Interactions between integrated pest management, pollinator supplementation, and normalized difference vegetation index in pumpkin, Cucurbita maxima (Cucurbitales: Cucurbitaceae), production.

Sustainable production of pumpkin (Cucurbita maxima Duchesne) partly relies on integrated pest management (IPM) and pollination services. A farmer-managed field study was carried out in Yatta and Masinga Sub-Counties of Machakos County, Kenya, to determine the effectiveness of a recommended IPM package and its interaction with stingless bee colonies (Hypotrigona sp.) for pollinator supplementation (PS). The IPM package comprised Lynfield traps with cuelure laced with the organophosphate malathion, sprays of Metarhizium anisopliae (Mechnikoff) Sorokin isolate ICIPE 69, the most widely used fungal biopesticide in sub-Saharan Africa, and protein baits incorporating spinosad. Four treatments-IPM, PS, integrated pest and pollinator management (which combined IPM and PS), and control-were replicated 4 times. The experiment was conducted in 600 m2 farms in 2 normalized difference vegetation index (NDVI) classes during 2 growing seasons (October 2019-March 2020 and March-July 2020). Fruits showing signs of infestation were incubated for emergence, fruit fly trap catches were counted weekly, and physiologically mature fruits were harvested. There was no effect of IPM, PS, and NDVI on yield across seasons. This study revealed no synergistic effect between IPM and PS in suppressing Tephritid fruit fly population densities and damage. Hypotrigona sp. is not an efficient pollinator of pumpkin. Therefore, we recommend testing other African stingless bees in pumpkin production systems for better pollination services and improved yields.

Electroantennogram and machine learning reveal a volatile blend mediating avoidance behavior by Tuta absoluta females to a wild tomato plant.

Tomato cultivation is threatened by the infestation of the nocturnal invasive tomato pinworm, Tuta absoluta. This study was based on field observations that a wild tomato plant, Solanum lycopersicum var. cerasiforme, grown in the Mount Kenya region, Kenya, is less attacked by T. absoluta, unlike the cultivated tomato plants like S. lycopersicum (var. Rambo F1). We hypothesized that the wild tomato plant may be actively avoided by gravid T. absoluta females because of the emission of repellent allelochemical constituents. Therefore, we compared infestation levels by the pest in field monocrops and intercrops of the two tomato genotypes, characterized the headspace volatiles, then determined the compounds detectable by the insect through gas chromatography-linked electroantennography (GC-EAG), and finally performed bioassays using a blend of four EAG-active compounds unique to the wild tomato. We found significant reductions in infestation levels in the monocrop of the wild tomato, and intercrops of wild and cultivated tomato plants compared to the monocrop of the cultivated tomato plant. Quantitative and qualitative differences were noted between volatiles of the wild and cultivated tomato plants, and between day and night volatile collections. The most discriminating compounds between the volatile treatments varied with the variable selection or machine learning methods used. In GC-EAG recordings, 16 compounds including hexanal, (Z)-3-hexenol, α-pinene, ß-myrcene, α-phellandrene, ß-phellandrene, (E)-ß-ocimene, terpinolene, limonene oxide, camphor, citronellal, methyl salicylate, (E)-ß-caryophyllene, and others tentatively identified as 3,7,7-Trimethyl-1,3,5-cycloheptatriene, germacrene D and cis-carvenone oxide were detected by antennae of T. absoluta females. Among these EAG-active compounds, (Z)-3-hexenol, α-pinene, α-phellandrene, limonene oxide, camphor, citronellal, (E)-ß-caryophyllene and ß-phellandrene are in the top 5 discriminating compounds highlighted by the machine learning methods. A blend of (Z)-3-hexenol, camphor, citronellal and limonene oxide detected only in the wild tomato showed dose-dependent repellence to T. absoluta females in wind tunnel. This study provides some groundwork for exploiting the allelochemicals of the wild tomato in the development of novel integrated pest management approaches against T. absoluta.

Chemical Cues From Honeydew and Cuticular Extracts of Trialeurodes Vaporariorum Serve as Kairomones for The Parasitoid Encarsia Formosa.

Kairomones are semiochemicals that are emitted by an organism and which mediate interspecific interaction that is of benefit to an organism of another species that receives these chemical substances. Parasitoids find and recognize their hosts through eavesdropping on the kairomones emitted from the by-products or the body of the host. Hemipteran insect pests feed on plant sap and excrete the digested plant materials as honeydew. Honeydew serves as a nutritional food source for parasitoids and a medium for micro-organisms whose activity induces the release of volatiles exploited by parasitoids for host location. The parasitoid Encarsia formosa preferentially parasitizes its host, the greenhouse whitefly, Trialeurodes vaporariorum, on tomato Solanum lycopersicum, but little is known about the chemicals that mediate these interactions. We investigated the olfactory responses of the parasitoid E. formosa to odours from honeydew and nymphs of T. vaporariorum in a Y-tube olfactometer. Arrestment behaviour of the parasitoid to honeydew and nymph extracts, as well as to synthetic hydrocarbons, was also observed in Petri-dish bioassays. We found that T. vaporariorum honeydew volatiles attracted the parasitoid E. formosa but odours from the whitefly nymphs did not. We also found that the parasitoid spent more time searching on areas treated with extracts of honeydew and nymphs than on untreated areas. Gas-chromatography-mass spectrometric analysis revealed that the honeydew volatiles contained compounds such as (Z)-3-hexenol, δ-3-carene, 3-octanone, α-phellandrene, methyl salicylate, ß-ocimene, ß-myrcene, and (E)-ß-caryophyllene which are known to be attractive to E. formosa. The cuticular extracts of the nymphs predominantly contained alkanes, alkenes, and esters. Among the alkanes, synthetic nonacosane arrested the parasitoid. Our findings are discussed in relation to how the parasitoid E. formosa uses these chemicals to locate its host, T. vaporariorum.