Insect Management for Sweet Potatoes

Sweet potatoes, both orange- and white-fleshed varieties, are widely grown in Florida. Foliar pests, leafminers, whiteflies and armyworms, are generally not difficult to manage; in fact insecticides should be avoided to conserve their natural enemies. More serious are those pests whose immature stages feed on roots: sweetpotato weevil, wireworms, banded cucumber beetles, pale-striped and sweetpotato flea beetles, and in south Florida, Diaprepes weevils and white grubs.

Defense Suppression through Interplant Communication Depends on the Attacking Herbivore Species

In response to herbivory, plants emit volatile compounds that play important roles in plant defense. Herbivore-induced plant volatiles (HIPVs) can deter herbivores, recruit natural enemies, and warn other plants of possible herbivore attack. Following HIPV detection, neighboring plants often respond by enhancing their anti-herbivore defenses, but a recent study found that herbivores can manipulate HIPV-interplant communication for their own benefit and suppress defenses in neighboring plants. Herbivores induce species-specific blends of HIPVs and how these different blends affect the specificity of plant defense responses remains unclear. Here we assessed how HIPVs from zucchini plants (Cucurbita pepo) challenged with different herbivore species affect resistance in neighboring plants. Volatile “emitter” plants were damaged by one of three herbivore species: saltmarsh caterpillars (Estigmene acrea), squash bugs (Anasa tristis), or striped cucumber beetles (Acalymma vittatum), or were left as undamaged controls. Neighboring “receiver” plants were exposed to HIPVs or control volatiles and then challenged by the associated herbivore species. As measures of plant resistance, we quantified herbivore feeding damage and defense-related phytohormones in receivers. We found that the three herbivore species induced different HIPV blends from squash plants. HIPVs induced by saltmarsh caterpillars suppressed defenses in receivers, leading to greater herbivory and lower defense induction compared to controls. In contrast, HIPVs induced by cucumber beetles and squash bugs did not affect plant resistance to subsequent herbivory in receivers. Our study shows that herbivore species identity affects volatile-mediated interplant communication in zucchini, revealing a new example of herbivore defense suppression through volatile cues.

Characterization of Erwinia tracheiphila bacteriophage FBB1 isolated from spotted cucumber beetles that vector E. tracheiphila

Erwinia tracheiphila, the causal pathogen of bacterial wilt of cucurbit crops, is disseminated by cucumber beetles. A bacteriophage, designated FBB1, was isolated from spotted cucumber beetles (Diabrotica undecimpunctata) that were collected from a field where E. tracheiphila is endemic. FBB1 was classified into the Myoviridae family based on its morphology, which includes an elongated icosahedral head (106 × 82 nm) and a putatively contractile tail (120 nm). FBB1 infected all 62 E. tracheiphila strains examined and also three Pantoea spp. strains. FBB1 virions were stable at 55°C for 1 h and tolerated a pH range from 3 to 12. FBB1 has a genome of 175,994 bp with 316 predicted coding sequences and a GC content of 36.5%. The genome contains genes for a major bacterial outer-membrane protein, a putative exopolysaccharide depolymerase, and 22 predicted tRNAs. The morphology and genome indicate that FBB1 is a T4-like virus and thus in the Tevenvirinae subfamily. FBB1 is the first virulent phage of E. tracheiphila to be reported, and to date, is one of only two bacteriophages to be isolated from insect vectors of phytopathogens. Collectively, the results support FBB1 as a promising candidate for biocontrol of E. tracheiphila based on its virulent (lytic) rather than lysogenic lifestyle, its infection of all E. tracheiphila strains examined to date, and its infection of a few non-pathogenic bacteria that could be used to support phage populations when pathogen numbers are low.

Insect Management for Leafy Vegetables (Lettuce, Endive and Escarole)

Damage to leafy vegetables results from holes chewed in leaves by caterpillars and beetles, leaf mining by fly larvae and disease transmission and head contamination by piercing sucking insects. Major pests of these crops are beet and southern armyworms, cutworms, cabbage loopers, dipterous leafminers, aphids, cucumber beetles and wireworms. Less common pests of leafy vegetables include seedcorn maggot, seedcorn beetle and corn earworm. This document is ENY-475 (which replaces ENY-430, ENY-432, and ENY-440), one of a series of the Department of Entomology and Nematology, UF/IFAS Extension. Original publication date July 2002. Revised September 2005. ENY-475/IG161: Insect Management for Leafy Vegetables (ufl.edu)

Insect Exclusion Screens Reduce Cucumber Beetle Infestations in High Tunnels, Increasing Cucurbit Yield

As high tunnel vegetable production acreage increases in the United States, so does the need for management strategies tailored to their unique growing environment. Cucumbers are an ideal crop in these systems; they can be vertically trellised to maximize the production area and provide high yields to balance the increased costs associated with high tunnel construction. One of the most limiting factors in cucurbit production in general is the cucumber beetle complex and the bacterial pathogen they transmit. In this study, we investigated the optimal size of netting installed on high tunnels to prevent cucumber beetle colonization while maintaining ventilation to reduce heat stress. Of the three mesh sizes investigated across 4 yr, the intermediate mesh with a pore size of 0.72 × 0.97 mm was optimal to exclude cucumber beetles, maintain ventilation, and produce the highest yields for both cucumber and melon plants. The smallest (0.16 mm2) and intermediate mesh sizes resulted in secondary pest outbreaks (e.g., aphids), which did not occur in open tunnels and to a lesser extent in tunnels covered with the largest (1.00 × 4.00 mm) mesh. Despite these secondary pests, yield was higher in small- and intermediate-sized mesh treatments due to relief from cucumber beetle infestations, including striped (Acalymma vittatum Fabr. (Coleoptera: Chrysomelidae)) and spotted (Diabrotica undecimpunctata howardi Barber (Coleoptera: Chrysomelidae)) beetles. Overall, we conclude that insect exclusion netting is an effective method to exclude cucumber beetles from high tunnels, but mesh size should be carefully considered when weighing the collective effects on yield and primary/secondary pest abundance.