Rammohan R. Balusu

Host Finding and Acceptance Preference of the Yellowmargined Leaf Beetle, Microtheca ochroloma (Coleoptera: Chrysomelidae), on Cruciferous Crops

ABSTRACT The yellowmargined leaf beetle, Microtheca ochroloma Stål (Coleoptera: Chrysomelidae), is an introduced pest of cruciferous crops in the southern United States, and arguably the most damaging pest of organic crucifer vegetable production in the region. Studies were conducted in the greenhouse and laboratory to investigate host finding and acceptance preference of M. ochroloma on four commonly grown cruciferous crops: cabbage (Brassica oleracea L. variety capitata), collards (B. oleracea L. variety acephala), napa cabbage [B. pekinensis (Lour.)], and turnip (B. rapa L.) First, adult beetles were allowed to choose among the four plants in a multiple-choice greenhouse cage experiment and host preference was evaluated by using three parameters: number of beetles on each plant, number of larvae on each plant, and plant damage ratings. The results showed that M. ochroloma adults actively discriminated among the four host plants, with significantly higher numbers recorded on turnip and napa cabbage than on cabbage or collards. Significantly higher numbers of larvae also were recorded on turnip and napa cabbage starting on day 10. Similarly, higher damage ratings were recorded on turnip and napa cabbage than on the remaining two hosts. Results of four-choice olfactometer experiments, which compared attraction of M. ochroloma to headspace volatiles of the four host plants, demonstrated that host preference is mediated primarily by plant volatiles. Both sexes were significantly more attracted to napa cabbage than to the remaining treatments, with turnip being the second most attractive plant. These results confirm that turnip and napa cabbage are two preferred host plants of M. ochroloma, and may support the development of a trap crop system and attractant-based strategies for managing M. ochroloma in crucrfer production.

Evaluation of organically acceptable insecticides as stand-alone treatments and in rotation for managing yellowmargined leaf beetle, Microtheca ochroloma (Coleoptera: Chrysomelidae), in organic crucifer production

BACKGROUND Yellowmargined leaf beetle, Microtheca ochroloma, is the most damaging pest of organic crucifer crops in the southern United States. Experiments were conducted over four growing seasons (2007-2010) in Alabama to evaluate some botanical and microbial insecticides approved by the Organic Materials Review Institute (OMRI) against M. ochroloma in organically grown crucifer crops. Insecticides evaluated included PyGanic(®) (pyrethrum), Aza-Direct(®) (azadiractin), Entrust(®) (spinosad), Mycotrol O(®) (Beauveria bassiana strain GHA) and NOFLY(®) [Isaria ( = Paecilomyces) fumosoroseus strain FE 9901]. Two experimental organic formulations, Tick-Ex (Metarhizium anisopliae strain F52) and MBI-203 (Chromobacterium subtsugae), and one non-OMRI-listed formulation, Novodor(®) (Bacillus thuringiensis subspecies tenebrionis), were also evaluated. The insecticides were applied as stand-alone treatments at recommended field rates on a weekly schedule. In 2010, some of the treatments were also evaluated in rotation/alternation with Entrust(®) . Insecticide efficacy was determined by comparing densities of M. ochroloma larvae and adults and crop damage ratings in treated versus untreated turnip plots. RESULTS Entrust(®) consistently performed well in suppressing M. ochroloma adults, larvae and crop damage. PyGanic(®) was the second best treatment. PyGanic(®) or NOFLY(™) can be applied in rotation with Entrust(®) for effective management of M. ochroloma. CONCLUSION Entrust(®) applied weekly or in alternation with PyGanic(®) or NOFLY(™) provided acceptable control of M. ochroloma in organic crucifer production.

Susceptibility of Microtheca ochroloma (Coleoptera: Chrysomelidae) to Botanical and Microbial Insecticide Formulations

ABSTRACT The yellowmargined leaf beetle, Microtheca ochroloma Stål (Coleoptera: Chrysomelidae), is a key pest of organic crucifer production in the southern United States. The susceptibility of larvae and adults of M. ochroloma to some botanical and microbial insecticide formulations was evaluated using laboratory leaf-dip bioassays. Insecticides evaluated included OMRI (Organic Material Review Institute) approved formulations of PyGanic® (pyrethrum), Entrust® (spinosad), Mycotrol O® (Beauveria bassiana strain GHA), and NOFLY® (Isaria fumosoroseus strain FE 9901). Others were MBI-203 (experimental organic formulation of Chromobacterium subtsugae) and BotaniGard® 22WP (conventional formulation of Beauveria bassiana strain GHA). The insecticides were first evaluated at the field recommended rate against M. ochroloma larvae and adults, followed by multiple-concentration assays to determine the LC50 and LT50 for promising formulations. At the field recommended rates, all tested formulations were toxic to the larvae compared to the untreated control, whereas only Entrust® and PyGanic® were effective against the adults. Entrust® and PyGanic® caused 100% mortality to the larvae and adults after just 24 h of exposure. The LC50 values of Entrust® and PyGanic® were 200 × and 15 × less than the field recommended rates, respectively. MBI-203 was effective against the larvae (100% mortality after 5 days) but not against the adults. The entomopathogenic fungal formulations, Mycotrol®, NOFLY®, and BotaniGard®, were much less toxic with LT50 values of 10, 12, and 9 days, respectively. Although all 3 fungal formulations caused significantly higher larval mortality than the untreated control after 5 days of exposure, none resulted in more than 50% larval or 14% adult mortalities over the 9-day exposure period.

Spodoptera exigua modulates gossypol biosynthesis in cotton Gossypium hirsutum

ABSTRACT Cotton plants induce high levels of gossypol in response to herbivore damage. However, little is known about the mechanisms by which insect herbivory modulates gossypol biosynthesis in cotton plants. Here, we report the mechanism by which herbivore damage or insect-originated elicitors modulate the biosynthesis of gossypol and jasmonic acid (JA) in plants. Spodoptera exigua larval-damaged (HD) cotton plants and mechanically damaged plants treated with S. exigua oral secretion (MDOS) showed higher levels of gossypol and JA as well as increased transcript levels of genes involved in the biosynthesis of both secondary plant metabolites, compared to undamaged (UD) or mechanically damaged (MD) plants. In correlation with the observed induction of gossypol and JA, S. exigua larvae that fed on HD and MDOS cotton plants showed significantly reduced weight. The findings provide a better insight into the molecular mechanisms mediating herbivore-induced plant defense.

Attraction of Paratelenomus saccharalis (Hymenoptera: Platygastridae), an Egg Parasitoid of Megacopta cribraria (Hemiptera: Plataspidae), to Host-Associated Olfactory Cues

Abstract Paratelenomus saccharalis (Dodd) (Hymenoptera: Platygastridae) is an egg parasitoid of Megacopta cribraria (F.) (Hemiptera: Plataspidae). Although the parasitoid has been previously reported in parts of Africa, Europe, Asia, and Australia, it was first reported in North America in 2013 on M. cribraria that was introduced from Asia into North America in 2009. Field observations showed that P. saccharalis females readily parasitize eggs of M. cribraria. However, the cues used by the parasitoid for host location have not been investigated. It was hypothesized that P. saccharalis uses olfactory cues to locate M. cribraria. The objective of this study was to test the attraction of P. saccharalis to host-associated cues in Y-tube olfactometer bioassays. Compared to the control of no host plant or eggs, female P. saccharalis showed significantly greater attraction to M. cribraria-damaged soybean, M. cribraria eggs only, and damaged soybean plus M. cribraria eggs, in separate bioassays. However, the parasitoid did not show significant attraction to undamaged soybean. The results suggest that host location by P. saccharalis is mediated by olfactory cues from the soybean host and M. cribraria eggs. This is the first behavioral study to demonstrate the response of P. saccharalis to induced soybean volatiles.

Management of Yellowmargined Leaf Beetle Microtheca ochroloma (Coleoptera: Chrysomelidae) Using Turnip as a Trap Crop.

ABSTRACT The yellowmargined leaf beetle, Microtheca ochroloma Stål, is a major pest of cruciferous vegetable crops in organic production systems. Very few organically acceptable management options are currently available for this pest. Field studies were conducted at a research station in Alabama and at a commercial organic vegetable farm in Florida to investigate the effectiveness of turnip, Brassica rapa rapa, as a trap crop for M. ochroloma. In the research station trial with cabbage planted as the cash crop, perimeter planting of turnip as a trap crop effectively reduced beetle numbers and crop damage below levels recorded in the control. During the first season of our on-farm trial, with napa cabbage and mustard as the cash crops, using turnip as a trap crop effectively reduced both beetle numbers and cash crop damage below levels found in the control plots, but economic damage was still high. In the second season, beetle populations were too low for significant differences in damage levels to occur between the trap crop and control plots. Together, these results suggest that turnip planted as a trap crop can be an effective control tactic for cruciferous crops, like cabbage, that are much less attractive to M. ochroloma than turnip. In crops, like mustard and napa cabbage, that are equally or only slightly less attractive than turnip, planting turnip as a trap crop would have to be used in combination with other tactics to manage M. ochroloma.

Topical and Vapor Toxicity of Saturated Fatty Acids to the German Cockroach (Dictyoptera: Blattellidae)

ABSTRACT Topical and fumigant toxicity of saturated aliphatic fatty acids with chain lengths of C1 through C14 were determined against the German cockroach, Blattella germanica (L.). In the C1 to C11 series, topical toxicity (LD50 in milligram per adult male) ranged from 0.145 (C1) to 0.322 mg (C2). Toxicity declined dramatically with C12 and C14 acids whose LD50 values could not be calculated. The relative fumigation toxicity (LC50 in microliter per liter) of C1 through C5 acids was positively correlated with topical toxicity with values ranging from 6.159 (C3) to 12.302 µl/liter (C2). Fumigant toxicity decreased sharply with C6 (LC50 = 37.691 µl/ liter) and there was no mortality of cockroaches exposed to vapors from C7 to C14 acids. The low fumigant toxicity of the C6 to C11 acids was correlated with their relatively low vapor pressure, but differences in diffusion of the vapors into the spiracles and subsequent passage to the target sites may have also been involved.

The First Record of Ooencyrtus nezarae (Hymenoptera: Encyrtidae) on Kudzu Bug (Hemiptera: Plataspidae) in North America

Abstract The kudzu bug, Megacopta cribraria (F.) (Heteroptera: Plataspidae), is an invasive insect pest introduced from Asia in 2009 that poses a threat to soybeans (Glycine max [L.] Merr. [Fabales: Fabaceae]) and other legume crops in the United States. Initially discovered in Georgia, M. cribraria rapidly expanded across the southeast until 2014 when a significant decline in its population was observed across many locations. This notable decline in M. cribraria populations is attributed to the emergence of new parasitoids and pathogens in its new invasive range. So far, only a single egg parasitoid, Paratelenomus saccharalis (Dodd) (Hymenoptera: Platygastridae), is known to parasitize the eggs of M. cribraria in the United States. Here, we report a new egg parasitoid of M. cribraria identified as Ooencyrtus nezarae Ishii, 1928 (Hymenoptera: Encyrtidae), recovered from egg masses of M. cribraria collected from soybean in Alabama. O. nezarae is reported to parasitize eggs from a variety of heteropteran families and has been observed parasitizing M. cribraria in China. To the best of our knowledge, this is the first report of O. nezarae in North America. The potentials of O. nezarae for biological control of M. cribraria in the United States and the direction of future studies are discussed.

Cuticular hydrocarbon chemistry, an important factor shaping the current distribution pattern of the imported fire ants in the USA

Two sibling species, Solenopsis richteri and S. invicta, were both introduced into the southern USA from South America in the early 20th century. Today, S. richteri occupies higher latitudes and colder areas, while S. invicta occupies lower latitudes. Between the distributions of the two species, there is a large area of viable hybrid (S. richteri × S. invicta) populations. This study aimed to characterize the forces driving this distribution pattern and the underlying mechanisms. Cuticular hydrocarbons (CHCs) of freshly killed workers of S. invicta, hybrids, and S. richteri were removed using hexane. Both intact and CHCs-extracted workers were subjected to a constant rate of increasing temperature from 10 to 60 °C to obtain relative water loss and the water loss transition temperature (Tc-ant). Mass loss and Tc-ant were both significantly increased with CHCs removal. We then examined the CHC composition of three species. CHC profiles of S. richteri are characterized by significant amounts of short-chain (C23-C27) saturated and unsaturated hydrocarbons. In contrast, profiles of S. invicta consist primarily of long-chain (C27-C29) saturated hydrocarbons; unsaturated alkenes are completely lacking. Hybrid fire ants show intermediate profiles of the two parent species. We measured the melting point (Tm) and water-loss transition temperature of CHC blends (Tc-CHC) of different ant species colonies using differential scanning calorimetry (DSC) and an artificial membrane system, respectively. There were 3-5 Tms of each CHCs sample of different ant colonies due to their complex chemistry. The highest Tms (Tm-maxs) of CHCs samples from S. invicta and the hybrid were significantly higher than that from S. richteri. The correlation between Tc-CHC and Tm-max obtained from the same CHCs sample was highly significant. These results reveal that species having higher Tc and Tm-max retain more water under relatively higher temperature, and consequently are able to occupy warmer environments. We conclude that CHC chemistry plays a role in shaping current distribution patterns of S. richteri, S. invicta and their hybrid in the United States.

First Record of Blattella vaga (Blattodea: Ectobiidae) from Southern Alabama

Abstract The field cockroach, Blattella vaga Hebard (Blattodea: Ectobiidae), is native to central Asia including Afghanistan, India, Iran, Pakistan, and Sri Lanka. It was described first in 1935; however, from specimens collected in Arizona and California. Since then, the distribution of B. vaga has slowly increased along the southern United States and Mexican border, apparently following major interstate highways. We report the first record of B. vaga from Mobile, Alabama, and suggest that this species will spread to Florida and possibly northward into Georgia and South Carolina. The identification was confirmed using morphological, chemical, and molecular methods. We suggest that when possible, multiple independent methods should be used to confirm species identifications.