBSP favor its primary spread, since bacteriliferous females prefer healthy leaves at early (asymptomatic) stages of the crop. At later stages, secondary spread may be favored because non-bacteriliferous females are initially attracted to infected (symptomatic) leaves, allowing pathogen acquisition and subsequent transmission as they move to healthy plants.

Habitat Management for Pest Management: Limitations and Prospects

Habitat management is an important strategy for pest control in integrated pest management (IPM). Various categories of habitat management such as trap cropping, intercropping, natural enemy refuges such as ‘beetle banks’, and floral resources for parasitoids and predators, have been used in applied insect ecology for many years. In a broader sense, two mechanisms, the ‘enemies hypothesis’ and the ‘resource concentration hypothesis’ have been identified as acting independently or combined in pest population dynamics. The ‘enemies hypothesis’ directly supports the conservation and enhancement of natural enemies, floral resources such as shelter, nectar, alternative food sources, and pollen (SNAP) to improve conservation biological control. The ‘resource concentration hypothesis’ emphasizes how the host selection behavior of herbivores in a diverse habitat can reduce pest colonization in crops. This review emphasizes the potential of these approaches, as well as possible dis-services, and includes limitations and considerations needed to boost the efficacy of these strategies worldwide.