In the Rosenheim lab my team is involved in investigating direct pests on citrus fruits from katydids, thrips, and earwigs. To do this, we gather and explore a large dataset of pest densities, damage assessments, yield, pesticide information, and several more variables collected by citrus crop consultants and field managers in the San Joaquin Valley. Once a strong correlation is identified we use manipulative field experiments to further understand factors affecting citrus yield and damage.
Past work in the lab has demonstrated that, while guidelines for citrus pests have primarily been developed from research on oranges (Citrus sinensis), citrus pest damage actually varies across citrus species and variety. For instance, forktailed bush katydid (Scudderia furcata) chew on developing orange fruits causing circular bruises that decrease fruit marketability, but after one taste of mandarins, such as Citrus reticulata, the katydids seem to reject the fruit. This implies that the pest management guidelines for mandarins should be adjusted to reflect this natural resistance to certain herbivores. Questions on the extent, seasonality, and variability of damage caused by citrus pests will expand to also encompass citrus thrips and earwigs in this upcoming spring field season. Earwigs are especially enigmatic in citrus since crop consultants have complained about them feeding on young citrus fruits but this has not been well documented and earwigs are also considered natural enemies, since they feed on pests such as aphids psyllids, and scales. Thus we will attempt to clear up the question of the role of earwigs in San Joaquin Valley citrus.
Hooks lab projects:
When grown as a living mulch, red clover can provide a wide range of benefits such as nitrogen fixation (allowing it to be a “green fertilizer”), weed control, breaking up soil compaction, adding organic matter, and erosion control. Moreover, red clover is attractive to a wide range of beneficial insects. It provides pollen, nectar, suitable microhabitat, and alternative prey for natural enemies. The Hooks lab has observed bumble bees, spiders, and soldier beetles regularly visiting red clover. Thus, red clover as a living mulch can serve as an insectary for benefical insects, increasing their number and contributions (via pest suppression and pollination). This can in turn lead to increase yield and profits for growers.
The striped cucumber beetle (Acalymma vittatum) and spotted cucumber beetle (Diabrotica undecimpunctata) are arguably the most destructive pests of cucurbit crops. They feed on the roots of the cucurbit plants as larvae and then emerge to feed on the leaves, stems, and flowers as adults. Through their feeding, they can transmit bacterial wilt (Erwinia tracheiphila), a bacterial disease that can spread fast and kill plants. Organic growers especially have limited options for controlling cucumber beetles. One option is to use conservation biological control (creating environments favorable for native natural enemies that consume pests). Spiders are important natural enemies of cucumber beetles. Previous research in the Hooks lab has shown that spiders benefit from ground cover provided by living mulch. Thus, red clover as a living mulch can be used to increase spiders, which can then suppress cucumber beetles. I am investigating this using cucumbers, a cucurbit crop that is widely grown in the Mid-Atlantic.
Red clover attracts a wide range of bees and butterflies. It is an especially important resource for bumble bees, highly effective pollinators. Red clover is frequently listed as a plant that is attractive to pollinators and can be easily integrated into the farming system. Yet, there has not been much research within the United States on what pollinators utilize red clover and whether visits vary across the season. Also, whether pollinators that visit red clover also visit crop flowers has also not been thoroughly examined. Therefore, I am aim to address these knowledge gaps by monitoring pollinators visiting red clover flowers and neighboring cucumber flowers using bee bowls and visual observation.
Greenhouse gas emissions
In collaboration with Gui Chen, a previous post-doctoral scholar in the Hooks lab, I worked on a project assessing whether the ground cover and reduced soil disturbance of red clover as a living mulch decreases soil emissions of carbon dioxide and nitrous oxide.
Before beginning research on managing cucumber beetles on cucumbers using living mulch, I tackled another pest complex. In the summer of 2015, the brown marmorated stink bug (Halyomorpha halys) was a dominant pest of several vegetable systems in the Mid-Atlantic, causing millions of dollars worth of damage. The brown marmorated stink bug commonly attacks bell pepper, causing “cat-facing” damage. I hypothesized that having a “green barrier” of living mulch would make movement onto the bell pepper plants more difficult for stink bugs, reducing stink bug damage to bell pepper fruits. I found that while stink bug damage was not effectively reduced by red clover, damage from another bell pepper pest was. The European Corn Borer (Ostrinia nubilis) causes less frequent but more severe damage to bell pepper fruits than stink bugs. The larvae of the European Corn Borer aptly bore into the fruits and consume the insides leaving tunnels of frass. There was less European Corn Borer damage in the bell pepper fruits that were surrounded by red clover living mulch than the fruits from bell pepper monoculture plots. This could have been due to the red clover confusing visual oviposition cues that adult European Corn Borers depend on to find a suitable plant to oviposit on.