Effects of Food Source Availability, Host Egg:Parasitoid Ratios, and Host Exposure Times on the Developmental Biology of Megacopta cribraria Egg Parasitoids.

Parasitoids forage for hosts in dynamic ecosystems and generally have a short period of time to access hosts. The current study examined the optimal reproductive attributes of two egg parasitoids, Paratelenomus saccharalis Dodd (Hymenoptera: Platygastridae) and Ooencyrtus nezarae Ishii (Hymenoptera: Encyrtidae), of the kudzu bug, Megacopta cribraria Fabricius (Hemiptera: Plataspidae). The proportion of O. nezarae and P. saccharalis adult offspring that emerged from M. cribraria eggs and the sex ratio of the parasitoid offspring were compared among treatments for the effects of different adult parasitoid food sources, host egg-to-adult parasitoid ratios, and host exposure times. Our results suggest that honey solution as a food source, a 21:7 host-to-parasitoid ratio, and three-to-five days of exposure time optimized the production of female O. nezarae offspring. For P. saccharalis, honey solution as a food source, a 21:7 host-to-parasitoid ratio, and one day were optimal for maximizing female offspring production. These findings provide new information about the biology of these egg parasitoids.

Predation and parasitism of naturally occurring and sentinel stink bug egg masses of Halyomorpha halys (Stål) and Nezara viridula (L.) (Hemiptera: Pentatomidae) in various southeastern habitats.

Stink bugs, including Halyomorpha halys (Stål) and Nezara viridula (L.), are agricultural pests that feed on fruit in a variety of crops. Monitoring predation and parasitism of stink bug egg masses furthers our understanding of potential biological control tactics. However, best practices for laboratory and field assessments of parasitism and predation of egg masses require further attention. We carried out a series of laboratory and field experiments to test whether parasitism and predation for three types of sentinel H. halys egg masses, fresh, frozen, and refrigerated, varied in agricultural commodities. In addition, we asked if predation and parasitism differed between sentinel and naturally occurring H. halys and N. viridula egg masses in soybean. In the laboratory, more H. halys eggs were parasitized by Trissolcus euschisti (Ashmead) (Hymenoptera: Scelionidae) if they were frozen or refrigerated compared to fresh eggs. Similarly, in the field, parasitism was higher for frozen egg masses than fresh. In 2018 and 2019, H. halys natural egg masses had higher parasitism and lower predation compared to sentinel egg masses in soybean. In a paired field test during 2020 and 2021, there was no difference in parasitism between H. halys natural and sentinel eggs, but much higher incidence of parasitism was detected in natural N. viridula egg masses than sentinel eggs. Collecting natural egg masses is the best methodology for field assessment of parasitism of stink bug egg masses; however, if natural egg masses are not easily available, deploying refrigerated sentinel egg masses is a good alternative.

Kudzu Bug (Megacopta cribraria) and Associated Egg Parasitoids Emergence Rates in Alabama are Predicted by Weather Indices.

The kudzu bug, Megacopta cribraria (Fabricius) (Hemiptera: Plataspidae), is a major economic pest of soybean in the southeastern United States. With climate warming, this pest is expected to move northward and cause additional crop damage. Parasitoid biocontrol is a potential method of integrated pest management for kudzu bug. Two species of egg parasitoid wasps have been observed emerging from kudzu bug egg masses in the southeastern United States: Paratelenomus saccharalis (Dodd) (Hymenoptera: Platygastridae) and Ooencyrtus nezarae (Ishii) (Hymenoptera: Encyrtidae). This paper used egg mass emergence data collected between 2018 and 2020 in Alabama soybean fields and compared the data to weather indices. Indices included the number of days with minimum temperatures below zero, accumulated rainfall (mm m-2), as well as species specific metrics of accumulated growing degree days, accumulated daily minimum temperature (°C), and accumulated daily maximum temperature (°C). Emergence of the generalist parasitoid, O. nezarae, was highly correlated with kudzu bug nymph abundance, accumulated degree day, accumulated daily temperatures, and precipitation. Ooencyrtus nezarae emergence was predicted in a stepwise regression equation by aggregated degree day and date of collection, which indicates that seasonality may be a predictor of its presence. In contrast, collections of the specialist parasitoid, P. saccharalis, were near-zero throughout the collection period, suggesting that this species may no longer be a usable biocontrol agent in the southeastern United States as a result of external limiting factors.

Direct and Indirect Competitive Interactions between Ooencyrtus nezarae and Paratelenomus saccharalis Parasitizing Megacopta cribraria Egg Patches.

The present study investigated egg parasitoid interspecific interactions between a generalist, Ooencyrtus nezarae Ishii (Hymenoptera: Encyrtidae) and a specialist, Paratelenomus saccharalis Dodd (Hymenoptera: Platygastridae) in a laboratory setting using kudzu bug (Megacopta cribraria Fabricius, (Hemiptera: Plataspidae)) eggs as their shared host. Three experiments were conducted to evaluate the emergence of wasps from parasitized hosts after the simultaneous and sequential release of wasps, monitor aggressive behavior of P. saccharalis, and quantify intraguild predation of O. nezarae larvae on heterospecific P. saccharalis larvae. Results showed that total host egg parasitism was higher when both wasps were released simultaneously than if wasps were released sequentially. Ooencyrtus nezarae produced more total offspring than P. saccharalis in all sequential/simultaneous treatments but produced male offspring in most cases. In the aggressive behavioral experiment, specialist, P. saccharalis used head butting to fight O. nezarae, but no other aggressions were observed. In an experiment examining intraguild predation, O. nezarae was able to develop in host eggs parasitized by P. saccharalis four days earlier, acting as a superior larval competitor. These findings shed light on the potential interspecific interactions between O. nezarae and P. saccharalis, which may determine their relative abundance and influence their compatibility in kudzu bug biological control programs.

Cuticular Hydrocarbon Profile of Parasitic Beetles, Aethina tumida (Coleoptera: Nitidulidae).

Cuticular hydrocarbons (CHCs) cover insects' bodies and play important roles in chemical communication, including nestmate recognition, for social insects. To enter colonies of a social host species, parasites may acquire host-specific CHCs or covertly maintain their own CHC profile by lowering its quantity. However, the chemical profile of small hive beetles (SHBs), Aethina tumida, which are parasites of honey bee, Apis mellifera, colonies, and other bee nests, is currently unknown. Here, adults of SHB and honey bee host workers were collected from the same field colonies and their CHC profiles were analysed using GC-MS. The chemical profiles of field-sampled SHBs were also compared with those of host-naive beetles reared in the laboratory. Laboratory-reared SHBs differed in their CHC profiles from field-sampled ones, which showed a more similar, but ten-fold lower, generic host CHC profile compared to host workers. While the data confirm colony-specific CHCs of honey bee workers, the profile of field-collected SHBs was not colony-specific. Adult SHBs often commute between different host colonies, thereby possibly preventing the acquisition of a colony-specific CHC profiles. An ester was exclusive to both groups of SHBs and might constitute an intraspecific recognition cue. Our data suggest that SHBs do not use any finely tuned chemical strategy to conceal their presence inside host colonies and instead probably rely on their hard exoskeleton and defence behaviours.

First record of Trissolcus basalis (Hymenoptera: Scelionidae) parasitizing Halyomorpha halys (Hemiptera: Pentatomidae) in the United States.

BACKGROUND: A parasitoid wasp, Trissolcus basalis (Wollaston), was recorded parasitizing eggs of the invasive stink bug Halyomorpha halys (Stål) in the United States. This is the first record of this species parasitizing fresh and frozen eggs of H. halys in the United States. NEW INFORMATION: First record of Trissolcus basalis parasitizing Halyomorpha halys eggs in the United States.

New record of Trissolcus solocis (Hymenoptera: Scelionidae) parasitising Halyomorpha halys (Hemiptera: Pentatomidae) in the United States of America.

BACKGROUND: A parasitoid wasp, Trissolcus solocis Johnson, was recorded parasitising eggs of the invasive stink bug Halyomorpha halys (Stål), in the United States. This is the first record of this species parasitising eggs of H. halys. NEW INFORMATION: First record of Trissolcus solocis parasitising Halyomorpha halys eggs in the United States and first record of T. solocis in Alabama.

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.

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

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).

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 microl/liter (C2). Fumigant toxicity decreased sharply with C6 (LC50 = 37.691 microl/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.

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.

Host finding and acceptance preference of the yellowmargined leaf beetle, Microtheca ochroloma (Coleoptera: Chrysomelidae), on cruciferous crops.

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 crucifer production.